Glossary of Terms

-- All definitions -- Ataxia / Olivopontocerebellar atrophy Bradykinesia Choreoathetosis Conditions associated with movement disorders Corticobasal degeneration Dyskinesias, paroxysmal Dystonia Essential tremor - See Tremor Hemiballismus Hemifacial spasm Hereditary Spastic Paraplegia Huntington's disease Multiple system atrophy Myoclonus Parkinson's disease Paroxysmal Dyskinesias Progressive supranuclear palsy Restless legs syndrome Rett syndrome Spasticity Stiff-person syndrome Sydenham's chorea Tardive dyskinesia / Dystonia Tics / Tourette's syndrome Tremor Wilson disease

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Ablation: Surgical destruction or removal of tissue, an organ, or a precise region of a particular structure. Ablation may involve surgical cutting (excision); chemical destruction, such as injection of phenol; or the use of high frequency electrical current or radio waves. For example, pallidotomy is a procedure used in the treatment of Parkinson's disease or certain other movement disorders. The procedure involves surgical ablation of part of the internal portion of the globus pallidus (GPi)--i.e., a brain region involved in regulating movement--in an attempt to "rebalance" movement and posture control. Once a wire probe is inserted into and precisely positioned within the GPi, it heats and destroys adjacent tissue through the emission of radio waves.

Accelerometer: A device used to measure the rate of change in velocity over a specific period of time. Measures the rate or "speed" of the tremor cycle.

Acetylcholine (ACh): A neurotransmitter present at junctions of nerve and muscle cells and various sites of the central nervous system, including the cerebral cortex and the basal ganglia. Primary functions of acetylcholine include regulating the delivery of messages from neurons to skeletal muscle fibers, smooth (involuntary) muscle fibers, and effector organs as well as between nerve cells in the brain and spinal cord. Acetylcholine also functions as a vasodilator and triggers certain actions within the parasympathetic nervous system, such as lowering blood pressure and slowing heart and breathing rates.

Action tremor: a tremor that occurs during the performance of voluntary movements. Such tremors include postural, isometric, kinetic, and intention tremors.

Activities of daily living (ADL): functions that are typically performed as part of a person's daily routine, such as dressing, bathing, eating, toileting, leisure activities, socialization, and other functions of daily living.

Acute: Referring to symptoms of abrupt onset, often of marked severity or intensity.

Adenosine triphosphate (ATP): ATP is the molecule that provides the energy in the cells of all living things.

Adverse event: According to the United States Food and Drug Administration, an adverse event is any undesirable experience associated with the use of a medical product in a patient. The event is serious and should be reported when the patient outcome is death or is life-threatening; results in hospitalization, disability, or congenital anomaly; or requires intervention to prevent permanent impairment or damage.

Agonist: A muscle whose contraction executes an intended movement.

Akathisia: a neurologic condition of motor restlessness, manifested by a sensation of muscular quivering, an urge to constantly move about, and an inability to sit still.

Akinesia: absence of movement or loss of the ability to move such as temporary or prolonged paralysis or "freezing in place."

Akinetic: Referring to absence or poverty of voluntary movement; loss of the ability to move all or part of the body.

Alpha 2-adrenergic agonist: A drug that reduces the activity of the neurotransmitter norepinephrine by stimulating certain receptors within the central nervous system (central presynaptic alpha 2-adrenergic receptors). The release of norepinephrine triggers action within the sympathetic nervous system. This part of the nervous system regulates certain involuntary activities during stress, such as increasing the heart rate, deepening breathing, and raising blood pressure. Norepinephrine also plays a role in regulating mood and emotion. The administration of alpha 2-adrenergic agonists may result in a reduced heart rate and lowered blood pressure and have depressive or sedative effects.

Alzheimer disease: Alzheimer disease is a disease of the nervous system in which tangles and plaques of proteins develop in the brain, and brain tissue shrinks. The result is impaired abstract thinking and judgment, personality changes, abnormal behavior, and memory problems. Alzheimer disease is one of the leading causes of dementia.

Ambulant (ambulatory): Able to walk; may be used to describe patients who do not require a wheelchair or are not confined to bed.

Ambulation: The act of walking.

Amino acid: The chemical "building blocks" or basic structural units of proteins. All proteins in the body are formed from a "pool" of 20 different amino acids. Some are essential amino acids and must be supplied by the diet. The remainder are classified as "nonessential." These can be made by the body and need not come from the diet.

Amniocentesis: A screening or diagnostic procedure during which a sample of amniotic fluid surrounding the developing fetus is withdrawn by means of an ultrasound-guided needle. The amniotic sac is a fluid-filled membrane that surrounds and protects the developing fetus within the uterus. Amniotic fluid contains cells that may be used for DNA analysis, chromosomal testing, and enzyme studies. Such testing may detect certain genetic disorders, metabolic diseases, chromosomal abnormalities, or developmental defects. This procedure is typically performed between the 14th and 18th week of pregnancy.

Amplitude: the "size" or "height" of a tremor; the extend or breadth of a tremor's range.

Analog (Analogue): (1) A chemical compound or agent that is similar to another in structure yet differs concerning a particular element; it may have a similar or different mode of action. (2) A tissue, organ, or other bodily structure that has the same function or organization as another yet has a different evolutionary origin.

Anosmia: Anosmia is a lack of sense of smell. People who have complete anosmia are not able to detect any odors. People who have partial anosmia are not able to detect one or more odors.

Antagonist: (1) A drug that blocks a receptor, preventing stimulation. (2) A muscle whose contraction opposes an intended movement.

Antibodies: Specialized proteins that function as an essential part of the immune system. Antibodies are produced by certain white blood cells (B cells) in response to the presence of specific, usually foreign proteins (i.e., antigens), helping the body to neutralize and destroy the invading microorganism, foreign tissue cell, or other antigen in question.

Anticholinergic agents: Anticholinergic agents: Anticholinergic medications are drugs that block the action of acetylcholine, a neurotransmitter with an effect opposite to that of dopamine. By blocking the action of acetylcholine, these drugs increase the ability of dopamine to control movement. Examples of anticholinergic drugs used in the treatment of Parkinson disease include trihexyphenidyl (Artane®), benztropine (Cogentin®), and ethopropazine (Parsidol®).

Anticholinesterase: An agent that inhibits action of acetylcholinesterase (AChE). AChE is an enzyme that inactivates acetylcholine, a neurotransmitter at the junctions of nerve and muscle cells (neuromuscular junctions) that regulates the delivery of messages from neurons to muscle fibers. By inhibiting the activity of AChE, such medications allow high levels of acetylcholine to accumulate, potentially enabling repeated stimulation of nerves at neuromuscular junctions.

Anticonvulsant medication: An agent that prevents or arrests convulsive seizures.

Antiemetic: A drug that reduces nausea and vomiting.

Antigen: Any substance that may trigger a particular immune response, such as the production of antibodies. Antigens may be foreign proteins of invading microorganisms (e.g., viruses, bacteria), toxins, or foreign tissue cells (e.g., used in transplantation).

Antihistamine: a drug that counters the effects of histamine, a compound that causes dilatation of capillaries, contraction of smooth muscle, and stimulation of gastric acid secretion and that is released during allergic reactions.

Antioxidants: Agents that inhibit or neutralize potentially harmful compounds known as free radicals. Free radicals are produced during metabolic activity. High levels of free radicals may eventually lead to impaired functioning and destruction of neurons and other bodily cells. Certain antioxidants are thought to neutralize free radicals before cellular damage occurs.

Aorta: The main artery of the body. The aorta receives oxygen-rich (oxygenated) blood from the lower left chamber (ventricle) of the heart for distribution to most arteries of the body, with the exception of the pulmonary artery, which distributes oxygen-deficient (deoxygenated) blood from the lower right ventricle to the lungs.

Apoptosis: Cell death due to a programmed pattern of gene expression; a form of cell death in which certain enzymes activate to degrade DNA within the nucleus, resulting in cellular degeneration and loss.

Apraxia: Loss of the ability to sequence, coordinate, and execute certain purposeful movements and gestures in the absence of motor weakness, paralysis, or sensory impairments. Apraxia is thought to result from damage to the cerebral cortex, such as due to stroke, brain tumors, head injury, or infection. It may also occur as a result of impaired development of the cortex as in certain neurodevelopmental disorders, including Rett syndrome. Apraxia may affect almost any voluntary movements, including those required for proper eye gaze, walking, speaking, or writing.

Archimedes spirals: a relatively simple test used to evaluate tremor severity. During this test, the patient is asked to draw increasingly wider circles on a piece of paper.

Asterixis: involuntary, jerking or flapping movements, especially of the hands. Extending the patient's arm with the wrist bend in a backward position may induce this form of tremor, which may be associated with advanced liver disease.

Astrocyte: A type of glial cell. Glial cells are the connective tissue cells of the central nervous system (CNS), serving as the supportive structure that holds together and protects neurons. Astrocytes are relatively large glial cells with thread-like projections that connect with neurons and small blood vessels (capillaries). These projections form part of the so-called "blood-brain barrier." This barrier slows or prevents the passage of unwanted substances, such as harmful chemicals, infectious agents, etc., from the bloodstream into the brain. Astrocytes also accumulate in areas where nerves have been damaged (astrocytosis), sealing off these areas. An excess of astrocytes in damaged areas of the CNS is known as gliosis.

Ataxia: A condition characterized by an impaired ability to coordinate voluntary movements. Ataxia may result from damage to the cerebellum, cerebellar pathways, or the spinal cord due to various underlying disorders, conditions, or other factors. These may include infection, head injury, stroke, brain tumors, neurodegenerative disorders, alcohol or drug intoxication, or certain hereditary diseases (e.g., Friedreich's ataxia, ataxia-telangiectasia). Associated symptoms may vary, depending upon the site of damage within the central nervous system. However, the condition is often characterized by incoordination, postural imbalance, and a lurching, unsteady manner of walking (gait). Additional findings may include slurred speech (dysarthria); rapid, involuntary, rhythmic eye movements (nystagmus); and/or other abnormalities.

Ataxia-telangiectasia (AT): A hereditary, progressive disorder that typically becomes apparent in early childhood and is characterized by increasing neurodegenerative changes of the cerebellum, a brain region involved in producing coordinated voluntary movements, sustaining balance, and maintaining proper posture. Associated symptoms typically include delayed motor development; an unsteady, awkward manner of walking; drooling; impaired articulation of speech (dysarthria); dependence on thrusts of the head to achieve proper focusing of the eyes; and involuntary, rapid, jerky eye movements (nystagmus). Affected children may also develop involuntary, "shock-like" muscle spasms (myoclonus); sustained muscle contractions that result in repetitive twisting motions or unusual postures or positions (dystonia); or irregular, jerky, relatively rapid involuntary movements (chorea). AT is also typically associated with permanent widening (dilation) of groups of blood vessels (telangiectasias), particularly in sun-exposed skin regions of the face and the transparent membranes covering the whites of the eyes. In addition, AT is characterized by deficient functioning of the immune system (immunodeficiency), leading to recurrent respiratory and skin infections and an increased risk of certain malignancies (e.g., certain leukemias or lymphomas). The disorder, which is transmitted as an autosomal recessive trait, is thought to result from defective repair of DNA.

Athetosis: Involuntary, relatively slow, writhing movements that essentially flow into one another. Athetosis is often associated with chorea, a related condition characterized by involuntary, rapid, irregular, jerky movements. Although athetosis may be most prominent in the face, neck, tongue, and hands, the condition may affect any muscle group. Athetosis may occur in association with certain neurodegenerative diseases, such as Huntington's or Wilson's disease, or cerebral palsy (CP). It may also result from infections affecting the brain or the use of particular medications.

Atrophy: Wasting away or loss of a cell, tissue, or organ due to disease, malnutrition, insufficient blood supply, or other causes, such as loss of skeletal muscle mass due to peripheral nerve damage.

Attention-deficit/hyperactivity disorder: a diagnosis applied to children and adults who consistently display certain characteristic behaviors over a period of time. The most common behaviors fall into three categories: inattention, hyperactivity, and impulsivity.

Atypical: Irregular; not standard or characteristic; not conforming to type.

Atypical neuroleptics: Antipsychotic drugs that cause less parkinsonian side effects than older treatments for psychosis.

Auditory: Pertaining to the sense of hearing or the organs involved in hearing.

Augmentation: A phenomenon that may occur as a result of the use of certain medications (particularly levodopa). Augmentation is characterized by the emergence of worsening symptoms earlier in the day (e.g., early evening, afternoon, or morning). Many people who take levodopa and some who take other dopamingeric agents develop augmentation, especially those who have severe symptoms or are taking high doses of the drug.

Autoimmune: Referring to an immune response against one's own tissues or organs. Autoimmune diseases result from abnormal immune reactions in which the actions of certain white blood cells (T cells) are directed against "self proteins" (autoantigens) or normal tissue components (i.e., cell-mediated immune response)--or in which specialized proteins (antibodies) produced in response to specific, usually foreign proteins (antigens) improperly act against certain of the body's own cells (i.e., antibody-mediated immune response). In certain disorders, the autoimmune process may be primarily directed against one organ, such as the thyroid gland in Hashimoto's thyroiditis or the pancreas in insulin-dependent diabetes mellitus, or may involve multiple organs and bodily systems, such as associated with systemic lupus erythematosus (lupus or SLE).

Automatic behavior: Automatic behaviors are those during which a person performs a routine task without any awareness of doing so.

Autonomic: The autonomic nervous system controls most of the involuntary reflexive activities of the human body. The system is constantly working to regulate the glands and many of the muscles of the body through the release or uptake of the neurotransmitters acetylcholine and norepinephrine. The autonomic nervous system is made up of two primary parts: the sympathetic and parasympathetic systems. The sympathetic nervous system prepares the body for emergencies or times of stress and is responsible for the body's "fight or flight" response when faced with a dangerous situation. During this response, the heart rate and blood pressure increase, the pupils of the eye dilate, and the digestive system slows down. The parasympathetic system helps the body's functions return to normal after they have been stimulated by the sympathetic nervous system and also has some responsibility for keeping the body's immune system properly functioning.

Autonomic dysregulation: malfunctioning of the autonomic nervous system, the portion of the nervous system that conveys impulses between the blood vessels, heart, and all the organs in the chest, abdomen, and pelvis and the brain (mainly the medulla, pons and hypothalamus).

Autonomic nervous system: The autonomic nervous system controls most of the involuntary reflexive activities of the human body. The system is constantly working to regulate the glands and many of the muscles of the body through the release or uptake of the neurotransmitters acetylcholine and norepinephrine. The autonomic nervous system is made up of two primary parts: the sympathetic and parasympathetic systems. The sympathetic nervous system prepares the body for emergencies or times of stress and is responsible for the body's "fight or flight" response when faced with a dangerous situation. During this response, the heart rate and blood pressure increase, the pupils of the eye dilate, and the digestive system slows down. The parasympathetic system helps the body's functions return to normal after they have been stimulated by the sympathetic nervous system and also has some responsibility for keeping the body's immune system properly functioning.

Autosomal dominant trait: Human traits, including an individual's eye color, hair color, or expression of certain diseases, result from the interaction of one gene inherited from the father and one gene from the mother. In autosomal dominant disorders, the presence of a single copy of a mutated gene may result in the disease. In other words, the mutated gene may dominate or "override" the instructions of the normal gene on the other chromosome, potentially leading to disease expression. Individuals with an autosomal dominant disease trait have a 50 percent risk of transmitting the mutated gene to their children.

Autosomal recessive trait: Human traits, including an individual's hair color, specific blood group, or expression of certain diseases, result from the interaction of one gene inherited from the mother and one from the father. With autosomal recessive disorders, two copies of the disease gene must be inherited in order for an individual to potentially develop the disease. If both the mother and father carry a copy of the disease gene, each child has a 25 percent risk of inheriting the two genes for the disease. There is a 50 percent risk that their children may inherit one copy of the disease gene and be carriers for the disease trait (heterozygous carriers). In addition, there is a 25 percent chance that the parents' offspring will inherit two normal copies of the gene and will not develop the disorder nor be carriers for this disease trait.

Axons: Nerve fibers. Axons are the relatively slender extensions of neurons that transmit nerve impulses away from nerve cell bodies. The ends of the axons or "terminals" release chemical substances known as neurotransmitters, enabling the transmission of nerve impulses to other neurons or effector organs. The whitish, fatty, protein-containing substance called myelin forms an insulating, protective, cylindrical sheath around some axons, serving to increase the speed and efficiency of nerve impulse transmissions.

Baclofen: A mainstay of antispastic drug therapy, baclofen is a GABA agonist that stimulates the GABAB autoreceptor. When stimulated, this autoreceptor inhibits muscle activity. In experimental systems, baclofen inhibits the release of noradrenaline, and acetylcholine from peripheral nerve endings, and acetylcholine, noradrenaline, dopamine, serotonin, and glutamate from CNS neurons.

Ballismus: An abnormal neuromuscular condition that is generally considered a severe form of chorea. Involvement of the upper muscles of the arms and legs results in uncontrolled, violent, flinging or throwing actions. These swinging or jerky movements may be sporadic or continuous and, in some patients, restricted to one side of the body (hemiballismus). Ballismus often occurs in association with other abnormal involuntary movements, including athetosis, chorea, and dystonia.

Basal ganglia: Specialized nerve cell clusters of gray matter deep within each cerebral hemisphere and the upper brainstem, including the striate body (caudate and lentiform nuclei) and other cells groups such as the subthalamic nucleus and substantia nigra. The basal ganglia assist in initiating and regulating movement.

Benign myoclonus of infancy: A neurologic condition that typically becomes apparent by approximately 4 months of age. Affected infants and children experience relatively short, mild episodes of myoclonus, or sudden, involuntary, "shock-like" spasms of muscles, particularly of the head, neck, trunk, and arms. Development is typically normal, and myoclonus usually ceases by age 2 or 3.

Benzodiazepines: A class of medications that act upon the central nervous system to reduce communication between certain neurons, lowering the level of activity in the brain. Benzodiazepines are effective in reducing anxiety, stress, or agitation; promoting sleep; alleviating restlessness; and relaxing muscles.

Beta-adrenergic receptor: a specialized molecular structure on the surface membrane of a neuron that selectively receives the neurotransmitter norepinephrine. Reception of this neurotransmitter causes changes in the neuron that increase its likelihood of "firing" or sending its own signal to other neurons. The activities of norepinephrine affect that part of the nervous system involved in the control of some involuntary body functions, such as blood pressure regulation, etc. (sympathetic nervous system).

Bilateral: Having or affecting two sides.

Biosynthesize: To form or produce (during normal physiologic functions) a chemical compound in the body.

Biphasic: having two distinct stages or phases.

Body mass index: The body mass index is a measure of body fat that is based on a person’s height and weight.

Botulinum toxin (BTX): Any of a group of toxins, designated as A through G, produced by Clostridium botulinum bacteria. Localized injection of minute amounts of commercially prepared BTX may help to relax an overactive muscle by blocking the release of acetylcholine, a neurotransmitter responsible for the activation of muscle contractions. BTX-A is currently the only form (i.e., serotype) of botulinum toxin approved for clinical use. (BTX-A [BOTOX®] is produced by Allergan, Inc. and used in the United States and many other countries. Outside the U.S., it is available as Dysport® from Ipsen, Ltd.) It was originally introduced in the 1970s for the treatment of misalignment of the eyes (strabismus) and involuntary contraction of eyelid muscles (blepharospasm) associated with dystonia or facial nerve disorders. BTX-A is now increasingly being used as a therapeutic option for selected patients with other disorders characterized by severely increased muscle activity (hyperactivity), such as tremor, other focal dystonias, and spasticity. BTX-B is currently under investigation (by Athena Neurosciences, Inc.) for patients with cervical dystonia.

Bradykinesia: The gradual loss of spontaneous movement; slowness of voluntary movements.

Brainstem: The region of the brain consisting of the medulla oblongata, pons, and midbrain. The brainstem primarily contains white matter interspersed with some gray matter. This area of the brain serves as a two-way conduction path, conveying nerve impulses between other brain regions and the spinal cord. In addition, most of the 12 pairs of cranial nerves from the brain arise from the brainstem, regulating breathing, digestion, heartbeat, blood pressure, pupil size, swallowing, and other basic functions.

Branched-chain amino acids: the essential amino acids, isoleucine, leucine, and valine.

Bruxism: Involuntary grinding, clenching, or gnashing of the teeth, particularly during sleep or times of stress. Without appropriate protection, such as the use of night guards that cover the teeth, severe dental problems may result. Bruxism may also be a feature of certain neurologic movement disorders, including dystonia of the jaw, mouth, and lower face (oromandibular dystonia [OMD]), Rett syndrome, or tardive dyskinesia.

Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS): The BFMDRS is a weighted scale that measures the severity and provoking factors for dystonia in 9 body areas, including the eyes, mouth, speech or swallowing, neck, right and left arms, trunk, and right and left legs

Cabergoline: Cabergoline is an ergotamine-based dopamine-receptor agonist with a half-life of 65 hours. In the United States, it is marketed as Dostinex for the treatment of the rare disorder, hyperprolactinaemia, or high levels of the hormone prolactin.

Carbidopa: Carbidopa is a drug that, when combined with levodopa, slows the peripheral breakdown of the levodopa, thereby allowing more of the levodopa to enter the brain.

Carbonic anhydrase inhibitors: A class of medications that inhibits activity of the enzyme carbonic anhydrase. This zinc-containing enzyme is present in red blood cells and the renal tubules. These tubules form part of the filtering units of the kidneys. Carbonic anhydrase activity serves to accelerate the transfer of carbon dioxide from tissue to the blood and on to the lungs. By restricting carbonic anhydrase activity, these agents decrease hydrogen ion concentrations in the renal tubules, increasing excretion of sodium, potassium, bicarbonate, and water. Certain carbonic anhydrase inhibitors are prescribed to promote urinary production and excretion (i.e., as diuretics) or to lower fluid pressure within the eyes for those with glaucoma. They are also used to treat other conditions including epilepsy or certain neurologic movement disorders.

Carnitine: A natural substance found in skeletal and cardiac muscle and the liver. Carnitine serves to transport fatty acids across mitochondrial membranes, thereby playing an important role in energy production and the metabolism of fatty acids.

Cataplexy: Cataplexy is a sudden loss of voluntary muscle control, usually triggered by emotions such as laughter, surprise, fear or anger. Cataplexy occurs most often during times of stress or tiredness. The loss of muscle control may vary from a feeling of weakness to total body collapse. Although people having a cataplectic attack may appear to be asleep, they are actually awake, just unable to move.

Catecholamine: any of a group of hormones that are catechol derivatives, e.g., adrenaline and noradrenaline.

Caudate: One of the three major substructures that, together with the globus pallidus and putamen, form the basal ganglia. The caudate nuclei and putamen, which are relatively similar structurally and functionally, are collectively known as the striatum. Specialized clusters of nerve cells or nuclei within the caudate receive input from certain regions of the cerebral cortex. This information is processed and then relayed (by way of the thalamus) to areas of the brain responsible for controlling complex motor functions. The caudate nuclei are specifically thought to process and transmit cognitive information that influences the initiation of complex motor activities.

Caudate nuclei: One of the 3 major substructures that, together with the globus pallidus and putamen, form the basal ganglia. The caudate nuclei and putamen, which are relatively similar structurally and functionally, are collectively known as the striatum. Specialized clusters of nerve cells or nuclei within the caudate receive input from certain regions of the cerebral cortex. This information is processed and then relayed (by way of the thalamus) to areas of the brain responsible for controlling complex motor functions. The caudate nuclei are specifically thought to process and transmit cognitive information that influences the initiation of complex motor activities.

Central nervous system (CNS): The brain and spinal cord. The CNS, which receives sensory impulses from and sends motor impulses to the peripheral nervous system (i.e., nerves outside the CNS), plays an essential role in the coordination and control of the entire body.

Central oscillators: nerve cells that discharge signals that result in alternating fluctuations of electrical impulses along certain tracts of the central nervous system.

Cerebellum: A two-lobed region of the brain located behind the brainstem. The cerebellum receives messages concerning balance, posture, muscle tone, and muscle contraction or extension. Working in coordination with the basal ganglia and thalamus, the cerebellum integrates, adjusts, and refines messages transmitted to muscle groups from the cerebral cortex (i.e., motor cortex). Thus, the cerebellum plays an essential role in producing smooth, coordinated voluntary movements; maintaining proper posture; and sustaining balance.

Cerebral cortex: The outer region of the brain's cerebral hemispheres. Comprised of gray matter, the cerebral cortex contains several deep folds (gyri) and grooves (sulci or fissures). Two sulci divide the surfaces of both cerebral hemispheres into four distinct lobes that are named for overlying bones of the skull. These include the frontal, temporal, occipital, and parietal lobes. The cerebral hemispheres are joined by a thick band of nerve fibers known as the corpus callosum. The cerebral cortex is responsible for integrating higher mental functioning and conscious thought, sensations, and general movements.

Cerebrospinal fluid (CSF): The fluid that flows through and protects the 4 cavities (ventricles) of the brain, the spinal cord's central canal, and the space (known as the subarachnoid space) between the middle and inner layers of the membrane (meninges) enclosing the brain and spinal cord. Laboratory analysis of CSF, usually obtained via lumbar puncture, may help to diagnose central nervous system infections, certain tumors, or particular neurologic disorders. During lumbar puncture, CSF is removed from the spinal canal via a hollow needle inserted between certain bones of the spinal column within the lower back (i.e., usually the third and fourth lumbar vertebrae).

Chemodenervation: Interruption of a nerve impulse pathway via administration of a chemical substance, such as botulinum toxin (BTX). For example, intramuscular injections of BTX produce local relaxation of treated muscles by inhibiting the release of acetylcholine, a neurotransmitter that is present at the junctions of nerve and muscle cells and that regulates the delivery of messages from neurons to muscle fibers.

Chorea: Jerky, irregular, relatively rapid involuntary movement that primarily involves muscles of the face or extremities. Choreic movements are relatively simple and discrete or highly complex in nature. Although involuntary and purposeless, these movements are sometimes incorporated into deliberate movement patterns. When several choreic movements are present, they often appear relatively slow, writhing, or sinuous, resembling athetosis. Chorea may occur in association with certain neurodegenerative diseases, including Wilson's disease and Huntington's disease, or systemic disorders, such as lupus. In addition, chorea is a dominant feature in Sydenham's chorea or may result from the use of certain medications, such as particular anticonvulsant or antipsychotic agents.

Chorionic villus sampling (CVS): A screening and diagnostic procedure performed during which tissue samples are obtained from a portion of the placenta using a specially guided needle via ultrasound. The placenta is the organ attached to the lining of the uterus that links the blood supplies of the developing fetus and the mother. The tissue sample is obtained from the layer from which the chorionic villi develop. Blood from the fetus flows through the umbilical cord to the placenta and enters minute blood vessels arranged in multiple "thread-like" projections or chorionic villi surrounded by maternal blood. Tissue samples obtained during chorionic villus sampling are analyzed to detect certain genetic or chromosomal abnormalities.

Chromosomes: The thread-like structures within the nuclei of cells comprised of DNA. Deoxyribonucleic acid or DNA carries genetic information involved in directing cellular activities, thus controlling bodily growth and functioning and determining the expression of inherited traits. The chromosomes contain thousands of hereditary units known as genes or segments of DNA molecules. The nuclei of all human cells--except the reproductive (i.e., egg and sperm) cells--normally contain 46 chromosomes, with one of each pair from the father and one from the mother. The chromosomal pairs are numbered from 1 through 22, as well as a 23rd pair that includes one X chromosome from the mother and an X or a Y chromosome from the father. In females, the 23rd pair consists of two X chromosomes, whereas males have one X and one Y chromosome. All chromosomes have a short arm known as "p" and a long arm known as "q." Both chromosomal arms are subdivided into numbered bands.

Circadian: A rhythm of biological functions occurring in a 24-hour periodic cycle (e.g., sleeping, eating, etc.).

Clinical Global Impression (CGI): The CGI is a scale to assess s patient’s response to treatment. At baseline, the doctor rates how much the disease or illness impacts a patient’s life. The patient receives the treatment, or, in some cases, a certain amount of time passes, and the doctor again rates the impact of the disease or illness, this time as very much improved, much improved, minimally improved, no change, minimally worse, much worse, or very much worse.

Clonus: movements characterized by alternate contractions and relaxations of a muscle, occurring in rapid succession. Clonus is frequently observed in conditions such as spasticity and certain seizure disorders.

Co-contraction: The simultaneous contraction of agonist and antagonist muscles.

Cognition: Cognition involves thinking skills such as perception, memory, awareness, reasoning, judgment, intellect, and imagination.

Cognitive impairment: Cognitive impairment is a decrease in the ability to process, learn, and remember information.

Cogwheel phenomenon: rhythmic brief increase in resistance during passive movement about a joint.

Complementary and alternative medicine: Complementary and alternative medicine, as defined by National Institutes of Health, is a group of diverse medical and health-care systems, practices, and products that are not presently considered to be part of conventional medicine

Composite Autonomic Scoring Scale: The Composite Autonomic Scoring Scale is a battery of validated, sensitive, and specific tests for the assessment of autonomic nervous systems, resulting in a 10-point composite score.

Computerized tomography (CT) imaging or scanning: An advanced diagnostic scanning technique during which cross-sectional images of tissues and organs are produced by passing x-rays through the body at various angles. In some cases, a contrast medium, which is opaque on x-rays, may be injected intravenously to produce enhanced images of certain tissues, organs, or blood vessels.

COMT inhibitors: Drugs that block catechol-O-methyltransferase, an enzyme that breaks down dopamine. COMT inhibitors include entacapone (Comtan®) and tolcapone (Tasmar®).

Congenital: Existing at birth.

Contractures: Fixed resistance to passive stretching of certain muscles due to shortening or wasting (atrophy) of muscle fibers or the development of scar tissue (fibrosis) over joints.

Contralateral: the opposite side. For example, during brain surgery for essential tremor, if the surgery is performed on the right side of the brain, the left side of the body will be affected.

Controlled-release formulation: A form of a drug (e.g., L-dopa) that is absorbed slowly by the digestive system, prolonging the duration of effect of each dose.

Corticobasal degeneration (CBD): A slowly progressive disorder characterized by neurodegenerative changes of certain brain regions, including the cerebral cortex (particularly the frontal and parietal lobes) and parts of the basal ganglia. Most patients initially develop symptoms in their 60s or 70s. Primary findings may include stiffness (rigidity); slowness of movement (bradykinesia); loss of the ability to coordinate and execute certain purposeful movements of the arms or legs (limb apraxia); the sensation that a limb is not one's own ("alien limb phenomenon"); and other sensory abnormalities. Affected individuals may also develop slurred, labored speech (dysarthria); dystonia; and irregular, involuntary, "shock-like" contractions of certain muscle groups, particularly of the hands and forearms, that may be provoked or aggravated by voluntary movement and certain external stimuli (action and reflex myoclonus).

Corticospinal: Referring to or connecting the outer region of the brain (cerebral cortex) and the spinal cord.

Corticosteroid agents: Synthetic medications similar to corticosteroid hormones, which are naturally produced by the outer regions of the adrenal glands (adrenal cortex). Corticosteroid agents may be prescribed to treat inflammatory conditions; as long-term therapy to suppress the immune system (immunosuppressive therapy) in order to prevent rejection of a transplanted organ; as hormone replacement therapy for those with insufficient levels of natural corticosteroid hormones; or as therapy for other conditions. High dose, long-term corticosteroid therapy may result in various adverse effects, including an increased susceptibility to infection; osteoporosis, a bone disorder characterized by a progressive loss of bone mass; high blood pressure (hypertension); tissue swelling (edema); or retarded bone growth in children.

Cranial: Of or from the cranium or skull.

Cranial nerve nuclei: Specialized groups of nerve cells (nuclei) that give rise to and convey or receive impulses from sensory and motor constituents of the cranial nerves, which are the 12 pairs of nerves that emerge from the brain. These nerve pairs convey sensory impulses for various functions including taste, smell, hearing, and vision; motor impulses involved in controlling eye movements, chewing, swallowing, facial expressions, etc.; and impulses for transmission to certain organs and glands for regulation of various involuntary or autonomic activities.

Cranial neuropathy: Disease or damage of a cranial nerve or nerves. The cranial nerves are the 12 nerve pairs that arise directly from the brain and are involved in conveying impulses for various functions including smell, hearing, vision, and taste; pupil contraction; eye movements; facial expressions; movements of the tongue, head, and shoulders; etc. Cranial neuropathy may result in associated muscle weakness; abnormal sensations, such as numbness, tingling, or pain; or other findings. Specific symptoms depend upon the specific nerve(s) affected.

Creutzfeldt-Jakob disease (CJD): A rare, degenerative, life-threatening brain disorder characterized by severe, progressive dementia; visual disturbances; muscle weakness; and abnormal involuntary movements, such as sudden, brief, "shock-like" muscle spasms (myoclonus), tremor, and relatively slow writhing motions that appear to flow into one another (athetosis). Although CJD usually appears to occur sporadically, about 10 percent of cases are familial, potentially suggesting a hereditary predisposition to the disease. In rare cases, CJD may also result from exposure to contaminated surgical instruments during brain surgery and was reported in the past due to therapy with pituitary-derived human growth hormone. In addition, a variant form of CJD (V-CJD) has been reported primarily in the United Kingdom; V-CJD has been potentially linked to consumption of beef from cows with bovine spongiform encephalopathy or BSE (so-called "mad cow disease"). Evidence suggests that CJD may be caused by mutations in the human prion* protein gene or contamination with abnormal prion protein. (*The term "prion" was named for "protein infectious agent.") Changes in the prion protein appear to lead to distinctive neurodegenerative abnormalities, i.e., relatively small, round, "sponge-like" (spongiform) cavities or gaps in certain brain regions. CJD and BSE belong to a group of related neurodegenerative disorders categorized as "transmissible spongiform encephalopathies."

Crossreact: Refers to the interaction of an antibody with an antigen that did not specifically or originally trigger its production. For example, in an abnormal autoimmune reaction, an antibody that was initially formed in response to an invading bacterium may inappropriately react against certain of the body's own tissues that contain some of the same amino acid sequences as within the microorganism.

Cytokine: Cytokines are small proteins that regulate the body’s immunity, inflammation, and blood-cell production responses.

Cytoplasm: The cytoplasm is the part of the cell that surrounds the nucleus.

DC inhibitors: Drugs that block decarboxylase, one type of enzyme that breaks down dopamine. Also called AADC inhibitors, they include carbidopa and benserazide.

Decarboxylase: A category or subclass of enzymes that removes or eliminates a molecule of carbon dioxide from a carboxylic group. Carbidopa is an inhibitor of the decarboxylation of levodopa.

Degenerative: Marked by or pertaining to deterioration; particularly, deterioration of the function or structure of tissue or changes from a higher to a lower or less functionally active form.

Delirium: A state of frenzied excitement or wild enthusiasm.

Delusions: Delusions are fixed beliefs about events or circumstances that have no basis in reality.

Dementia: Dementia is not a disease itself but, rather, a group of symptoms that may have a variety of causes. A person with dementia loses the ability to think, remember, learn, make decisions, and solve problems. The person may also have personality and other behavioral changes.

Dendrites: The relatively narrow, branching projections that extend from the cell bodies of neurons. Nerve cells may contain multiple dendrites, which are stimulated by neurotransmitters, receive impulses from the nerve fibers (axons) of other neurons, and convey them toward their nerve cell bodies.

Dentatorubropallidoluysian atrophy: A rare genetic disorder that is most commonly described in Japan. Associated symptoms may become apparent in adolescence or adulthood. Early-onset disease may be characterized by rapidly progressive neurodegenerative changes, including seizures, cognitive impairment, and brief, "shock-like" muscle spasms of certain muscles or muscle groups (myoclonus). Late-onset disease may be associated with progressively impaired control of voluntary movement (ataxia) and symptoms often seen in Huntington's disease (HD), including chorea and gradual loss of thought processing and acquired intellectual abilities (dementia). Brain imaging studies typically reveal degenerative changes of the globus pallidus and specialized nerve cell clusters within the cerebellum (dentate nucleus). Similar to HD, the disorder may result from abnormally long sequences or "repeats" of particular coded instructions (unstable expanded CAG repeats) within a gene (located on chromosome 12).

Detoxification: Detoxification is the process of removing or neutralizing toxins in the body

Diaphragm: The dome-shaped muscle that separates the chest and abdomen. The diaphragm plays an essential role in breathing, contracting when air is drawn into the lungs and relaxing upon exhalation.

Differential diagnosis: Distinguishing between two or more diseases and conditions with similar symptoms by systematically comparing and contrasting their clinical findings, including physical signs, symptoms, as well as the results of laboratory tests and other appropriate diagnostic procedures.

Diuretics: Medications that promote the excretion of urine. Such medications are often prescribed to help reduce excess fluid levels in the body, such as associated with chronic heart failure, high blood pressure (hypertension), or certain kidney (renal) or liver (hepatic) disorders. Diuretics help to remove excess water from the body by increasing the amount that is excreted as urine.

DNA: Deoxyribonucleic acid. DNA is a spiraling, ladder-like (helical) molecule that is the carrier of the genetic code. Nucleic acids are the primary components of the chromosomes within the nuclei of cells. DNA is also found in mitochondria, the rod-like structures outside the nuclei of cells that function as a primary source of cellular energy.

Dopamine: Dopamine is a chemical that is known as a neurotransmitter. Neurotransmitters help relay messages from one nerve cell to another. Dopamine is especially important in relaying messages about movement.

Dopamine agonist (DA): A drug that acts like dopamine. DAs combine with dopamine receptors to mimic dopamine actions. Such medications stimulate dopamine receptors and produce dopamine-like effects.

Dopamine autoreceptor: A type of dopamine receptor that acts like a thermostat, preventing excess dopamine release as levels rise.

Dopamine receptor: A molecule on a receiving nerve cell (neuron) that is sensitive (or receptive) to stimulation (arousal) by dopamine or a dopamine agonist. At least five types have been identified including D1, D2, D3 receptors and the dopamine autoreceptor.

Dopamine receptor antagonist: A pharmacologic agent that binds to and blocks the action of dopamine receptors, essentially hindering receptor activity by preventing stimulation by dopamine.

Dopamine transporter: Dopamine is a chemical in the body that allows one nerve cell to send a message or signal to another nerve cell and helps to control movement. After dopamine finishes sending its message, a substance called a dopamine transporter carries the dopamine back from the nerve ending to the cell that produced it so that the dopamine can be reused. The number of dopamine transporters is a sign of the number of nerve endings that produce or release dopamine.

Dopaminergic: Having the effect of dopamine or related to dopamine-producing cells

Dopaminergic drug: A dopaminergic drug is any drug that has the effect of dopamine. Levodopa is converted in the body to dopamine, and dopamine agonists mimic the effects of dopamine at the receptors.

Dopaminergic dysfunction: Malfunction of dopamine receptors.

Double-blind trial: A double-blind trial is a clinical experiment in which neither the patients nor the researchers are aware of which patients are receiving the active treatment and which are receiving placebo.

duodenum: The duodenum is the part of the small intestine that is connected to the stomach.

Dysarthria: Disordered or impaired articulation of speech due to disturbances of muscular control, usually resulting from damage to the central or peripheral nervous system. Dysarthria is associated with certain neurodegenerative disorders, such as Parkinson's disease or Huntington's disease; cerebral palsy; brain tumors or stroke; or certain types of brain surgery.

Dysesthesias: Unpleasant sensations that are produced in response to normal stimuli.

Dyskinesias: Abnormal neuromuscular conditions characterized by disorganized or excessive movement (also known as hyperkinesia). Forms of dyskinesia include sudden, brief, "shock-like" muscle contractions (myoclonus); involuntary, rhythmic, oscillatory movements of a body part (tremor); rapid involuntary jerky movements (chorea); relatively slow writhing motions (athetosis); or abrupt, purposeless, simple or complex muscle movements or vocalizations (motor or vocal tics).

Dyskinesias while awake (DWA): Uncontrolled, sporadic movements of the legs and, in some cases, the arms. These movements may be very rapid (myoclonic) or quite slow and prolonged (dystonic); they usually disappear upon voluntary action. Some researchers suspect that these movements may represent a wakeful form of periodic limb movements in sleep (PLMS).

Dysphagia: Difficulty in swallowing. Dysphagia may be associated with esophageal obstruction as well as certain neurodegenerative or motor disorders involving the esophagus.

Dyspraxia: Partial loss of the ability to coordinate and perform certain purposeful movements and gestures in the absence of motor or sensory impairments.

Dystonia: A neurologic movement disorder characterized by sustained muscle contractions, resulting in repetitive, involuntary, twisting or writhing movements and unusual postures or positioning. Dystonia may be limited to specific muscle groups (focal dystonia), such as dystonia affecting muscles of the neck (cervical dystonia or spasmodic torticollis) or the eyes, resulting in closure of the eyelids (blepharospasm). Dystonia is associated with certain underlying genetic disorders, such as dystonia musculorum deformans, dopa-responsive dystonia, and paroxysmal kinesigenic and paroxysmal non-kinesigenic dystonic choreoathetosis. The condition may result from the use of certain medications, lack of oxygen during or immediately after birth, or other causes of brain trauma.

Dystonic: Referring to dystonia; sudden jerky or repetitive movements and muscle spasms due to impaired muscle tone and abnormal muscle rigidity.

DYT-1 dystonia: The DYT-1 gene regulates or "encodes" production of a protein called torsinA. Although its specific function is not know, torrsinA appears to be related to a class of proteins that enable cells to recover from injury or stress. The change, or mutation, that causes DYT-1 dystonia involves one of a pair of three basic chemical "building blocks" of DNA. These are called guanine, adenine, and guanine, or "GAG" trinucleotides and are part of the genetic code within the DYT-1 gene. The specific mutation that occurs in DYT-1 dystonia is an absence, or deletion, of GAG. This relatively tiny change in the blueprint for torsinA apparently causes critical changes in the function of the protein and may lead to the symptoms of dystonia.

Echocardiogram: An echocardiogram is a medical test that is used to study the structure and function of the heart. A computer captures echoes that are created from sound waves (ultrasound).

Economic burden: Economic burden involves both direct medical costs such as expenditures for drugs, physicians, and institutions, as well as indirect costs due to lost wages from illness, premature death, and disability.

Edema: Fluid accumulation in the tissues causing swelling

Edentulousness: lack of permanent teeth.

Effector organs: Organs that produce a nerve-stimulated effect, such as a muscle contraction or glandular secretion.

Electrical stimulation (ES): A test in which a small electrical charge is applied to a muscle via a needle to determine the level of muscle responsiveness.

Electrocardiogram (ECG, EKG): A noninvasive, diagnostic test that assesses the electrical activity of the heart muscle (myocardium). The heart's conduction system transmits electrical impulses that serve to coordinate contractions of the heart. During an ECG, the electrical activity of the cardiac conduction system is translated into recordings that assist in evaluating any abnormal alterations. The test may be administered while a patient is at rest or performing certain designated exercises. ECGs may help to detect or characterize cardiac conduction defects, abnormal heart rhythms (arrhythmias), enlargement (cardiac hypertrophy), or localized damage in heart muscle.

Electroencephalography (EEG): A noninvasive, diagnostic technique that records the electrical impulses produced by brain cell activity. An EEG reveals characteristic brain wave patterns that may assist in the diagnosis of particular neurologic conditions, such as seizure disorders, impaired consciousness, and brain lesions or tumors.

Electromyography (EMG): A diagnostic test that records the electrical responses of skeletal muscles while at rest and during voluntary action and electrical stimulation. During this test, a small needle is inserted into a muscle to record the level of activity.

Electron microscopy: An electron microscope beams electrons, instead of light beams, to magnify an object, providing very detailed images that are approximately 1000 times the magnification of a typical light-beam microscope.

Electrophysiologic recording : Electrophysiologic recordings include the study of the electrical activity associated with a specific body function (e.g., electromyogram [muscles], electroencephalogram [brain waves], etc.).

Electrophysiologic studies: The study of the electrical activity associated with a specific body function (e.g., EMG, EEG, etc.).

Encephalitis: Inflammation of the brain. Encephalitis is most commonly caused by certain viral infections or may occur subsequent to prior infection due to immune reactions that indirectly result in inflammation (postinfectious encephalitis). Although associated symptoms and findings may be variable, features may include fever, headache, irritability, listlessness (lethargy), and weakness. Some affected individuals may also develop confusion, disturbances of speech and memory, abnormal involuntary movements, paralysis of one side of the body, seizures, and/or coma. For those with involvement of the protective membranes enclosing the brain and spinal cord (meningitis), characteristic findings may include nausea, vomiting, stiffness of the neck, abnormal sensitivity to light (photophobia), and/or other symptoms.

Encephalopathies: Any abnormal conditions or diseases of the structure or function of the brain, particularly chronic, degenerative conditions.

Endogenous opiate system: A morphine-like substance that is produced within the body.

Endoplasmic reticulum (ER): The ER consists of a membrane system that branches out through the cytoplasm and includes rough ER, which is found in eukaryotic cells and contains ribosomes, and smooth ER, which is biochemically similar to rough ER but lacks ribosomes.

Endoscopy: A study in which the doctor looks inside the stomach or intestine using a hollow, thin, flexible tube that has a lens or miniature camera on the end of it.

Endotoxin: An endotoxin is a poisonous substance that is released from bacteria after the bacteria die or break apart.

Enzyme: A protein produced by cells that accelerates the rate of or "catalyzes" a specific chemical reaction in the body without being consumed or permanently changed in the process. A chemical substance that is acted upon by an enzyme is called a "substrate." In many cases, enzymes are named by adding the suffix "-ase" to the name of the substrate upon which the enzyme exerts its action.

Epidemiological study: examination of the distribution of disease as well as the determining factors related to specific diseases or health-related problems in a specific population.

Epidemiology : Epidemiology is the study of the patterns and causes of disease in groups of people.

Epworth Sleepiness Scale (ESS): The ESS is a paper-and-pencil test. In this test, you record how likely you are to fall asleep in seven different situations: sitting and reading, watching TV, sitting inactive in a public place (such as at a theater or in a meeting), as a passenger in a car for an hour without a break, Lying down to rest in the afternoon when circumstances permit, sitting and talking with someone, sitting quietly after a lunch without alcohol, while driving a car, while stopped for a few minutes in traffic.

Eradication: Eradication is the process of permanently eliminating something.

Ergot: A plant alkaloid produced by the fungus Claviceps purpurea.

Ergot-derived medication: A medication that has a chemical structure based on ergot, a plant alkaloid produced by a fungus called Claviceps purpurea. Permax® and Parlodel® are examples of ergot-derived medications that may be used to treat certain neurologic movement disorders.

Esophageal atony: Lack of normal muscle tone within the esophagus, the muscular tube that transports food from the throat to the stomach.

Essential tremor (ET): A common, slowly and variably progressive neurologic movement disorder characterized by involuntary, rhythmic, "back and forth" movements (i.e., tremor) of a body part or parts. In ET patients, tremor is primarily a "postural" or "kinetic" tremor or may be a combination of both types: i.e., tremor occurs while voluntarily maintaining a fixed position against gravity (postural tremor) and/or when conducting self-directed, targeted actions (kinetic intention tremor). In many individuals with ET, both hands are affected, although the condition may sometimes initially be noted in the dominant hand. ET also frequently affects the head, with tremor occurring in a "no-no" horizontal pattern in about three quarters of patients and the remainder affected by vertical "yes-yes" tremors. Less commonly, patients have tremor involving the voice, tongue, or roof of the mouth (palate), leading to impaired articulation of speech (dysarthria). Rarely, tremor may affect the trunk or lower limbs, particularly with advanced stages of disease. ET may appear to occur randomly for unknown reasons (sporadically) or be transmitted as an autosomal dominant trait.

Estrogen: (1) Any of several, naturally occurring female sex hormones that promote the development of female secondary sexual characteristics and the proper functioning of the reproductive system; (2) synthetically produced agents used in birth control pills (oral contraceptives) or in the treatment of symptoms of menopause; osteoporosis, which is a bone disorder characterized by a progressive loss of bone mass; particular types of advanced postmenopausal breast cancer and prostate cancer; and other conditions.

Eukaryotic: Meaning literally "true nucleus," eukaryotic organisms include protists, plants, animals and fungi, all of which have separate membrane-bound nuclei that contain genetic material (mDNA).

Executive function: Executive function refers to a person’s ability to establish a goal and then make decisions and put into action activities to meet that goal.

Exon: An exon is a region of a gene that contains part of the code for producing the gene's protein. Each exon codes for a specific portion of the complete protein. Exons are separated by long regions of DNA (called introns or sometimes "junk DNA") that have no apparent function.

Extrapyramidal system: Refers to central nervous system structures (i.e., outside the cerebrospinal pyramidal tracts) that play a role in controlling motor functions. The extrapyramidal system includes substructures of the basal ganglia and the brainstem and interconnections with certain regions of the cerebellum, cerebrum, and other areas of the central nervous system. Extrapyramidal disturbances may result in postural and muscle tone abnormalities as well as the development of certain involuntary movements.

Fatigue: Fatigue is a feeling of tiredness or a sense of having low energy that may lead to a decrease in a person's ability to perform work or daily activities.

Feldenkrais: Feldenkrais is a method of improving the body’s ability to function, learn, and change by increasing awareness of movement, posture, and breathing.

Ferritin: A serum ferritin level is a blood test that measures the amount of ferritin in your cells. Ferritin is a protein that stores iron inside your cells so that your body can use the iron when it is needed. The amount of ferritin stored, or your serum ferritin level, reflects the amount of iron that is stored in your body. Symptoms of RLS have been shown to be increased in people who have low ferritin levels.

Fibrosis: Build-up of fibrous tissue in an abnormal place in the body

First-, second- and third-degree relatives: First-degree relatives include your mother, father, sisters, brothers, sons, and daughters. Second-degree relatives are your aunts, grandmothers, uncles, and grandfathers. Third-degree relatives include your great-grandmothers, great-aunts, great-uncles, and first cousins.

First-degree relatives: First-degree relatives include a person’s mother, father, brothers, sisters, sons, and daughters who are related by blood and not through adoption or marriage.

Flexion: The act of bending (as opposed to extending) a joint.

Food and Drug Administration (FDA): The FDA is a federal agency charged with ensuring that the food supply in the United States is safe and wholesome, that cosmetics are not harmful, and that medicines, medical devices, and radiation-emitting consumer products are safe and effective.

Free radicals: Unstable molecular fragments that can damage cells. One hypothesis holds that free radical formation in the substantia nigra causes the loss of nigral cells (leading to Parkinson's disease).

Frequency: number of cycles or repetitions within a fixed unit of time such as the number of cycles per second (Hertz or Hz). For example, essential tremor is typically 4 to 12 Hz.

Friedreich's ataxia: Friedreich's ataxia is the most common autosomal recessively inherited type of ataxia. Like the autosomal dominant spinocerebellar ataxias, the main symptoms are loss of coordination and unsteadiness of gait. Other systems may also be affected and people with Friedreich's ataxia should be monitored for heart disease and diabetes. The affected protein is called frataxin, and is thought to be involved in iron metabolism.

Froment's sign: Increased resistance to passive movements of a limb that may be detected upon voluntary activity of another body part.

Functional Magnetic Resonance Imaging (fMRI): A noninvasive, diagnostic scanning procedure that produces detailed, computerized images. The use of a "contrast agent" or dye enhances the detail of the images. Sequencing of these images may help physicians visualize the body's functioning, thus aiding differential diagnosis.

Gait: The style or manner of walking. Gait disturbances may be associated with certain neurologic or neuromuscular disorders, orthopedic conditions, inflammatory conditions of the joints (i.e., arthritic changes), or other abnormalities.

Gait apraxia: Loss of the ability to consciously sequence and execute the movements required to coordinate walking. Gait apraxia may result in unsteady walking patterns; "toe-walking"; a widely based, jerky gait; and balance difficulties.

Gamma knife radiosurgery: a highly specialized technique using a device that produces ionizing radiation to produce a lesion in the target tissue. This device focuses a beam of high intensity irradiation to a targeted area and is used as localized therapy to treat individuals with certain brain diseases (e.g., brain tumors, certain movement disorders, etc.).

Gamma-aminobutyric acid (GABA): An amino acid neurotransmitter that inhibits or decreases the electrical activities of nerve cells. GABA is the primary inhibitory neurotransmitter in the brain.

Gastroesophageal reflux: Backflow of stomach contents into the esophagus. This condition may be chronic and cause weakness of the lower esophageal sphincter, the ring-shaped muscle located at the junction of the esophagus and stomach.

Gastrointestinal: Gastrointestinal refers to the stomach and small and large intestines, as well as to the mouth, esophagus, anus, and related organs.

Gastrostomy tube: A plastic tube inserted into the stomach through a surgical incision in the abdomen. A gastrostomy tube is used to deliver liquified food to the digestive system when swallowing becomes dangerous or difficult.

Gene: Genes are the smallest units of heredity. The information from all the genes, taken together, makes up the blueprint or plan for the human body and its functions. A gene is a short segment of DNA, which is interpreted by the body as a plan or template for building a specific protein.

Genetic anticipation: A phenomenon in which the onset of symptoms of a hereditary disease appears to occur at a progressively earlier age in successive generations. Genetic anticipation has been demonstrated in a number of hereditary disorders (such as Huntington's disease, dentatorubropallidoluysian atrophy, etc.) in which the gene mutation consists of abnormally long sequences or "repeats" of particular coded instructions (e.g., unstable expansion of CAG repeats). With other disorders in which genetic anticipation has previously been suggested (e.g., essential tremor), studies have indicated that increased awareness of the condition in affected families may be responsible for earlier recognition of symptom onset.

Genetic heterogeneity: Manifestation of similar or the same observable characteristics or traits (i.e., phenotype) resulting from different genetic mechanisms, such as changes (mutations) of different genes or a combination of genes.

Germline mosaicism: The presence of a gene mutation for a disease trait in some yet not all of an individual's sexual reproductive cells (germ cells) within the ovaries or testes (gonads). Germline mosaicism is sometimes suspected when parents have more than one child with a genetic disorder transmitted as a dominant trait yet neither parent appears to be affected by the condition.

Gland: A gland is a structure or organ that makes a substance, such as a hormone or chemical, that is used elsewhere in the body. Some of these hormones and chemicals are insulin, bile, growth hormone, estrogen, and testosterone.

Gliosis: A proliferation of astrocytes in damaged areas of the central nervous system (CNS). Astrocytes are relatively large glial cells, which are the connective tissue cells of the CNS. Astrocytes have various functions, including accumulating in areas where nerve cells (neurons) have been damaged. Gliosis and neuronal loss in certain brain regions are findings seen in various neurodegenerative disorders.

Globus pallidus: A major substructure of the basal ganglia deep within the brain. Specialized groups of nerve cells in the globus pallidus function as an "intermediate relay system." This system processes and transmits information from the basal ganglia by way of the thalamus to areas of the brain that regulate complex motor functions (e.g., motor cortex, premotor area of frontal lobe).

Glottis: The slit-like opening between the vocal cords; the region of the voice box (larynx) consisting of the vocal cords and the opening between them.

Glutamate: An amino acid that is a primary excitatory neurotransmitter in the central nervous system. This chemical agent plays an essential role in initiating and transmitting nerve impulses, crossing synapses to stimulate postsynaptic neurons.

Gram staining: Gram staining is a method used to classify bacteria. In the first step of the process bacteria are stained with gentian violet and then treated with Gram solution (named after Dr. Gram, the inventor of the technique). After the bacteria have been decolorized with alcohol and treated with safranine, a red organic dye, and washed in water, those bacteria that keep the gentian violet are gram-positive and those that do not are gram-negative.

Gray matter: Nerve tissue that primarily consists of nerve cell bodies, dendrites, and unmyelinated axons, thus having a gray appearance. In contrast, white matter predominantly contains myelinated nerve fibers.

Half life: The half life of a drug is the time it takes for the blood level to decrease by half after a drug is stopped.

Hallervorden-Spatz disease: A slowly progressive hereditary disorder characterized by abnormal accumulations of iron pigments in certain regions of the basal ganglia (e.g., globus pallidus and substantia nigra). This autosomal recessive disorder typically becomes apparent during late childhood or adolescence. Associated symptoms may include progressive stiffness and resistance to movement (rigidity); increasing difficulties speaking and eating; sustained muscle contractions that result in repetitive twisting motions or unusual postures or positions (dystonia); the presence of multiple, irregular, jerky motions that may combine to appear flowing or writhing in nature (choreoathetosis); and/or other abnormalities.

Hallucinations: Hallucinations are alterations in sensory perception, usually involving hearing voices or seeing images that do not exist. Hallucinations may be simple or complex.

Heat pain: Heat pain arises from warm or hot temperatures.

Hemichorea: Irregular, abrupt, relatively rapid involuntary (i.e., choreic) movements that are unilateral or involve muscle groups on one side of the body.

Hemidystonia: Hemidystonia is a form of dystonia that affects one side of the body or is characterized by unilateral involvement of the upper and lower limbs.

Hemizygote: Refers to a cell, organism, or individual with only one of a pair of genes for a specific trait. This term is often used to describe males who inherit one copy of an X-linked disease trait. It may also refer to the state in which genetic material is deleted from one member of a chromosomal pair.

Hereditary: Inherited; inborn; referring to the genetic transmission of a trait, condition, or disorder from parent to offspring.

Heredodegenerative: Pertaining to genetically transmitted (hereditary) neurologic disorders characterized by progressive neuronal loss and other neurodegenerative changes (e.g., associated gliosis). For example, the term "heredodegenerative dystonias" is used to refer to several, usually hereditary disorders in which neurodegenerative changes may lead to dystonia as a primary feature and other neurologic symptoms are typically present. However, in some patients with such disorders, dystonia may not always develop and other neurologic features may be primary findings. Disorders that have been categorized as heredodegenerative dystonias include ataxia-telangiectasia, Hallervorden-Spatz disease, Huntington's disease, Parkinson's disease, progressive supranuclear palsy, neuroacanthocytosis, and Wilson's disease.

Hertz (Hz): cycles per second.

Heterogeneity: comprising unrelated or differing parts or elements.

Heterozygous carriers: The term "heterozygosity" refers to the state of having different genes that occupy the same position (locus) on one or more paired chromosomes. "Heterozygous carriers" describes individuals who carry a single copy of a mutated gene for a disease trait, such as females who have a copy of a disease gene for an X-linked disorder. Because females have two X chromosomes yet only one functioning copy is necessary, a percentage of X chromosomes with the mutated gene may not be expressed, typically in a random pattern (known as "random X chromosome inactivation"). Therefore, females who are heterozygous for an X-linked disease trait often have no disease manifestations or less severe symptoms than affected males. However, because males have one X chromosome from the mother and one Y chromosome from the father, males who carry an X-linked disease trait will typically fully express the mutated gene. Rarely, females who are heterozygous for an X-linked disease trait may manifest symptoms with about the same severity as affected males.

Hoehn and Yahr Scale: The Hoehn and Yahr Scale is a commonly used physician-administered rating of the global severity of the motor symptoms of Parkinson's disease. Scores range from 0, no signs of disease, to 5, wheelchair bound or bedridden without assistance.

Homeopathy: Homeopathy is a system of medicine that is based on the Law of Similars, a belief in which substances that cause healthy people to exhibit symptoms can, conversely, be used to restore the body to health.

Homeostasis: Homeostasis exists when an organism’s internal state of being is in balance even when the external environment is changing.

Homocystinuria: A metabolic abnormality characterized by excessive amounts of the amino acid homocystine in the urine. Homocystinuria, which may be transmitted as an autosomal recessive trait, may result from deficient activity of certain enzymes involved in the metabolic conversion of the amino acid methionine to cysteine. Associated symptoms and findings often include developmental delay; dislocated lens of the eyes (ectopia lentis); thin, weak muscles; progressive mental retardation; psychiatric abnormalities; skeletal defects; blockage of a blood vessel by a piece of a blood clot (thrombus) carried in the bloodstream (thromboembolism); and/or other abnormalities.

Huntington disease: Huntington disease (HD) causes a specific type of nerve cells in the brain to die off. In the early stages of the disease, symptoms may include slight personality changes, forgetfulness, clumsiness, and "fidgeting" movements of the fingers, eyes, or toes. As HD becomes worse, it may cause memory, thinking, behavior, and planning problems, as well trouble talking, swallowing, and walking. HD is an autosomal-dominant inherited condition, meaning that if one of your parents has HD, you have a 50-50 chance of getting it. A blood test can tell you if have the HD gene and will develop the disease. Genetic counseling can help you weigh the risks and benefits of taking the test. There is no cure for HD, but some medicines may help with the symptoms.

Huntington’s Disease-like 2 (HDL2): This rare disease strongly resembles Huntington’s disease in its inheritance and symptoms, which include abnormal movements, personality changes, and changes in the ability to think and process information. HDL2 is due to damage to the same parts of the brain as in HD; however, it is caused by mutation of a different gene, and also has an increased number of repeats. To date, almost all affected families have been of African ancestry. The other “Huntington’s disease-like” disorders (types 1, 3, and 4) are even rarer and have only been reported in one family each.

Hyperglycemia: An abnormally high level of the simple sugar glucose in the blood.

Hyperkalemic: Pertaining to hyperkalemia, a condition characterized by unusually high concentrations of potassium in the blood. Potassium, a positively charged ion, helps to regulate water balance, nerve conduction, and muscle contraction. Hyperkalemia may lead to various signs and symptoms, such as diarrhea, nausea, abdominal cramps, weakness, and, with increasing severity, abnormal heart rhythms and muscle paralysis.

Hyperkinetic: Characterized by excessive movement because of abnormally increased motor activity or function. Certain movement disorders are termed "hyperkinetic" such as tics or essential tremor.

Hypertension: Hypertension, also referred to as high blood pressure, is an abnormal increase in the pressure of blood against the walls of the arteries. Hypertension may be essential, meaning that it has no known cause, or may be related to another disease such as kidney disease or diabetes.

Hyperthyroidism: a condition caused by the effects of too much thyroid hormone on tissues of the body.

Hyperventilation: Abnormally rapid breathing usually accompanied by air swallowing. Hyperventilation results in excessive intake of oxygen and increased elimination of carbon dioxide, which may eventually lead to a disturbance in the body's acid-base balance.

Hypnagogic hallucinations: Hypnagogic hallucinations are vivid, realistic, often frightening dreams that occur while the person is falling asleep or immediately upon awakening.

Hypocretin: Hypocretin (also known as orexin) 1 and 2 are neuropeptides. These protein-like molecules are found in the brain and act as hormones or neurotransmitters. They are involved in the regulation of sleep and wakefulness.

Hypokalemic: Referring to hypokalemia, which is characterized by abnormally low potassium levels in the blood. Potassium, the primary positively charged ion (cation) of muscle, plays an important role in regulating muscle contraction, nerve conduction, and other bodily functions. Hypokalemia may result in confusion, fatigue, weakness, and, in severe cases, paralysis and heart rhythm abnormalities.

Hypokinetic: Diminished movement and decreased motor function. Some movement disorders are hypokinetic, such as Parkinson's disease.

Hypoparathyroidism: An endocrine condition characterized by insufficient secretion of parathyroid hormone due to injury, disease, or congenital abnormalities of the parathyroid glands. Parathyroid hormone plays an essential role in regulating calcium balance in the body. Hypoparathyroidism results in low calcium blood levels (hypocalcemia), leading to various symptoms and findings. For example, hypoparathyroidism may cause a condition known as tetany in which increased excitability of nerves and muscles results in uncontrollable, painful muscle spasms and cramping; abnormal involuntary movements resembling chorea; spasmodic closure of the larynx (laryngospasm); and other findings. Hypoparathyroidism may also lead to seizures; abnormal calcium deposits (calcifications) in the basal ganglia; loss of transparency of the lenses of the eyes (cataracts); dry, scaly skin; weakened tooth enamel; and/or other abnormalities.

Hyposmia: Hyposmia refers to a decreased sense of smell.

hypoxia: abnormally low levels of oxygen

Iatrogenic: a disease or disorder that is induced inadvertently by a physician or surgeon or by medical treatment or diagnostic procedures.

Idiopathic: A disorder or condition of spontaneous origin; self-originated or of unknown cause. The term is derived from the prefix "idio-" meaning one's own and "pathos" indicating disease.

Idiopathic epilepsy: Recurrent seizures of unknown origin or cause; repeated episodes of uncontrolled electrical activity in the brain that occur in the absence of detectable brain lesions. Also known as essential or primary epilepsy, these conditions are often thought to have a genetic component. This may suggest that affected individuals have an inherited predisposition for recurrent seizures.

Illusions: Illusions occur when a person sees something that is real but misinterprets what it is.

Immunofluorescence: This technique uses antibodies linked to a light-emitting or fluorescent dye in order to study foreign substances in a tissue sample.

Immunogenicity: The ability to or the degree to which a particular substance may provoke an immune response; having the properties of an antigen or any substance that may trigger a particular immune reaction, such as the production of antibodies.

Implantable Pulse Generator (IPG): A device that is placed under the skin near the collarbone as part of a surgical procedure known as deep brain stimulation. Wire leads from electrodes implanted in the brain are connected to the pulse generator, which then delivers continuous high frequency electrical stimulation to the thalamus via the implanted electrodes. This form of stimulation probably "jams" the nucleus and therefore modifies the message in the movement control centers of the brain, serving to suppress tremor.

Inflammation: Inflammation is the body’s first response to injury or irritation. The classic signs of inflammation are pain, heat, redness, swelling, and loss of function.

Inhibition: The restraint, suppression, or arrest of a process or the action of a particular cell or organ; the prevention or slowing of the rate of a chemical or an organic reaction. The term "reciprocal inhibition" refers to the restraint or "checking" of one group of muscles upon stimulation (excitation) and contraction of their opposing (antagonist) muscles.

Inhibitor: A substance that blocks, restricts, or interferes with a particular chemical reaction or other biologic activity.

Innervate: To supply a body part, tissue, or organ with nerves or nervous stimulation.

Insidious: Of subtle, gradual, or imperceptible development; referring to the development of symptoms that may not be recognized by an affected individual until the disorder in question is established.

Intestine: The intestine is sometimes called the bowel or the gut. It is the part of the digestive system that extends from the stomach to the rectum. It is made up of the small and large intestines and serves to absorb water and nutrients from the food and liquids that we drink and eat. The small intestine extends from the stomach to the large intestine and is made up of three segments: the duodenum, the jejunum, and the ileum.

Intravenous: Within a vein or veins, as in introducing certain substances, such as fluids, nutrients, or medications, directly into a vein.

Ion: An electrically charged atom or group of atoms due to the loss or gain of one or more electrons. Positively charged ions, known as cations, include potassium, calcium, sodium, hydrogen, ammonium, and magnesium. Negatively charged ions, called anions, include chloride, phosphate, and bicarbonate. The transfer of ions across cellular membranes plays an essential role in vital bodily processes, including enzyme activation, protein metabolism, acid-base balance, nerve impulse transmission, and muscle contraction.

ischemia: Ischemia occurs when the flow of oxygen-rich blood to tissue in the body is reduced or stopped.

Isoleucine: an essential amino acid.

Jejunostomy tube: The jejunostomy tube is similar to a gastrostomy tube, although this tube is longer and is inserted through the abdominal wall into the jejunum, the middle section of the small intestine.

Joint contractures: Permanent flexing or extension of joints in fixed postures due to shortening of muscle fibers. Contractures, abnormal fixation of the limbs, and associated deformity may result from prolonged immobility of developing joints.

Juvenile myoclonic epilepsy: A form of idiopathic epilepsy or recurrent seizures of unknown origin, with symptom onset typically occurring from approximately 12 to 16 years of age. The condition is characterized by sudden, involuntary, "shock-like" muscle jerks (myoclonus) that primarily occur during the morning or with stress, fatigue, or alcohol consumption. Patients may later develop generalized tonic-clonic seizures associated with loss of consciousness and rhythmic contraction and relaxation of all muscle groups.

Kinesigenic: Caused by sudden voluntary movement; movement induced. More specifically, this term is often used to describe abrupt episodes of involuntary movement that are provoked by sudden motions or unexpected stimuli.

Lafora's disease: A progressive myoclonic encephalopathy (PME) that is inherited as an autosomal recessive trait. Associated symptoms typically begin in childhood or early adolescence and include frequent seizures characterized by loss of consciousness and rhythmic contraction and relaxation of all muscle groups (generalized tonic-clonic seizures); sudden, involuntary, "shock-like" muscle jerks (myoclonus); and rapidly progressive deterioration of thought processing and acquired intellectual abilities (dementia). Removal and microscopic examination of minute tissue samples (e.g., muscle fibers, liver cells, etc.) reveal abnormal, characteristic deposits of complex proteins and carbohydrates within the fluid portion of cells (intracytoplasmic inclusions known as "Lafora bodies").

Lance-Adams syndrome: Also known as "posthypoxic" or "postanoxic action myoclonus," this condition is characterized by the development of chronic action myoclonus due to a temporary lack or inadequate supply of oxygen to the brain (cerebral hypoxia or anoxia). Patients with action myoclonus experience sudden, involuntary, "shock-like" muscle contractions that may be triggered or aggravated by voluntary movement. Lance-Adams syndrome is also often associated with cerebellar ataxia or lack of coordination, postural imbalance, and other associated findings.

Lateral: Sideways; of, on, from, or toward the side.

Leigh disease: A disorder of mitochondrial function that typically becomes apparent during infancy. Also known as subacute necrotizing encephalomyelopathy, the disorder may be characterized by feeding and swallowing difficulties, vomiting, muscle weakness, low muscle tone (hypotonia), and delayed acquisition of motor and language skills. Affected infants and children may also develop seizures; an impaired ability to coordinate voluntary movements (ataxia); involuntary, rapid, rhythmic eye movements (nystagmus); tremor; dystonia; and/or other abnormalities. The disorder, which has a number of underlying causes, may occur randomly for unknown reasons (sporadically) or be transmitted as an autosomal recessive or X-linked trait. Leigh disease is associated with characteristic changes of the central nervous system (CNS), including symmetric regions of localized tissue loss (necrosis) and neurodegenerative changes of the basal ganglia, thalamus, brainstem, spinal cord, and other regions of the CNS.

Leucine: an essential amino acid.

Levodopa: Levodopa is a drug used to treat Parkinson's disease. It is also called L-dopa and, in the United States, is sold as Sinemet. Levodopa crosses the blood-brain barrier and is converted by the body to dopamine. A loss of dopamine-producing nerve cells in the part of the brain that controls movements leads to the symptoms of Parkinson's disease.

Lewy body: A Lewy body is a mass of protein found in dying nerve cells in the brain.

Lewy Body Disease: Also called diffuse Lewy body disease, Lewy body dementia. Lewy body disease is a common cause of dementia, accounting for approximately 15%-20% of all cases. The age of onset is typically in the late 50s through the 70s. It is more common in men than women. Lewy Body Disease is characterized by more daily fluctuations in symptoms than Alzheimer's disease, as well as more prominent psychosis. Patients are prone to have adverse reactions to antipsychotics. Patients also have parkinsonian features early in the disease, including slowed movements and rigidity, though usually without tremor. The Lewy body is a protein aggregate found in dying neurons in the brain. In Lewy body disease, the Lewy bodies are most prominently found in the cortex, or surface of the brain, versus in the midbrain for Parkinson's disease.

Lipopolysaccharide: A lipopolysaccharide is a molecule made up of a lipid (a fat) with a polysaccharide (a complex sugar). In most circumstances, the terms lipopolysaccharide and endotoxin can be used interchangeably.

LRKK2: LRRK2 (pronounced as lark-two) stands for leucine-rich repeat kinase 2. It is the name of a gene that is responsible for providing instructions for making a protein called dardarin. The gene is thought to be active in the brain. Although little is known about the LRRK2 gene or dardarin protein, researchers do know that part of the LRRK2 gene provides instructions to make a protein segment that is rich in a protein building block (amino acid) called leucine. Proteins with leucine-rich regions appear to play a role in activities that require protein-protein interactions, such as transmitting signals or helping to assemble the cell's structural framework (cytoskeleton). Other parts of dardarin, such as a region called the WD40 domain, also indicate that dardarin is capable of multiple protein-protein interactions. Researchers also suspect that the dardarin protein has an enzyme activity known as kinase. Proteins with kinase activity assist in the transfer of a phosphate group (a cluster of oxygen and phosphate atoms) from the energy molecule ATP to amino acids in certain proteins. This phosphate transfer is called phosphorylation, and it is a necessary step in turning on and off many cell activities.

Lumbar puncture: A procedure during which a sample of fluid (i.e., cerebrospinal fluid [CSF]) is removed from the spinal canal for diagnostic or therapeutic purposes. During the procedure, CSF is obtained via a hollow needle inserted between two bones of the spinal column within the lower back (i.e., usually the third and fourth lumbar vertebrae). Laboratory analysis conducted on CSF may help to diagnose central nervous system infections, certain tumors, or particular neurologic disorders. In some cases, lumbar puncture may also be performed to inject certain medications into the CSF, such as particular anticancer (chemotherapeutic) agents.

Lysosomal: Referring to lysosomes, which are membrane-bound bodies (organelles) outside the nuclei of cells that contain various enzymes engaged in intracellular digestion.

Lysosomal storage diseases: Inborn errors of metabolism in which deficiency or impaired functioning of particular lysosomal enzymes leads to an abnormal accumulation of certain substances (e.g., fats, complex carbohydrates) within particular cells, progressively affecting multiple bodily tissues and organs. (Lysosomes are membrane-bound, enzyme-containing bodies within cells that engage in digestive processes; enzymes are proteins that accelerate the rate of certain chemical reactions in the body.) Most lysosomal storage disorders (e.g., mucolipidoses, mucopolysaccharidoses, lipidoses, etc.) are thought to be inherited as autosomal recessive traits.

Machado-Joseph disease: Machado-Joseph disease, also known as spinocerebellar ataxia (SCA) type III, is probably the most common autosomal dominant SCA. This disorder was previously known as Azorean disease, as a large number of Portuguese families from the Azores Islands were found to be affected; however, SCA type III has now been reported in many other ethnic groups. In addition to unsteadiness of gait (ataxia), symptoms may involve parkinsonism, dystonia, and chorea. The affected protein is called ataxin-3; however, its function is not yet known.

Magnetic resonance imaging (MRI): A diagnostic scanning technique during which radio waves and an electromagnetic field are used to help create detailed, cross-sectional images of specific organs and tissues. MRI is often considered a particularly valuable imaging technique for studies of the brain and spinal cord because of the MRI’s ability to scan images from various angles and provide strong contrast between healthy and abnormal tissues.

MAO inhibitors: MAO inhibitors are drugs that inhibit or prevent the action of an enzyme called monoamine oxidase (MAO). This enzyme helps to break down dopamine. When MAO is inhibited, the amount of time that dopamine acts in the brain is lengthened. Examples of MAO inhibitors that are used in the treatment of Parkinson disease include rasagiline, (Azilect®) and selegiline (Eldepryl®, Zelapar®).

MAO-B inhibitors: Inhibitors of the enzyme monoamine oxidase B. MAO-B helps break down dopamine; inhibiting it prolongs the action of dopamine in the brain.

Matched control subjects : Matched control subjects are people who have similar characteristics, such as age, height, weight, education, sex, or other characteristics, as the patients being studied, but they do not have the disease. In this study, the control subjects were matched with regard to age and sex to each person who had PD. The control subjects did not have PD, parkinsonism, or any other form of tremor.

Mean: An average; intermediate or middle position in value, quantity, or degree. The "arithmetic mean" is a statistical measure derived by adding a set of values and dividing the total by the number of values.

Mechanical pain: Mechanical pain arises from pressure or touch.

Media impression: A media impression is the interaction between a web site, radio spot, television program, or newspaper or magazine article and a single member of the audience who is exposed to that medium.

Medially: Toward the middle; closer to or oriented toward the midline or median plane of a body or structure. The "median plane" refers to the imaginary plane that divides a body into symmetrical parts.

Melanoma: Melanoma is the most serious life-threatening type of skin cancer. The tumor cells develop in the melanocytes, the cells that give skin its color.

Membrane: A membrane is a thin film that allows only some substances to pass through it or that prevents the mixing of two substances.

Membrane lipid peroxidation: the oxidative deterioration of polyunsaturated fatty acids in which polyunsaturated fatty acids are converted to lipid hydroperoxides.

Meningitis: Meningitis is an infection of the meninges, the thin three-layer membranes that cover and protect the brain and spinal cord.

MERFF syndrome (myoclonus epilepsy with ragged-red fibers): A rare hereditary disorder characterized by neurologic and muscle abnormalities due to defects of genetic material (DNA) in mitochondria, the rod-like structures outside the nuclei of cells that serve as a primary source of cellular energy. Removal and microscopic examination of minute samples of muscle fibers reveal structurally abnormal mitochondria (a finding known as "ragged-red fibers"). Associated symptoms include muscle weakness; sudden, involuntary, "shock-like" muscle contractions induced by voluntary movements or in response to external stimuli (action or reflex myoclonus); repeated seizures (epilepsy); progressively impaired coordination of voluntary movements (ataxia); and/or gradual deterioration of intellectual functioning (dementia). Some affected individuals may also have additional abnormalities, such as hearing loss; degeneration of the nerves (i.e., optic nerves) that convey impulses from the retinas to the brain (optic atrophy); short stature; heart muscle disease (cardiomyopathy); or other findings.

Metabolism: Refers to the ongoing chemical processes of cells of the body, including catabolism and anabolism. Catabolism or so-called "destructive metabolism" is the breakdown of complex chemical compounds into simpler substances, typically liberating or releasing energy. In contrast, anabolism or "constructive metabolism" refers to the "building up" or conversion of simple substances into more complex chemical compounds, requiring energy consumption (provided by catabolic processes).

Methylphenidate: Methylphenidate is a drug that is used as a central nervous system stimulant. A common trade name is Ritalin®. This drug is usually used to treat symptoms of attention-deficit/ hyperactivity disorder or narcolepsy. It acts like caffeine but has a more powerful alerting effect and is not as potent as amphetamines.

Metoclopramide: Metoclopramide is a medication used to treat nausea and vomiting or migraine and to help with emptying the stomach for people with specific medical conditions. It works by blocking dopamine receptors.

Mini-Mental State Examination : This short clinician-administered test measures cognitive status (the ability to think, calculate, and reason) in adults. This test is used to measure the presence of impaired cognition or a change in cognition over time.

Mitochondrial: Referring to mitochondria or rod-like structures inside cells of the body whose primary functions include the production and regulation of energy.

Mitochondrial dysfunction: Mitochondria are the main energy source of cells. Mitochondria convert nutrients into energy and also perform many other specialized tasks. Dysfunction means that something is not working or functioning in the correct way. Therefore, mitochondrial dysfunction refers to a situation in which the mitochondria are not working properly.

Monoamine: A molecule containing one amine group. An amine is an organic compound containing nitrogen. The so-called "biogenic monoamines" are natural, biologically active compounds that often function as neurotransmitters, including dopamine, serotonin, noradrenaline, and epinephrine.

Monotherapy: A drug used alone to treat a disease (opposite of combination therapy).

Mood or bipolar disorder: Mood or bipolar disorder is a mental illness in which people have wide mood swings. The moods include mania, during which the person has lots of energy or is excessively irritable, and depression, during which the person feels sad and hopeless. The person with bipolar can have normal moods between the swings but may also switch quickly between the highs and lows. Psychosis: Psychosis is a thought disorder characterized by impaired ability to distinguish reality from unreality, personality changes, and deterioration of normal social functioning. People with psychosis may experience hallucinations, illusions, or delusions, or they may be paranoid or have distorted thinking.

Motor fluctuations: Motor fluctuations occur when levodopa is used to treat Parkinson’s disease. As the disease becomes worse, the number of cells in the brain that store dopamine decreases, the symptoms of Parkinson’s disease worsen, and levodopa is not as effective in controlling the symptoms. When this happens, a person is said to have “off” episodes.

Motor symptoms: The motor symptoms of Parkinson's disease include tremor, stiffness (called rigidity), slowness or absence of movement (called bradykinesia or akinesia, respectively), and difficulty maintaining balance or unstable posture.

Multiple sclerosis (MS): A progressive disease of the central nervous system characterized by destruction of myelin (demyelination), the fatty substance that forms a protective sheath around certain long nerve fibers (axons). Myelin serves as an electrical insulator, enabling the effective transmission of nerve signals. Patients with MS may develop paresthesias, such as numbness or tingling; muscle weakness and stiffness; impaired coordination; abnormal reflexes; an inability to control urination (urinary incontinence); slurred speech; visual disturbances; and/or other symptoms and findings.

Multiple Sleep Latency Test (MSLT): The MSLT is used to measure how likely a person is to fall asleep. The test takes place over a seven-hour period during the day. Every two hours, for 20 minutes, the patient lies in a quiet dark room and is hooked up to a machine that measures brain waves, heart rate, muscle activity, and eye movements. This recording allows the doctor to see how quickly the patient falls asleep in this situation or if the patient falls asleep at all.

Multiple System Atrophy: A neurodegenerative disorder characterized by parkinsonism, ataxia, and dysfunction of the autonomic nervous system

Muscle tone: The low level of contraction in a muscle not being intentionally contracted.

Mutated: Altered; a mutation is a change in a gene

Mutation: A change in a gene, such as loss, gain, or substitution of genetic material, that alters its function or expression. This change is passed along with subsequent divisions of the affected cell. Gene mutations may occur randomly for unknown reasons or may be inherited.

Myelin: The whitish, fatty substance forming the segmented, multilayered wrappings or "sheaths" around certain long nerve fibers or axons. Myelin sheaths electrically insulate axons, serving to speed the transmission of nerve signals (action potentials).

Myelinated: Referring to long nerve fibers (axons) that have myelin sheaths. Consisting of segmented, multilayered wrappings of myelin, a whitish protein, myelin sheaths wrap around certain nerve fibers, providing electrical insulation and serving to speed the transmission of nerve signals.

Myoclonic: Pertaining to myoclonus or irregular, involuntary, shock-like contractions or spasms of a muscle or muscle group.

Myoclonus: A neurologic movement disorder characterized by brief, involuntary, twitching or "shock-like" contractions of a muscle or muscle group. These jerk-like movements may be accompanied by periodic, unexpected interruptions in voluntary muscle contraction, leading to lapses of sustained posture (known as "negative myoclonus"). So-called "positive" and "negative" myoclonus are often seen in the same individuals and may affect the same muscle groups. Myoclonus is often a nonspecific finding, meaning that it may occur in the setting of additional neurologic abnormalities and be associated with any number of underlying conditions or disorders. In other patients, myoclonus appears as an isolated or a primary finding. Depending on the underlying cause and other factors, the shock-like muscle jerks may occur repeatedly or infrequently; may tend to appear under specific circumstances (e.g., with voluntary movements or in response to specific external sensory stimuli); and may affect any body region or regions.

Narcolepsy: Narcolepsy is a sleep disorder marked by sudden, uncontrollable urges to sleep that cause a person to fall asleep at inappropriate times.

Nasoduodenal tube: A nasoduodenal tube is a flexible rubber tube that is inserted through the nose and into the duodenum (the section of the small intestine closest to the stomach) via the esophagus and stomach. It can be used to remove the contents of or decompress the small intestine or to provide nutrition support or medication.

National Institutes of Health (NIH): The NIH is one of the world’s foremost medical research centers and the federal focal point for medical research in the United States. The NIH, comprising 27 separate Institutes and Centers, is one of eight health agencies of the Public Health Service that, in turn, is part of the U.S. Department of Health and Human Services.

Necrosis: Cell death. Loss of cells, tissues, or parts of a structure or organ due to the progressively degrading actions of certain enzymes, such as the degradation of DNA within the nucleus of dying cells. Necrosis may result from a loss of blood supply (ischemia), infection, excessive exposure to ionizing radiation, certain chemicals, or extreme temperatures.

Neoplastic: Relating to the formation of a neoplasm (tumor) or a new, abnormal growth characterized by uncontrolled, progressive multiplication of cells. Neoplasms may be benign or malignant.

Nerve conduction velocity (NCV) test: A diagnostic study during which both sensory and motor nerves are repeatedly stimulated in order to measure the speed at which nerve impulses are conducted. Unusually slow conduction velocities suggest damage to nerve fibers (e.g., loss of the protective covering surrounding certain nerve fibers [demyelination] or other disease process).

Nervous system: The nervous system of the human body is divided into two interconnected systems: the central nervous system, which is made up of the brain and spinal cord, and the peripheral nervous system. The peripheral nervous system is further divided into the somatic nervous system (made up of peripheral nerve fibers that send sensory information to the central nervous system and motor nerve fibers that project to skeletal muscle) and the autonomic nervous system.

Neuroacanthocytosis: Also known as choreoacanthocytosis, this is a genetic disorder that most often becomes apparent between the ages of 25 to 45 years. The disorder is usually transmitted as an autosomal recessive trait. Associated symptoms may include generalized chorea; dystonia affecting muscles of the mouth and tongue; potentially mutilating lip- and tongue-biting; and sudden, involuntary, repetitive muscle movements (motor tics) and vocalizations (vocal tics). Patients may also develop personality changes and cognitive decline, seizures, parkinsonism, atrophy of muscle tissue (amyotrophy), and difficulties speaking and swallowing. Neuroimaging studies may reveal atrophy of certain regions of the basal ganglia (e.g., caudate nuclei and putamen [striatum]). The disorder may be confirmed by blood tests revealing the presence of abnormal circulating red blood cells that have spur-like or thorny projections (acanthocytosis).

Neurochemical: Referring to the chemistry or biochemical processes of the nervous system, such as activities involving naturally produced chemicals (i.e., neurotransmitters) that enable nerve cells (neurons) to communicate.

Neurodegenerative: Marked by or pertaining to neurologic degeneration; deterioration of the structure or function of tissue within the nervous system.

Neuroimaging: The production of detail, contrast, and clearness in images of the brain and spinal cord (central nervous system) through the use of computed tomography (CT) scanning, magnetic resonance imaging (MRI), positron emission tomography (PET) scanning, or other imaging techniques to assist in diagnosis, treatment decisions, or research.

Neuroleptic: a drug used to treat psychotic behavior.

Neuroleptic malignant syndrome: a life-threatening neurologic disorder most often caused by an adverse reaction to neuroleptic or antipsychotic drugs. Symptoms include high fever, sweating, unstable blood pressure, stupor, muscular rigidity, and autonomic dysfunction. In most cases, the disorder develops within the first 2 weeks of treatment with the drug; however, the disorder may develop any time during the therapy period. The syndrome can also occur in people taking anti-parkinsonism drugs known as dopaminergics if those drugs are discontinued abruptly.

Neuron: An individual nerve cell.

Neuronal: Pertaining to a neuron or neurons.

Neuroprotective effect: Having the ability to prevent or slow the death of neurons. The drug selegiline (Eldepryl®) may have a neuroprotective effect, possibly by preventing formation of free radicals.

Neuroreceptor: Specific sites on the surface of a nerve cell to which certain special substances (neurotransmitters) bind, initiating the conduction of impulses (or signals) to other nerve cells.

Neurotoxin: a substance that interferes with the electrical activity or functioning of nerve cells (neurons), preventing them from communicating with each other.

Neurotransmitter: A specialized substance (such as norepinephrine or acetylcholine) that transfers nerve impulses across spaces between nerve cells (synapses). Neurotransmitters are naturally produced chemicals by which nerve cells communicate.

Nigrostriatal system: Referring to the substantia nigra, the striatum, and the connection between them.

Nocardia asteroides: Nocardia asteroides are gram-positive bacteria that are found throughout the world in the soil. Localized infections usually occur in the skin following contamination of a scrape or scratch, and disseminated infections typically occur when a person with a compromised immune system inhales the bacteria. The primary site of disseminated infection is typically the lungs, where abscesses form, but the infection may spread to other parts of the body, including the brain, liver, and kidneys.

Nomenclature: System of names used in a particular scientific discipline to consistently and methodically designate certain classifications and avoid confusion or ambiguity.

Non-ergotoline medication: A dopamine agonist me