Definitions Used In HD
"A" through "B"


"A" through "B"
"C" through "D"
"E" through "J"
"K" through "P"
"Q" through "X"

Color coding:
Other diseases similiar to HD
Action tremora 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. (see HD Activities of Daily Living)
Referring to symptoms of abrupt onset, often of marked severity or intensity.
Auditory-evoked potentials, or "brainstem auditory-evoked response") are the responses of the brainstem and auditory regions of the cortex to brief sounds in the ear. In addition to determining abnormalities of hearing, AEPs may be helpful in finding subtle problems with the function of the brainstem.
Akathisia  (restlessness)
Is an extremely uncomfortable internal sense of restlessness, sometimes
induced by neuroleptics, which may cause patients to pace, or be unable to sit still. It can be mistaken for agitation or anxiety, prompting the physician to increase the dose of the offending drug, creating a vicious cycle.

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

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: (prenatal test)
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.

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

Lack of interest in acts that previously provided pleasure

During this test, a series of regular x-rays are taken as a radiopaque (impenetrable by x-ray) contrast material (dye) is injected directly into an artery. The resulting radiographic image is like a map of the blood vessels. An angiogram is an accurate way of looking at arteries and veins of the head, neck and brain, and provides information that cannot be obtained with other tests. It is often used to determine the degree of narrowing of an artery in the head or neck.  It can also be used to detect the location and size of aneurysms and vascular malformations. 
This is an invasive test, requiring a physician to insert a catheter into the major artery near the groin and direct it "upstream" to the arteries near the brain.

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

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.

Drugs that block the action of acetylcholine, a neurotransmitter whose effects oppose dopamine. By blocking acetylcholine's action, these drugs increase dopamine's ability to  control movement.

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.

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.

Anxiety   -is a word  that can be used to mean the same thing are worry, stress, or nervousness. In psychology-speak, anxiety is seen as a feeling that a person
has when they think there is some sort of threat or danger to them. 
Anxiety is usually split into two different types; Panic Attacks, and Generalised Anxiety States which you can think of as people who worry too much about everything. Physical signs of Generalised anxiety can include Shakiness, Tensed up muscles, Sweating, Palpitations, Dry mouth, Finding it hard to concentrate and Going to the toilet a lot.
Some of the most effective forms of therapy for this problem include Cognitive-Behavioural Therapy, Behavioural Therapy, and various techniques such as Relaxation. Various drugs can also be used, and there are now specialist treatment packages available specifically designed to help manage anxiety.
Aphasia: (Language/speech)
Loss or impairment of language comprehension or production is called
aphasia. The difficulties in language function must not be attributable to
impairment of the speech or writing production apparatus, such as muscles of
the tongue and throat, or peripheral sensory loss. Although the person
suffering such impairment may have trouble articulating a language
utterance, the brain centers moderating language are presumably intact.

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 is a collective term used to describe impairment in carrying out purposeful movements. 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. Impaired or absent language function, usually referring to speech; which results from an injury to brain structures usually in the dominant hemisphere (the side of the brain that controls language function is usually the side opposite to the handedness of the person and is referred to as the dominant hemisphere by definition).
People with severe aphasia are usually extremely limited in explaining themselves by pantomime or gesture, except for expressions of emotion. Commonly they will show you something in their wallet, or lead you to show you something, but this is the extent of their non-verbal communication.
Specific examination usually shows that they are unable to perform common expressive gestures on request, such as waving good-bye, beckoning, or saluting, or to pantomime drinking, brushing teeth, etc. (limb apraxia). Apraxia may also primarily affect oral, non-speech movements, like pretending to cough or blow out a candle (facial apraxia).
This disorder may even extend to the inability to manipulate real objects. More often, however, apraxia is not very apparent unless one asks the patient to perform or imitate a pretended action. For this reason it is almost never presented as a complaint by the patient or the family. Nevertheless it may underlie the very limited ability of people with aphasia to compensate for the speech impairment by using informative gestures.
This term is applied to persons who are left with a persistent inability to supply the words for the very things they want to talk about-particularly the significant nouns and verbs. As a result their speech, while fluent in grammatical form and output  is full of vague circumlocutions and expressions of frustration. They understand speech well, and in most cases, read adequately.  Difficulty finding words is as evident in writing as in speech.

Apraxia of speech
This term is frequently used by speech pathologists to designate an impairment  in the voluntary production of articulation and prosody (the rhythm and timing) of speech. It is  characterized by highly inconsistent errors. This web site provides
information on ocular motor apraxia including message boards and mailing lists.
Apraxia-Ocular Motor
Ocular Motor Apraxia (OMA) is a visual condition where a child or person has difficulty in controlling their horizontal eye movements. This web site provides information  on ocular motor apraxia including message boards and mailing lists.

Aphasia--Mixed non-fluent
This term is applied to patients who have sparse and effortful speech, resembling severe Broca's aphasia. However, unlike persons with Broca's aphasia, they remain limited in their comprehension of speech and do not read or write  beyond an elementary level.
In this form of aphasia the ability to grasp the meaning of spoken words is chiefly impaired, while the ease of producing connected speech is not much affected. Therefore Wernicke's aphasia is referred to as a 'fluent aphasia.' However, speech is far from normal.Sentences do not hang together and irrelevant words intrude-sometimes to the point of jargon, in severe cases. Reading and writing are often severely impaired.
Aphasia--Other varieties 
In addition to the foregoing syndromes that are seen repeatedly by speech clinicians, there are many other possible combinations of deficits that do not exactly fit into these categories. Some of the components of a complex aphasia  syndrome may also occur in isolation.  This may be the case for disorders of reading (alexia) or disorders affecting both reading and writing  (alexia and agraphia), following a stroke. Severe impairments of calculation often accompany aphasia,  yet in some instances patients retain excellent calculation in spite of the loss of language.

Apraxia - Links:
"global apraxia," or "developmental dyspraxia". and Motor Disorders of Speech and the PROMPT System (click on titles to go there)
describes the category of drug whose original or most common use and intended therapeutic effect is to control or prevent psychiatric symptoms of psychosis or to treat mental disorders whose features include psychotic symptoms such as
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

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.
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. 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.
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.

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.

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

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).

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.

Syptoms that occur prior to a particular neurological ATAXIA: Un-coordination; Inability to coordinate the muscles in voluntary movement.

Athetosis and Ballismus:
are opposite ends of the spectrum of chorea, ballismus consisting of a violent  flinging movement.  Athetosis is a slow, worm-like writhing movement of the limbs, trunk, head, face  or tongue. These two disorders have different neuropathologic substrates; however, they seldom occur in pure form.
When athetosis merges with chorea, it is called choreoathetosis; when merged with dystonia it is athetotic dystonia.  Athetosis and ballisumus respond to drugs  similarly (tetrabenazine) depletes dopamine],  clonazepam or valproate.  Problems (such as seizure or migraine) that serve as a warning that the abnormal spell may follow. Includes disturbances in vision, smell or perception.
An abnormal response of the immune system, causing antibodies and immune mediated cells to attack parts of the body. This mechanism may explain many diseases.

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.

The inner core of peripheral nerves.  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.
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.
Nervous System, including pathway from brainstem
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:
A series of structures located deep in the brain responsible for initiating and regulating motor movements. 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 purpose for the basal ganglia is not known, but much is known about the types of symptoms that occur when they are damaged. One recent theory suggests that a purpose of the basal ganglia is to select and accentuate certain motor patterns while
inhibiting other "nearby" patterns. Once the pattern is selected by the basal ganglia, it is then fed back onto the motor cortex and amplified in order to begin movement. At the same time, all other possible patterns are inhibited in order that only the desired pattern becomes active.
This system must be very finely tuned. When it is damaged, there may be errors in the selected pattern, excessive feedback that may cause oscillations, or insufficient feedback to initiate rapid movement.
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).

Biopsy of  brain-is used only in the most severe cases and is performed in the operating room by a neurosurgeon. The skull must be opened and several days are usually required for recovery.

Biopsy of Muscle-is performed in the operating room. This is a relatively simple procedure and the person can usually go home the same day. The incision leaves a small scar over the area where the muscle or nerve is removed.

Biopsy of  nerve-a relatively unimportant nerve is chosen to minimize the effect for the procedure. For muscle biopsy, only a small piece of tissue is taken so there is no effect on strength. For certain tests, the muscle must be immediately analyzed or flash-frozen for transport to a specialized laboratory.

Biopsy of skin-is a rapid procedure during which a small circular knife is used to extract a 2 to 3 millimeter piece of skin. The resulting hole heals rapidly. This entire procedure may be performed with local anesthesia and is usually done in the doctor's office.

Botulinum toxin (BTX - Botox) injection- This is a procedure performed to alleviate a variety of neurological conditions such as spasticity, torticollis, hemifacial spasm, blepharospasm, and occupational cramps (e.g., writers cramp).  A very small amount of toxin is injected directly into the involved muscle(s).  The procedure takes to 1 hour and is only a little uncomfortable. 

Side effects are minimal but can include bruising or infection from the needle and less than 24 hours of generalized malaise.  Of note, the muscles injected will become weakened in about 5-7 days.  The weakness is designed to reduce the activity of the overactive muscle(s). In some cases, insufficient weakness may require a reinjection and in some cases, excessive weakness may temporarily interfere with the injected muscles functioning. 

There is also the risk of toxin spreading to adjacent muscles and making them weak as well.  However, all weakness is temporary as the effect of Botox lasts for about 3 months.  If the effect is beneficial, repeated injections will be recommended.

Bradykinesia: The slowing of motor movements due to dysfunction of the basal ganglia and related structures. 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.

Broca's aphasia - This is a form of aphasia in which speech output is severely reduced and is limited mainly to short utterances, of less than four words.
Vocabulary access is limited in persons with Broca's aphasia, and their formation of sounds is often laborious and clumsy. The person may understand speech relatively well and be able to read, but be limited in writing. Broca's aphasia is often referred to as a 'non fluent aphasia' because of the halting and effortful quality of speech.

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