Definitions Used In HD
"K" through "P"


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

Color coding:
Other diseases similiar to HD
Kinematics is the study of the position of the limbs.

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").

LACTATE or LACTIC ACID: A chemical that is formed when sugars are broken down for energy without the presence of adequate oxygen. Lactic acid cannot be used by the body and will accumulate in blood and urine. Lactic acid causes the muscle pain when one runs too fast for too long. In people with mitochondrial disorders, lactic acid forms when the oxidative capacity  (ability to burn foods using oxidative phosphorylation) of the person is impaired.

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.

Lacunar: A subtype of stroke that affects the deeper parts of the brain and involves the tiny perforating arteries.

Leigh disease: A disorder of mitochondrial function that typically becomes apparent during infancy. Also known as subacute necrotizingencephalomyelopathy,
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 neuro-degenerative changes of the basal ganglia, thalamus, brainstem, spinal cord, and other regions of the CNS.

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.

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 MRIs ability to scan images from various angles and provide strong contrast between healthy and abnormal tissues.

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.

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.

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.

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.

Metabolic Tests - measurements of ammonia, lactate, amino acids (as measured in blood and urine, and sometimes CSF), and organic acids (measured in urine). More specialized metabolic tests include measurements of carnitine and acylcarnitines, as well as white blood cell enzyme function.

METABOLISM: The process of cells burning food to produce energy. This is similar to a car's engine (the cell's mitochondria) burning gasoline (the food we eat) to produce the energy or torque that turns the drive train that spins the car's wheels (the energy we need to move and think).
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
MITOCHONDRIA: A part of the cell (organelle) that is responsible for energy production. The organelle consists of two sets of membranes, a smooth continuous outer coat and an inner membrane arranged in tubules or in folds that form plate-like double membranes (cristae); the principal energy source of the cell, containing the cytochrome enzymes of terminal electron transport and the enzymes of the citric acid cycle, fatty acid oxidation, and oxidative phosphorylation. Responsible for converting nutrients into energy as well as many other specialized tasks.

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

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).

Motor neuron cells: The cells located in the spinal cord that give rise to the nerves that supply the muscles.

Movement disorders can be classified into two basic categories: those characterized by disordered or excessive movement (termed "hyperkinesia" or "dyskinesia "), and those that are characterized by slowness, or a lack of movement (termed "hypokinesia," "bradykinesia," or "akinesia").
An example of a "hyperkinetic" movement disorder is a tremor or a tic while Parkinson's disease can be classified as "hypokinetic," because it is often characterized by slow, deliberate movements, or even "freezing" in place.

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

mtDNA: Mitochondrial DNA contain the genes that code for some of the enzymes and some of the necessary molecules needed to make those enzymes of the respiratory chain. Mitochondria are the only part of the body cell with their own separate and unique DNA. Regardless, most of the mitochondria and the respiratory chain are coded by nDNA. MtDNA is inherited only from the mother.

multi-infarct dementia: A dementia that is caused by the cumulative affect of having had many strokes in the brain.

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.

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

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.

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

A single spasm or twitching of a muscle. Myoclonus can be a single event (twitch) or repeated events. Myoclonus can be a normal
event (the jerks that occur when we fall asleep) or an abnormal event (those that occur while awake, or those associated with seizures or mitochondrial diseases). Clonus is the repeated spasms of muscles, due to a seizure or increased muscle tone.

Myodonus -sudden brief jerks involving groups of muscles. It may be mistaken for a
seizure. Like chorea, myoclonus may not be disabling or particularly distressing, but may respond to treatment with clonazepam or divalproex sodium if treatment is necessary
myopathy: A disease resulting in dysfunction of the muscles usually causing weakness and atrophy
"Olivopontocerebellar" implies involvement and degeneration of the olives (structures in the medulla, a part of the brainstem), the pons (a part of the
brainstem), and the cerebellum (the part of the brain that controls coordination and balance). Symptoms may include:
  • ataxia
  • kintetic tremor;
  • dysarthria (difficulty with articulating words)
  • weakness;
  • dystonia (the muscles may be in a state of abnormal tension);
  • chorea (irregular, spasmodic, involuntary movement of the limbs or facial muscles);
  • spasticity (state of increased muscular tone with exaggerated tendon reflexes);
  • kinetic tremor;
  • degeneration of the retina;
  • and neuropathy.
Opsoclonus-Myoclonus Syndrome:
The association of opsoclonus, myoclonus, ataxia, and encephalopathy bears many names such as Kinsbourne syndrome, dancing eye-dancing feet, and infantile polymyoclonia. Opsoclonus usually refers to conjugate, chaotic, rapid eye movements. There is generally no temporal association of myoclonus with opsoclonus; myoclonus may begin before or without opsoclonus. Approximately half of the pediatric cases, regardless of cause are encephalopathic, but mental cloudiness is not usually a feature in children. Tumors outside the CNS and viral infections are the principal causes in children, each accounting for about half of the cases. The mean age at onset is about 18 to 20 months. Several types of infection are associated with opsoclonus-myoclonus; in children neural crest-derived tumors such as neuroblastoma predominate. Only 2-3% of neuroblastoma cases are manifested as
paraneoplastic opsoclonus-myoclonus syndrome. Failure to find a neuroblastoma does not preclude it as a cause of opsoclonus-myoclonus because a neuro-blastoma may be difficult to find due to the possibility of spontaneous regression of the tumor. In 60% of patients the tumor is found within 3 months, but there may be a delay in diagnosing neuro-blastoma for up to 4 years after opsoclonus-myoclonus first appears.

PTOSIS: Droopy eyelids