Chorea Huntington

Huntington's disease (HD) is an autosomal dominant disorder with a high penetrance that leads to motoric and cognitive dysfunctions. It shows irregular, suddenly occurring, uncoordinated movements of the distal extremities. In the early phase of HD these movements appear only segmental or focal, in advanced stadium they include more parts of the body. In addition, the patients develop dementia, behavioral and psychiatric problems. Another complication is the weight loss despite an adequate caloric intake. In most cases the first symptoms occur in mid-adult life (30 -50 years) and progress over 10 to 15 years till death.

HD is caused by an increase of the polyglutamine (CAG)-repeats in the Huntington gene on chromosome 4. It is assumed that the mutated Huntingtin protein is toxic, affecting among others the mitochondria in the central nervous system. On MRI scans first impresses a progressing atrophy of the nucleus caudatus. Then in later stages a diffuse cortical atrophy can be seen. HD cannot be cured and a causal therapy does not exist. Therefore several therapeutics are available for a symptomatic therapy.

For example, tetrabenazine inhibits the re-uptake of monoamines (dopamine, noradrenaline, serotonine) into the presynaptic vesicle due to a blockade of the VMAT-2 transporter. Thus higher amounts of monoamines are decomposed in the cytoplasm and existing vesicles are evacuated. Together this leads to a presynaptic depletion of monoamines. Furthermore an antagonist effect of tetrabenazine to the dopamine D2 receptor is described, but the affinity is so low that no clinical consequence can be seen.

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