Spinocerebellar Ataxia Type 17, SCA17 - TBP

Klinische Symptomatik

Spinocerebellar Ataxia Type 17 (SCA17) is the only form of spinocerebellar ataxia with a clinical manifestation similar to and, in some cases, indistinguishable from, Huntington's Disease. First manifestation lies anywhere between the first and seventh decade of life, but occurs on average in a patient's 20s. Cerebellar symptoms are ataxia of the rump and extremities, particularly gait ataxia with bulbar symptoms (dysarthria and dysphagia) and nystagmus. Intellectual deterioration with signs of dementia is noticeable, as well as the occurrence of psychiatric problems such as depression, aggression, mutism or hallucinations. Extra-pyramidal participation can display itself in dystonia, choreatiform movements and Parkinsonism. Epilepsy can also occur in connection with SCA17.

Genetik

SCA17 is caused by a CAG triplet repeat expansion in the TATA Box binding Protein gene (TBP gene, 6q27).

 

	Triplet Repeats
Normal allele	25 - 42
Intermediary allele, partial penetrance	43 - 48
Pathological allele, complete penetrance	49 - 66

A higher number of repeats is normally linked to earlier onset and more severe progression of the disease. The question of possible anticipation in following generations cannot be conclusively determined given the current knowledge of the disease.

Häufigkeit

To date, only a few families are known to be affected.

 

Diagnostik