The abovementioned symptoms
Persons at risk in affected families
Spinocerebellar Ataxia Type 17, SCA17 - TBP
Clinical Features
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.
Genetic Information
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.
Prevalence
To date, only a few families are known to be affected.
Diagnostic
Indication
Method
Normal and pathologically lengthened CAG triplets are detected using PCR and a subsequent fragment length analysis and, if necessary, DNA sequencing.
Sample Requirement
2 - 4 ml of EDTA blood
Duration
approx. 2 weeks