Objective: We aimed to investigate status of SCA17 in Indian population and tried to minimise the category of unidentified cerebellar ataxia cases.

Background: Spinocerebellar ataxia type 17 (SCA17) is an Autosomal dominant, progressive, neurodegenerative disorder.  The causal mutation in SCA17 is the expansion of CAG/CAA (>41) repeats in exon 3 of TBP on chromosome 6q²⁷. Genetic studies are lacking for SCA17 in India, only few case reports have been published from Indian population.

Methods: A total of unrelated 670 cases with evidence of cerebellar ataxia and genetically negative for SCA1-3, SCA6-8, SCA12, and FRDA mutation (Uk-SCAs) were screened for SCA17 mutation. CAG/CAA (TBP) length distribution analysis in 229 cases of genetically known SCAs other than SCA17 (K-SCA) and 820 healthy controls (HC) was also carried out. CAG/CAA (TBP) expansion was measured by fragment analysis and confirmed by sequencing in ABI 3130xl sequencer.

Results: We identified a cerebellar ataxia patient carrying TBP-CAG/CAA- 37/129 repeats. One patient of SCA17 carrying a homozygous-CAG/CAA-45/46 with manifestations of cerebellar ataxia, psychiatric disorder and with extrapyramidal features conforming to the SCA17 diagnosis.  In addition 45 patients were found to carry repeats of alleles 41-44 in unknown SCAs however the 41-44 carriers were also found in kn-SCAs (11 Patients). The CAG/CAA length distribution showed the observed range (% alleles with >39 repeats) as following; in HC 32-43(16%), in K-SCA 35-44(42%) and Uk-SCA 32-129 (35%).

Conclusions: TBP CAG/CAA- 37/129 is the largest repeat size reported till date.  SCA17 seems to be a rare SCA-subtype in India and individuals with more than 41 repeats should be followed-up periodically for assessment of SCA17 features.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/spinocerebellar-ataxia-type-17-an-indian-scenario/