Isolated Generalized Chorea in a Patient with Small-Expanded Allele Spinocerebellar Ataxia 17

Area of Science:

• Genetics
• Neurology
• Molecular Biology

Background:

• Spinocerebellar ataxia type 17 (SCA17) is an autosomal dominant neurodegenerative disorder.
• It results from polyglutamine-encoding CAG/CAA repeat expansions in the TATA box-binding protein (TBP) gene.
• SCA17 exhibits significant clinical heterogeneity and complex genotype-phenotype correlations.

Purpose of the Study:

• To report the clinical, neuropsychological, and neuroimaging findings of a patient with SCA17.
• To investigate the genotype-phenotype relationship in a case with a small-expanded allele.
• To contribute to the understanding of reduced penetrance in SCA17.

Main Methods:

• Case study of a 73-year-old patient with a 10-year history of hyperkinetic movements and depressive symptoms.
• Clinical neurological examination, neuropsychological evaluation, and brain imaging were performed.
• Genetic analysis of the TBP gene was conducted to identify repeat expansions.

Main Results:

• The patient presented with generalized choreic movements and depressive symptoms without other neurological signs.
• Neuropsychological and neuroimaging results were within normal limits.
• Genetic analysis revealed a 41-CAG repeat expansion in the TBP gene, indicating reduced penetrance.

Conclusions:

• This case report deepens insights into the phenotype associated with small-expanded alleles in SCA17.
• The findings support recent updates in the genotype-phenotype assessment for SCA17.
• It underscores the variability of SCA17 presentation, even with reduced penetrance alleles.