Parkinson's disease associated with pure repeat expansion.

Large, non-coding pentanucleotide repeat expansions of ATTCT in intron 9 of the gene typically cause progressive spinocerebellar ataxia with or without seizures and present neuropathologically with Purkinje cell loss resulting in symmetrical cerebellar atrophy. These repeat expansions can be interrupted by sequence motifs which have been attributed to seizures and are likely to act as genetic modifiers. We identified a Mexican kindred with multiple affected family members with expansions. Four affected family members showed clinical features of spinocerebellar ataxia type 10 (SCA10). However, one affected individual presented with early-onset levodopa-responsive parkinsonism, and one family member carried a large repeat expansion, but was clinically unaffected. To characterize the repeat, we used a novel technology of single-molecule real-time (SMRT) sequencing and CRISPR/Cas9-based capture. We sequenced the entire span of ~5.3-7.0 kb repeat expansions. The Parkinson's patient carried an expansion with no repeat interruption motifs as well as an unaffected sister. In the siblings with typical SCA10, we found a repeat pattern of ATTCC repeat motifs that have not been associated with seizures previously. Our data suggest that the absence of repeat interruptions is likely a genetic modifier for the clinical presentation of l-Dopa responsive parkinsonism, whereas repeat interruption motifs contribute clinically to epilepsy. Repeat interruptions are important genetic modifiers of the clinical phenotype in SCA10. Advanced sequencing techniques now allow to better characterize the underlying genetic architecture for determining accurate phenotype-genotype correlations.