Frequency of spinocerebellar ataxia mutations in patients with multiple system atrophy

Purpose: Investigate single nucleotide variants and short tandem repeats in 39 genes related to spinocerebellar ataxia in clinical and pathologically defined cohorts of multiple system atrophy. Methods: Exome sequencing was conducted in 28 clinical multiple system atrophy patients to identify single nucleotide variants in spinocerebellar ataxia-related genes. Novel variants were validated in two independent disease cohorts: 86 clinically diagnosed multiple system atrophy patients and 166 pathological multiple system atrophy cases. Expanded repeat alleles in spinocerebellar ataxia genes were evaluated in 36 clinically diagnosed multiple system atrophy patients, and CAG/CAA repeats in TATA-Box Binding Protein (TBP, causative of SCA17) were screened in 216 clinical and pathological multiple system atrophy patients and 346 controls. Results: No known pathogenic spinocerebellar ataxia single nucleotide variants or pathogenic range expanded repeat alleles of ATXN1, ATXN2, ATXN3, CACNA1A, AXTN7, ATXN8OS, ATXN10, PPP2R2B, and TBP were detected in any clinical multiple system atrophy patients. However, four novel variants were identified in four spinocerebellar ataxia-related genes across three multiple system atrophy patients. Additionally, four multiple system atrophy patients (1.6%) and one control (0.3%) carried an intermediate length 41 TBP CAG/CAA repeat allele (OR = 4.11, P = 0.21). There was a significant association between the occurrence of a repeat length of longer alleles (> 38 repeats) and an increased risk of multiple system atrophy (OR = 1.64, P = 0.03). Conclusion: Occurrence of TBP CAG/CAA repeat length of longer alleles (> 38 repeats) is significantly associated with increased multiple system atrophy risk. This discovery warrants further investigation and supports a possible genetic overlap of multiple system atrophy with SCA17.