A non-synonymous SNP in SIRT6 predicts neurological severity in Friedreich ataxia

Friedreich ataxia (FRDA) is a recessive neurodegenerative disease characterized by progressive ataxia, dyscoordination, and loss of vision. The variable length of the pathogenic GAA triplet repeat expansion in the FXN gene in part explains Inter-individual variability in severity of disease. The GAA repeat expansion leads to epigenetic silencing of FXN; therefore, variability in properties of epigenetic effector proteins could also regulate the severity of FRDA. In an exploratory analysis, DNA from 88 FRDA patients was analyzed to determine if any of 5 non-synonymous SNPs in HDACs/ SIRTs predicted FRDA disease severity. Results suggested the need for a full analysis (569 FRDA patients) at the rs352493 locus in SIRT6 (S46N SNP). Disease features were compared between patients with the common N46 SIRT6 variant and the less common S46 variant. Biochemical properties of SIRT6 were compared between S46 and N46. Linear regression of the exploratory cohort suggested a SNP (rs352493) in SIRT6 predicted neurologic severity. In follow up analysis, the genotype of SIRT6 at the locus rs352493 predicted disease features of FRDA. Patients with the S46 SIRT6 variant performed better on measures of neurological and visual function over time when compared to the more common N46 SIRT6 variant. S46 SIRT6 did not alter expression or enzymatic activity of SIRT6 or FXN however, S46 patients showed whole transcriptome differences compared to N46 patients, indicative of compensatory mechanisms against whole transcriptome changes seen in FRDA. rnaseq and chipseq assay for 4 Friedreich Ataxia patients, 2 of which have the N46 genotype, the other two have the S46 genotype