Given the role of MSH2 in repeat instability in DM1, FXS and FRDA cells [65–68] and the propensity for increased DNA damage at DMPK, FMR1 and FXN alleles with expanded repeats, it is possible that, as was seen with the DMPK locus in DM1, the maintenance of the repeat-induced DNA methylation at the FMR1 and FXN loci may also be MSH2-dependent. This evidence concerns the gene FXN and fragile X syndrome.