Polymorphisms in DNA methylation–related genes are linked to the phenotype of Machado-Joseph disease

DNA methylation has been reported as an important regulator of genomic structure stability, including large tandem repeats. To test the modulation effect of variants in DNA methylation–related genes on distribution of expanded (CAG)_n alleles and age at onset (AO) of patients with Machado-Joseph disease (MJD), we conducted an association analysis on 23 selected SNPs in these genes in 613 patients with MJD and 581 controls. There were significant differences in the distribution of rs12957023 between patients and controls (OR = 1.296, p = 0.007 and OR = 1.206, p = 0.008, for genotype and alleles, respectively). The distribution of (CAG)_n size was also different between patients carrying a CC and the other genotypes (TT and TC, p = 0.011 for expanded (CAG)_n and p = 0.012 for normal size alleles), indicating that DNA methylation might modulate the (CAG)_n instability. We found also that rs13420827 in DNMT3A and rs7354779 in DNMT3L contribute to AO of MJD (p = 0.019 and p = 0.008, respectively). In conclusion, our data provide the first evidence that SNPs in DNA methylation–related genes may contribute to (CAG)_n instability and modulate the AO of this disease.