A large analysis of the Huntington Disease (HD) cohort revealed a clear association between several polymorphisms within DNA repair genes, such as MSH3, LIG1, FAN1, and MLH1, and the degree of somatic mosaicism, suggesting that LIG1 or FAN1 polymorphisms may also explain the variability in DM1 patients, in addition to the MMR proteins [68,69]. This evidence concerns the gene LIG1 and juvenile Huntington disease.