Inactivation of DNA mismatch repair (MMR) genes (MSH3, MSH2, MLH1, PMS2, and MLH3) in cellular and animal models of neurological conditions such as Huntington’s disease (HD), myotonic dystrophy type1 (DM1), and fragile-X related disorders (FXDs) has been shown to attenuate triplet repeat expansion (reviewed in ref. 9). This evidence concerns the gene MLH3 and Huntington disease.