Crossing mouse models of HD with mice that carry different DNA repair gene mutations has shown that deficiencies in specific MMR genes (e.g. Msh2, Msh3, Mlh1 or Mlh3), or BER genes (e.g. Ogg1 or Neil1) can abrogate somatic and/or germline CAG repeat expansion and, in some cases, ameliorate HD-like phenotypes (Budworth et al., 2015; Kovalenko et al., 2012; Pinto et al., 2013; Usdin et al., 2015; Wheeler et al., 2003). Here, MSH2 is linked to Huntington disease.