MSH3 and myotonic dystrophy: However, in Huntington’s disease and myotonic dystrophy mouse models, loss of MSH3 decreases somatic mutability of very long [CAG/GTC] and [CTG/GAC] alleles, but has no significant effect on germline mutability or directionality biases (van den Broek et al. 2002; Dragileva et al. 2009).