The loss of one B6 Msh3 allele in mice heterozygous for both variants was sufficient to decrease CTG/CAG instability; consistent with results which shows that MSH3 protein levels are a limiting factor in CAG/CTG repeat expansions in DM1 and HD mouse models, where MSH3/null mice have less expansions than MSH3/MSH3 mice, but more than null/null mice [16], [27], [35]. Here, MSH3 is linked to myotonic dystrophy type 1.