MSH2 and colorectal neoplasm: This increase in the frequency of G-to-A transition in Msh2-KO mice is consistent with our previous observations that G-to-A transition frequently occurred in Ctnnb1 in tumors in the small intestine of Msh2-KO mice [5], and that the most frequent base substitution in CTNNB1 in human colorectal tumors was G-to-A transition [22].