MSH2 and mismatch repair cancer syndrome 1: Mice harboring Msh2 cKO alleles and EIIa-Cre transgene (the transgene allows constitutive gene recombination of floxed sequences in the zygote [228]) recapitulated the phenotype observed in Msh2−/− mice, i.e., they displayed MMR deficiency and developed intestinal tumors.