MSH2 and Leigh syndrome: In this study, the conditional knockout Aldh1b1flox/flox alleles and constitutive knockout Aldh1b1−/− alleles were introduced by cross-breeding into the Msh2-LS mouse model of LS, in order to study the interactive effects of dMMR with increased acetaldehyde on intestinal tumour formation in LS model mice placed on long-term ethanol treatment.