MRC1 and colorectal cancer: In this study and others (Clendenning et al., 2008; Senter et al., 2008), heterozygous PMS2 mutations displayed lower penetrance than mutations involving other MMR genes, as reflected by later onset of colorectal cancer (average: 59 years vs. 45 years in MLH1/MSH2 mutation carriers) and weaker family histories of Lynch-syndrome associated cancers.