Mutations in MMR genes are associated with hereditary nonpolyposis colorectal cancer (HNPCC), also referred to as Lynch Syndrome (Fishel et al. 1993; Bronner et al. 1994; Nicolaides et al. 1994; Papadopoulos et al. 1994; Miyaki et al. 1997). The gene discussed is MRC1; the disease is hereditary nonpolyposis colon cancer.