The MMR genes mutated in the germline in HNPCC have been identified so far as hMSH2 (located on 2p), hMLH1 (located on 3p), hPMS1, hPMS2 and hMSH6. Over 60% of cases of HNPCC are caused by mutations in hMSH2 and hMLH1 [11, 12]. Here, MLH1 is linked to hereditary nonpolyposis colon cancer.