At least five genes of the pathway, namely hMLH1, hMSH2, hMSH6, hPMS1 and hPMS2, have been implicated in HNPCC (Leach et al, 1993; Papadopoulos and Lindblom, 1997; Peltomäki and Vasen, 1997). Here, MLH1 is linked to hereditary nonpolyposis colon cancer.