Molecular investigations have shown that most HNPCC families are associated with constitutional mutations in a class of genes (called hMSH2, hMLH1, hMSH6, hPMS2 and probably others) which are components of a DNA mismatch repair pathway (Wheeler et al, 2000; Calvert and Frucht, 2002). Here, MSH2 is linked to hereditary nonpolyposis colon cancer.