In hereditary nonpolyposis colorectal cancer (HNPCC) the cause is a germline mutation in one of the DNA mismatch repair genes (MLH1, MSH2, MSH6, and PMS2), while MSI in sporadic colorectal cancer is predominantly due to hypermethylation of the MLH1 promoter and sometimes sporadic mutations [11]. Here, PMS2 is linked to hereditary nonpolyposis colon cancer.