LS, also known as hereditary non-polyposis colorectal cancer (HNPCC), OMIM #120435, is an autosomal dominant genetic disorder linked to the germline mutation of a DNA mismatch repair (MMR) gene (MLH1, MSH2, MSH6, PMS2) or to a deletion in the 3′ region of the epithelial cell adhesion molecule (EPCAM) gene 4. The gene discussed is MLH1; the disease is hereditary nonpolyposis colon cancer.