MLH1 and hereditary nonpolyposis colon cancer: HNPCC is most frequently caused by mutations in MLH1, PMS1, PMS2, MSH2 or MSH6, (MutL Homolog 1, Post‐Meiotic Segregation Increased 1 and 2 and MutS Homolog 2 and 6, respectively) that encode the enzymatic machinery of DNA mismatch repair.