The system involves several proteins encoded by 5 different genes namely [MLH1 (MIM# 120436), MSH2 (MIM# 609309), MSH6 (MIM# 600678), PMS1 (MIM# 600258), and PMS2 (MIM# 600259)] have been implicated in HNPCC [2]. Here, PMS1 is linked to hereditary nonpolyposis colon cancer.