PMS2 and Leigh syndrome: LS is a relatively common disorder (affects one in 250-400 individuals) with a high lifetime risk of cancer caused by the deficiency of one of the main four DNA mismatch repair genes: MLH1, MSH2, MSH6, or PMS2, or by transcriptional silencing of MSH2 via 3’ deletion of EPCAM. Typically, LS families display autosomal dominant inheritance of colorectal cancer (CRC) (and various extracolonic cancers such as endometrial cancer) with a relatively young age at onset (< 50 years) (1, 2).