PMS2 and Leigh syndrome: LS cancer risk is inherited in an autosomal dominant pattern, and is caused by germline variations in DNA mismatch repair (MMR) genes such as MLH1, MSH2, MSH6, or PMS2. Approximately 90% of LS patients could potentially carry variations in MLH1 and MSH2, 7% carry mutations in MSH6, and less than 5% are likely to have PMS2 mutations [4].