PMS2 and Leigh syndrome: LS is caused by germline inactivation of one of four genes acting in DNA mismatch repair (dMMR) pathways (MLH1, MSH2, MSH6 and PMS2), typically due to inherited pathogenic variants (PVs).1 2 Early identification of patients with LS offers opportunities to reduce the chance of lethal cancers through colonoscopy surveillance, aspirin chemoprophylaxis, risk-reducing gynaecological surgeries and cascade testing of relatives.3, 6 EC is one of the canonical cancers associated with LS and for many females is the first LS cancer to be diagnosed.7