Formally established as a recommendation in 2009, patients with newly diagnosed colorectal carcinoma are now universally screened for MMR mutations, using either the Amsterdam or the Bethesda criteria.3 Multiple factors are used to identify patients who would benefit from screening, including personal history, age, family history, and histological morphology.4, 5, 6 The Society of Gynecologic Oncologists has established guidelines for screening patients with gynecologic tumors (Table 1)7; however, these may miss the diagnosis of LS in patients with EC because of the narrow screening criteria. The gene discussed is MRC1; the disease is Leigh syndrome.