Six (5.4%) patients were ultimately diagnosed with LS-EC with a mutation in one of the MMR genes: 1 in MLH1, 2 in MSH2, and 3 in MSH6. The cumulative cases of LS among the EC patients were 2 (6.3%), 6 (8.6%), and 6 (5.9%) before the ages of 50, 60, and 70, respectively. The gene discussed is MLH1; the disease is Leigh syndrome.