LS is caused by a heterozygous germline pathogenic variant (PV) in one of four genes involved in the DNA mismatch repair (MMR) system: MLH1, MSH2, MSH6, and PMS2. Deletions of the EPCAM gene cause hypermethylation of the MSH2 promoter region and are also associated with LS [3]. The gene discussed is PMS2; the disease is Leigh syndrome.