Lynch syndrome is caused by heritable constitutional pathogenic mutations in the mismatch repair (MMR) genes (MLH1, MSH2, MSH6 and PMS2) or, rarely, by certain mutations in nearby genes that affect expression of the adjacent MMR gene, (i.e. EPCAM and MSH2, and LRRFIP2 and MLH1), due to epigenetic silencing caused by promoter methylation [1, 2]. The gene discussed is MLH1; the disease is Lynch syndrome.