MRC1 and Leigh syndrome: Several mutations in MMR genes have already been described in LS and are shared in the main international variants databases, such as InSiGHT, VarSome, and Human Genetic Variation Database (HGVD).(15-17) The description of mutations and associated phenotypes assists in the pursuit of better care by identifying specific population or family risk groups.(14) It is fundamental to accurately characterize the pathogenic potential of newly identified genetic variants, and the strategies required vary according to each variant.