PMS2 and Leigh syndrome: As this SV affects multiple exons resulting in a frameshift mutation (PVS1—very strong), we have confirmed the functional consequence on the mRNA level (PS3 – strong) and have confirmed the occurrence of the variant in three independent families with a clinical diagnosis of LS, among which 3 CRCs from two families exhibited the highly specific phenotype (MLH1- and PMS2-deficient CRC), satisfying the PP4 criteria (supporting), the ACMG classification of this variant is pathogenic.