FEN1 and Cornelia de Lange syndrome: The diagnosis of CdLS is established in two ways: through clinical findings of the classic phenotypic characteristics of CdLS and/or through the identification of a variant heterozygous pathogen in theNIPBL,RAD2,SMC3, andBRD4genes, or a pathogenic homozygous variant in theHDAC8orSMC1Agenes.