Cornelia de Lange Syndrome (CdLS) is a genetically heterogeneous disorder predominantly caused by De Novo heterozygous pathogenic variants in NIPBL (80% of cases), with less frequent involvement of SMC1A (5%), HDAC8 (4%), SMC3 (1–2%), RAD21 (<1%), and BRD4 (<1%). This evidence concerns the gene RAD21 and Cornelia de Lange syndrome.