SMC1A and Cornelia de Lange syndrome: To date, it is widely believed that CdLS is primarily caused by variants in seven genes, including NIPBL, SMC1A, SMC3, RAD21, BRD4, HDAC8 and ANKRD11. Through February 1, 2020, 27 cases of CdLS with definite variants of SMC3 were reported (Tables 1 and 2), including 22 cases with detailed clinical data including sex and age.