The fact that a minority of cases of mild CdLS result from mutations in the SMC1L1/SMC1A (∼5%; OMIM 300590) and SMC3 (1 case; OMIM 610579) genes, which encode two of the four cohesin structural components, supports the view that CdLS is caused by abnormal cohesin function [22],[23]. This evidence concerns the gene SMC3 and Cornelia de Lange syndrome.