RAD21 and Cornelia de Lange syndrome: Pathogenic variants most likely cause CdLS in one of the cohesin complex genes, including NIPBL (NIPBL cohesin loading factor-OMIM:608667), which accounts for about 50–60% of cases; SMC1A (structural maintenance of chromosomes protein 1A-OMIM:300040) and HDAC8 (histone deacetylase 8-OMIM:300269), linked to the X chromosome; and SMC3 (structural maintenance of chromosomes 3-OMIM:606062) and RAD21 (RAD21 cohesin complex component-OMIM:606462). They can be spontaneous, autosomal dominant, or X-recessive [2,6].