SMC3 and Cornelia de Lange syndrome: In humans, subtle perturbations in cohesin activity contribute to disorders now known as ‘cohesinopathies’, such as CdLS and RBS, which are caused by mutations in NIPBL, SMC1A, SMC3, and ESCO2. While ∼50% of CdLS patients have identifiable mutations in NIPBL, mutations in other cohesion components (such as SMC1A and SMC3) appear to be much rarer (∼5%), leaving many clinically defined CdLS patients with no identified genetic lesion [4].