Cohesin is critical for the timely repair of DNA double-strand breaks, and cell lines derived from CdLS patients carrying mutations in NIPBL (SCC2 in budding yeast), SMC1A, and SMC3 exhibit sensitivity to ionizing radiation (Vrouwe et al. 2007; Revenkova et al. 2009). Here, SMC1A is linked to Cornelia de Lange syndrome.