Most cases of CS reflect mutations in the Cockayne syndrome Group B (CSB, also known as ERCC6) gene, a SWI/SNF-like DNA-dependent ATPase [17]–[19] that can wind DNA [20] and remodel chromatin in vitro[21]; the remaining cases of CS are caused by mutations in the CSA gene, and by rare alleles of the xeroderma pigmentosum genes XPB, XPD, and XPG[22]. Here, ERCC2 is linked to Cowden syndrome 1.