Mutations in some genes of the NER incision complex, i.e., in XPB, XPD, XPF and XPG, can cause a syndrome with combined features of XP and CS referred to as xeroderma pigmentosum-Cockayne syndrome (XPCS) complex, or, in its most severe form, as cerebro-oculo-facio-skeletal syndrome (COFS)29,30. This evidence concerns the gene ERCC4 and Cowden syndrome 1.