Apart from the two principal complementation groups of CS (CSA and CSB) with mutations in the ERCC8 and ERCC6 genes, respectively, a small number of CS cases have been reported to carry mutations in the ERCC1 and ERCC4 (xeroderma pigmentosum complementation group F-XPF) genes [64]. This evidence concerns the gene ERCC6 and Cowden syndrome 1.