ERCC3 and xeroderma pigmentosum: Mutations interfering with the proper function of XPB and XPD helicases in humans have been linked to disorders such as Xeroderma Pigmentosum (XP), Cockayne syndrome (CS) and trichothiodystrophy (TTD) (Hoeijmakers, 1994; Vermeulen et al., 1994; de Boer & Hoeijmakers, 2000).