Mutations in the TFIIH subunits XPB, XPD and TTDA have been associated with the three diseases: Xeroderma Pigmentosum (XP [MIM 278700-780]), Cockayne Syndrome (CS [MIM 214150]) and Trichothiodystrophy (TTD [MIM 601675]), all characterized by deficiencies in DNA repair [13]. The gene discussed is ERCC3; the disease is xeroderma pigmentosum.