Among eight XP causative genes, XPD (also known as ERCC2) and XPB (also known as ERCC3) encode two helicases of the transcription factor IIH (TFIIH) complex, which functions in transcription and nucleotide excision repair (NER), and one of them, XPD, also functions in cell cycle regulation and chromosome segregation (Cameroni et al., 2010; Egly and Coin, 2011). The gene discussed is GTF2H4; the disease is xeroderma pigmentosum.