ERCC2 and xeroderma pigmentosum group D: The xeroderma pigmentosum group D (XPD, also named excision reair cross-complementing group 2, ERCC2) gene encodes for an ATP-dependent DNA helicase, a subunit of the basal transcription factor II H (TFII H) which mediates DNA unwinding for the initiation of NER [14].