ERCC3 and Xeroderma pigmentosum complementation group D: Within photo-sensitive TTD, three TFIIH coding genes are implicated: xeroderma pigmentosum complementation group B (XPB) [8], xeroderma pigmentosum complementation group D (XPD) [9,10], and the newly identified protein termed “TTD group A” (TTDA) [11,12].