In the NER pathway, ERCC1 protein and xeroderma pigmentosum complementation group D (XPD) together form a heterodimer of ERCC1-XPD, which is a 5ʹ-3ʹ DNA restricted endonuclease in NER, and also functions in DNA repair connection and inner chain cross repair [34]. The gene discussed is ERCC1; the disease is Xeroderma pigmentosum complementation group D.