XPA and xeroderma pigmentosum: Xeroderma pigmentosum, characterized by extreme photosensitivity to UV radiation, results from the mutations in any of genes xeroderma pigmentosum complementation group A, B, C, D, E, F, G (XPA, -B/ERCC3, -C, -D/ERCC2, -E, -F/ERCC4, -G), xeroderma pigmentosum variant (XPV), or excision repair cross-complementation group 1 (ERCC1) [152].