XPA and xeroderma pigmentosum: After recognition of the lesion, the helicases xeroderma pigmentosum groups B (XPB) and D (XPD) unwind the DNA, and replication protein A (RPA) and xeroderma pigmentosum groups A (XPA) and G (XPG) are recruited to form the xeroderma pigmentosum group C (XPC) protein complex, which coordinates excision and repair [11].