Biallelic pathogenic variants in one of the seven NER genes coding for the so-called complementation groups, XPA, ERCC3, XPC, ERCC2, DDB2, ERCC4, ERCC5, the NER gene ERCC1, and the gene coding for XP variant, POLH, are the causes of the rare hereditary disease Xeroderma pigmentosum (XP) (38). The gene discussed is ERCC1; the disease is xeroderma pigmentosum.