Variants in eight genes associated with eight complementation groups (XP-A (ERCC1), XP-B (ERCC3), XP-C (XPC), XP-D (ERCC2), XP-E (DDB2), XP-F (ERCC4), XP-G (ERCC5) and XP-V (POLH)) are known to cause XP. Here, XPC is linked to xeroderma pigmentosum.