ERCC4 and xeroderma pigmentosum: In exceptional cases, patients with rare variants in ERCC4/XPF, encoding a subunit of the ERCC1-XPF NER endonuclease, exhibit the combined phenotypes of XP, CS, and Fanconi anemia (FA), a rare inherited bone marrow failure syndrome (IBMFS), designated XPCSFA (15).