However, these XP patients showed no altered B-cell subsets as found in the TTD1 patients (data not shown), thus indicating that other NER factors are unlikely to compensate for the B cell abnormalities described in ERCC2-deficiency, and rather points to the unique role ERCC2 might play in regulating transcription of essential B cell factors as an explanation for the immunodeficient phenotype. This evidence concerns the gene ERCC2 and xeroderma pigmentosum.