We also measured MHCI mRNA expression by quantitative real-time RT-PCR (qRT-PCR) in in vitro-generated B cell mutants and B cell lines derived from bare lymphocyte syndrome (BLS) patients carrying inactivating mutations in CIITA, RFX5, RFXAP, and RFXANK. The gene discussed is RFXAP; the disease is MHC class II deficiency.