ImmunoDeficiency Resource (IDR)

Defects in MHC2TA are a cause of hereditary MHC class II deficiency (also known as Bare lymphocyte syndrome (BLS) or HLA class II-deficient combined immunodeficiency); a form of severe combined immunodeficiency disease (SCID). MHC2TA is linked with BLS complementation group A. Bare lymphocyte syndromes (BLS) resemble selective T-cell immunodeficiencies but, in some patients, are indistinguishable from that of SCID. MHC class II molecules are expressed at less than 5% of normal intensity on hematopoietic cells from affected patients. The syndrome is caused not only by mutations in the MHC genes, but also by mutations in one of several genes encoding gene-regulatory proteins that are requiered for the transcriptional activation of MHC class II promoters. Four complementing gene defects (known as A, B, C ,D) have been defined in patients who fail to express MHC class II molecules. The gene mutated in group A is MHC class II transactivator, or CIITA, the genes mutated in Groups B, C, and D are named RFXANK, RFX5, and RFXAP. Less than 100 cases have been reported worldwide.