Mutation of RFXAP, a Regulator of MHC Class II Genes, in Primary MHC Class II Deficiency
Jean Villard, M.D., Barbara Lisowska-Grospierre, M.D., Peter van den Elsen, Ph.D., Alain Fischer, M.D., Ph.D., Walter Reith, Ph.D., and Bernard Mach, M.D., Ph.D.
Background Major-histocompatibility-complex (MHC) class II deficiencyis an autosomal recessive primary immunodeficiency disease inwhich MHC class II molecules are absent. It is a geneticallyheterogeneous disease of gene regulation resulting from defectsin several transactivating genes that regulate the expressionof MHC class II genes. The mutations responsible for MHC classII deficiency are classified according to complementation group(a group in which the phenotype remains uncorrected in pairwisefusions of cells). There are three known complementation groups(A, B, and C).
Methods To elucidate the genetic defect in patients with MHCclass II deficiency that was not classified genetically, weperformed direct complementation assays with the three genesknown to regulate the expression of MHC class II genes, CIITA,RFX5, and RFXAP, and the relevant mutations were identifiedin each patient.
Results Mutations in the RFXAP gene were found in three patientsfrom unrelated families, and the resulting defect was classifiedas belonging to a novel complementation group (D). Transfectionwith the wild-type RFXAP gene restored the expression of MHCclass II molecules in the patients' cells.
Conclusions Mutations in a novel MHC class II transactivatingfactor, RFXAP, can cause MHC class II deficiency. These mutationsabolish the expression of MHC class II genes and lead to thesame clinical picture of immunodeficiency as in patients withmutations in the other two MHC class II regulatory genes.
Source Information
From the Louis Jeantet Laboratory of Molecular Genetics, Department of Genetics and Microbiology, University of Geneva Medical School, Geneva (J.V., W.R., B.M.); INSERM Unité 429, Hôpital NeckerEnfants Malades, Paris (B.L.-G., A.F.); and the Department of Immunohematology and Bloodbank, University Hospital Leiden, Leiden, the Netherlands (P.E.).
Address reprint requests to Dr. Mach at the Department of Genetics and Microbiology, University of Geneva Medical School, 1 rue Michel-Servet, CH-1211 Geneva 4, Switzerland.
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