Founder effect for a 26-bp deletion in the RFXANK gene in North African major histocompatibility complex class II-deficient patients belonging to complementation group B

Expression of major histocompatibility complex (MHC) class II genes is cont rolled at the transcriptional level by at least four trans-acting genes, CI ITA, RFXANK, RFX5, and RFXAP. Defects in these regulatory genes result in t he absence of MHC class II molecule expression and, thereby, cause a combin ed immunodeficiency. MHC class II deficiency is inherited as an autosomal r ecessive trait. Since the first description of the disease, about 70 patien ts from 50 families have been reported. Forty-three of these families have been classified into four complementation groups: A, B, C, and D. In the la rgest group, B, the majority of patients are of North African origin. In tw o of these patients, the same mutation in the RFXANK gene (752delG-25) was identified. We performed a mutation analysis in 20 additional patients belo nging to complementation group B and detected the 752delG-25 mutation in 17 . All of these patients are of North African origin. A founder effect for t his mutation was documented, since all tested patients, except one, display a common haplotype spanning the RFXANK locus.