Shared HLA class II-associated genetic susceptibility and resistance, related to the HLA-DQB1 gene, in IgA deficiency and common variable immunodeficiency.

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Abstract
Most cases of selective IgA deficiency (IgA-D) and common variable immunodeficiency (CVID) occur sporadically. However, familial clustering is not uncommon, and the two disorders can occur within the same family. We have previously described positive associations with three DR-DQ haplotypes as well as a strong negative association with DRw15,DQw6,Dw2 in IgA-D. Different amino acids at position 57 of the HLA-DQ beta chain were found to be related to susceptibility and resistance to IgA-D. Now we have found identical, although somewhat weaker, positive and negative DR-DQ associations in a large group of CVID patients (n = 86), as well as the same associations with codon 57 of the DQB1 gene. In addition, we have confirmed our earlier observations in an independent group of IgA-D individuals (n = 69), and in sib-pair analysis we have found linkage of the genetic susceptibility to IgA-D to the HLA class II region. In IgA-D individuals not carrying the three overrepresented DR-DQ haplotypes, the same positive association with a non-aspartic acid residue at position 57 of the HLA-DQ beta chain was seen. The previously reported associations with deletions of the HLA class III genes C4A (fourth component of complement) and CYP21P (steroid 21-hydroxylase pseudogene) were, in our groups of immunodeficient individuals, statistically secondary to the association with the DQB1 allele 0201. The shared HLA class II associations in the two humoral immunodeficiencies support the hypothesis that IgA-D and CVID are related disorders. Disease susceptibility and resistance are most closely associated with a gene(s) within the DR-DQ region, alleles of the DQB1 locus being candidate genes.