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C4 polymorphism and major histocompatibility complex haplotypes in IgA deficiency: association with C4A null
D Bućin1, L Truedsson, L Hammarström
1Blood Center, University Hospital of Lund, Sweden.
Experimental and Clinical Immunogenetics
|January 1, 1991
Summary
Individuals with Immunoglobulin A (IgA) deficiency show a higher prevalence of specific Human Leukocyte Antigen (HLA) and complement C4 gene variants. These findings suggest a genetic link, possibly involving a recessive gene within the Major Histocompatibility Complex (MHC).
Area of Science:
- Immunogenetics
- Human Leukocyte Antigen (HLA) complex
- Complement system genetics
Background:
- Selective IgA deficiency is the most common primary immunodeficiency.
- The genetic basis for IgA deficiency is not fully understood, but associations with the Major Histocompatibility Complex (MHC) have been proposed.
- Previous studies suggest a potential role for specific MHC haplotypes in the development of IgA deficiency.
Purpose of the Study:
- To investigate the association of specific Human Leukocyte Antigen (HLA) and complement C4 gene variants with Immunoglobulin A (IgA) deficiency.
- To examine the inheritance patterns of these genetic markers within families affected by IgA deficiency.
- To explore the potential role of the Major Histocompatibility Complex (MHC) in the pathogenesis of IgA deficiency.
Main Methods:
- Typing of HLA-A, -B, -DR, C4, and factor B in 110 individuals with IgA deficiency and six families (9 cases).
- Comparison of phenotype frequencies between IgA-deficient individuals and controls.
- Family studies to analyze the inheritance of MHC haplotypes.
Main Results:
- Increased frequencies of HLA-B8, HLA-DR3, and homozygous C4AQ0 were observed in IgA-deficient individuals compared to controls.
- Decreased frequencies of HLA-B7, HLA-DR2, and C4A3 were noted.
- Homozygous C4A deficiency was present in 20% of IgA-deficient individuals. The extended MHC haplotype [HLA-A1, B8, C4AQ0, C4B1, BfS, DR3] was highly prevalent in IgA deficiency, with 8 out of 9 family cases carrying it, and 4 being homozygous.
Conclusions:
- The findings strongly suggest a significant association between specific MHC haplotypes, particularly the [HLA-A1, B8, C4AQ0, C4B1, BfS, DR3] haplotype, and IgA deficiency.
- The presence of two MHC haplotypes associated with IgA deficiency appears necessary but not sufficient for the condition's manifestation.
- A recessive gene within the MHC with regulatory function over IgA gene expression is a plausible explanation for the observed genetic associations.