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C4 phenotypic variation suggests an unusual class III gene organization

D J Schendel, R Wank, G J O'Neill

    Vox Sanguinis
    |January 1, 1985
    PubMed

    Insights

    Genetic analysis of complement C4A, C4B, C2, and BF genes in families revealed a duplicated C4A locus. This common haplotype in Northern Europeans influences complement gene inheritance patterns.

    Area of Science:

    • Immunogenetics
    • Human Genetics
    • Molecular Biology

    Background:

    • The complement system, particularly the C4 gene locus, plays a crucial role in immune responses.
    • Understanding the genetic variations and inheritance patterns of complement genes is essential for studying immune-related diseases.

    Purpose of the Study:

    • To investigate the genetic inheritance of class III complement gene markers (C4A, C4B, C2, BF) within HLA-genotyped families.
    • To analyze unusual inheritance patterns of C4A electrophoretic phenotypes and their association with other genetic markers.

    Main Methods:

    • Family-based genetic typing of C4A, C4B, C2, and BF genes.
    • HLA genotyping of 26 families.
    • Electrophoretic phenotyping of C4A variants.

    Main Results:

    • An inheritance pattern inconsistent with a single C4A locus was observed in 6 out of 26 families, suggesting a duplicated C4A locus.
    • This duplicated C4A locus haplotype (C4A 3, A 2) is prevalent in Northern Europeans (≥6% frequency).
    • The C4A 3, A 2 variant was associated with specific HLA-B alleles (HLA-Bw35, HLA-Bw55) and a distinct complotype (FC3/20).

    Conclusions:

    • The findings indicate the existence and frequency of a duplicated C4A locus haplotype in Northern European populations.
    • This genetic variation may influence complement system function and susceptibility to certain immune-related conditions.
    • Further research is warranted to explore the functional implications of this duplicated C4A locus.

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