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Genetic analysis of C4 deficiency

Z L Awdeh, H D Ochs, C A Alper

    The Journal of Clinical Investigation
    |January 1, 1981
    PubMed

    Insights

    Inherited structural variations in the fourth complement component (C4) can lead to undetectable protein levels. The number of expressed C4 genes in a family directly correlated with serum C4 levels, impacting complement function.

    Area of Science:

    • Immunogenetics
    • Complement System Biology
    • Molecular Immunology

    Background:

    • The fourth component of complement (C4) exists in several structural forms, influencing its function and serum levels.
    • Polymorphisms in C4 genes can lead to deficiencies or altered protein expression, with implications for immune response.
    • Understanding C4 gene structure and expression is crucial for diagnosing and managing complement-related disorders.

    Purpose of the Study:

    • To investigate the inherited structural polymorphism of the fourth component of complement (C4) within a family.
    • To determine the genetic basis for homozygous C4 deficiency in a child.
    • To correlate C4 gene copy number with serum C4 protein levels in family members.

    Main Methods:

    • Family-based genetic analysis of C4 structural polymorphism.
    • Detection of C4 haplotypes, including null variants (C4A*QO, C4B*QO).
    • Quantification of serum C4 levels and correlation with the number of expressed C4 genes.

    Main Results:

    • Identified a C4 haplotype (C4A*QO C4B*QO) in family members that resulted in undetectable Chido (C4B) and Rodgers (C4A) antigens.
    • Documented individuals with varying numbers of expressed C4 genes (one to four).
    • Demonstrated a positive correlation between the number of expressed C4 genes and mean serum C4 levels.

    Conclusions:

    • Inherited C4 structural polymorphism, specifically null haplotypes, can cause undetectable C4 protein.
    • The number of expressed C4 genes is a significant determinant of serum C4 levels.
    • This study elucidates the genetic basis of C4 deficiency and its impact on complement component levels within a family.

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