C4A
Description
The C4A (complement C4A (Chido/Rodgers blood group)) is a protein-coding gene located on chromosome 6.
Complement C4-A is a protein encoded by the C4A gene in humans. It is part of the classical activation pathway of the complement system and exists as the acidic form of complement factor 4. This protein is initially expressed as a single chain precursor that is cleaved into three chains (alpha, beta, and gamma) before secretion. This trimer facilitates interactions between the antigen-antibody complex and other complement components. The alpha chain can be cleaved to release C4 anaphylatoxin, which triggers inflammation locally. C4A deficiency is linked to systemic lupus erythematosus and type 1 diabetes mellitus. Conversely, an increased copy number of the gene is strongly associated with schizophrenia and bipolar disorder with psychosis, potentially explaining the hereditary nature of these illnesses. The C4A gene resides within the major histocompatibility complex (MHC) class III region on chromosome 6, specifically in the RCCX locus. Different haplotypes of this gene cluster exist, leading to individuals having 1, 2, or 3 copies of the C4A gene. Due to five adjacent nucleotide substitutions, each gene copy can be classified as either C4A or C4B. These variations result in four amino acid changes and immunological subfunctionalization. Each gene consists of 41 exons and exhibits size variations between 22 kb and 16 kb. The longer variant arises from the integration of the endogenous retrovirus HERV-K(C4) into intron 9.
C4A is also known as C4, C4A2, C4A3, C4A4, C4A6, C4AD, C4S, CO4, CPAMD2, RG.
