Complement C4-A is a protein that in humans is encoded by the C4A gene.[5]

Available structures
PDBOrtholog search: PDBe RCSB
AliasesC4A, C4, C4A2, C4A3, C4A4, C4A6, C4AD, C4S, CO4, CPAMD2, RG, complement component 4A (Rodgers blood group), complement C4A (Rodgers blood group)
External IDsOMIM: 120810 MGI: 88228 HomoloGene: 36030 GeneCards: C4A
Gene location (Human)
Chr.Chromosome 6 (human)[1]
Band6p21.33Start31,982,057 bp[1]
End32,002,681 bp[1]
RNA expression pattern

More reference expression data









RefSeq (mRNA)



RefSeq (protein)



Location (UCSC)Chr 6: 31.98 – 32 MbChr 17: 34.73 – 34.74 Mb
PubMed search[3][4]
View/Edit HumanView/Edit Mouse


This gene encodes the acidic form of complement factor 4, part of the classical activation pathway. The protein is expressed as a single chain precursor which is proteolytically cleaved into a trimer of alpha, beta, and gamma chains prior to secretion. The trimer provides a surface for interaction between the antigen-antibody complex and other complement components. The alpha chain may be cleaved to release C4 anaphylatoxin, a mediator of local inflammation. Deficiency of this protein is associated with systemic lupus erythematosus and type I diabetes mellitus.[6][7][8][9][10][11] Excess production is associated with schizophrenia and bipolar disorder with psychosis.[12] This gene localizes to the major histocompatibility complex (MHC) class III region on chromosome 6. Varying haplotypes of this gene cluster exist, such that individuals may have 1, 2, or 3 copies of this gene.[5]

See also


  1. ENSG00000206340, ENSG00000244731, ENSG00000227746 GRCh38: Ensembl release 89: ENSG00000244207, ENSG00000206340, ENSG00000244731, ENSG00000227746 - Ensembl, May 2017
  2. GRCm38: Ensembl release 89: ENSMUSG00000073418 - Ensembl, May 2017
  3. "Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
  4. "Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
  5. "Entrez Gene: C4A complement component 4A (Rodgers blood group)".
  6. Dawkins RL, Uko G, Christiansen FT, Kay PH (Sep 1983). "Low C4 concentrations in insulin dependent diabetes mellitus". British Medical Journal. 287 (6395): 839. doi:10.1136/bmj.287.6395.839-b. PMC 1549128. PMID 6412852.
  7. Vergani D, Johnston C, B-Abdullah N, Barnett AH (Mar 1983). "Low serum C4 concentrations: an inherited predisposition to insulin dependent diabetes?". British Medical Journal. 286 (6369): 926–8. doi:10.1136/bmj.286.6369.926. PMC 1547358. PMID 6403137.
  8. Mijovic CH, Fletcher JA, Bradwell AR, Barnett AH (Oct 1987). "Low C4 levels in type 1 (insulin-dependent) diabetes". Diabetologia. 30 (10): 824. doi:10.1007/bf00275752. PMID 3428499.
  9. Thomsen M, Mølvig J, Zerbib A, de Preval C, Abbal M, Dugoujon JM, Ohayon E, Svejgaard A, Cambon-Thomsen A, Nerup J (1988). "The susceptibility to insulin-dependent diabetes mellitus is associated with C4 allotypes independently of the association with HLA-DQ alleles in HLA-DR3,4 heterozygotes". Immunogenetics. 28 (5): 320–7. doi:10.1007/BF00364230. PMID 3139557.
  10. Jenhani F, Bardi R, Gorgi Y, Ayed K, Jeddi M (Apr 1992). "C4 polymorphism in multiplex families with insulin dependent diabetes in the Tunisian population: standard C4 typing methods and RFLP analysis". Journal of Autoimmunity. 5 (2): 149–60. doi:10.1016/0896-8411(92)90196-w. PMID 1352685.
  11. Lhotta K, Auinger M, Kronenberg F, Irsigler K, König P (1996). "Polymorphism of complement C4 and susceptibility to IDDM and microvascular complications". Diabetes Care. 19 (1): 53–55. doi:10.2337/diacare.19.1.53. PMID 8720534.
  12. Sharma, RP (2018). "C4A mRNA expression in PBMCs predicts the presence and severity of delusions in schizophrenia and bipolar disorder with psychosis". Schizophr. Res. 197: 321–327. doi:10.1016/j.schres.2018.01.018. PMC 6087677. PMID 29449061.
  • Media related to C4A at Wikimedia Commons
  • Human C4A genome location and C4A gene details page in the UCSC Genome Browser.

Further reading

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