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Genetics Home Reference: your guide to understanding genetic conditions     A service of the U.S. National Library of Medicine®


Reviewed July 2009

What is the official name of the CPOX gene?

The official name of this gene is “coproporphyrinogen oxidase.”

CPOX is the gene's official symbol. The CPOX gene is also known by other names, listed below.

What is the normal function of the CPOX gene?

The CPOX gene provides instructions for making an enzyme known as coproporphyrinogen oxidase. This enzyme is involved in the production of a molecule called heme. Heme is vital for all of the body's organs, although it is most abundant in the blood, bone marrow, and liver. Heme is an essential component of iron-containing proteins called hemoproteins, including hemoglobin (the protein that carries oxygen in the blood).

The production of heme is a multi-step process that requires eight different enzymes. Coproporphyrinogen oxidase is responsible for the sixth step in this process, the removal of carbon and oxygen atoms from coproporphyrinogen III (the product of the fifth step) to form protoporphyrinogen IX. In subsequent steps, two other enzymes modify protoporphyrinogen IX and incorporate an iron atom to produce heme.

How are changes in the CPOX gene related to health conditions?

porphyria - caused by mutations in the CPOX gene

At least 45 mutations in the CPOX gene have been found to cause porphyria. Mutations in this gene can cause two types of porphyria: hereditary coproporphyria and a variant known as harderoporphyria.

Most CPOX gene mutations change single protein building blocks (amino acids) in coproporphyrinogen oxidase. A single mutation appears to be responsible for harderoporphyria; this genetic change replaces the amino acid glycine with the amino acid glutamic acid at position 404 (written as Lys404Glu or K404E). Mutations in the CPOX gene reduce the activity of coproporphyrinogen oxidase, allowing compounds called porphyrins to build up in the body. These compounds are formed during the normal process of heme production, but reduced activity of coproporphyrinogen oxidase allows them to accumulate to toxic levels. This buildup, in combination with nongenetic factors such as certain drugs, alcohol, and dieting, leads to the signs and symptoms of hereditary coproporphyria and harderoporphyria.

Where is the CPOX gene located?

Cytogenetic Location: 3q12

Molecular Location on chromosome 3: base pairs 98,576,414 to 98,593,668

(Homo sapiens Annotation Release 107, GRCh38.p2) (NCBI (

The CPOX gene is located on the long (q) arm of chromosome 3 at position 12.

The CPOX gene is located on the long (q) arm of chromosome 3 at position 12.

More precisely, the CPOX gene is located from base pair 98,576,414 to base pair 98,593,668 on chromosome 3.

See How do geneticists indicate the location of a gene? ( in the Handbook.

Where can I find additional information about CPOX?

You and your healthcare professional may find the following resources about CPOX helpful.

You may also be interested in these resources, which are designed for genetics professionals and researchers.

What other names do people use for the CPOX gene or gene products?

  • Coprogen oxidase
  • Coproporphyrinogenase
  • Coproporphyrinogen III oxidase, mitochondrial
  • Coproporphyrinogen III Oxidases
  • coproporphyrinogen oxidase (coproporphyria, harderoporphyria)
  • Coproporphyrinogen:oxygen oxidoreductase (decarboxylating)
  • COX
  • CPO
  • CPX
  • HCP

See How are genetic conditions and genes named? ( in the Handbook.

What glossary definitions help with understanding CPOX?

acids ; amino acid ; atom ; bone marrow ; enzyme ; gene ; glutamic acid ; glycine ; heme ; hemoglobin ; hereditary ; iron ; molecule ; mutation ; oxidase ; oxidoreductase ; oxygen ; protein ; toxic

You may find definitions for these and many other terms in the Genetics Home Reference Glossary.


  • Badminton MN, Elder GH. Molecular mechanisms of dominant expression in porphyria. J Inherit Metab Dis. 2005;28(3):277-86. Review. (
  • Elder GH. Genetic defects in the porphyrias: types and significance. Clin Dermatol. 1998 Mar-Apr;16(2):225-33. Review. (
  • Gouya L, Puy H, Robreau AM, Lyoumi S, Lamoril J, Da Silva V, Grandchamp B, Deybach JC. Modulation of penetrance by the wild-type allele in dominantly inherited erythropoietic protoporphyria and acute hepatic porphyrias. Hum Genet. 2004 Feb;114(3):256-62. Epub 2003 Dec 11. (
  • Kauppinen R. Porphyrias. Lancet. 2005 Jan 15-21;365(9455):241-52. Review. (
  • Lamoril J, Puy H, Whatley SD, Martin C, Woolf JR, Da Silva V, Deybach JC, Elder GH. Characterization of mutations in the CPO gene in British patients demonstrates absence of genotype-phenotype correlation and identifies relationship between hereditary coproporphyria and harderoporphyria. Am J Hum Genet. 2001 May;68(5):1130-8. Epub 2001 Apr 16. (
  • Lee DS, Flachsová E, Bodnárová M, Demeler B, Martásek P, Raman CS. Structural basis of hereditary coproporphyria. Proc Natl Acad Sci U S A. 2005 Oct 4;102(40):14232-7. Epub 2005 Sep 21. (
  • NCBI Gene (
  • Rosipal R, Lamoril J, Puy H, Da Silva V, Gouya L, De Rooij FW, Te Velde K, Nordmann Y, Martàsek P, Deybach JC. Systematic analysis of coproporphyrinogen oxidase gene defects in hereditary coproporphyria and mutation update. Hum Mutat. 1999;13(1):44-53. (
  • Sassa S, Kappas A. Molecular aspects of the inherited porphyrias. J Intern Med. 2000 Feb;247(2):169-78. Review. (
  • Schmitt C, Gouya L, Malonova E, Lamoril J, Camadro JM, Flamme M, Rose C, Lyoumi S, Da Silva V, Boileau C, Grandchamp B, Beaumont C, Deybach JC, Puy H. Mutations in human CPO gene predict clinical expression of either hepatic hereditary coproporphyria or erythropoietic harderoporphyria. Hum Mol Genet. 2005 Oct 15;14(20):3089-98. Epub 2005 Sep 13. (


The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? ( in the Handbook.

Reviewed: July 2009
Published: February 8, 2016