CPOX

The CPOX gene provides instructions for the production of an enzyme called coproporphyrinogen oxidase. This enzyme is responsible for the sixth step in the production of heme, the iron-containing part of hemoglobin. Hemoglobin is the oxygen-carrying protein in red blood cells. Each step in heme production is controlled by a different enzyme, each of which is produced from a single gene. Coproporphyrinogen oxidase removes carbon and oxygen from coproporphyrinogen III (the product of the fifth step in the production of heme) to form protoporphyrinogen IX. This reaction occurs in structures known as mitochondria, the energy-producing centers within cells. Two additional enzymes modify protoporphyrinogen IX before it becomes heme. The heme molecule is incorporated into hemoglobin and packaged into red blood cells, or it is used in the liver for the production of certain liver enzymes.

porphyria - caused by mutations in the CPOX gene

More than 35 mutations that cause hereditary coproporphyria (a type of porphyria) and a more severe form of the disorder, harderoporphyria, have been identified in the CPOX gene. One mutation in particular has been found in all families with harderoporphyria. This mutation changes one of the building blocks (amino acids) used to make coproporphyrinogen oxidase. Specifically, this genetic change substitutes the amino acid glutamic acid for the amino acid lysine at position 404 (written as Lys404Glu or K404E). Mutations in the CPOX gene reduce the activity of coproporphyrinogen oxidase, allowing byproducts of heme production called porphyrins to build up in the body. This buildup, in combination with nongenetic factors (such as certain drugs, alcohol, and dieting), causes the signs and symptoms of these types of porphyria.