UROS

The UROS gene provides instructions for the production of an enzyme called uroporphyrinogen III synthase. This enzyme is responsible for the fourth 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. The enzyme made by the UROS gene rearranges atoms in hydroxymethylbilane (the product of the third step in the manufacture of heme) to produce uroporphyrinogen III. Four more enzymes modify this compound to produce 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 UROS gene

At least 35 mutations that cause congenital erythropoietic porphyria (sometimes referred to as Gunther disease) have been identified in the UROS gene. Mutations have also been discovered in a segment of nearby DNA that regulates the gene's activity. Many UROS mutations partially or almost completely inactivate uroporphyrinogen III synthase. An inactive enzyme allows porphyrins, which are byproducts of heme production, to build up in the body and cause this disorder. A common UROS mutation, which occurs in about 40 percent of cases, changes a single building block (amino acid) used to make the enzyme. This particular mutation replaces the amino acid cysteine with the amino acid arginine at position 73 (written as Cys73Arg or C73R). People who have this mutation in each copy of the UROS gene usually experience severe signs and symptoms of congenital erythropoietic porphyria beginning in infancy.