Overview of porphyrias

[Sommer]

Porphyrias are a group of disorders caused by deficiencies of enzymes involved in the production of heme.
Heme is a chemical compound that contains iron and gives blood its red color. Heme is the key component of several important proteins in the body. One of the proteins is hemoglobin, which enables red blood cells to carry oxygen. Heme is also an important part of certain enzymes made by the liver.
Heme is produced mainly in the bone marrow and liver through a complex process regulated by eight different enzymes. The enzymes work one after another in separate steps that take the starting compound through several different intermediate compounds (called porphyrins), finally producing heme. The porphyrins themselves are made up of compounds called porphyrin precursors. If there is a deficiency in one of these enzymes, certain porphyrins and porphyrin precursors may accumulate. These may accumulate in the

Bone marrow
Liver
Skin
Other tissues

Heme precursors may also appear in excess in the blood or be excreted in the urine or stool. The accumulated heme precursors cause symptoms. The specific heme precursors that accumulate and the symptoms that develop depend on which enzyme is deficient.
Porphyrias are a number of different disorders, each caused by a deficiency in one of the enzymes needed for heme production. Each enzyme deficiency is caused by damage to the gene (a mutation) responsible for the production of the enzyme in question. The damaged gene is almost always inherited from one of the parents or, rarely, both.