The most commonly encountered porphyrias are acute intermittent porphyria (AIP), porphyria cutanea tarda (PCT)erythropoietic protoporphyria (EPP) and variegate porphyria. Each of these is described in detail on its own pages.

The haem synthetic pathway
The remaining porphyrias are much more rarely encountered and are briefly summarised here. As with all porphyrias, they result from enzyme defects in the haem synthetic pathway as illustrated on the right.

Hereditary Coproporphyria

This is an autosomal dominant condition. In simple terms, this means that only one parent need be affected for the children to run the risk of showing the disease. In fact, each child will have a 50% chance of inheriting that disease. Both boys and girls stand an equal chance of inheriting the disease.

Patients may develop photosensitivity with typical skin disease and are also at risk of the acute attack. They must therefore observe drug precautions.

The disease arises from a mutation in the gene for the enzyme coproporphyrinogen oxidase. This deficiency results in a characteristic accumulation of coproporphyrin, particularly in the stool, which may be tested in making the diagnosis.

Congenital Erythropoietic Porphyria (CEP)

This is an autosomal recessive condition. Both parents need to carry a mutation in the gene for the enzyme uroporphyrinogen cosynthase in order for the disease to manifest. CEP is extremely rare. It presents with skin disease, which is often severe and accompanied by  photomutilation . In CEP, haem synthesis within the bone marrow is affected, and this may lead to some relatively minor abnormalities in the blood including anaemia, haemolysis (breakdown of red blood cells) and a slightly enlarged spleen.

It is diagnosed by showing an abnormal accumulation of porphyrins  in the red blood cells and urine.

Ala Dehydratase (DOSS) Porphyria

This excessively rare porphyria is associated with acute attacks only. Skin disease is not a feature. It is autosomal recessive  condition. Both parents need to carry a mutation in the gene  for the enzyme ALA dehydratase in order for the disease to manifest.

It is diagnosed by showing very high levels of ALA with a low or normal PBG level in the urine.