The porphyrias are a group of uncommon diseases that cause either disease affecting the skin, disease affecting the nervous system, or both.
Porphyria results from accumulation of porphyrins either in the skin, which results in sensitivity to sunlight, or in the liver, which results in acute attacks of porphyria. Normally, porphyrins are converted from one type of porphyrin to another, in a sequence of chemical reactions, each one under the control of a specific enzyme. The end product of this sequence is haem, an essential component of haemoglobin, which is responsible for transporting oxygen around our body. If one of these enzymes is deficient or defective, there is a build up of porphyrins which may accumulate to toxic levels. In all, there are seven types of porphyria of which four are acute porphyrias, the others affect the skin predominantly.
Porphyria cutanea tarda
The most common type of porphyria is called porphyria cutanea tarda or PCT. PCT does not usually occur until middle age and affects the skin in sun-affected areas causing fluid-filled blisters. Over time the skin becomes scarred, brown and blotchy and fragile. Sometimes excess hair grows in the affected areas. Unlike the other porphyrias, PCT is rarely inherited and is usually triggered by some other factor or condition. Even in cases where it appears to be inherited from a parent, another factor is usually required before it causes symptoms. The most common factor is excessive alcohol consumption but the presence of other diseases such as haemochromatosis, hepatitis C and HIV infection or some drugs, eg oestrogens may precipitate PCT symptoms.
Acute intermittent porphyria
The next most common form of porphyria is acute intermittent porphyria or AIP. AIP causes only neurological symptoms and does not affect the skin. AIP is inherited in an autosomal dominant fashion which means that half of an affected parent's children are likely to have the condition. However, it may appear to skip generations as many people who inherit the disease never get any symptoms. AIP virtually never appears prior to puberty. Affected people get attacks that develop over hours or days and can last for days or weeks if untreated.
The most common symptom is pain in the abdomen, often severe, but the pain may affect other areas of the body as well. Muscle weakness of the arms and legs may occur and in severe cases weakness of the breathing muscles may require the person to be placed on a ventilator. A variety of other symptoms may occur due to various parts of nervous system being affected, these include, loss of sensation, confusion, fits, palpitations, high blood pressure and constipation or diarrhoea. AIP is often precipitated by factors such as drugs (see the list in the links at the end of this article), hormones, starvation and dieting and stress caused by infections, surgery, accidents or even psychological stress.
The third most common form of porphyria is erythropoietic protoporphyria or EPP. EPP affects the skin mainly and is unusual in that it often starts in childhood. Children with EPP are unusually sensitive to the sun and develop itching, burning pain and swelling in sun-exposed skin often within minutes of sun exposure. Over time the skin becomes thickened and waxy in appearance and permanent spots, scars and other changes may appear. A small number of affected children also develop liver disease and gallstones and rarely the liver disease can be very serious.
Other forms of porphyria are very rare. Variegate porphyria or VP, (more common in white people of South African ancestry) and hereditary coproporphyria or HCP can both cause neurological symptoms like AIP and skin symptoms like PCT. Aminolevulinate dehydratase deficiency porphyria (ADP) is an extremely rare condition and in the few cases described is similar to AIP. Congenital Erythropoietic Porphyria (CEP) is the rarest of the porphyrias. It is primarily a skin condition and uniquely is inherited as a recessive condition. That means that both parents are asymptomatic carriers.