The porphyrias are inherited or acquired disorders of certain enzymes in the heme biosynthetic pathway (also called porphyrin pathway). They are broadly classified as hepatic porphyrias or erythropoietic porphyrias, based on the site of the overproduction and mainly accumulation of the porphyrins (or their chemical precursors).
The hepatic porphyrias primarily affect the nervous system, resulting in abdominal pain, vomiting, acute neuropathy, seizures, and mental disturbances, including hallucinations, depression, anxiety, and paranoia. Cardiac arrhythmias and tachycardia (fast heart rate) may develop as the autonomic nervous system is affected. Pain can be severe and can, in some cases, be both acute and chronic in nature. Constipation is frequently present, as the nervous system of the gut is affected.
The erythropoietic porphyrias primarily affect the skin, causing photosensitivity (photodermatitis), blisters, necrosis of the skin and gums, itching, and swelling, and increased hair growth on areas such as the forehead.
In some forms of porphyria, accumulated heme precursors excreted in the urine may change its color, after exposure to sunlight, to a dark reddish or dark brown color. Even a purple hue may be seen. Heme precursors may also accumulate in the teeth and fingernails, giving them a reddish appearance.
Attacks of the disease can be triggered by drugs (e.g., barbiturates, alcohol, sulfa drugs, oral contraceptives, sedatives, and certain antibiotics), other chemicals, certain foods, and exposure to the sun. Fasting can also trigger attacks.