Clinical medicine of disorders of porphyrin metabolism in man

: Porphyrin metabolism disorders are grouped into three classes. 1) Hereditary porphyrias including those caused by an inherited deficiency in one of the enzymes responsible for porphyrin synthesis. 2) Secondary porphyrias: well defined clinical situations due to disturbed porphyrin metabolism caused by a variety of toxic substances or drugs or secondary to other pathological conditions. 3) porphyrin metabolism disorders as concomitant featured of certain types of poisoning or particular pathologies. This is followed by a brief description of porphyrin synthesis and the enzymes involved in it, and the distribution of porphyrins and their precursors in certain tissues and biological materials. Hereditary porphyrins are treated individually and not classified since all the classification systems proposed are open to criticism. However the value of grouping acute intermittent porphyria, hereditary coproporphyria, variegated porphyria and the porphyria caused by PBG-synthetase deficiency under "acute porphyrias" is recognised since all involve acute attacks with similar symptoms and prognoses, all are triggered by the same factors and all are treated in the same way. The various forms of hereditary porphyrias are grouped into 3 main categories: a) acute attacks featuring abdominal colics and signs of distress on the cerebral and peripheral nervous systems; b) skin alteration due to photosensitisation; c) haemolytic anaemia. Treatment is divided into preventive, symptomatic and aetiopathogenic. The individual hereditary porphyrias are then examined. The secondary porphyrias examined include lead poisoning, porphyria of the skin caused by hexachlorobenzene, subacute or chronic tyrosinaemia and acute intermittent porphyria caused by carbamazepine. Finally the porphyrin metabolism disorders concomitant with other diseases are examined including those encountered in anaemia, liver disease, dermatological conditions and infections and conditions caused by drugs and toxic substances.