Hereditary coproporphyria. Demonstration of the abnormalities in haem biosynthesis in peripheral blood

Hereditary coproporphyria is biochemically distinct from the other porphyrias and is characterized by excessive excretion of coproporphyrin in faeces and usually in urine. The laboratory findings in 28 patients with this disease are presented and the clinical details of eight patients who have been in attack summarised. The remaining 20 patients were latent for the disease. In all patients studied the activity of delta-aminolaevulinic acid synthase was raised and coproporphyrinogen oxidase depressed in the leucocyte. This indicates the partial enzyme block in the haem biosynthetic pathway in this disease. The activities of the other enzymes in the pathway, leucocyte ferrochelatase and erythrocyte delta-aminolaevulinic acid dehydratase, porphobilinogen deaminase and uroporphyrinogen decarboxylase showed no consistent change. On review of 111 cases, 35 per cent presented in acute attack: 80 per cent had abdominal pain, 34 per cent vomiting, 29 per cent solar sensitivity, 23 per cent neurological involvement, 23 per cent psychiatric symptoms and 20 per cent severe constipation. Only two fatalities have been published, both from respiratory failure. There was a female preponderance of cases in attack of 2-5:1 and in the latent cases of 1-5:1 suggesting hormonal provocation in the uncovering of the disease. Drugs were implicated as precipitating 54 per cent of acute attacks and in 34 per cent of cases, these were barbiturates. This study demonstrates the reduction in activity of coproporphyrinogen oxidase in the haem biosynthetic pathway and the elevation of delta-aminolaevulinic acid synthase in the peripheral blood. These features, together with the typical abnormal porphyrin excretion pattern, appear to be diagnostic of hereditary coproporphyria whether in attack, remission, or in the latent form.