Hereditary coproporphyria with onset usu. before puberty; autosomal dominant condition. Clinical expression during attacks ranges from asymptomatic to fatal; marked by recurrent abdominal pain, neurologic deficits, psychiatric disturbances, and hepatic insufficiency. Cause is partial defect in coproporphyrin oxidase with deficient conversion of coproporphyrinogen-9. Treatment is high-carbohydrate diet, heme arginate, and general supportive care.