The activities of uroporphyrinogen synthetase and cosynthetase in congenital erythropoietic porphyria (CEP)

Congenital erythropoietic porphyria

Congenital erythropoietic porphyria is a rare autosomal-recessive disorder of the porphyrin metabolism caused by the homozygous defect of uroporphyrinogen III cosynthase. High amounts of uroporphyrin I accumulate in all cells and tissues, reflected by an increased erythrocyte porphyrin concentration and excretion of high porphyrin amounts in urine and feces. Dermal deposits of uroporphyrin frequently induce a dramatic phototoxic oxygen-dependent skin damage with extensive ulcerations and mutilations. Splenomegaly and hemolytic anemia are typical internal symptoms. Skeletal changes such as osteolysis and calcifications are frequent. To date 130 cases of congenital erythropoietic porphyria have been published and are summarized here. Splenectomy, erythrocyte transfusions, and bone marrow transplantation have shown some beneficial effect. The best therapy is the avoidance of sunlight. In the two patients with congenital erythropoietic porphyria described here, oral administration of the oxygen quenchers ascorbic acid and alpha-tocopherol resulted in an improvement in the reduced hemoglobin and erythrocyte concentrations.

Biochemical diagnosis of a fatal case of Günther's disease in a newborn with hydrops foetalis

The birth of a male baby was induced at 32 weeks. In utero, the child presented, inter alia, signs of hydrops, hepatosplenomegaly and anaemia. Two in utero transfusions for correction of the anaemia were performed at 28 and 29 weeks, respectively. The baby rapidly presented respiratory distress with mixed acidosis. Three hours after birth, pink urine was excreted. Signs of icterus necessitated phototherapy, after which photosensitivity occurred. Erythrocytes were fluorescent under long-wavelength UV light. The baby died 24 hours after birth, displaying severe acidosis, a diffuse haemorrhagic syndrome, and repeated brady-cardia which did not respond to isoprenaline. The analysis of porphyrins in urine, blood and faeces of the baby gave the following results: 1) uroporphyrin (I and III isomeric series) was increased in urine and faeces, with traces in erythrocytes and plasma; 2) heptacarboxyporphyrin I was found mainly in urine and much less in erythrocytes, plasma and faeces; 3) coproporphyrin I was increased in urine, erythrocytes, plasma and faeces, and 4) 5-aminolaevulinic acid and porphobilinogen in urine and plasma were within the reference ranges. Determination of the enzymes of haem biosynthesis in erythrocytes and lymphocytes showed that both parents possessed only 50% of the normal activity of cosynthase. A previously described point mutation in codon 73 was observed in one parent. Fatal cases of neonatal Günther's disease are extremely rare and such an observation, according to our knowledge, is probably one of the first described.

Acquired and inherited porphyria: clinical and biochemical features

Inheritance in 30 cases of porphyria cutanea tarda (PCT) and their relatives was investigated. Seventeen families were studied using the clinical criteria, quantitation, and thin layer chromatography of urinary porphyrins. Thirteen families (13 propositus and 48 relatives) were investigated by using the above criteria and in vitro porphyrin biosynthesis by erythrocytes from delta-aminolevulinic acid. Three different types of PCT were identified: overt, subclinical, and latent. Among 61 members examined, 13 had overt PCT. In six families, ten members had subclinical PCT and six latent PCT showing that in these six families PCT was a hereditary disorder. In seven other families inheritance could not be demonstrated.

Treatment of the porphyrias: mechanisms of action

The porphyrias are diseases that result from inherited or acquired abnormalities of porphyrin-heme synthesis in the liver and the bone marrow. Only the hepatic porphyrias are known to be aggravated by exposure to a variety of exogenous drugs and chemicals. Simple avoidance of these agents will reduce the risk of developing hepatic porphyria and may lead to clinical improvement in patients with active disease. Some types of therapy of the hepatic porphyrias are effective because of their ability to modulate the activity of delta-aminolevulinic acid synthetase, the rate-limiting enzyme for heme synthesis. Most of the porphyrias are associated with cutaneous photosensitivity, the treatment of which centers about either reducing the excessive production of porphyrins or of inhibiting the photobiological response to these photosensitizing chemicals in the skin.

Enzyme defects in the porphyrias and their relevance to the biochemical abnormalities in these disorders

Defects in enzymes of the heme biosynthesis pathway underlie the biochemical abnormalities which occur in the porphyrias. Porphyrins and porphyrin precursors are accumulated and excreted in excessive amounts because of the enzyme defects. This is illustrated by studies in protoporphyria and variegate porphyria, disorders in which the biochemical abnormalities indicate a defect(s) in the terminal part of the heme biosynthesis pathway. The activity of heme synthease (ferrochelatase), which catalyzes the chelation of ferrous iron to protoporphyrin, is deficient in tissues of patients with protoporphyria. This causes protoporphyrin to be accumulated and excreted excessively. In variegate porphyria protoporphyrinogen oxidase, which catalyzes the oxidation of protoporphyrinogen to protoporphyrin, appears to be defective. As a result, protoporphyrinogen may be excreted in increased amounts in bile, where it is subsequently auto-oxidized to protoporphyrin. The following questions have arisen as a result of the demonstrations of enzyme defects in tissues of patients with porphyria: (1) Will different defects in the same enzyme be found among patients who fulfill the clinical and biochemical criteria for diagnosis of a specific porphyria? That is, does genetic heterogeneity exist in each of the porphyrias? (2) Why do some patients with an enzyme defect not have biochemical abnormalities? (3) Why is one type of tissue, usually the liver, the major site of expression of the biochemical abnormality, when the enzyme defect can be demonstrated in all tissues?

Prenatal exclusion of congenital erythropoietic porphyria (Günther's disease) in a fetus at risk

Amniotic fluid porphyrins, biosynthesis of porphyrins by amniotic cells, and uroporphyrinogen III cosynthetase were studied after the 17th week of a pregnancy at risk for congenital erythropoietic porphyria (CEP). Only coproporphyrin was found in amniotic fluid. A diagnosis of CEP was ruled out by the demonstration of normal cosynthetase activity; biosynthesis of porphyrins was identical, not only in the porpositus and in control amniotic cells, but also in patients with CEP and in control skin fibroblasts.

Enzymatic defects of hereditary porphyrias: an explanation of dominance at the molecular level

In four of the five autosomal dominant porphyrias four different partial enzymatic defects of the porphyrin biosynthetic pathway have been discovered in the last few years. With the exception of protoporphyria, the residual enzymatic activity in carriers of these defects is approximately equal to 50% of that found in controls. In each case the pattern of excretion of porphyrin and/or porphyrin precursors reflects the stie of the partial metabolic block. There are indications, at least in intermittent acute porphyria, that the degree of penetrance of the disorder varies according to the level of phenotypic expression, being highest for the enzyme deficiency, lower for the excretion of precursors and lowest for the clinical symptoms. It is proposed that environmental factors, and probably also gene interaction, are the cause of the different degrees of penetrance.