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

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.

Familial and sporadic porphyria cutanea: two different diseases

Uroporphyrinogen (URO) decarboxylase was measured in hemoglobin-free erythrocytes from subjects with familial porphyria cutanea: the mean activity was about 50% of that found in erythrocytes from normal subjects. Asymptomatic carriers were always found in the family. No enzyme deficiency was found in erythrocytes from subjects with sporadic porphyria cutanea. The measurement of URO decarboxylase in erythrocytes seems to allow an easy distinction between these two groups of porphyria cutanea.