Protoporphyrin accumulation by mitogen stimulated lymphocytes and protoporphyrinogen oxidase activity in patients with porphyria variegata and erythropoietic protoporphyria: evidence for deficiency of protoporphyrinogen oxidase and ferrochelatase in both diseases

Abstract

In erythropoietic protoporphyria (EPP) and porphyria variegata (PV) excess protoporphyrin is excreted in the stool, suggesting one or more enzyme defects in the terminal steps of the haem biosynthetic pathway. We measured protoporphyrinogen oxidase (PPO), which catalyses the oxidation of protoporphyrinogen to protoporphyrin, in both EPP and PV patients and in the offspring of PV patients. In the same subjects we measured protoporphyrin formation by mitogen stimulated lymphocytes, with delta aminolaevulinic acid (ALA) as substrate and with the addition of chelators or iron, an indirect measure of ferrochelatase activity. PPO activity was reduced by 41% (P less than 0.001) in PV patients and in 50% of their offspring, and by 36% (P less than 0.001) in EPP patients. Protoporphyrin accumulation in stimulated lymphocytes was increased by 1.3-fold (P less than 0.001) in EPP and 1.5-fold (P less than 0.001) in PV patients compared to normal subjects. There was a significant difference in protoporphyrin accumulation between iron deficient and iron replete cells from PV patients as compared to normals but not as marked as for EPP cells treated similarly. Stimulated lymphocytes from prepubertal PV offspring with reduced PPO activity accumulated normal amounts of protoporphyrin. We have interpreted our findings as follows: PPO is significantly reduced in both diseases. Ferrochelatase becomes defective in PV patients after puberty. This could explain why PV is clinically and biochemically manifest only after puberty. As it has been repeatedly shown that ferrochelatase is markedly reduced in EPP, it would appear that both enzymes are deficient in these two porphyrias.