Molecular defects in ferrochelatase in patients with protoporphyria requiring liver transplantation.

Abstract

Protoporphyria is a genetic disorder in which a deficiency of mitochondrial ferrochelatase activity causes accumulation of protoporphyrin that produces severe liver damage in some patients. In this study, mutations of the ferrochelatase gene were examined in eight unrelated patients who had liver transplantation. RNA was prepared from liver and/ or lymphoblasts, and specific reverse transcriptase-nested polymerase chain reactions amplified and sequenced ferrochelatase cDNAs. Products shorter than normal resulted from an exon 3 deletion in three patients, exon 10 deletion in two, exon 2 deletion in one, and deletion of five nucleotides in exon 5 in one. Sequence of normal-size products revealed no other mutations. Western blot showed a reduced quantity of normal-size ferrochelatase protein in protoporphyria liver compared with normal liver (19-51%, mean 32% of normal). Levels of the mitochondrial protein F 1 -ATPase ␤ -subunit were not decreased to a similar degree. Liver ferrochelatase activity was reduced more than could be explained by the decrease in ferrochelatase protein (4-20%, mean 9% of normal). These results establish genetic heterogeneity in the most severe phenotype of protoporphyria. However, the gene mutations found share the property of causing a major structural alteration in the ferrochelatase protein.

Liver transplantation for erythropoietic protoporphyria liver disease

“…Ferrochelatase DNA analysis in ten patients showed that each was heterozygous for a mutation in the ferrochelatase gene that caused splicing abnormality in six, frame shift or nonsense in three, and missense in one; nine patients also had a polymorphism in the other ferrochelatase allele (IVS3-48c) that caused low expression of the gene. [1][2][3] The diagnosis of EPP liver disease was confirmed by examination of the explants, which were enlarged and black in color, and with most having micronodular cirrhosis ( Fig. 1).…”

“…[1][2][3] Patients with EPP have excessive production of protoporphyrin, primarily in the bone marrow, resulting in increased biliary excretion of this compound. 4 The major clinical manifestation in EPP is photosensitivity, which is caused by the photo-active damage to skin by protoporphyrin.…”

Posttranslational stability of the heme biosynthetic enzyme ferrochelatase is dependent on iron availability and intact iron-sulfur cluster assembly machinery

“…EPP is characterized by elevated erythrocyte PPIX, resulting in painful cutaneous photosensitivity and, infrequently, hepatic failure caused by biliary occlusions of crystalline protoporphyrin. 8 Whereas elevated erythrocyte PPIX levels in Irp2 Ϫ/Ϫ mice are associated with the loss of IRP2-mediated translational repression of ALAS2, 6 EPP in humans is usually caused by mutations in the ferrochelatase (FECH) gene. 9 EPP patients usually possess less than one-third of the normal level of ferrochelatase activity, 10 which most frequently results from inheritance of a mutated FECH allele with decreased activity together with a low-expressing normal FECH allele.…”

Mdr P-glycoproteins are not essential for biliary excretion of the hydrophobic heme precursor protoporphyrin in a griseofulvin-induced mouse model of erythropoietic protoporphyria

“…1 In erythropoietic protoporphyria (EPP), an inherited disease caused by a mutated ferrochelatase gene, ferrochelatase activity is markedly reduced, i.e., in severe cases to 4% to 20% of control values. 2 Impaired ferrochelatase activity leads to a reduced heme synthesis rate and, via induction of the preceding steps in the biosynthetic cascade, to accumulation of the highly hydrophobic heme precursor PP in erythrocytes and liver. 1 Common clinical signs of EPP are erythema and edema caused by PP phototoxicity in the skin.…”