MOLECULAR DEFECTS IN FERROCHELATASE IN PATIENTS WITH PROTOPORPHYRIA REQUIRING LIVER-TRANSPLANTATION

Protoporphyria is a genetic disorder in which a deficiency of mitochon drial ferrochelatase activity causes accumulation of protoporphyrin th at produces severe liver damage in some patients. In this study, mutat ions of the ferrochelatase gene were examined in eight unrelated patie nts who had liver transplantation. RNA was prepared from liver and/or lymphoblasts, and specific reverse transcriptase-nested polymerase cha in reactions amplified and sequenced ferrochelatase cDNAs. Products sh orter 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 reveale d no other mutations. Western blot showed a reduced quantity of normal -size ferrochelatase protein in protoporphyria liver compared with nor mal liver (19-51%, mean 32% of normal). Levels of the mitochondrial pr otein F-1-ATPase P-subunit were not decreased to a similar degree. Liv er ferrochelatase activity was reduced more than could be explained by the decrease in ferrochelatase protein (4-20%, mean 9% of normal). Th ese results establish genetic heterogeneity in the most severe phenoty pe of protoporphyria. However, the gene mutations found share the prop erty of causing a major structural alteration in the ferrochelatase pr otein.