MUTATIONS IN THE FERROCHELATASE GENE OF 4 SPANISH PATIENTS WITH ERYTHROPOIETIC PROTOPORPHYRIA

Erythropoietic protoporphyria is a hereditary disorder of porphyrin me tabolism caused by mutations in the ferrochelatase gene, Ferrochelatas e catalyzes the chelation of ferrous iron into protoporphyrin IX to fo rm heme. Mutation analysis was performed in four Spanish erythropoieti c protoporphyria families resulting in the identification of four diff erent mutations in the ferrochelatase gene. Two of them were novel mut ations, a missense mutation (1157 A-->C, H386P) and a frameshift mutat ion (843delC) found in two Spanish families, respectively. The third a nd the forth Spanish patients carried already published ferrochelatase gene mutations, a nonsense mutation (343 C-->T, R115X) and a missense mutation (557T-->C, I186T), respectively. The newly described framesh ift mutation (843delC) predicted formation of an abrupt mRNA. The dele terious effect of His386 to Pro substitution as a result of mutation 1 157 AC on the ferrochelatase activity was investigated by expressing t he mutant ferrochelatase in Escherichia coli. The mutant ferrochelatas e exhibited only 0.8% of the wild-type ferrochelatase activity. Predic tion of the secondary structure of ferrochelatase suggested that the H 386P mutation disrupted the original a-helical structure by way of int roducing a turn, a rather drastic structural change of the enzyme suff icient to cause activity loss.