SYSTEMATIC ANALYSIS OF MOLECULAR DEFECTS IN THE FERROCHELATASE GENE FROM PATIENTS WITH ERYTHROPOIETIC PROTOPORPHYRIA

Erythropoietic protoporphyria (EPP; MIM 177000) is an inherited disord er caused by partial deficiency of ferrochelatase (FECH), the last enz yme in the heme biosynthetic pathway. In EPP patients, the FECH defici ency causes accumulation of free protoporphyrin in the erythron, assoc iated with a painful skin photosensitivity. In rare cases, the massive accumulation of protoporphyrin in hepatocytes may lead to a rapidly p rogressive liver failure. The mode of inheritance in EPP is complex an d can be either autosomal dominant with low clinical penetrance, as it is in most cases, or autosomal recessive. To acquire an in-depth know ledge of the genetic basis of EPP, we conducted a systematic mutation analysis of the FECH gene, following a procedure that combines the exo n-by-exon denaturing-gradient-gel-electrophoresis screening of the FEC H genomic DNA and direct sequencing. Twenty different mutations, 15 of which are newly described here, have been characterized in 26 of 29 E PP patients of Swiss and French origin. All the EPP patients, includin g those with liver complications, were heterozygous for the mutations identified in the FECH gene. The deleterious effect of all missense mu tations has been assessed by bacterial expression of the respective FE CH cDNAs generated by site-directed mutagenesis. Mutations leading to a null allele were a common feature among three EPP pedigrees with liv er complications. Our systematic molecular study has resulted in a sig nificant enlargement of the mutation repertoire in the FECH gene and h as shed new light on the hereditary behavior of EPP.