Erythropoietic protoporphyria (EPP) is an autosomal dominant disease with incomplete penetrance due to reduced activity of ferrochelatase (FECH), a mitochondrial enzyme that catalyzes the final step of the heme biosynthetic pathway. The clinical phenotype of EPP results from co-inheritance of a mutated allele and a wild-type low-expressed allele of the FECH gene. To date, more than 88 different mutations have been identified in the FECH gene of patients with EPP. There are evidences suggesting that an entire haplotype (-251G, IVS1-23T and IVS3-48C) reduces allele expression. In this study, we searched for the -251A/G, IVS1-23C/T and IVS3-48T/C polymorphisms in two unrelated Italian families with EPP. In all the patients, carrying the -250G>C mutation in the promoter region, the IVS3-48C on the other allele showed apparent homozygosity and absence of Mendelian segregation. By RNA and long polymerase chain reaction analysis, we identified a deletion of 5576 bp (g12490_18067), including exons 3 and 4, in cis with the -250G>C mutation in the promoter.

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Porphyrias are disorders caused by the genetic defects of enzymes of the heme pathway and are characterized by such a wide genetic heterogeneity that even the molecular analysis is not always decisive for a correct diagnosis. In the past few years, deletion with a size range of few kilobase pairs have been reported. These peculiar mutations, missed by both sequencing and cytogenetic techniques, have been identified by time consuming and technically demanding methods. To provide a rapid and sensitive method for the detection of deletions responsible for porphyria, we successfully designed and tested seven chemically synthesized probe sets specific for each heme gene and their flanking regions, to be used in multiplex ligation-dependent probe amplification technique.