Haplotype analysis of families with erythropoietic protoporphyria and novel mutations of the ferrochelatase gene

Ferrochelatase, the enzyme that catalyzes the terminal step in the heme bio synthetic pathway, is the site of the defect in the human inherited disease erythropoietic protoporphyria. Molecular genetic studies have shown that t he majority of erythropoietic protoporphyria cases are transmitted in domin ant fashion and that mutations underlying erythropoietic protoporphyria are heterogeneous. We performed haplotype analysis of American families that s hared recurrent ferrochelatase gene mutations yet had forebears from severa l European countries, This was to gain insight into whether these mutations represent mutational hotspots at the ferrochelatase gene, or propagation o f ancestral alleles bearing the mutations. Two recurrent mutations were fou nd to occur on distinctive chromosome 18 haplotypes, consistent with being hotspot mutations. On the other hand, we found three sets of two unrelated families that shared the same haplotypes bearing these mutations, which cou ld reflect geographic dispersion of ancestral mutant alleles, In addition, we report novel mutations associated with erythropoietic protoporphyria: g( + 1)-->t transversion of the exon 4 donor site, g(+ 1)-->a transition of th e exon 6 donor site, and t(+ 2)-->a substitution at the exon 9 donor site; these mutations are predicted to cause splicing defects of the associated e xons, We also identified a g(+ 5)-->a transition of the exon 1 donor site i n four unrelated families with erythropoietic protoporphyria, and a G(- 1)- ->A substitution at the exon 9 donor site in an additional family, The prob ability that these sequence changes are normal polymorphisms was virtually excluded (p < 0.0001) by their absence in 120 ferrochelatase alleles from 3 0 normal subjects and 30 individuals with manifested erythropoietic protopo rphyria with or without a known mutation.