[Inheritance in erythropoietic protoporphyria]. / La protoporphyrie érythropoïétique: une maladie, deux gènes et trois mécanismes moléculaires.

Erythropoietic protoporphyria (EPP) is an inherited disorder of heme biosynthesis that results from an accumulation of protoporphyrin IX in erythroid cells, plasma, skin and liver. EPP leads to acute photosensitivity and, in about 2% of patients, liver disease. EPP is a complex syndrome in which two genes are independently involved: FECH and ALAS2. More than 96% of unrelated EPP patients have ferrochelatase (FECH) deficiency (MIM 177000). Four percent of them present with autosomal recessive inheritance with two mutated FECH alleles. In dominant cases (95%) the inheritance of a common hypomorphic IVS3-48C FECH allele trans to a deleterious FECH mutation reduces FECH activity below a critical threshold. The frequency of the IVS3-48C allele differs widely from the Japanese (45%), to Black West Africans (<1%) populations. These differences in the frequency of this single common SNP account for the prevalence of overt EPP in different countries and for the absence of EPP in Black Africans. The phylogenic origin of the IVS3-48C haplotypes strongly suggests that the IVS3-48C allele arose from a single recent mutational event that occurred 60 Kyears ago. Acquired somatic mutation of FECH secondary to myeloid disease may also exceptionally cause EPP (<1%). Finally, about 4% of unrelated EPP patients have X-linked dominant protoporphyria (XLDPP) (MIM 300752) caused by gain-of-function mutations in the ALAS2 gene leading to an increased erythroid heme biosynthesis and subsequently an accumulation of protoporphyrin without any FECH deficiency.

A novel splicing mutation and haplotype analysis of the FECH gene in a Chinese family with erythropoietic protoporphyria.

BACKGROUND: Erythropoietic protoporphyria (EPP) is a rare autosomal dominant disorder of haeme biosynthesis resulting from a partial decrease in ferrochelatase (FECH) activity leading to excessive accumulation of protoporphyrin. Clinical manifestation normally requires coinheritance of a common hypomorphic FECH allele and a deleterious FECH mutation. OBJECTIVE: The aim of this study was to characterize the inheritance of a Chinese family with EPP at molecular level, by identification and analysis of FECH sequence variation, including the IVS3-48C polymorphisms. METHODS: Polymerase chain reaction amplification was employed to identify the FECH sequence variation, including the IVS3-48C polymorphism, in a Chinese EPP family and a matched control cohort. RESULTS: A splicing mutation in IVS3 + 1G-->A was identified in the proband as well as his symptomatic sister, cousin, his grandfather and his asymptomatic mother, but was absent in his father and grandmother. All the family members with overt photosensitivity carried the low-expressed allele IVS3-48C, which were absent in the asymptomatic EPP patients of this family. CONCLUSION: We described a novel splicing FECH mutation in a Chinese EPP family and analysed the hypomorphic IVS3-48C allele, which were believed to be responsible for generating the phenotypic symptoms in this family.