Mason NG1, Khan M1, Whatley SD1, Badminton MN1, Dailey T2, Dailey H2, Elder GH1
1Department of Medical Biochemistry and Immunology, University Hospital of Wales and University of Wales College of Medicine, Cardiff, UK, 2Biomedical and Health Sciences Institute, University of Georgia, Athens, Georgia, USA
In most families, clinical expression of erythropoietic protoporphyria (EPP) appears to require inheritance of a low expression ferrochelatase (FECH) allele (IVS3-48C) trans to a severe FECH mutation [1]. Autosomal recessive (AR) inheritance has confirmed by molecular analysis in 2 families [2,3] but its prevalence remains uncertain. To determine the prevalence of these modes of inheritance in the United Kingdom, we investigated 111 consecutively referred, unrelated patients with clinically overt EPP. Patients and 100 control subjects were genotyped for the FECH IVS3-48C/T polymorphism [1]. The IVS3-48C allele was present in 108 (97%) of 111 patients compared with 13% of control subjects (chi2 = 97; p<0.001). The 3 patients without an IVS3-48C allele were investigated by mutational analysis. For mutation detection, all exons with 30-250bp of flanking sequences and 250bp of the promoter region of the FECH gene were PCR-amplified from genomic DNA and sequenced using an ABI Prism 3100 Sequence Analyzer. One patient was homozygous for a missense mutation (416A>T; Q139L). Another was a compound heterozygote for the missense mutations 707G>A (C236Y) and 1137G>C (K379N). Expression of the C236Y and K379N mutants in E. coli showed that they decreased FECH activity to 12% and 38% of wild-type activity, respectively. In an asymptomatic parent, the C236Y mutation was trans to an IVS3-48C allele. No FECH mutation was found in the third patient. To search for AR EPP among patients with an IVS3-48C allele, the FECH gene was sequenced in 14 randomly selected patients. Mutations were identified in 11 patients (79%). One patient was an apparent compound heterozygote for the previously described missense mutations P334L and G55C, the latter having been reported only in AR EPP [2]. Our findings confirm the association between the IVS3-48C allele and overt EPP, suggest a minimum prevalence of 3% for AR EPP and have implications for genetic counselling of families with this disease. (1) Gouya L et al. Nature Genet 2002;30:27, (2) Lamoril J et al. Biochim Biophys Acta 1991;181:594, (3) Sarkany R et al. Lancet 1994;343:1394.