Risheg Hiba, Chen Fu-Ping, Bloomer Joseph R
Department of Genetics, University of Alabama at Birmingham, Birmingham, AL, USA.
Mol Genet Metab. 2003 Sep-Oct;80(1-2):196-206. doi: 10.1016/j.ymgme.2003.07.001.
Erythropoietic protoporphyria (EPP) is characterized by excess accumulation of protoporphyrin, which is due to deficient activity of the enzyme ferrochelatase (FECH). This results in photosensitivity and in some patients liver disease which may necessitate liver transplantation. The aim of this study was to delineate the abnormalities in the FECH gene which cause phenotypic expression in EPP. We identified 43 individuals from 25 North American families with EPP who were heterozygous for various FECH mutations, but the mutations did not adequately explain the variable phenotype. We also examined the presence of an intron polymorphism (IVS3-48c) in the FECH gene which was shown to cause the formation of aberrantly spliced FECH mRNA. FECH DNA analysis demonstrated that 94% of 31 symptomatic individuals with FECH mutations were heterozygous for IVS3-48c, whereas 12 asymptomatic individuals with FECH mutations were homozygous for IVS3-48t. Haplotype analysis in four families showed that symptomatic members had the IVS3-48c polymorphism in the non-mutant FECH allele. Sequencing of the proximal FECH gene promoter showed no additional changes which might affect gene expression. The levels of normal FECH mRNA, measured by relative quantitative RT-PCR, and FECH enzyme activity were correspondingly lower in the cultured lymphoblasts of family members with the IVS3-48c polymorphism. These results indicate that symptomatic disease in most North American patients with EPP is explained by the inheritance of a mutation in one FECH allele which causes a structural alteration in the protein, together with a low expressing non-mutant FECH allele which is caused by the IVS3-48c polymorphism.
红细胞生成性原卟啉病（EPP）的特征是原卟啉过度蓄积，这是由于亚铁螯合酶（FECH）活性不足所致。这会导致光敏性，在一些患者中还会引发肝脏疾病，可能需要进行肝移植。本研究的目的是明确导致EPP表型表达的FECH基因异常。我们从25个北美EPP家庭中鉴定出43名个体，他们为各种FECH突变的杂合子，但这些突变并不能充分解释可变的表型。我们还检测了FECH基因中内含子多态性（IVS3 - 48c）的存在，该多态性已被证明会导致异常剪接的FECH mRNA形成。FECH DNA分析表明，31名有症状的FECH突变个体中有94%为IVS3 - 48c杂合子，而12名无症状的FECH突变个体为IVS3 - 48t纯合子。对四个家庭的单倍型分析表明，有症状的成员在非突变的FECH等位基因中具有IVS3 - 48c多态性。对FECH基因近端启动子的测序未发现可能影响基因表达的其他变化。通过相对定量RT - PCR测量，具有IVS3 - 48c多态性的家庭成员培养的淋巴母细胞中正常FECH mRNA水平和FECH酶活性相应较低。这些结果表明，大多数北美EPP患者的症状性疾病可解释为一个FECH等位基因突变导致蛋白质结构改变的遗传，以及由IVS3 - 48c多态性导致的低表达非突变FECH等位基因的遗传。
