Rootwelt H, Brodtkorb E, Kvittingen E A
Institute of Clinical Biochemistry, University of Oslo, Rikshospitalet, Norway.
Am J Hum Genet. 1994 Dec;55(6):1122-7.
In healthy individuals, fumarylacetoacetase (FAH) activities close to the range found in hereditary tyrosinemia type 1 (HT1) patients indicated the existence of a "pseudodeficiency" allele. In an individual homozygous for pseudodeficiency of FAH and in three HT1 families also carrying the pseudodeficiency allele, western blotting of fibroblast extracts showed that the pseudodeficiency allele gave very little immunoreactive FAH protein, whereas northern analysis revealed a normal amount of FAH mRNA. Sequencing revealed an identical mutation, C1021-->T (Arg341Trp), in all the pseudodeficiency alleles. Site-directed mutagenesis and expression in a rabbit reticulocyte lysate system demonstrated that the C1021-->T mutation gave reduced FAH activity and reduced amounts of the full-length protein. Bs1EI restriction digestion of PCR products distinguished between the normal and the mutated sequences. Among 516 healthy volunteers of Norwegian origin, the C1021-->T mutation was found in 2.2% of the alleles. Testing for the C1021-->T mutation may solve the problem of prenatal diagnosis and carrier detection in families with compound heterozygote genotypes for HT1 and pseudodeficiency.
在健康个体中，延胡索酰乙酰乙酸酶（FAH）的活性接近遗传性酪氨酸血症1型（HT1）患者的水平，这表明存在“假缺陷”等位基因。在一名FAH假缺陷纯合个体以及三个同样携带假缺陷等位基因的HT1家族中，对成纤维细胞提取物进行的蛋白质免疫印迹分析显示，该假缺陷等位基因产生的免疫反应性FAH蛋白极少，而Northern印迹分析显示FAH mRNA的量正常。测序结果表明，所有假缺陷等位基因中均存在相同的突变，即C1021→T（Arg341Trp）。定点诱变以及在兔网织红细胞裂解物系统中的表达证明，C1021→T突变导致FAH活性降低，全长蛋白量减少。对PCR产物进行Bs1EI限制性酶切可区分正常序列和突变序列。在516名挪威血统的健康志愿者中，2.2%的等位基因存在C1021→T突变。对C1021→T突变进行检测可能会解决HT1和假缺陷复合杂合子基因型家庭中的产前诊断和携带者检测问题。
