Schafer B L, Bishop R W, Kratunis V J, Kalinowski S S, Mosley S T, Gibson K M, Tanaka R D
Department of Metabolic Diseases, Bristol-Myers Squibb Pharmaceutical Research Institute, Princeton, New Jersey 08543-4000.
J Biol Chem. 1992 Jul 5;267(19):13229-38.
Mevalonic aciduria is the first proposed inherited disorder of the cholesterol/isoprene biosynthetic pathway in humans, and it is presumed to be caused by a mutation in the gene coding for mevalonate kinase. To elucidate the molecular basis of this inherited disorder, a 2.0-kilobase human mevalonate kinase cDNA clone was isolated and sequenced. The 1188-base pair open reading frame coded for a 396-amino acid polypeptide with a deduced M(r) of 42,450. The predicted protein sequence displayed similarity to those of galactokinase and the yeast RAR1 protein, indicating that they may belong to a common gene family. Southern hybridization studies demonstrated that the mevalonate kinase gene is located on human chromosome 12 and is a single copy gene. No major rearrangements were detected in the mevalonic aciduria subject. The relative size (2 kilobases) and amounts of human mevalonate kinase mRNA were not changed in mevalonic aciduria fibroblasts. Approximately half of the mevalonic aciduria cDNA clones encoding mevalonate kinase contained a single base substitution (A to C) in the coding region at nucleotide 902 that changed an asparagine residue to a threonine residue. The presence of this missense mutation was confirmed by polymerase chain reaction amplification and allele-specific hybridization of the genomic DNAs from the proband and the proband's father and brother. Similar analysis failed to detect this mutation in the proband's mother, seven normal subjects, or four additional mevalonic aciduria subjects, indicating that the mutation does not represent a common gene polymorphism. Functional analysis of the defect by transient expression confirmed that the mutation produced an enzyme with diminished activity. Our data suggest that the index case is a compound heterozygote for a mutation in the mevalonate kinase gene.
甲羟戊酸尿症是人类胆固醇/异戊二烯生物合成途径中首个被提出的遗传性疾病，据推测是由甲羟戊酸激酶编码基因的突变所致。为阐明这种遗传性疾病的分子基础，分离并测序了一个2.0千碱基的人甲羟戊酸激酶cDNA克隆。1188个碱基对的开放阅读框编码一个396个氨基酸的多肽，推导的分子量为42450。预测的蛋白质序列与半乳糖激酶和酵母RAR1蛋白的序列相似，表明它们可能属于一个共同的基因家族。Southern杂交研究表明，甲羟戊酸激酶基因位于人类12号染色体上，是一个单拷贝基因。在甲羟戊酸尿症患者中未检测到重大重排。甲羟戊酸尿症成纤维细胞中人类甲羟戊酸激酶mRNA的相对大小（2千碱基）和数量没有变化。大约一半编码甲羟戊酸激酶的甲羟戊酸尿症cDNA克隆在编码区第902位核苷酸处有一个单碱基替换（A到C），将一个天冬酰胺残基变为苏氨酸残基。通过聚合酶链反应扩增以及先证者及其父亲和兄弟的基因组DNA的等位基因特异性杂交，证实了这种错义突变的存在。类似分析在先证者的母亲、7名正常受试者或另外4名甲羟戊酸尿症患者中未检测到这种突变，表明该突变并非常见的基因多态性。通过瞬时表达对缺陷进行功能分析证实，该突变产生了一种活性降低的酶。我们的数据表明，该索引病例是甲羟戊酸激酶基因突变的复合杂合子。
