Blasi Paola, Boyl Pietro Pilo, Ledda Mario, Novelletto Andrea, Gibson K Michael, Jakobs Cornelis, Hogema Boris, Akaboshi Shinjiro, Loreni Fabrizio, Malaspina Patrizia
Department of Biology, Tor Vergata University, Via della Ricerca Scientifica s.n.c., Rome 00133, Italy.
Mol Genet Metab. 2002 Aug;76(4):348-62. doi: 10.1016/s1096-7192(02)00105-1.
Mitochondrial NAD(+)-dependent succinic semialdehyde dehydrogenase (ALDH5A1, SSADH) represents the last enzyme in the GABA catabolism and irreversibly oxidizes SSA to succinate. In human, SSADH deficiency results in 4-hydroxybutyric aciduria, an autosomal recessive disorder due to an accumulation of GABA and 4-hydroxybutyric acid in the CNS. We already identified SSADH gene on human chromosome 6p22 and characterized the coding region. Furthermore, we described the first two mutations causing the disease. We report here the complete cDNA and genomic structure of the gene. A single transcription start site was identified by RNase protection 122 bp upstream of the ATG. EST database search and reporter gene constructs of the 3(') genomic region showed that the two major SSADH mRNA isoforms are due to alternative polyadenylation sites. The two mRNAs of 1827 and 5225 nt were analyzed for differential stability and translation efficiency. The analysis of mRNA turnover showed that both SSADH transcripts are equally stable. Similarly, a measurement of polysomal association capability of the two GFP-SSADH reporter mRNAs (containing the 3' UTR regions of the two SSADH mRNAs) did not reveal any difference. However, we cannot exclude the fact that differential properties could be restricted to particular physiological conditions and/or specific tissues. We have also identified an alternatively spliced small exon, which may lead to a novel isoform of the enzyme. Furthermore, we report here on naturally occurring missense variants, which may significantly contribute to inter-individual variation of SSADH activity, possibly influencing GABA and GHB endogenous levels.
线粒体NAD⁺依赖性琥珀酸半醛脱氢酶（ALDH5A1，SSADH）是GABA分解代谢的最后一种酶，可将琥珀酸半醛不可逆地氧化为琥珀酸。在人类中，SSADH缺乏会导致4-羟基丁酸尿症，这是一种常染色体隐性疾病，由于中枢神经系统中GABA和4-羟基丁酸的积累所致。我们已经在人类6号染色体p22上鉴定出SSADH基因并对其编码区进行了表征。此外，我们描述了导致该疾病的前两个突变。我们在此报告该基因的完整cDNA和基因组结构。通过RNase保护在ATG上游122 bp处鉴定出一个单一的转录起始位点。EST数据库搜索和3′基因组区域的报告基因构建体表明，两种主要的SSADH mRNA异构体是由于可变聚腺苷酸化位点所致。对1827和5225 nt的两种mRNA进行了差异稳定性和翻译效率分析。mRNA周转分析表明，两种SSADH转录本同样稳定。同样，对两种GFP-SSADH报告mRNA（包含两种SSADH mRNA的3′UTR区域）的多核糖体结合能力的测量未发现任何差异。然而，我们不能排除差异特性可能仅限于特定生理条件和/或特定组织的事实。我们还鉴定出一个可变剪接的小外显子，它可能导致该酶产生一种新的异构体。此外，我们在此报告自然发生的错义变体，它们可能对SSADH活性的个体间差异有显著贡献，可能影响GABA和GHB的内源性水平。
