Wellcome Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, UK.
State Key Laboratory of Molecular Biology, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences, University of Chinese Academy of Sciences, Shanghai, China.
Hum Mol Genet. 2019 Jan 15;28(2):258-268. doi: 10.1093/hmg/ddy294.
Recessively inherited variants in AARS2 (NM_020745.2) encoding mitochondrial alanyl-tRNA synthetase (mt-AlaRS) were first described in patients presenting with fatal infantile cardiomyopathy and multiple oxidative phosphorylation defects. To date, all described patients with AARS2-related fatal infantile cardiomyopathy are united by either a homozygous or compound heterozygous c.1774C>T (p.Arg592Trp) missense founder mutation that is absent in patients with other AARS2-related phenotypes. We describe the clinical, biochemical and molecular investigations of two unrelated boys presenting with fatal infantile cardiomyopathy, lactic acidosis and respiratory failure. Oxidative histochemistry showed cytochrome c oxidase-deficient fibres in skeletal and cardiac muscle. Biochemical studies showed markedly decreased activities of mitochondrial respiratory chain complexes I and IV with a mild decrease of complex III activity in skeletal and cardiac muscle. Using next-generation sequencing, we identified a c.1738C>T (p.Arg580Trp) AARS2 variant shared by both patients that was in trans with a loss-of-function heterozygous AARS2 variant; a c.1008dupT (p.Asp337*) nonsense variant or an intragenic deletion encompassing AARS2 exons 5-7. Interestingly, our patients did not harbour the p.Arg592Trp AARS2 founder mutation. In silico modelling of the p.Arg580Trp substitution suggested a deleterious impact on protein stability and folding. We confirmed markedly decreased mt-AlaRS protein levels in patient fibroblasts, skeletal and cardiac muscle, although mitochondrial protein synthesis defects were confined to skeletal and cardiac muscle. In vitro data showed that the p.Arg580Trp variant had a minimal effect on activation, aminoacylation or misaminoacylation activities relative to wild-type mt-AlaRS, demonstrating that instability of mt-AlaRS is the biological mechanism underlying the fatal cardiomyopathy phenotype in our patients.
AARS2（NM_020745.2）编码线粒体丙氨酰-tRNA 合成酶（mt-AlaRS）的隐性遗传变异首先在表现为致命婴儿期心肌病和多种氧化磷酸化缺陷的患者中被描述。迄今为止，所有描述的 AARS2 相关致命婴儿期心肌病患者均由纯合或复合杂合的 c.1774C>T（p.Arg592Trp）错义起始突变引起，该突变在具有其他 AARS2 相关表型的患者中不存在。我们描述了两个无关男孩的临床、生化和分子研究，他们均患有致命婴儿期心肌病、乳酸酸中毒和呼吸衰竭。氧化组织化学显示骨骼肌和心肌中细胞色素 c 氧化酶缺陷纤维。生化研究显示，骨骼肌和心肌中 mt 呼吸链复合物 I 和 IV 的活性显著降低，复合物 III 的活性轻度降低。使用下一代测序，我们在两个患者中共鉴定出一个 c.1738C>T（p.Arg580Trp）AARS2 变异，该变异与功能丧失的杂合 AARS2 变异在 trans 位置；c.1008dupT（p.Asp337*）无义变异或包含 AARS2 外显子 5-7 的内含子缺失。有趣的是，我们的患者不携带 p.Arg592Trp AARS2 起始突变。p.Arg580Trp 取代的计算机建模表明对蛋白质稳定性和折叠有有害影响。我们在患者成纤维细胞、骨骼肌和心肌中证实了 mt-AlaRS 蛋白水平明显降低，尽管线粒体蛋白合成缺陷仅限于骨骼肌和心肌。体外数据显示，与野生型 mt-AlaRS 相比，p.Arg580Trp 变体对激活、氨酰化或错误氨酰化活性的影响最小，表明 mt-AlaRS 的不稳定性是导致我们患者致命心肌病表型的生物学机制。
