Hippen Marius, Zsurka Gábor, Peeva Viktoriya, Machts Judith, Schwiecker Kati, Debska-Vielhaber Grazyna, Wiesner Rudolf J, Vielhaber Stefan, Kunz Wolfram S
Division of Neurochemistry (M.H., G.Z., V.P., W.S.K.), Institute of Experimental Epileptology and Cognition Research, University of Bonn; Department of Epileptology (G.Z., W.S.K.), University of Bonn; Center for Behavioral Brain Sciences (CBBS) (J.M.), Magdeburg; Department of Neurology (K.S., G.D.-V., S.V.), University of Magdeburg; and Institute of Vegetative Physiology (R.J.W.), University of Cologne, Germany.
Neurol Genet. 2021 Mar 3;8(2):e660. doi: 10.1212/NXG.0000000000000660. eCollection 2022 Apr.
We report the pathogenic sequence variant m.5789T>C in the anticodon stem of the mitochondrial tRNA for cysteine as a novel cause of neuropathy, ataxia, and retinitis pigmentosa (NARP), which is usually associated with pathogenic variants in the gene.
To address the correlation of oxidative phosphorylation deficiency with mutation loads, we performed genotyping on single laser-dissected skeletal muscle fibers. Stability of the mitochondrial tRNA was investigated by Northern blotting. Accompanying deletions of the mitochondrial genome were detected by long-range PCR and their breakpoints were determined by sequencing of single-molecule amplicons.
The sequence variant m.5789T>C, originating from the patient's mother, decreases the stability of the mitochondrial tRNA for cysteine by disrupting the anticodon stem, which subsequently leads to a combined oxidative phosphorylation deficiency. In parallel, we observed a prominent cluster of low-abundance somatic deletions with breakpoints in the immediate vicinity of the m.5789T>C variant. Strikingly, all deletion-carrying mitochondrial DNA (mtDNA) species, in which the corresponding nucleotide position was not removed, harbored the mutant allele, and none carried the wild-type allele.
In addition to providing evidence for the novel association of a tRNA sequence alteration with NARP syndrome, our observations support the hypothesis that single nucleotide changes can lead to increased occurrence of site-specific mtDNA deletions through the formation of an imperfect repeat. This finding might be relevant for understanding mechanisms of deletion generation in the human mitochondrial genome.
我们报告了线粒体半胱氨酸转运RNA反密码子茎中的致病序列变异m.5789T>C，它是神经病变、共济失调和色素性视网膜炎（NARP）的一种新病因，该病通常与该基因中的致病变异相关。
为了研究氧化磷酸化缺陷与突变负荷的相关性，我们对单根激光切割的骨骼肌纤维进行了基因分型。通过Northern印迹法研究线粒体转运RNA的稳定性。通过长程PCR检测线粒体基因组的伴随缺失，并通过单分子扩增子测序确定其断点。
源自患者母亲的序列变异m.5789T>C通过破坏反密码子茎降低了线粒体半胱氨酸转运RNA的稳定性，进而导致氧化磷酸化联合缺陷。同时，我们观察到在m.5789T>C变异紧邻区域有一个明显的低丰度体细胞缺失簇。引人注目的是，所有携带缺失的线粒体DNA（mtDNA）种类中，相应核苷酸位置未被去除的都含有突变等位基因，没有一个携带野生型等位基因。
除了为tRNA序列改变与NARP综合征的新关联提供证据外，我们的观察结果支持这样一种假说，即单核苷酸变化可通过形成不完全重复导致位点特异性mtDNA缺失发生率增加。这一发现可能与理解人类线粒体基因组中缺失产生的机制有关。
