Table_1_Identification of a Novel Variant in MT-CO3 Causing MELAS.DOCX

Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) is a maternally inherited mitochondrial disease. Most cases of MELAS are caused by the m.3243A > G variant in the MT-TL1 gene encoding tRNALeu(UUR). However, the genetic cause in 10% of patients with MELAS is unknown. We investigated the pathogenicity of the novel mtDNA variant m.9396G > A/MT-CO3 (p.E64K), which affects an extremely conserved amino acid in the CO3 subunit of mitochondrial respiratory chain (MRC) complex IV (CIV) in a patient with MELAS. Biochemical assays of a muscle biopsy confirmed remarkable CIV deficiency, and pathological examination showed ragged red fibers and generalized COX non-reactive muscle fibers. Transfer of the mutant mtDNA into cybrids impaired CIV assembly, followed by remarkable mitochondrial dysfunction and ROS production. Our findings highlight the pathogenicity of a novel m.9396G > A variant and extend the spectrum of pathogenic mtDNA variants.

线粒体脑肌病伴高乳酸血症和卒中样发作（MELAS）是一类母系遗传性线粒体疾病。绝大多数MELAS病例由编码tRNA亮氨酸(UUR)的MT-TL1基因上的m.3243A>G变异所致，但仍有10%的MELAS患者的遗传病因尚未明确。本研究针对一例MELAS患者体内的新型线粒体DNA（mtDNA）变异m.9396G>A/MT-CO3（p.E64K）的致病性展开分析，该变异会影响线粒体呼吸链（MRC）复合物IV（CIV）CO3亚基中一个高度保守的氨基酸残基。肌肉活检的生化检测证实存在显著的复合物IV缺陷，病理检查可见破碎红纤维与广泛分布的细胞色素氧化酶（COX）阴性肌纤维。将突变型线粒体DNA转入胞质杂种细胞后，复合物IV的组装受到损伤，继而引发显著的线粒体功能障碍与活性氧（ROS）产生。本研究结果证实了新型m.9396G>A变异的致病性，并拓宽了致病性线粒体DNA变异的谱系。