Introduction Mitochondrial diseases exhibit wide phenotypic heterogeneity, and can present as progressive myoclonic epilepsy. Summary We report a case of adult-onset drug-resistant epilepsy, cortical myoclonus and bilateral optic neuropathies due to m.14487T>C, a rare mitochondrial gene mutation identified on whole-genome sequencing. This mutation, which affects the NADH dehydrogenase 6 (ND6) subunit of the mitochondrial respiratory chain, is most commonly implicated in cases of infantile-onset Leigh syndrome, although a broader phenotypic spectrum including migraine with aura and progressive myoclonic epilepsy have been described. Serial MRI scans over a 2-year period demonstrated the interval development of bihemispheric stroke-like lesions. Giant somatosensory evoked potentials and short-duration myoclonic jerks with craniocaudal spread on surface electromyography were consistent with cortical myoclonus. Optical coherence tomography showed bilateral symmetric thinning of the nerve fibre layer in the papillomacular bundles. Conclusion Whole-genome sequencing can help to provide a definitive diagnosis for mitochondrial disease and should be considered in situations where clinical suspicion remains high despite normal genetic panels or muscle histopathology. Mitochondrial disease can present as adult-onset progressive myoclonic epilepsy, and bilateral optic neuropathies can be a striking feature of ND6 mitochondrial gene mutations. In our case, severe cortical myoclonus affecting speech and swallowing remained highly drug-resistant, however, symptomatic benefit was derived from targeted onabotulinum toxin A injections. All relevant data are included in the article.

中文翻译：

---

罕见的线粒体 ND6 突变导致进行性肌阵挛性癫痫，m.14487T>C

简介 线粒体疾病表现出广泛的表型异质性，可表现为进行性肌阵挛性癫痫。总结 我们报告了一例成人起病的耐药性癫痫、皮质肌阵挛和双侧视神经病变，原因是 m.14487T>C，这是一种在全基因组测序中发现的罕见线粒体基因突变。这种影响线粒体呼吸链的 NADH 脱氢酶 6 (ND6) 亚基的突变最常见于婴儿期 Leigh 综合征的病例，尽管已经描述了更广泛的表型谱，包括先兆偏头痛和进行性肌阵挛性癫痫。为期 2 年的系列 MRI 扫描显示了双半球中风样病变的间隔发展。巨大的体感诱发电位和表面肌电图上伴有颅尾扩散的短期肌阵挛抽动与皮质肌阵挛一致。光学相干断层扫描显示乳头状黄斑束中神经纤维层的双侧对称变薄。结论全基因组测序有助于为线粒体疾病提供明确的诊断，并且应在尽管基因组或肌肉组织病理学正常但临床怀疑仍然很高的情况下考虑。线粒体疾病可表现为成人发病的进行性肌阵挛性癫痫，双侧视神经病变可能是 ND6 线粒体基因突变的显着特征。在我们的案例中，影响言语和吞咽的严重皮质肌阵挛仍然具有高度耐药性，然而，对症的益处来自于靶向肉毒杆菌毒素 A 注射。所有相关数据都包含在文章中。