Molecular Neurogenomics group, VIB Center for Molecular Neurology, VIB, Antwerp, Belgium; Molecular Neurogenomics group, Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium.
Neurogenetics Unit, 1st Department of Neurology, Eginitio Hospital, Medical School, National and Kapodistrian University of Athens, Athens, Greece.
Genet Med. 2024 Jun;26(6):101117. doi: 10.1016/j.gim.2024.101117. Epub 2024 Mar 6.
We describe 3 families with Charcot-Marie-Tooth neuropathy (CMT), harboring a homozygous NDUFS6 NM_004553.6:c.309+5G>A variant previously linked to fatal Leigh syndrome. We aimed to characterize clinically and molecularly the newly identified patients and understand the mechanism underlying their milder phenotype.
The patients underwent extensive clinical examinations. Exome sequencing was done in 4 affected individuals. The functional effect of the c.309+5G>A variant was investigated in patient-derived EBV-transformed lymphoblasts at the complementary DNA, protein, and mitochondrial level. Alternative splicing was evaluated using complementary DNA long-read sequencing.
All patients presented with early-onset, slowly progressive axonal CMT, and nystagmus; some exhibited additional central nervous system symptoms. The c.309+5G>A substitution caused the expression of aberrantly spliced transcripts and negligible levels of the canonical transcript. Immunoblotting showed reduced levels of mutant isoforms. No detectable defects in mitochondrial complex stability or bioenergetics were found.
We expand the clinical spectrum of NDUFS6-related mitochondrial disorders to include axonal CMT, emphasizing the clinical and pathophysiologic overlap between these 2 clinical entities. This work demonstrates the critical role that alternative splicing may play in modulating the severity of a genetic disorder, emphasizing the need for careful consideration when interpreting splice variants and their implications on disease prognosis.
我们描述了 3 个具有腓骨肌萎缩症（CMT）的家系，携带先前与致死性 Leigh 综合征相关的 NDUFS6 NM_004553.6:c.309+5G>A 纯合变异。我们旨在对新鉴定的患者进行临床和分子特征分析，并了解其较轻表型的潜在机制。
患者接受了广泛的临床检查。对 4 名受影响的个体进行了外显子组测序。在患者衍生的 EBV 转化的淋巴母细胞中，从 cDNA、蛋白质和线粒体水平研究了 c.309+5G>A 变异的功能效应。使用 cDNA 长读测序评估了选择性剪接。
所有患者均表现为早发性、进行性缓慢的轴索性 CMT 和眼球震颤，部分患者还存在其他中枢神经系统症状。c.309+5G>A 取代导致异常剪接转录本的表达和规范转录本的低水平。免疫印迹显示突变型同工型水平降低。未发现线粒体复合物稳定性或生物能量学的可检测缺陷。
我们将 NDUFS6 相关线粒体疾病的临床谱扩展到包括轴索性 CMT，强调了这两种临床实体之间的临床和病理生理重叠。这项工作表明，选择性剪接可能在调节遗传疾病的严重程度方面发挥关键作用，强调在解释剪接变体及其对疾病预后的影响时需要谨慎考虑。
