Leigh syndrome is one of the most common neurological phenotypes observed in pediatric mitochondrial disease presentations. It is characterized by symmetrical lesions found on neuroimaging in the basal ganglia, thalamus, and brainstem and by a loss of motor skills and delayed developmental milestones. Genetic diagnosis of Leigh syndrome is complicated on account of the vast genetic heterogeneity with >75 candidate disease-associated genes having been reported to date. Candidate genes are still emerging, being identified when "omics" tools (genomics, proteomics, and transcriptomics) are applied to manipulated cell lines and cohorts of clinically characterized individuals who lack a genetic diagnosis. NDUFAF8 is one such protein; it has been found to interact with the well-characterized complex I (CI) assembly factor NDUFAF5 in a large-scale protein-protein interaction screen. Diagnostic next-generation sequencing has identified three unrelated pediatric subjects, each with a clinical diagnosis of Leigh syndrome, who harbor bi-allelic pathogenic variants in NDUFAF8. These variants include a recurrent splicing variant that was initially overlooked due to its deep-intronic location. Subject fibroblasts were found to express a complex I deficiency, and lentiviral transduction with wild-type NDUFAF8-cDNA ameliorated both the assembly defect and the biochemical deficiency. Complexome profiling of subject fibroblasts demonstrated a complex I assembly defect, and the stalled assembly intermediates corroborate the role of NDUFAF8 in early complex I assembly. This report serves to expand the genetic heterogeneity associated with Leigh syndrome and to validate the clinical utility of orphan protein characterization. We also highlight the importance of evaluating intronic sequence when a single, definitively pathogenic variant is identified during diagnostic testing.

中文翻译：

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NDUFAF8 中的致病性双等位基因突变导致 Leigh 综合征与孤立的复合物 I 缺乏。

Leigh 综合征是在儿科线粒体疾病表现中观察到的最常见的神经学表型之一。它的特征是在基底节、丘脑和脑干的神经影像学上发现对称性病变，以及运动技能丧失和发育里程碑延迟。由于巨大的遗传异质性，Leigh 综合征的基因诊断很复杂，迄今为止已报道了超过 75 个候选疾病相关基因。候选基因仍在不断涌现，当“组学”工具（基因组学、蛋白质组学和转录组学）应用于操纵的细胞系和缺乏基因诊断的临床特征个体群组时，候选基因就会被识别出来。NDUFAF8 就是这样一种蛋白质。在大规模蛋白质-蛋白质相互作用筛选中发现它与充分表征的复合物 I (CI) 组装因子 NDUFAF5 相互作用。诊断性下一代测序已经确定了三名不相关的儿科受试者，每名受试者都有 Leigh 综合征的临床诊断，他们在 NDUFAF8 中具有双等位基因致病变异。这些变体包括一个反复出现的剪接变体，由于其深层内含子位置而最初被忽视。发现对象成纤维细胞表达复合物 I 缺陷，用野生型 NDUFAF8-cDNA 进行慢病毒转导改善了组装缺陷和生化缺陷。受试成纤维细胞的复合体分析显示出复杂的 I 装配缺陷，而停滞的装配中间体证实了 NDUFAF8 在早期复合物 I 装配中的作用。本报告旨在扩大与 Leigh 综合征相关的遗传异质性，并验证孤儿蛋白表征的临床效用。我们还强调了在诊断测试期间鉴定出单个明确致病性变异时评估内含子序列的重要性。