The diagnosis of mitochondrial disorders remains a challenging and often unmet need. We sought to investigate a sibling pair with suspected mitochondrial disease and a clinical presentation notable for global developmental delay, poor growth, sensorineural hearing loss, and brain MRI abnormalities, both with early death. Following uninformative exome and genome sequencing of the family quartet, RNA sequencing was pursued as an orthogonal testing strategy. RNA sequencing of fibroblasts from the older sibling identified the presence of a cryptic exon in intron 1 of NDUFB10, that included an in-frame stop codon. NDUFB10 encodes a subunit of mitochondrial OXPHOS complex I. Differential expression analysis relative to control samples suggested significantly decreased expression. The cryptic exon was found to contain a rare intronic variant, NM_004548.3:c.131-442G>C, that was homozygous in both affected siblings and absent from population allele frequency databases. Immunoblot and quantitative proteomic analysis of fibroblasts from the older sibling revealed decreased abundance of complex I subunits associated with NDUFB10, providing evidence of isolated complex I deficiency. Biallelic variants in NDUFB10 have previously been reported in a single individual with infantile-onset mitochondrial disease. We present data implicating a deep intronic variant in NDUFB10 as the cause of mitochondrial disease in two further individuals. This variant results in loss of expression and overall destabilization of mitochondrial OXPHOS complex I and highlights the importance of RNA sequencing as a complementary diagnostic tool in patients undergoing genome-wide diagnostic evaluation.

中文翻译：

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RNA测序鉴定出由NDUFB10中的深内含子变异体引起的隐秘外显子，导致分离出的Complex I缺陷。

线粒体疾病的诊断仍然是具有挑战性的，并且常常是未满足的需求。我们试图研究一对疑似线粒体疾病的兄弟姐妹，以及临床表现显着的整体发育迟缓，生长不良，感觉神经性听力损失和脑部MRI异常，均与早期死亡有关。继无性的外显子组和四重奏的基因组测序之后，RNA测序被作为一种正交测试策略。来自较老同胞的成纤维细胞的RNA测序鉴定出NDUFB10内含子1中存在一个隐性外显子，其中包括一个读码框终止密码子。NDUFB10编码线粒体OXPHOS复合体I的一个亚基。相对于对照样品的差异表达分析表明表达明显降低。发现神秘的外显子包含罕见的内含子变体NM_004548.3：c.131-442G> C，在受影响的同胞中都是纯合子，而在群体等位基因频率数据库中却没有。对来自较老同胞的成纤维细胞的免疫印迹和定量蛋白质组学分析显示，与NDUFB10相关的复杂I亚基的丰度降低，提供了孤立的复杂I缺乏的证据。NDUFB10中的双等位基因变体先前已在患有婴儿发作的线粒体疾病的单个个体中报道。我们目前的数据牵涉到NDUFB10中的一个深度内含子变异体，作为另外两个人中线粒体疾病的原因。这种变异导致线粒体OXPHOS复合体I的表达丧失和整体不稳定，并突出显示了RNA测序作为进行全基因组诊断评估的患者的补充诊断工具的重要性。在受影响的同胞中都是纯合子，而在群体等位基因频率数据库中则没有。对来自较老同胞的成纤维细胞的免疫印迹和定量蛋白质组学分析显示，与NDUFB10相关的复杂I亚基的丰度降低，提供了孤立的复杂I缺乏的证据。NDUFB10中的双等位基因变体先前已在患有婴儿发作的线粒体疾病的单个个体中报道。我们目前的数据牵涉到NDUFB10中的一个深度内含子变异体，作为另外两个人中线粒体疾病的原因。这种变异导致线粒体OXPHOS复合体I的表达丧失和整体不稳定，并突出显示了RNA测序作为进行全基因组诊断评估的患者的补充诊断工具的重要性。在受影响的同胞中都是纯合子，而在群体等位基因频率数据库中则没有。对来自较老同胞的成纤维细胞的免疫印迹和定量蛋白质组学分析显示，与NDUFB10相关的复杂I亚基的丰度降低，提供了孤立的复杂I缺乏的证据。NDUFB10中的双等位基因变体先前已在患有婴儿发作的线粒体疾病的单个个体中报道。我们目前的数据牵涉到NDUFB10中的一个深度内含子变异体，作为另外两个人中线粒体疾病的原因。这种变异导致线粒体OXPHOS复合体I的表达丧失和整体不稳定，并突出显示了RNA测序作为进行全基因组诊断评估的患者的补充诊断工具的重要性。