OBJECTIVE To investigate the molecular cause(s) underlying a severe form of infantile-onset parkinsonism and characterize functionally the identified variants. METHODS A trio-based whole exome sequencing (WES) approach was used to identify the candidate variants underlying the disorder. In silico modeling, and in vitro and in vivo studies were performed to explore the impact of these variants on protein function and relevant cellular processes. RESULTS WES analysis identified biallelic variants in WARS2, encoding the mitochondrial tryptophanyl tRNA synthetase (mtTrpRS), a gene whose mutations have recently been associated with multiple neurological phenotypes, including childhood-onset, levodopa-responsive or unresponsive parkinsonism in a few patients. A substantial reduction of mtTrpRS levels in mitochondria and reduced OXPHOS function was demonstrated, supporting their pathogenicity. Based on the infantile-onset and severity of the phenotype, additional variants were considered as possible genetic modifiers. Functional assessment of a selected panel of candidates pointed to a de novo missense mutation in CHRNA6, encoding the α6 subunit of neuronal nicotinic receptors, which are involved in the cholinergic modulation of dopamine release in the striatum, as a second event likely contributing to the phenotype. In silico, in vitro (Xenopus oocytes and GH4C1 cells) and in vivo (C. elegans) analyses demonstrated the disruptive effects of the mutation on acetylcholine receptor structure and function. CONCLUSION Our findings consolidate the association between biallelic WARS2 mutations and movement disorders, and suggest CHRNA6 as a genetic modifier of the phenotype.

中文翻译：

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患有严重形式的婴儿帕金森病的儿童中同时发生的WARS2和CHRNA6突变。

目的研究导致严重形式的婴儿发作性帕金森病的分子原因，并从功能上鉴定已鉴定的变异体。方法采用基于三重基因的全外显子组测序（WES）方法来鉴定该疾病的潜在候选变体。在计算机模拟中，进行了体外和体内研究，以探索这些变异对蛋白质功能和相关细胞过程的影响。结果WES分析确定了WARS2中的双等位基因变异体，该变异体编码线粒体色氨酸tRNA合成酶（mtTrpRS），该基因的突变最近与多种神经系统表型相关，包括一些患者的儿童期发病，左旋多巴反应性或无反应性帕金森氏病。线粒体中的mtTrpRS水平显着降低，OXPHOS功能降低，证明了其致病性。根据表型的婴儿发作和严重程度，其他变异被认为是可能的遗传修饰因子。对选定候选人小组的功能评估指出，CHRNA6中发生了从头错义突变，该突变编码神经元烟碱样受体的α6亚基，参与了纹状体中多巴胺释放的胆碱能调节，这是第二种可能有助于表型的事件。在计算机上，体外（非洲爪蟾卵母细胞和GH4C1细胞）和体内（秀丽隐杆线虫）分析显示该突变对乙酰胆碱受体结构和功能的破坏作用。