Abstract：
OBJECTIVE: Limb-girdle congenital myasthenic syndrome (LG-CMS) is a genetically heterogeneous disorder characterized by muscle weakness and fatigability. The LG-CMS gene DPAGT1 codes for an essential enzyme of the glycosylation pathway, a posttranslational modification mechanism shaping the structure and function of proteins. In DPAGT1-related LG-CMS, reduced glycosylation of the acetylcholine receptor (AChR) reduces its localization at the neuromuscular junction (NMJ), and results in diminished neuromuscular transmission. LG-CMS patients also show tubular aggregates on muscle biopsy, but the origin and potential contribution of the aggregates to disease development are not understood. Here, we describe two LG-CMS patients with the aim of providing a molecular diagnosis and to shed light on the pathways implicated in tubular aggregate formation.
METHODS: Following clinical examination of the patients, we performed next-generation sequencing (NGS) to identify the genetic causes, analysed the biopsies at the histological and ultrastructural levels, investigated the composition of the tubular aggregates, and performed experiments on protein glycosylation.
RESULTS: We identified novel pathogenic DPAGT1 variants in both patients, and pyridostigmine treatment quantitatively improved muscle force and function. The tubular aggregates contained proteins of the sarcoplasmic reticulum (SR) and structurally conformed to the aggregates observed in tubular aggregate myopathy (TAM). TAM arises from overactivation of the plasma membrane calcium channel ORAI1, and functional studies on muscle extracts from our LG-CMS patients evidenced abnormal ORAI1 glycosylation.
CONCLUSIONS: We expand the genetic variant spectrum of LG-CMS and provide a genotype/phenotype correlation for pathogenic DPAGT1 variants. The discovery of ORAI1 hypoglycosylation in our patients highlights a physiopathological link between LG-CMS and TAM.
METHODS: Following clinical examination of the patients, we performed next-generation sequencing (NGS) to identify the genetic causes, analysed the biopsies at the histological and ultrastructural levels, investigated the composition of the tubular aggregates, and performed experiments on protein glycosylation.
RESULTS: We identified novel pathogenic DPAGT1 variants in both patients, and pyridostigmine treatment quantitatively improved muscle force and function. The tubular aggregates contained proteins of the sarcoplasmic reticulum (SR) and structurally conformed to the aggregates observed in tubular aggregate myopathy (TAM). TAM arises from overactivation of the plasma membrane calcium channel ORAI1, and functional studies on muscle extracts from our LG-CMS patients evidenced abnormal ORAI1 glycosylation.
CONCLUSIONS: We expand the genetic variant spectrum of LG-CMS and provide a genotype/phenotype correlation for pathogenic DPAGT1 variants. The discovery of ORAI1 hypoglycosylation in our patients highlights a physiopathological link between LG-CMS and TAM.
摘要：
目的：四肢带先天性肌无力综合征（LG-CMS）是一种遗传异质性疾病，其特征是肌肉无力和易疲劳。LG-CMS基因DPAGT1编码糖基化途径的必需酶，形成蛋白质结构和功能的翻译后修饰机制。在DPAGT1相关的LG-CMS中，乙酰胆碱受体（AChR）的糖基化减少其在神经肌肉接头（NMJ）的定位，并导致神经肌肉传递减弱。LG-CMS患者在肌肉活检中也显示出管状聚集体，但是这些聚集体的起源和对疾病发展的潜在贡献尚不清楚。这里,我们描述了两名LG-CMS患者，目的是提供分子诊断，并阐明与肾小管聚集体形成有关的途径。
方法：在对患者进行临床检查后，我们进行了下一代测序（NGS）以确定遗传原因，分析了组织学和超微结构水平的活检，调查了管状骨料的组成，并进行了蛋白质糖基化实验。
结果：我们在两名患者中发现了新的致病性DPAGT1变异体，和吡啶斯的明治疗定量改善肌肉力量和功能。肾小管聚集体含有肌浆网（SR）的蛋白质，在结构上与肾小管聚集肌病（TAM）中观察到的聚集体相符。TAM起因于质膜钙通道ORAI1的过度激活，对LG-CMS患者肌肉提取物的功能研究证明ORAI1糖基化异常。
结论：我们扩展了LG-CMS的遗传变异谱，并为致病性DPAGT1变异提供了基因型/表型相关性。在我们的患者中发现ORAI1低糖基化突出了LG-CMS和TAM之间的病理生理联系。
方法：在对患者进行临床检查后，我们进行了下一代测序（NGS）以确定遗传原因，分析了组织学和超微结构水平的活检，调查了管状骨料的组成，并进行了蛋白质糖基化实验。
结果：我们在两名患者中发现了新的致病性DPAGT1变异体，和吡啶斯的明治疗定量改善肌肉力量和功能。肾小管聚集体含有肌浆网（SR）的蛋白质，在结构上与肾小管聚集肌病（TAM）中观察到的聚集体相符。TAM起因于质膜钙通道ORAI1的过度激活，对LG-CMS患者肌肉提取物的功能研究证明ORAI1糖基化异常。
结论：我们扩展了LG-CMS的遗传变异谱，并为致病性DPAGT1变异提供了基因型/表型相关性。在我们的患者中发现ORAI1低糖基化突出了LG-CMS和TAM之间的病理生理联系。
