Zhang Lu, Duan Yiran, Ma Rui, Han Jiaqi, Pan Na, Gao Lehong, Wang Yuping
Department of Neurology, Xuanwu Hospital, Capital Medical University, Beijing, China.
Center of Epilepsy, Beijing Institute for Brain Disorders, Capital Medical University, Ministry of Science and Technology, Beijing, China.
Epilepsia Open. 2024 Dec;9(6):2306-2318. doi: 10.1002/epi4.13057. Epub 2024 Oct 30.
N-methyl-D-aspartate receptors are glutamate-gated ion channels that play a crucial role in brain function. Numerous inherited or de novo variants in the GRIN2A gene, encoding the GluN2A subunit of the receptor, have been identified in patients with epilepsy. In addition, it is worth noting that GRIN2A variants exhibit a strong correlation with epilepsy-aphasia syndromes, a group of age-dependent epileptic, cognitive, and language disorders with a characteristic electroencephalographic pattern.
Whole exome sequencing was conducted in enrolled patients with epilepsy-aphasia syndromes, and GRIN2A variants were screened. The conservation of substituted residues, conformational changes of mutant subunits, and in silico predictions of pathogenicity were thoroughly assessed in our study. Functional alterations of the variants were examined using whole-cell voltage-clamp current recordings while the relative surface expression levels of subunit proteins were assessed via immunofluorescence assays. A summary of previously published GRIN2A missense variants was conducted to investigate the genotypic-phenotypic-functional correlations.
Two missense GRIN2A variants (c. 2482A >G/p. M828V, c. 2627 T >C/p. I876T) were identified, which are located in the transmembrane helix M4 and C-terminus domain of the GluN2A subunit, respectively. Both variants exhibited reduced current density of NMDARs and surface/total expression levels of GluN2A subunits, while M828V showed a decreased extent of desensitization as well. A further summary of the previously reported GRIN2A variants demonstrated that more variable phenotypes were observed for variants situated in the C-terminus domain or those with loss-of-function effects.
Our study expands the phenotypic and functional range of GRIN2A-related disorders. In order to optimally establish the domain-function-phenotype correlations in GRIN2A variants, it is imperative to gather a more extensive set of clinical and functional data.
This study has identified two genetic variants of the GRIN2A gene in patients with epilepsy-aphasia syndrome. We assess the variants' harmfulness through a variety of functional experiments, including evaluating the expression level of the mutated protein and the resulting changes in electrophysiological activities. Also, we reviewed previously published papers about GRIN2A variants in epilepsy to learn more about the correlations between their locations, functional changes, and clinical manifestations.
N-甲基-D-天冬氨酸受体是谷氨酸门控离子通道，在脑功能中起关键作用。在癫痫患者中已鉴定出编码该受体GluN2A亚基的GRIN2A基因的众多遗传或新生变异。此外，值得注意的是，GRIN2A变异与癫痫性失语综合征密切相关，癫痫性失语综合征是一组与年龄相关的癫痫、认知和语言障碍，具有特征性脑电图模式。
对纳入的癫痫性失语综合征患者进行全外显子组测序，并筛选GRIN2A变异。在我们的研究中，对取代残基的保守性、突变亚基的构象变化以及致病性的计算机预测进行了全面评估。使用全细胞电压钳电流记录检查变异的功能改变，同时通过免疫荧光测定评估亚基蛋白的相对表面表达水平。对先前发表的GRIN2A错义变异进行总结，以研究基因型-表型-功能相关性。
鉴定出两个GRIN2A错义变异（c.2482A＞G/p.M828V，c.2627T＞C/p.I876T），分别位于GluN2A亚基的跨膜螺旋M4和C末端结构域。两个变异均表现出NMDAR电流密度降低以及GluN2A亚基的表面/总表达水平降低，而M828V的脱敏程度也降低。对先前报道的GRIN2A变异的进一步总结表明，位于C末端结构域的变异或具有功能丧失效应的变异观察到更多可变表型。
我们的研究扩展了GRIN2A相关疾病的表型和功能范围。为了最佳地建立GRIN2A变异中的结构域-功能-表型相关性，必须收集更广泛的临床和功能数据。
本研究在癫痫性失语综合征患者中鉴定出GRIN2A基因的两个遗传变异。我们通过各种功能实验评估变异体的有害性，包括评估突变蛋白的表达水平以及由此产生的电生理活动变化。此外，我们回顾了先前发表的关于癫痫中GRIN2A变异的论文，以更多地了解它们的位置、功能变化和临床表现之间的相关性。
