Plumereau Quentin, Lile Spencer, Johnson Christopher N, Chahine Mohamed
CERVO Brain Research Centre, 2601, chemin de la Canardière, Quebec City, QC, G1J 2G3, Canada.
Department of Chemistry, Mississippi State University, Starkville, MS, USA.
Sci Rep. 2025 Sep 26;15(1):33101. doi: 10.1038/s41598-025-17816-2.
Myotonia and paramyotonia congenita (PC) are rare neuromuscular disorders characterized by muscle stiffness that intensifies in cold environments. These disorders are associated with variants in the SCN4A gene, that encodes the alpha subunit of the voltage-gated sodium channel Nav1.4. We report here the case of a 36-year-old female who experiences diverse neurological symptoms, including myotonia, cold induced myotonia, resulting in muscle stiffness, and tightness. A whole exome sequencing revealed a missense variant in the SCN4A gene at position c.1354G > A, named p.E452K. We characterized the biophysical properties of this SCN4A variant by overexpressing the wild-type (WT) and mutant channels with the β1 regulatory subunit in HEK293 cells by transfection. Sodium currents were recorded at different temperatures and different extracellular potassium concentrations using the patch-clamp technique. Functional studies of the E452K variant revealed both loss and gain of function phenotypes at different temperatures, which were characterized by a decrease in current density and an increase in the window current. This was related to the shift of inactivation toward more depolarized voltages at both 22 °C and 10 °C and a slower slope factor of activation at 22 °C. A further gain-of-function effect was also observed, which was characterized by a faster onset and recovery from slow inactivation. MD simulation of the alpha subunit in a lipid bilayer suggested that the charge reversal destabilized a native salt bridge (E452-K249). We concluded that the observed enhanced functionality facilitates the activation process, leading to enhanced muscle excitability.
强直性肌营养不良症和先天性副肌强直症（PC）是罕见的神经肌肉疾病，其特征是在寒冷环境中肌肉僵硬会加剧。这些疾病与SCN4A基因的变异有关，该基因编码电压门控钠通道Nav1.4的α亚基。我们在此报告一例36岁女性病例，该患者出现多种神经症状，包括强直性肌营养不良症、寒冷诱发的肌强直，导致肌肉僵硬和紧绷。全外显子组测序显示SCN4A基因第c.1354G＞A位置存在一个错义变异，命名为p.E452K。我们通过转染在HEK293细胞中过表达野生型（WT）和带有β1调节亚基的突变通道，来表征该SCN4A变异体的生物物理特性。使用膜片钳技术在不同温度和不同细胞外钾浓度下记录钠电流。E452K变异体的功能研究显示，在不同温度下存在功能丧失和功能获得两种表型，其特征分别为电流密度降低和窗电流增加。这与22℃和10℃时失活向更正的去极化电压偏移以及22℃时激活斜率因子变慢有关。还观察到了进一步的功能获得效应，其特征为慢失活的起始和恢复更快。脂质双分子层中α亚基的分子动力学模拟表明，电荷反转使一个天然盐桥（E452-K249）不稳定。我们得出结论，观察到的增强功能促进了激活过程，导致肌肉兴奋性增强。
