Ion Channels and Disease Group, Florey Institute of Neuroscience and Mental Health, University of Melbourne, Parkville, Victoria, Australia.
Blue Brain Project, Swiss Federal Institute of Technology in Lausanne, Geneva, Switzerland.
Ann Neurol. 2019 Apr;85(4):514-525. doi: 10.1002/ana.25438. Epub 2019 Mar 7.
To elucidate the biophysical basis underlying the distinct and severe clinical presentation in patients with the recurrent missense SCN1A variant, p.Thr226Met. Patients with this variant show a well-defined genotype-phenotype correlation and present with developmental and early infantile epileptic encephalopathy that is far more severe than typical SCN1A Dravet syndrome.
Whole cell patch clamp and dynamic action potential clamp were used to study T226M Na 1.1 channels expressed in mammalian cells. Computational modeling was used to explore the neuronal scale mechanisms that account for altered action potential firing.
T226M channels exhibited hyperpolarizing shifts of the activation and inactivation curves and enhanced fast inactivation. Dynamic action potential clamp hybrid simulation showed that model neurons containing T226M conductance displayed a left shift in rheobase relative to control. At current stimulation levels that produced repetitive action potential firing in control model neurons, depolarization block and cessation of action potential firing occurred in T226M model neurons. Fully computationally simulated neuron models recapitulated the findings from dynamic action potential clamp and showed that heterozygous T226M models were also more susceptible to depolarization block.
From a biophysical perspective, the T226M mutation produces gain of function. Somewhat paradoxically, our data suggest that this gain of function would cause interneurons to more readily develop depolarization block. This "functional dominant negative" interaction would produce a more profound disinhibition than seen with haploinsufficiency that is typical of Dravet syndrome and could readily explain the more severe phenotype of patients with T226M mutation. Ann Neurol 2019;85:514-525.
阐明反复出现的错义 SCN1A 变异 p.Thr226Met 患者临床表现明显且严重的生物物理基础。该变异的患者表现出明确的基因型-表型相关性，并表现出发育性和婴儿早期癫痫性脑病，其严重程度远超过典型 SCN1A 德拉维特综合征。
使用全细胞膜片钳和动态动作电位钳研究在哺乳动物细胞中表达的 T226M Na 1.1 通道。使用计算模型探索解释动作电位发放改变的神经元规模机制。
T226M 通道表现出激活和失活曲线的超极化偏移以及增强的快速失活。动态动作电位钳混合模拟表明，含有 T226M 电导的模型神经元相对于对照显示出基强度的左移。在产生对照模型神经元重复动作电位放电的电流刺激水平下，T226M 模型神经元发生去极化阻断和动作电位放电停止。完全计算模拟神经元模型再现了动态动作电位钳的发现，并表明杂合 T226M 模型也更容易发生去极化阻断。
从生物物理角度来看，T226M 突变产生功能获得。有些矛盾的是，我们的数据表明，这种功能获得会导致中间神经元更容易发生去极化阻断。这种“功能显性负性”相互作用产生的去抑制作用比典型德拉维特综合征的杂合子不足更为明显，并且可以很容易地解释 T226M 突变患者更为严重的表型。神经病学年鉴 2019；85：514-525。
