Department of Human Genetics, Emory University, Atlanta, Georgia, 30322, USA.
Genetics and Molecular Biology Program, Graduate Division of Biological and Biomedical Sciences, Laney Graduate School, Emory University, Atlanta, Georgia, 30322, USA.
Brain. 2018 Aug 1;141(8):2392-2405. doi: 10.1093/brain/awy171.
GABAA receptors are ligand-gated anion channels that are important regulators of neuronal inhibition. Mutations in several genes encoding receptor subunits have been identified in patients with various types of epilepsy, ranging from mild febrile seizures to severe epileptic encephalopathy. Using whole-genome sequencing, we identified a novel de novo missense variant in GABRA5 (c.880G > C, p.V294L) in a patient with severe early-onset epilepsy and developmental delay. Targeted resequencing of 279 additional epilepsy patients identified 19 rare variants from nine GABAA receptor genes, including a novel de novo missense variant in GABRA2 (c.875C > A, p.T292K) and a recurrent missense variant in GABRB3 (c.902C > T, p.P301L). Patients with the GABRA2 and GABRB3 variants also presented with severe epilepsy and developmental delay. We evaluated the effects of the GABRA5, GABRA2 and GABRB3 missense variants on receptor function using whole-cell patch-clamp recordings from human embryonic kidney 293T cells expressing appropriate α, β and γ subunits. The GABRA5 p.V294L variant produced receptors that were 10-times more sensitive to GABA but had reduced maximal GABA-evoked current due to increased receptor desensitization. The GABRA2 p.T292K variant reduced channel expression and produced mutant channels that were tonically open, even in the absence of GABA. Receptors containing the GABRB3 p.P301L variant were less sensitive to GABA and produced less GABA-evoked current. These results provide the first functional evidence that de novo variants in the GABRA5 and GABRA2 genes contribute to early-onset epilepsy and developmental delay, and demonstrate that epilepsy can result from reduced neuronal inhibition via a wide range of alterations in GABAA receptor function.
GABAA 受体是配体门控阴离子通道，是神经元抑制的重要调节剂。在患有各种类型癫痫的患者中，已经鉴定出几个编码受体亚基的基因突变，从轻度热性惊厥到严重癫痫性脑病不等。使用全基因组测序，我们在一名患有严重早发性癫痫和发育迟缓的患者中发现了 GABRA5 中的一个新的从头错义变异（c.880G > C，p.V294L）。对 279 名额外癫痫患者的靶向重测序鉴定了九个 GABAA 受体基因中的 19 个罕见变异，包括 GABRA2 中的一个新的从头错义变异（c.875C > A，p.T292K）和 GABRB3 中的一个反复出现的错义变异（c.902C > T，p.P301L）。携带 GABRA2 和 GABRB3 变异的患者也表现出严重的癫痫和发育迟缓。我们使用表达适当的 α、β 和 γ 亚基的人胚肾 293T 细胞中的全细胞膜片钳记录评估了 GABRA5、GABRA2 和 GABRB3 错义变异对受体功能的影响。GABRA5 p.V294L 变异产生的受体对 GABA 的敏感性增加了 10 倍，但由于受体脱敏增加，最大 GABA 诱发电流降低。GABRA2 p.T292K 变异降低了通道表达，并产生了即使在没有 GABA 的情况下也持续开放的突变通道。含有 GABRB3 p.P301L 变异的受体对 GABA 的敏感性降低，产生的 GABA 诱发电流减少。这些结果首次提供了功能证据，证明 GABRA5 和 GABRA2 基因中的从头变异导致早发性癫痫和发育迟缓，并表明癫痫可以通过 GABA 受体功能的广泛改变导致神经元抑制减少而发生。
