Department of Neurology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts.
Division of Genetics and Genomics, Manton Center for Orphan Disease Research, Boston Children's Hospital, Boston, Massachusetts.
JAMA Neurol. 2023 Jun 1;80(6):578-587. doi: 10.1001/jamaneurol.2023.0473.
Mesial temporal lobe epilepsy (MTLE) is the most common focal epilepsy subtype and is often refractory to antiseizure medications. While most patients with MTLE do not have pathogenic germline genetic variants, the contribution of postzygotic (ie, somatic) variants in the brain is unknown.
To test the association between pathogenic somatic variants in the hippocampus and MTLE.
DESIGN, SETTING, AND PARTICIPANTS: This case-control genetic association study analyzed the DNA derived from hippocampal tissue of neurosurgically treated patients with MTLE and age-matched and sex-matched neurotypical controls. Participants treated at level 4 epilepsy centers were enrolled from 1988 through 2019, and clinical data were collected retrospectively. Whole-exome and gene-panel sequencing (each genomic region sequenced more than 500 times on average) were used to identify candidate pathogenic somatic variants. A subset of novel variants was functionally evaluated using cellular and molecular assays. Patients with nonlesional and lesional (mesial temporal sclerosis, focal cortical dysplasia, and low-grade epilepsy-associated tumors) drug-resistant MTLE who underwent anterior medial temporal lobectomy were eligible. All patients with available frozen tissue and appropriate consents were included. Control brain tissue was obtained from neurotypical donors at brain banks. Data were analyzed from June 2020 to August 2022.
Drug-resistant MTLE.
Presence and abundance of pathogenic somatic variants in the hippocampus vs the unaffected temporal neocortex.
Of 105 included patients with MTLE, 53 (50.5%) were female, and the median (IQR) age was 32 (26-44) years; of 30 neurotypical controls, 11 (36.7%) were female, and the median (IQR) age was 37 (18-53) years. Eleven pathogenic somatic variants enriched in the hippocampus relative to the unaffected temporal neocortex (median [IQR] variant allele frequency, 1.92 [1.5-2.7] vs 0.3 [0-0.9]; P = .01) were detected in patients with MTLE but not in controls. Ten of these variants were in PTPN11, SOS1, KRAS, BRAF, and NF1, all predicted to constitutively activate Ras/Raf/mitogen-activated protein kinase (MAPK) signaling. Immunohistochemical studies of variant-positive hippocampal tissue demonstrated increased Erk1/2 phosphorylation, indicative of Ras/Raf/MAPK activation, predominantly in glial cells. Molecular assays showed abnormal liquid-liquid phase separation for the PTPN11 variants as a possible dominant gain-of-function mechanism.
Hippocampal somatic variants, particularly those activating Ras/Raf/MAPK signaling, may contribute to the pathogenesis of sporadic, drug-resistant MTLE. These findings may provide a novel genetic mechanism and highlight new therapeutic targets for this common indication for epilepsy surgery.
内侧颞叶癫痫（MTLE）是最常见的局灶性癫痫亚型，通常对抗癫痫药物有抗性。虽然大多数 MTLE 患者没有致病性种系遗传变异，但大脑中的后合子（即体细胞）变异的贡献尚不清楚。
检测海马体细胞变异与 MTLE 之间的关联。
设计、地点和参与者：本病例对照遗传关联研究分析了接受神经外科治疗的 MTLE 患者和年龄匹配、性别匹配的神经典型对照的海马组织中的 DNA。1988 年至 2019 年期间，在 4 级癫痫中心招募了接受治疗的患者，并回顾性收集临床数据。使用全外显子组和基因面板测序（每个基因组区域平均测序超过 500 次）来鉴定候选致病性体细胞变异。使用细胞和分子测定法对一组新的变体进行了功能评估。有非病变和病变（内侧颞叶硬化、局灶性皮质发育不良和低级别癫痫相关肿瘤）药物难治性 MTLE 患者符合条件，他们接受了前内侧颞叶切除术。所有有可用冷冻组织和适当同意书的患者均包括在内。对照脑组织取自脑库的神经典型供体。数据分析于 2020 年 6 月至 2022 年 8 月进行。
药物难治性 MTLE。
海马体与未受影响的颞叶新皮质相比，致病性体细胞变异的存在和丰度。
在 105 名纳入的 MTLE 患者中，53 名（50.5%）为女性，中位（IQR）年龄为 32（26-44）岁；30 名神经典型对照中，11 名（36.7%）为女性，中位（IQR）年龄为 37（18-53）岁。在 MTLE 患者中检测到 11 种在海马体中富集而在未受影响的颞叶新皮质中富集的致病性体细胞变异（中位数[IQR]变异等位基因频率，1.92[1.5-2.7]与 0.3[0-0.9]；P = .01），但在对照组中未检测到。其中 10 种变异位于 PTPN11、SOS1、KRAS、BRAF 和 NF1 中，均预测为 Ras/Raf/丝裂原活化蛋白激酶（MAPK）信号通路的组成性激活。对变异阳性海马组织的免疫组织化学研究表明，Erk1/2 磷酸化增加，表明 Ras/Raf/MAPK 激活，主要发生在神经胶质细胞中。分子测定表明 PTPN11 变异的异常液-液相分离可能是一种显性获得性功能机制。
海马体细胞变异，特别是那些激活 Ras/Raf/MAPK 信号的变异，可能导致散发性、耐药性 MTLE 的发病机制。这些发现可能为这种常见的癫痫手术适应证提供新的遗传机制，并突出新的治疗靶点。
