Loss of MUNC13-1 function causes microcephaly, cortical hyperexcitability, and fatal myasthenia.
Loss of MUNC13-1 function causes microcephaly, cortical hyperexcitability, and fatal myasthenia.
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DOI：
10.1212/nxg.0000000000000105
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发表时间：
2016-10
期刊：
影响因子：
--
通讯作者：
Harper CM
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文献类型：
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作者：
Engel AG;Selcen D;Shen XM;Milone M;Harper CM
确定小头畸形、皮质过度兴奋和肌无力等致命综合征的分子基础。我们进行了神经肌肉传递的临床和体外微电极研究，通过细胞化学和电子显微镜 (EM) 检查神经肌肉接头，并通过桑格和外显子组测序寻找突变。由于易于释放的量子池明显耗尽，神经肌肉传输受到严重损害，但量子释放的概率是正常的。细胞化学和电镜研究揭示了正常的终板结构。外显子组测序在 MUNC13-1 (UNC13A) 的 N 末端结构域中发现了纯合无义突变，在 101 个残基后截断了蛋白质。 Munc13-1 功能的丢失预示着 Syntaxin 1B 将进入非功能性关闭状态；这抑制了神经肌肉接头处的胆碱能传递和大脑中的谷氨酸能传递。 Syntaxin 1B 的失活可能是患者皮质过度兴奋的原因，因为 Syntaxin 1B 的突变会导致伴有或不伴有癫痫的热性惊厥，STX1B 的单倍体不足与肌阵挛性不稳定性癫痫有关，而斑马鱼幼虫中 stx1b 的反义敲低会引发癫痫样放电。最近的一篇出版物还表明，突触蛋白 1B 对于维持发育和成熟神经元具有单独的强制性作用，并说明突触蛋白 1A/1B 双敲除小鼠的大脑发育受损。因此，我们将患者的小头畸形归因于截短的纯合 Munc13-1 突变，该突变使突触融合蛋白 1B 处于类似于基因敲除的永久关闭的非功能状态。
To identify the molecular basis of a fatal syndrome of microcephaly, cortical hyperexcitability, and myasthenia. We performed clinical and in vitro microelectrode studies of neuromuscular transmission, examined neuromuscular junctions cytochemically and by electron microscopy (EM), and searched for mutations by Sanger and exome sequencing. Neuromuscular transmission was severely compromised by marked depletion of the readily releasable pool of quanta, but the probability of quantal release was normal. Cytochemical and EM studies revealed normal endplate architecture. Exome sequencing identified a homozygous nonsense mutation in the N-terminal domain of MUNC13-1 (UNC13A) truncating the protein after 101 residues. Loss of Munc13-1 function predicts that syntaxin 1B is consigned to a nonfunctional closed state; this inhibits cholinergic transmission at the neuromuscular junction and glutamatergic transmission in the brain. Inactivation of syntaxin 1B likely accounts for the patient's cortical hyperexcitability because mutations of syntaxin 1B cause febrile seizures with or without epilepsy, haploinsufficiency of the STX1B is associated with myoclonic astatic epilepsy, and antisense knockdown of stx1b in zebrafish larvae elicits epileptiform discharges. A very recent publication also shows that syntaxin 1B has a separate obligatory role for maintenance of developing and mature neurons and illustrates impaired brain development in syntaxin 1A/1B double knockout mice. We therefore attribute our patient's microcephaly to the truncating homozygous Munc13-1 mutation that consigns syntaxin 1B to a permanently closed nonfunctional state akin to a knockout.