INTRODUCTION In 2011, a homozygous mutation in GOSR2 (c.430G > T; p. Gly144Trp) was reported as a novel cause of Progressive Myoclonus Epilepsy (PME) with early-onset ataxia. Interestingly, the ancestors of patients originate from countries bound to the North Sea, hence the condition was termed North Sea PME (NSPME). Until now, only 20 patients have been reported in literature. Here, we provide a detailed description of clinical and neurophysiological data of seventeen patients. METHODS We collected clinical and neurophysiological data from the medical records of seventeen NSPME patients (5-46 years). In addition, we conducted an interview focused on factors influencing myoclonus severity. RESULTS The core clinical features of NSPME are early-onset ataxia, myoclonus and seizures, with additionally areflexia and scoliosis. Factors such as fever, illness, heat, emotions, stress, noise and light (flashes) all exacerbated myoclonic jerks. Epilepsy severity ranged from the absence of or incidental clinical seizures to frequent daily seizures and status epilepticus. Some patients made use of a wheelchair during their first decade, whereas others still walked independently during their third decade. Neurophysiological features suggesting neuromuscular involvement in NSPME were variable, with findings ranging from indicative of sensory neuronopathy and anterior horn cell involvement to an isolated absent H-reflex. CONCLUSION Although the sequence of symptoms is rather homogeneous, the severity of symptoms and rate of progression varied considerably among individual patients. Common triggers for myoclonus can be identified and myoclonus is difficult to treat; to what extent neuromuscular involvement contributes to the phenotype remains to be further elucidated.

中文翻译：

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在十七名患者中，对北海进行性肌阵挛性癫痫的表型谱进行了详细描述。

引言2011年，GOSR2的纯合突变（c.430G> T； p。Gly144Trp）被报道为发生早期共济失调的进行性肌阵挛性癫痫（PME）的新病因。有趣的是，患者的祖先来自北海国家，因此将该病称为北海PME（NSPME）。迄今为止，文献中仅报道了20名患者。在这里，我们提供了十七名患者的临床和神经生理学数据的详细说明。方法我们从17名NSPME患者（5-46岁）的病历中收集了临床和神经生理学数据。此外，我们针对影响肌阵挛严重程度的因素进行了访谈。结果NSPME的核心临床特征是早发性共济失调，肌阵挛和癫痫发作，另外还有反射障碍和脊柱侧弯。发烧，疾病，热量，情绪，压力，噪音和光线（闪烁）等因素都会加剧肌阵挛性抽搐。癫痫的严重程度从不存在或偶然发生临床发作到频繁的每日发作和癫痫持续状态不等。一些患者在他们的第一个十年中使用轮椅，而其他患者在他们的第三个十年中仍然独立行走。提示NSPME中神经肌肉受累的神经生理学特征是可变的，其发现范围从感觉神经元病变和前角细胞受累到孤立的H反射不等。结论尽管症状序列相当均一，但各个患者的症状严重程度和进展速度差异很大。可以识别肌阵挛的常见诱因，并且肌阵挛难以治疗。