Non-dystrophic myotonias are a group of rare neuromuscular diseases linked to SCN4A or CLCN1. Among the subtypes, myotonia permanens, associated with the Gly1306Glu variant of SCN4A, is a relatively less frequent but more severe form. Most reports of non-dystrophic myotonias describe European populations. Therefore, to expand the genetic and phenotypic spectrum of this disorder, we evaluated 30 Chilean patients with non-dystrophic myotonias for associated variants and clinical characteristics. SCN4A variants were observed in 28 (93%) of patients, including 25 (83%) with myotonia permanens due to the Gly1306Glu variant. Myotonia permanens was inherited in 24 (96%) patients; the mean age of onset was 6 months, and the initial symptoms were orbicularis oculi myotonia in 17 (74%) patients and larynx myotonia in 12 (52%) patients. The extraocular muscles were involved in 11 (44%) patients, upper limbs in 20 (80%), and lower limbs in 21 (84%). Thirteen (52%) patients experienced recurrent pain and 10 (40%) patients reported limitations in daily life activities. Carbamazepine reduced myotonia in eight treated patients. The high frequency of the Gly1306Glu variant in SCN4A in Chilean patients suggests a founder effect and expands its phenotypic spectrum.

中文翻译：

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以 SCN4A Gly1306Glu 变体为主的非营养不良性肌强直智利队列

非营养不良性肌强直是一组与 SCN4A 或 CLCN1 相关的罕见神经肌肉疾病。在亚型中，与 SCN4A 的 Gly1306Glu 变体相关的永久性肌强直是一种相对较少见但更严重的形式。大多数非营养不良性肌强直的报告描述了欧洲人群。因此，为了扩大这种疾病的遗传和表型谱，我们评估了 30 名智利非营养不良性肌强直患者的相关变异和临床特征。在 28 (93%) 名患者中观察到 SCN4A 变异，其中 25 (83%) 名因 Gly1306Glu 变异而患有永久性肌强直。24 名 (96%) 患者遗传了永久性肌强直；平均发病年龄为 6 个月，17 名 (74%) 患者的初始症状为眼轮匝肌肌强直，12 名 (52%) 患者为喉部肌强直。眼外肌受累 11 例（44%），上肢受累 20 例（80%），下肢受累 21 例（84%）。13 名 (52%) 患者出现复发性疼痛，10 名 (40%) 患者报告日常生活活动受限。卡马西平减轻了 8 名接受治疗的患者的肌强直。智利患者 SCN4A 中 Gly1306Glu 变体的高频率表明存在创始人效应并扩展了其表型谱。