摘要： 目的 报道SCN4A基因R672G位点突变致低钾性周期性瘫痪伴肌萎缩一家系，结合文献总结其临床表现、骨骼肌病理学和MRI特点。方法与结果 男性先证者，27岁，7岁时以反复发作性四肢肌无力为首发表现，后发作频率增加，并逐渐出现下肢肌无力、肌萎缩；其母有类似发作史。发作时血清钾水平降低。长程肌电图提示0~45分钟尺神经复合肌肉动作电位波幅逐渐降低，长时间运动后小指展肌复合肌肉动作电位波幅下降75.8%，波幅下面积降低67.4%。骨骼肌MRI显示双侧股外侧肌、股内侧肌、腓肠肌、比目鱼肌等水肿。骨骼肌病理学可见肌纤维膜下团块状沉积物，透射电子显微镜可见肌纤维膜下沉积物为排列紊乱的原始肌丝团。基因检测显示，先证者及其母均存在SCN4A基因外显子12 c.2014C > G（Arg672Gly）杂合突变。最终明确诊断为低钾性周期性瘫痪，该家系诊断为SCN4A基因Arg672Gly突变致低钾性周期性瘫痪家系。结论 SCN4A基因R672G位点突变致周期性瘫痪可出现肌萎缩和肌纤维膜下肌原纤维沉积的病理表现，肌纤维膜下沉积物的本质尚待进一步研究。

关键词: 低钾性周期性瘫痪（非MeSH词）, 肌萎缩, 钠通道, 基因, 突变, 系谱

Abstract: Objective To report a family of hypokalaemic periodic paralysis (HypoPP) with muscle atrophy due to SCN4A gene R672G mutation. The clinical, pathological and MRI characteristics of HypoPP were summarized combining literatures review. Methods and Results The proband was a 27 - year - old male patient who firstly presented periodic muscle weakness from 7 years old. The episode frequency increased with age, and gradually accompanied with muscle atrophy and permanent weakness. His mother has the similar episode but lower frequency. Serum potassium level decreased at the episode. The long - term EMG showed the compound muscle action potential (CMAP) on ulnar nerve gradually decreased from 0-45 min. The CMAP in abductor digiti minimi was decreased by 75.8% after long - time exercise test. Muscle MRI showed edema in vastus lateralis, vastus medialis, gastrocnemius lateralis, gastrocnemius medialis, soleus, et al. Muscle pathology showed eosinophilic light-stained sediment under the sarcolemma. Transmission electron microscopy (TEM) showed the sediment under the sarcolemma were primitive myofilaments with disordered arrangement. Gene test showed heterozygous mutation on exon 12 c.2014C > G (Arg672Gly) in SCN4A gene in proband and his mother. Finally, the proband was diagnosed HypoPP, and the family was confirmed HypoPP due to SCN4A gene R672G mutation. Conclusions HypoPP due to SCN4A gene R672G mutation can have pathological feature of muscle atrophy and sediment of primitive myofilament. The nature of the sediment needs further study.

Key words: Hypokalemic periodic paralysis (not in MeSH), Muscular atrophy, Sodium channels, Genes, Mutation, Pedigree