[Clinical, myopathological and genetic features of two Chinese families with paramyotonia congenita]

Objective: To investigate the clinical, myopathological and genetic mutation characteristics in two Chinese families with paramyotonia congenita (PMC). Methods: Clinical manifestations, electrophysiology, muscle pathology and gene sequencing of two Chinese families with PMC were analyzed retrospectively. Results: Family 1 involved 12 patients in 4 consecutive generations and family 2 involved only 1 patient in 3 generations. The onset of symptoms in all patients started at early childhood. Both probands presented with myotonia triggered by cold and paroxysmal weakness. However, the other 11 patients in family 1 only manifested cold-induced myotonia. Serum creatine kinase (CK) was slightly elevated between attacks of weakness in the 2 probands, and was even greater than 10 000 U/L during the episodes of weakness in the second proband, whose lower limb MRI revealed edema in bilateral medial gastrocnemius. Electromyography showed diffuse myotonia discharge and myogenic impairment in both probands, and myotonia discharge in the first proband's mother. Muscle pathology of both probands showed mild myopathic changes, and tube aggregation was occasionally observed in the second one. Genetic testing revealed a maternally inherited heterozygous R1448H mutation of SCN4A gene in the first proband and part of his family. A novel heterozygous R1448G mutation of SCN4A gene was reported in the second proband. Conclusions: Cold-triggered myotonia with or without paroxysmal weakness are the common characteristics of PMC. Myotonic potential and myogenic impairment can be tested in electromyography. The p.R1448G mutation is a new missense mutation.

目的： 探讨2个先天性副肌强直（PMC）家系的临床、病理和基因突变特点。 方法： 回顾性分析2个PMC家系部分患者的临床和病理资料，并对部分家系成员进行基因检测。 结果： 家系1为连续4代12人发病，家系2为3代仅先证者1人发病。2个家系13例患者均自幼起病，其中2个家系先证者的主要临床表现均为遇冷肌强直及发作性无力，而家系1中的其他11例患者均只有肌强直而无发作性无力表现。2个家系先证者肌无力发作间期的肌酸激酶（CK）均轻度升高，家系2的先证者曾于肌无力发作期查CK显著升高，>10 000 U/L。家系2的先证者下肢肌肉磁共振显示双侧腓肠肌内头水肿。2个家系先证者的肌电图均有明显肌强直电位，且主动收缩有早募集现象。2个家系先证者的病理均呈轻微肌源性病理改变，其中家系2的先证者偶见有管聚集。基因检测示家系1的先证者及其母亲、姐姐发现SCN4A基因p.R1448H单杂合突变，家系2的先证者为SCN4A基因p.R1448G单杂合突变。 结论： 遇冷肌强直伴或不伴发作性无力为PMC的主要临床表现，肌电图示除了肌强直放电外还可有肌源性损害，肌肉病理缺乏特异性。p.R1448G为本研究发现的新发错义突变。.

Keywords: Paramyotonia congenita; Pathology; SCN4A gene; Sodium channels.