[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.

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