[A novel mutation of SCN4A gene causes hypokalemic periodic paralysis in a Chinese family].

To report a Chinese family with hypokalemic periodic paralysis (HOKPP) and investigate the clinical and pathogenic gene characteristics of the family. The clinical, electrophysiological and pathological data of the proband of the family were analyzed, and the information of the family was investigated in detail. The peripheral venous blood of the six members of the family was collected and their genomic DNA was extracted. The genes related to periodic paralysis analysis of the proband were performed by the second generation sequencing. The pathogenicity of the mutant protein was respectively analyzed by the bioinformatics software SIFT, Polyphen2 and Mutation Tasker. The cosegregation analysis of phenotype and genotype of the family was performed by the first generation sequencing. There were 3 patients in the family with the onset age of 21 to 42 years old. All the patients manifested with vomiting as the first symptoms, then presented with muscle weakness accompanied by muscle soreness. The muscle weakness gradually relieved in 3 to 5 days. Creatine kinase (CK) of the proband significantly increased. Electromyographic exercise test was positive, however, electromyography and muscle pathological analysis were normal. The genes related to periodic paralysis analysis of the proband found a novel mutation (c.2458A>T (p.N.820Y)) of SCN4A gene which was located in the conservative region. The function analysis showed it was a pathogenic mutation. Moreover, the first generation sequencing confirmed that the mutation was cosegregated with patients in the family. Meanwhile, it was found that the proband's son carried the same mutation, but without any symptom, indicating that he was a pre-symptomatic patient. Vomiting can be one of the symptoms of the patients with HOKPP. The novel mutation of SCN4A gene c.2458 A>T is the pathogenic mutation of the family. Patients with periodic paralysis should be tested for blood potassium and genes as early as possible to facilitate early diagnosis and genetic counseling.