Identification of a SCN4A mutation in a large Chinese family with atypical normokalemic periodic paralysis using whole-exome sequencing

OBJECTIVES: Normokalemic periodic paralysis (NormoKPP) of skeletal muscle is an autosomal dominant disorder caused by mutations in the gene encoding voltage-gated sodium channel protein type 4 subunit alpha (SCN4A), which leads to ion channel dysfunction. Little is known about the relationship between genotype and the clinical symptoms of NormoKPP. The present study aimed to evaluate the genetic variation in a large Chinese family with NormoKPP. The patients in this pedigree did not respond to saline treatment, but calcium gluconate treatment was effective. METHODS: We performed a series of clinical examinations and genetic analyses, using whole-exome and Sanger sequencing, to examine the mutation status of SCN4A in a Chinese family segregating for NormoKPP. RESULTS: Whole-exome sequencing revealed a c.2111C>T substitution in SCN4A in most of the affected family members. This mutation results in the amino acid substitution p.T704M. CONCLUSIONS: These results support a causative role of this mutation in SCN4A in NormoKPP, and provide information about the relationship between genotype and atypical clinical symptoms.