Thyrotoxic periodic paralysis (TPP), familial periodic paralysis (FPP), and sporadic periodic paralysis (SPP) are the most common causes of hypokalemic periodic paralysis (hypoKPP). The patients present with similar clinical features characterized by episodic attacks of muscle weakness and a decrease in blood potassium. Mutations in the gene encoding the voltage-sensor coding regions of the skeletal muscle sodium channel gene (SCN4A) and the alpha-1 subunit of the skeletal muscle calcium channel gene were analyzed in 23 Chinese hypoKPP patients, including 1 FPP pedigree, 14 TPP patients, and 8 SPP patients. In addition, R83H mutation of the potassium channel subunit gene which was originally published as periodic paralysis mutation was also analyzed. A heterozygous CGT-TGT mutation at codon 672 in SCN4A gene was identified to segregate with the disease in the FPP family. Mutations in these regions were excluded in those patients with SPP and TPP. The results suggest that a likely genetic basis for FPP does not contribute to TPP and SPP, despite close similarities among FPP, TPP, and SPP.