The seizure phenotypes of a Japanese family with missense mutations in SCN2A are described. The proband of the family had partial epilepsy after febrile seizures plus. He had three missense mutations of SCN2A (R19K, R188W, and R524Q). The R188W mutation was suggested by electrophysiologic studies to be the main disease mutation. However, it is suggested that the penetrance rate of this pedigree is extremely low, or that other genes may have modified the phenotype of the proband.