Hypokalemic periodic paralysis (hypoPP) is an autosomal dominant, rare disorder with a prevalence of 1:100,000 that is caused by variants in the gene coding for calcium channel CaV1.1 (CACNA1S OMIM 170,400) or less frequently in the gene for sodium channel NaV1.4 (SCN4A OMIM 613,345). This evidence concerns the gene SCN4A and hypokalemic periodic paralysis.