Based on specific gene mutations, hypoPPs are subdivided into two different groups: hypokalemic periodic paralysis Type 1 (MIM #170400), due to heterozygous mutations in the CACNA1S gene (occurring in 80% of cases) and hypokalemic periodic paralysis Type 2 (MIM #613345) due to mutations in SCN4A gene (occurring in 10% of cases) [1]. The gene discussed is SCN4A; the disease is hypokalemic periodic paralysis.