SCN4A and Andersen-Tawil syndrome: The PP are classified as hyperkalemic PP (hyperPP; prevalence: 1-9/1000,000), hypokalemic PP (hypoPP; prevalence: 1-9/100,000), or Andersen-Tawil syndrome (ATS), and are caused by mutations of sodium (Nav1.4), calcium (Cav1.1), and several inward-rectifier potassium channels (Kir2.1, Kir2.6, and Kir3.4).