CACNA1S and hypokalemic periodic paralysis: Clinically, patients with PP with decreased serum potassium level (<3.5 mmol/L) during the paralytic attacks are subtyped as hypokalemic periodic paralysis (hypoPP), genetically linked to the mutations in CACNA1S (encoding α1-subunit of the skeletal muscle L-type calcium channel Cav1.1; hypoPP1) or SCN4A (encoding α1-subunit of voltage-gated sodium channel Nav1.4; hypoPP2) (3, 4).