Subclinical myotonia was identified in four patients with hypokalemic periodic paralysis because of sodium voltage-gated channel alpha subunit 4 mutations.
As a result, heterozygous mutations c.2024G>A (R675Q) and c.1333G>A (V445M) of gene SCN4A were identified in the hypokalemic periodic paralysis patient and the paramyotonia congenita family respectively.
Sporadic periodic paralysis (SPP), the second leading cause of hypokalemic periodic paralysis (HPP) in Asia, has a presentation similar to that of familial periodic paralysis (FPP) and is caused by gene mutations in the calcium (Ca(2+)) (CACNA1S) and sodium (Na(+)) (SCN4A) channels of skeletal muscle.