Background: Familial hypokalemic periodic paralysis (FHPP) is an autosomal dominant disease presented by the presence of painless weakness attacks accompanied by a low level of serum potassium. Mutations in genes encoding ion channels Calcium voltage-gated channel subunit alpha 1S, SCN4, and KCNJ2 have been recognized in this disorder.
Case Report: A 15-year-old male patient was admitted to our hospital with a complaint of muscle weakness, which started about 4 years ago, recurring almost twice a week. Especially when he ate carb-rich meals or stayed after a long time in the cold, he described a feeling of numbness and weakness. FHPP was diagnosed due to CACNA1S gene mutation from the family in which six members are affected in three generations.
Conclusion: FHPP, which is an uncommon cause in cases presenting with sudden muscle weakness, is an important neu-romuscular emergency, which should be kept in mind and may cause mortal results when not treated.