KCNJ18 encodes Kir2.6, an inwardly rectifying potassium channel that plays a critical role in maintaining muscle membrane excitability and resting potential 1. The channel allows greater potassium influx than efflux, with its voltage dependence regulated by extracellular potassium concentration and inward rectification primarily due to internal magnesium blockade 1. KCNJ18 demonstrates high sequence homology with related channels KCNJ2 and KCNJ12, making accurate genetic analysis challenging 2. The gene exhibits two distinct haplotypes (RRAI and QHEV) with functional differences, and haplotype 1 (AAAG) shows significantly higher frequency in East Asian populations (80.8%) compared to Caucasians (48.4%) 3. Mutations in KCNJ18 cause hypokalemic periodic paralysis, including both thyrotoxic periodic paralysis (TPP) and familial forms without hyperthyroidism 13. The G169R mutation demonstrates severe functional defects, reducing inward and outward current densities by approximately 48-65% 1. The Asian haplotype confers 19.6-fold increased susceptibility to TPP, explaining the higher prevalence in East Asian populations 3. Additionally, KCNJ18 variants have been identified in esophageal squamous cell carcinoma and non-small cell lung cancer, suggesting potential roles in oncogenesis 45.