KCNJ2 and Familial short QT syndrome: It is composed of small hydrophobic residues that may reduce the diameter of the pore in some channel states (Nishida et al., 2007), and certain mutations linked to Andersen-Tawil syndrome or familial short QT syndrome (both are Kir2.1-linked channelopathies, Section Cardiac arrhythmias related to Kir2.x channels and polyamine block) have been identified in the G-loop (Pegan et al., 2006; Hattori et al., 2012; Deo et al., 2013).