KCNJ2 and short QT syndrome type 3: Interestingly, Xia et al. [48] reported a gain-of-function mutation in Kir2.1 (V93I (p.Val93Ile)) that was clearly associated with familial atrial fibrillation but showed no clinical effects on the ventricles, unlike the four gain-of-function mutation in Kir2.1 associated with SQT3.