NKX2-5 and atrioventricular block: Nkx2.5 haploinsufficiency in humans is associated with ASDs, AVSDs, and tetralogy of Fallot (ToF), as well as conduction defects, such as atrial fibrillation, arrhythmias, and atrioventricular (AV) block [3,4,15,108,121,123,132,133], consistent with the multiple roles Nkx2.5 plays during cardiogenesis (Table 1).