NKX2-5 and ventricular septal defect 1: NKX2.5 mutations have also been reported in ventricular septal defect (VSD), tetralogy of Fallot (TOF), aortic stenosis, and hypoplastic left heart syndrome (HLHS), demonstrating that NKX2.5 has multiple roles during heart development.17, 18, 19, 20, 21