NKX2-5 and ventricular septal defect 1: The most of Nkx2-5 mutations have been observed in CHD cases, including tetralogy of Fallot (TOF), ventricular septal defect (VSD), atrial septal defect (ASD), and transposition of the great arteries (TGA).5 Studies in human and animal models indicated Nkx2-5 expression only in cardiac tissue, thereby emphasizing its significant role in heart development.