NKX2-1 and Esophageal atresia: Mouse models with reduced expression Sox2 or absence of Nkx2-1 resulted in separation defects, resembling the human congenital condition called tracheoesophageal fistula (TEF), where the airway is connected with the stomach and/or esophageal atresia (EA), a short and blunted esophagus (Minoo et al., 1999; Que et al., 2006; Que et al., 2007).