For example, proper levels of SOX2 expression are required during early development for the complete separation of the anterior foregut into the esophagus and trachea in mice (25,32,33) and in humans (34–36), as the disruption of SOX2 expression leads to an abnormal developmental condition known as esophageal atresia with distal tracheoesophageal fistula (EA/TEF) (reviewed in 37,38). This evidence concerns the gene SOX2 and esophageal atresia/tracheoesophageal fistula.