NKX2-1 and congenital diaphragmatic hernia: TITF1 has long been considered a possible candidate gene in CDH pathogenesis because (i) it is expressed in lung endoderm and epithelium throughout lung development starting from 10 days of gestation, (ii) null mutation of Titf1 in murine models determines a failure of tracheo-esophageal separation and branching resulting in PH [23,24], and (iii) the epithelial cells of these hypoplastic lungs do not undergo proper differentiation [23].