NKX2-1 and congenital diaphragmatic hernia: Since Titf1 is essential for lung development [25,26,27,28,29] and null mutation can cause PH in the mouse model, the authors undertook two lines of research to investigate the possible role of TITF1 in the development of CDH in humans, namely: (a) an examination of TITF1 expression in the trachea and lungs of human fetuses which died for causes other than CDH; and (b) the first direct TITF1 mutation analysis of the genes of CDH patients.