NR1H4 and progressive familial intrahepatic cholestasis type 1: To discover the additional regulatory molecules engaged in the pathogenesis of cholestasis and concomitant disorders, we sought previously undescribed molecules associated with FXR and cholestasis, because evidence exists that FXR critically influences the pathophysiology of cholestasis in mouse models [4-6] and human familial intrahepatic cholestasis type 1 (also known as Byler's disease) [7].