ATP8B1 and progressive familial intrahepatic cholestasis type 1: Another example for the protective role of membrane proteins against potentially toxic bile acids may be the decreased resistance of the hepato-canalicular membrane to hydrophobic bile salts observed in progressive familial intrahepatic cholestasis type 1 (PFIC1), which is caused by a deficiency of the phospholipid flippase ATP8B1 (Paulusma et al., 2006).