ABCB4 and Tangier disease: Considerable efforts have been made to achieve two clinical goals: 1) turn off ABC drug pumps such P-gp (ABCB1), BCRP (ABCG2), and MRP1 (ABCC1) to prevent multidrug resistance; and 2) repair folding mutants of CFTR (ABCC7; cystic fibrosis), BCRP (ABCG2; gout), ABCB4/ABCB11 (progressive familial intrahepatic cholestasis), ABCA1 (Tangier disease), ABCC2 (Dubin-Johnson syndrome), ABCC6 (pseudoxanthoma elasticum), and ABCC8 (hyperinsulinimic hypoglycemia of infancy) using small molecules called correctors or pharmacological chaperones.