ABCB4 and progressive familial intrahepatic cholestasis: Studies of the gene ABCB4, (ATP binding cassette subfamily B member 4) encoding the phosphotidylcholine floppase MDR3 and homozygously mutated in progressive familial intrahepatic cholestasis (PFIC) type 3, identified a heterozygous mutation of ABCB4 first in a familial case23 and then in a sporadic instance of ICP24.