ABCB4 and familial intrahepatic cholestasis: Heterozygous ABCB4 variants contribute to mild cholestatic phenotypes, while homozygous deficiency leads to Progressive Intrahepatic Familial Cholestasis (PFIC) Type 3, and increased risk of cholesterol gallstones [http://www.ncbi.nlm.nih.gov/pubmed/23583734?dopt=AbstractPlus].