ABCB4 and gallbladder disease 1: Although ABCB4 mutations and variations have been identified as a monogenetic risk factor for LPAC in humans and the ABCB4 KO mouse model has provided a physical-chemical explanation for the formation of gallstones, how needle-like “anhydrous” cholesterol crystals nucleate and crystallize in phospholipid-deficient bile remains elusive.