ABCB4 and gallstones: It has also been shown that substantial amounts of cholesterol are secreted by Mdr2 (-/-) mice on a cholate-supplemented diet and microscopic examination of the gallbladder reveals massive amount of cholesterol crystals and that after 12 weeks, 50% of the Mdr2 (-/-) mice on chow also developed gallstones composed of needlike "anhydrous" cholesterol crystals and mucin [21,22].