Calbindin is a calcium-binding protein belonging to the troponin C superfamily. It was originally described as a 27-kD;protein induced by vitamin D in the duodenum of the chick. In the brain, its synthesis is independent of;vitamin-D-derived hormones. Calbindin contains 4 active calcium-binding domains, and 2 modified domains that;presumably have lost their calcium-binding capacity. The neurons in brains of patients with Huntington disease are;calbindin-depleted.