An inability to control blood glucose levels by insulin signaling is the molecular basis for the disease diabetes. Type 1 diabetes is characterized by lack of insulin production in the pancreas in response to increased glucose levels. Type 2 diabetes is characterized by defects in insulin receptor signaling, which is diagnosed as insulin resistance. The effect of insulin resistance is high glucose levels in the blood, which can lead to heart disease, problems with eyesight, kidney failure, and poor circulation in extremities. Thiazolidinediones have been used to treat patients with insulin-resistant type 2 diabetes because these drugs improve insulin sensitivity through modulation of glucose and fatty acid metabolism. Thiazolidinediones function as ligands for the peroxisome proliferator–activated receptor gamma (PPARγ) protein. Although thiazolidinedione-mediated activation of PPARγ improves insulin sensitivity, this treatment has been associated with an increased risk of cardiovascular disease and is considered an alternative treatment for type 2 diabetes.