The beta cells of the pancreatic islets of Langerhans are the only cells in the body that produce and secrete insulin, a key metabolic hormone, which plays a central role in the maintenance of glucose homeostasis regulating glucose uptake in muscle and adipose tissue as well as carbohydrate, fat, and protein metabolism in these tissues and the liver. Failure of normal beta-cell function can lead to hyperglycemia (diabetes mellitus) or hypoglycemia. While hy- glycemia is a rare and life-threatening condition in which the beta cell secretes too much insulin, diabetes mellitus is a common...