Diabetes mellitus (type-1 diabetes) is a group of metabolic diseases characterized by high blood sugar levels resulting from defects in insulin secretion, or action, or both. Normally, blood glucose levels are tightly controlled by insulin, a hormone produced by the pancreas. Insulin lowers the blood glucose level. When the blood glucose elevates (for example, after eating food), insulin is released from the pancreas to normalize the glucose level. In patients with diabetes, the absence or insufficient production of insulin causes hyperglycemia.