disease diabetes mellitus type I diabetes mellitus A subtype of DIABETES MELLITUS that is characterized by INSULIN deficiency. It is manifested by the sudden onset of severe HYPERGLYCEMIA, rapid progression to DIABETIC KETOACIDOSIS, and DEATH unless treated with insulin. The disease may occur at any age, but is most common in childhood or adolescence. An autoimmune disease of endocrine system and is_a diabetes mellitus that results from autoimmune destruction of insulin-producing beta cells of the pancreas. Diabetes mellitus characterized by insulin deficiency, sudden onset, severe hyperglycemia, rapid progression to ketoacidosis, and death unless treated with insulin. The disease may occur at any age, but is most common in childhood or adolescence.