type 1 diabetes or type 1 diabetes mellitusn. A chronic autoimmune disease in which the insulin-producing beta cells of the pancreas are destroyed, leading to high glucose levels in the blood and resulting in impaired metabolism of carbohydrates, fats, and proteins. The disease, which is characterized by excessive thirst, frequent urination, metabolic acidosis, and wasting, typically appears in childhood or adolescence and requires lifelong administration of insulin. Also called insulin-dependent diabetes, insulin-dependent diabetes mellitus.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.