Type 1 diabetes is caused by an absolute deficiency of insulin from an autoimmune destruction of pancreatic beta cells or degeneration of these cells. The infiltration of mononuclear cells can be precipitated by environmental factors such as viruses, chemicals, and cow's milk or caused by unknown or idiopathic reactions. Ordinarily the individual has an inherited susceptibility to this autoimmune reaction and diabetes develops suddenly. Most often this onset occurs in childhood or in the young adult years. Type 1 diabetes encompasses about 10% of diabetes cases.
Because of the beta cell destruction, type 1 diabetic patients require insulin to prevent ketosis and reduce complications of this disease. The rate of beta cell destruction is quite variable, being rapid in some individuals (mainly infants and children) and slow in others (mainly adults).
This class was formerly called type I insulin dependent diabetes mellitus (IDDM) and referred to as juvenile-onset diabetes or insulin-dependent diabetes.
Idiopathic diabetes: This is a form of type 1 diabetes whereby patients have no known etiologies. Typically, these patients have a lack of insulin and are prone to ketoacidosis with no evidence of autoimmunity. A very small minority of patients have type 1 diabetes that are considered idiopathic diabetics, with most being of African or Asian ancestry. These individuals typically have episodic ketoacidosis and have varying degrees of insulin deficiency between episodes. Idiopathic diabetes is strongly inherited but lacks evidence of any beta cell autoimmunity. Moreover, patients with idiopathic diabetes may have a variable requirement for insulin therapy.