Causes for Diabetes Type 1&2

This question comes up quite often (usually among patients who are diagnosed late in life, but its virtually impossible to have type 1 diabetes and not know it because it happens rapidly, is usually accompanied by unintended weight loss and the symptoms are impossible to ignore).  I think the best way to explain it is as follows.  "Diabetes" is not one disease, but a group of metabolic diseases characterized by hyperglycemia resulting from defects in insulin secretion, insulin action, or both.  However, in spite of sharing a similar name, they are different diseases with unique and unrelated etiologies.

Of the different "types" of diabetes, type 2 is by far the most common, and usually results from a combination of the inability for insulin to work properly, combined with a defect in insulin secretion.  Type 1 (more specifically type 1a) is most commonly caused by the immune system mistakenly attacking and destroying the pancreatic beta cells (which makes type 1 an autoimmune disease), resulting in complete insulin idependence.  Markers of the immune destruction of the beta-cell include islet cell autoantibodies (ICAs), autoantibodies to insulin (IAAs), autoantobodies to glutamic acid decarboxylase (GAD 65), and autoantibodies to tyrosine phophatases IA-2 and IA-2beta.  One or usually more of these autoantibodies are present in 85-90% of individuals with type 1, but will rarely (if ever) be present in patients with type 2, therefore lab blood tests are the most definitive way to identify someone as having type 1 diabetes.

There is some debate within the scientific community over whether the issue of insulin deficiency in type 2 diabetes is due to cell death (aptosis) or cell exhaustion triggered by insulin resistance, whereas we knowthat type 1 is due to cell aptosis.  While they do not know the answer to this, the debate is irrelevant.  Patients with type 2 diabetes usually suffer from a relativeloss of insulin secretion rather than an absolute insulin deficiency as is the case with type 1.  At least initially, and often throughout their lifetime, patients with type 2 diabetes do not require insulin treatment for the patient's survival.  It is vital to note that insulin usage does not render someone "insulin dependent", it merely describes the manner in which their condition is treated.

As an FYI, the Report of the Expert Committee on the Diagnosis and Classification of Diabetes Mellitus is probably the best source for answering any questions:

An international Expert Committee, working under the sponsorship of the American Diabetes Association, was established in May 1995 to review the scientific literature since 1979 and to decide if changes to the classification and diagnosis of diabetes were warranted. The Committee met on multiple occasions and widely circulated a draft report of their findings and preliminary recommendations to the international diabetes community. In 2003, the Committee discussed and revised numerous drafts of a manuscript that culminated in this published document. (Diabetes Care 26:S5-S20, 2003)

http://care.diabetesjournals.org/cgi/content/full/26/suppl_1/s5

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