There was awareness of different grades of severity of diabetes for many centuries; however, the possibility that there were two distinct types only emerged at the beginning of the 20th century. Even then there was no real clue to distinct etiologies.
In the 1930s, Himsworth suggested that there were two phenotypes. The first real attempt to classify diabetes came with the first WHO Expert Committee on Diabetes Mellitus which felt that the only reliable classification was by age of onset and divided diabetes into juvenile - onset and maturity - onset disease.
There were many other phenotypes in vogue at that time including brittle, gestational, pancreatic, endocrine, insulin - resistant and iatrogenic diabetes, but for most cases there was no clear indication of etiology.
Clarity began to emerge in the 1970s with the discovery of the human leukocyte antigen (HLA) genotypes common in juvenile - onset diabetes and the discovery of islet call antibodies. This gave a clear indication that younger patients with diabetes, all of whom required insulin therapy, had an autoimmune disorder.
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The beginning of the modern era came with the second WHO Expert Committee which reviewed and modifi ed the revised classification published by the National Diabetes Data Group . This proposed two main classes of diabetes: insulin - dependent diabetes mellitus (IDDM; type 1) and non - insulin - dependent diabetes (NIDDM; type 2) together with “ other types ” and gestational diabetes.
There were also two risk classes: previous abnormality of glucose intolerance (PrevAGT) and potential abnormality of glucose tolerance (PotAGT) which replaced previous types known as pre - diabetes or potential diabetes.
Malnutrition - related diabetes mellitus was also introduced in recognition of a different phenotype found particularly in Asia and sub - Saharan Africa. Impaired glucose tolerance (IGT) was also introduced as a high risk class. Based on increasing knowledge, WHO revisited the classification in 1999 as did the American Diabetes Association (ADA).
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