People with diabetes are usually diagnosed in one of a few ways: For Type 1 diabetes, the diagnosis is typically based on symptoms (such as unquenchable thirst, constant urination, weight loss, and fatigue) followed by a blood glucose measurement. For Type 2 diabetes, it is generally based on the results of a fasting plasma glucose test or an oral glucose tolerance test that has been ordered because of risk factors for diabetes. (The HbA1c test is also being considered for use as a diagnostic tool.)
In cases where it’s not clear what type of diabetes a person has, there are other tests that can be done — primarily those that look for antibodies in the blood that would indicate an autoimmune condition. However, Type 1 and Type 2 diabetes are not the only types of diabetes: A few, less common, types exist, some of which are caused by particular genetic defects, and special tests may be necessary to diagnose those types.
Last week, the Chicago Tribune published an article about a nine-year-old girl, Lilly Jaffe, who was found to have a rare genetic mutation that caused her diabetes. In the three years since this discovery, 70 others nationwide were found to have the same mutation, which causes a form of diabetes (known as a monogenic diabetes, since it is caused by one gene) that can be treated with an oral drug rather than insulin despite the outward appearance of Type 1 diabetes. At the urging of the researchers who discovered Lilly’s condition, the state of Illinois passed a law last month requiring doctors to register all children who develop diabetes before they are 12 months old in a database. (This type of diabetes almost always occurs within the first six months of life.) The researchers hope that by analyzing the database, likely cases of Lilly’s type of monogenic diabetes can be detected and then followed up. This condition is assumed to be severely underdetected, with potentially 2,000 cases in the United States.
But Lilly’s is not the only type of diabetes believed to be frequently underdetected or misdiagnosed. Maturity-Onset Diabetes of the Young (MODY), another type of monogenic diabetes that tends to begin in young adulthood and can usually be treated without insulin, is often misdiagnosed as Type 1 diabetes; the genetic test to detect MODY is often not performed. Similarly, Latent Autoimmune Diabetes in Adults (