An autoantibody may be thought of as an antibody against one's own cells, tissues, or organs. An antibody, in turn, is a protein produced by the immune system to fight off invading micro-organisms that may cause disease or damage. If a person has an autoimmune response, the immune system is incorrectly triggered to attack parts of one's own body. One such autoimmune disease is Type 1 diabetes, in which a person cannot make the necessary hormone insulin. In Type 1 diabetes, patients may test positive for several types of autoantibodies.
Glutamic Acid Decarboxylase
Glutamic acid decarboxylase (GAD) is an enzyme that is found within the islet cells of the pancreas; these are the cells that produce insulin in healthy, non-diabetic, individuals. Dr. George Eisenbarth and Dr. David McCulloch, writing in the medical reference UpToDate, report that around 70 percent of patients diagnosed with TType 1 diabetes will test positive for this antibody at the time of diagnosis. It is important to note that this testing positive for anti-GAD antibodies does not mean that a patient does have Type 1 diabetes; furthermore, having a negative GAD antibody test does not mean that Type 1 diabetes is an incorrect diagnosis. However, a positive GAD antibody test may suggest to a physician that a patient with symptoms of high blood sugar may indeed have Type 1 diabetes.
Insulin Autoantibodies
Drs. Eisenbarth and McCulloch, summarizing the results of two different studies looking at the development of antibodies to insulin, suggest that anti-insulin antibodies, also called insulin autoantibodies, or IAA, play an important role in the progression of Type 1 diabetes. In addition, even before an official diagnosis of Type 1 diabetes is made, the presence of insulin autoantibodies may be used to predict the development of Type 1 diabetes. For instance, a large study of over 1,300 children of parents with Type 1 diabetes was published in 1999 in the journal "Diabetes." The authors of the study found that the presence of anti-insulin antibodies was a consistent feature in children who went on to develop Type 1 diabetes. This does not mean that a patient with a positive anti-insulin antibody test will be certain to develop this chronic disease, but does provide a valuable marker to alert physicians that a patient is at-risk for the disease.
Islet Cell Antibodies
As their name suggests, islet cell antibodies, or ICA, are immune cells that attack the body's own pancreatic islet cells--the cells that are required to produce insulin. Drs. David McCulloch and Massimo Pietropaolo, writing in UpToDate, report that a variety of studies have found that the presence of ICA--a positive islet cell antibody test--is linked to a higher risk of developing Type 1 diabetes. In addition, having more than one antibody type--for instance, islet cell antibodies and insulin autoantibodies--increases the risk further. This was demonstrated in a study of over 800 healthy children of parents with Type 1 diabetes; those children who tested positive for any two of three types of antibodies--GAD, insulin, and islet cell--had a 68 percent risk of developing diabetes within five years. This result suggests that having multiple antibodies within the bloodstream, even before symptoms of diabetes are seen, may predict the development of Type 1 diabetes.
References
- "UpToDate;" Prediction of Type 1 Diabetes Mellitus; D. McCulloch and M. Pietropaolo; April 2010
- "Diabetes;" Autoantibody appearance and risk for development of childhood diabetes in offspring of parents with type 1 diabetes: the 2-year analysis of the German BABYDIAB Study; A.G. Ziegler et. al.; March 1999
- "UpToDate;" Pathogenesis of Type 1 Diabetes Mellitus; G. Eisenbarth and D. McCulloch; May 2010
- "Diabetes;" Prediction of Type I Diabetes in First-Degree Relatives Using a Combination of Insulin, GAD, and ICA512bdc/IA-2 Autoantibodies; C.F. Verge et. al.; July 1996
