The measurement of GAD65 antibodies is used for the laboratory diagnosis of type I (insulin-dependent) autoimmune diabetes mellitus.
Screening for antibodies against the GAD antigen is used also to investigate patients with neurological diseases such as stiff-person syndrome (or stiff-man syndrome), limbic encephalitis, epilepsy, and cerebral ataxia.
There are two isoforms of the GAD enzyme with a molecular weight of 65 kDa and 67 kDa. GAD-65 is mainly expressed in the pancreas, whereas both GAD-65 and GAD-67 are expressed in the CNS.
Type I diabetes mellitus is insulin-dependent diabetes. Type I diabetes mellitus is a form of organ-specific autoimmune disease that results in the destruction of pancreatic islet cells and their products. These antibodies are used to differentiate type I diabetes from non-insulin-dependent type II diabetes. Almost 90% of type I diabetics have one or more of the following autoantibodies at the time of diagnosis: anti-GAD65 (glutamic acid decarboxylase), anti-ICA (pancreatic islet cells), and insulin antibodies.
These antibodies may appear years before the onset of symptoms in patients with type I diabetes mellitus. Test of autoantibodies is also useful for relatives of insulin-dependent diabetes patients to determine if they are at risk of developing the disease. The presence of GAD65 antibodies confirms the disease. The presence of these antibodies during pregnancy (gestational diabetes) ultimately requires the administration of insulin permanently.
Testing for these autoantibodies is also used in the monitoring of patients who have received pancreatic islet cell transplantation. Finally, these antibodies can be used to detect the delayed onset of type I diabetes in patients previously diagnosed with type II diabetes.
Type II diabetics have low or negative titers of these autoantibodies.
Anti-GAD antibodies also occur in 60% of patients with stiff-person syndrome and have been observed in both serum and cerebrospinal fluid (CSF). Anti-GAD antibodies can also occur in limbic encephalitis, epilepsy, and cerebral ataxia. The association of antibodies against GAD with cancer is unusual but has been reported in various forms of cancer (breast cancer, small cell lung, endocrine tumors). Patients with neurological symptoms often have much higher anti-GAD antibody titers than patients with type 1 diabetes mellitus.
What Do Pathological Values Mean?
- Increase: Insulin-dependent diabetes mellitus, insulin resistance, insulin allergies, stiff-person syndrome, limbic encephalitis, epilepsy, cerebral ataxia
Laboratory test results are the most important parameter for the diagnosis and monitoring of all pathological conditions. 70%-80% of diagnostic decisions are based on laboratory tests. Correct interpretation of laboratory results allows a doctor to distinguish "healthy" from "diseased".
Laboratory test results should not be interpreted from the numerical result of a single analysis. Test results should be interpreted in relation to each individual case and family history, clinical findings and the results of other laboratory tests and information. Your personal physician should explain the importance of your test results.
At Diagnostiki Athinon we answer any questions you may have about the test you perform in our laboratory and we contact your doctor to get the best possible medical care.