Glutamic Acid Decarboxylase (GAD) Autoantibody

This test allows for the detection of the presence of antibodies to glutamic acid decarboxylase, which provides early evidence of autoimmune disease activity; its measurement has been shown to be useful in assisting the physician in the prediction, diagnosis, and management of patients with diabetes.^2-6

Glutamic acid decarboxylase (GAD₆₅) is an enzyme that is produced primarily by pancreatic islet cells. A number of recent studies indicate that patients with insulin-dependent diabetes mellitus (IDDM) often have antibodies to GAD₆₅ and several other islet cell antigens.⁷ This is consistent with the hypothesis that IDDM is an autoimmune disease and that autoantibody production is an early step in the development of IDDM.⁸ Autoantibodies can be detected in many cases prior to the onset of glucose intolerance. The presence of GAD65 autoantibodies can be detected in many cases prior to the onset of glucose intolerance. The presence of GAD₆₅ autoantibodies has been shown to be a strong predictive marker for the eventual onset of IDDM. Measurement of GAD₆₅ antibody can also be of use in distinguishing insulin-dependent from non−insulin-dependent diabetics when the clinical history is ambiguous. GAD₆₅ autoantibodies are often markedly elevated in patients with the stiff-person syndrome (also referred to as stiff-man syndrome), a condition that is associated with fluctuating stiffness and paroxysmal spasms of the trunk and legs.^9,10