Two forms anti-glutamic acid decarboxylase (GAD antibody) exist, having molecular size of 65 (diabetic GAD) and 67 kDa.

All ages can be affected and in majority of patients there is no underlying tumour. Isolated cases of colonic and small cell lung carcinomas have been reported.

GAD67 is found in about 60% of patients with stiff person’s syndrome. Other autoimmune neurological disorders for example, cerebellar ataxia,  have been associated with anti-GAD antibody. Diabetes is often seen in these patients.

Top image: Autoimmune reaction of GAD antibody to the cerebellar granular layer.
Bottom image: GAD positivity on primate pancreas.