GAD2 and stiff-person syndrome: Firstly, immunization against GAD, which induced very high GADAb levels similar to those found in patients with SPS, resulted in IgG reactivity not only against the intracellular compartment of the GAD-EGFP expressing neurons, where GAD65 is located, but also against the extracellular surface of unpermeabilized GAD-EGFP positive and negative cerebellar neurons in both mouse and rat cultures.