GAD2 and stiff-person syndrome: An epitope mapping assay (epitope-specific radioligand binding assay (ES-RBA)) allows the detection of conformational and linear GAD65-specific antibody epitopes and was able to distinguish between anti-GAD Abs in sera of patients with type 1 DM, SPS, limbic encephalitis, CA, and anti-GAD Ab-positive epilepsy [40, 41] (Fig. 3).