GAD2 and stiff-person syndrome: These GAD-associated syndromes, all characterized by abnormal synaptic neurotransmission, comprise the “GAD antibody-spectrum disorders (GAD-SD)” or “SPS-SD” since SPS remains the hallmark disease among all of them, although one or more of these disorders coexists in approximately 70% of patients with GAD65 neurological autoimmunity [3, 6–9, 30–38].