Regarding intracellular synaptic antibodies, there has been one placebo-controlled cross-over trial showing beneficial effects of intravenous immunoglobulin in patients with stiff person syndrome and GAD antibodies (Dalakas et al., 2001) but, overall, treatment response in GAD-antibody-related disease is mixed and unpredictable (Arino et al., 2014; Martinez-Hernandez et al., 2016). This evidence concerns the gene GAD1 and stiff-person syndrome.