GAD1 and stiff-person syndrome: In five SPS patients with cerebellar disease (SPS-Cer), the mean ratio of anti-GAD CSF/ serum was 0.03 (range, 0.007–0.057) and the mean ratio of CSF/ serum IgG was 0.002 (range, 0.001–0.005), indicating a 10-fold increase of intrathecal antibody production, 2.5-fold higher compared to typical SPS [26], suggesting an enhanced B-cell activation within the CNS, consistent with the more extensive neurological phenotype.