GAD1 and paraneoplastic cerebellar degeneration: Depending on the etiopathology, the clinical presentation, and the expression of autoantibodies, ACA can be divided into the following subtypes: primary ACA (PACA), paraneoplastic cerebellar degeneration (PCD), autoimmune encephalitis-associated ACA, anti-glutamate decarboxylase (GAD)-associated cerebellar ataxia, opsoclonus–myoclonus syndrome (OMS), and Miller Fisher syndrome (MFS).