AP3B2 is a neuronal subunit of the adaptor protein complex 3 (AP-3), a vesicle coat protein involved in protein trafficking and synaptic function. As a component of AP-3, AP3B2 mediates cargo recognition and clathrin recruitment at the trans-Golgi network and endosomes, playing a role in sorting transmembrane proteins destined for lysosomes and lysosome-related organelles 1. The protein is specifically expressed in central nervous system neurons with elevated levels in brain tissue 2, and functions in anterograde synaptic vesicle transport and establishment of synaptic vesicle localization 3. Clinically, AP3B2 is associated with autoimmune cerebellar ataxia when targeted by autoantibodies (anti-AP3B2 IgG) 4. Affected patients typically present with subacute-onset gait disturbance, sensory ataxia, paresthesia, and myeloneuropathy 1. AP3B2 antibodies bind prominently to Purkinje cells, granular layer synapses, and spinal cord gray matter 4. Additionally, AP3B2 mutations cause developmental and epileptic encephalopathy 48 5, and upregulation of AP3B2 expression has been documented in paraneoplastic Lambert-Eaton myasthenic syndrome, suggesting involvement in autoimmune neuromuscular pathology 3. Immunotherapy may stabilize disease progression in autoimmune AP3B2-associated disorders 1.