Neuronal surface autoantibodies at cerebellar and brainstem synapses: mechanisms, phenotypes, and translational gaps.

Pathogenic neuronal-surface autoantibodies can disrupt extracellular receptors, ion-channel complexes, and synaptic proteins, yet their regional neurological phenotypes differ substantially. This variability is particularly informative in the cerebellum and brainstem, where precisely timed excitatory and inhibitory signaling supports motor coordination, ocular-motor control, autonomic regulation, arousal, and respiration. In this Mini Review, we examine how antibody effector mechanisms, regional antigen distribution, and local synaptic physiology interact to shape cerebellar and brainstem manifestations of neuronal-surface-antibody disease. Autoimmunity against metabotropic glutamate receptor 1 (mGluR1) provides a model of cerebellar synaptic dysfunction because mGluR1 is strongly linked to Purkinje-cell signaling and synaptic plasticity, whereas glycine receptor (GlyR) autoimmunity illustrates how impaired inhibitory transmission can destabilize brainstem and spinal networks. NMDAR, AMPAR, GABA_A receptor, GABA_B receptor, LGI1, and CASPR2 autoimmunity provide mechanistic comparators showing that extracellular antigen accessibility alone does not determine neurological phenotype. Direct antibody-mediated synaptic dysfunction may be reversible, but persistent structural injury occurs in a subset of patients; current evidence does not determine whether such injury is attributable to sustained antibody exposure, accompanying T-cell inflammation, or both. Evidence from acute physiological experiments, individual follow-up cases, and heterogeneous cohorts comes from different settings and does not establish a uniform progression from synaptic dysfunction to atrophy.