There is general agreement that auto-
antibodies against
ion channels and synaptic machinery
proteins can induce
limbic encephalitis. In immune-mediated
cerebellar ataxias (IMCAs), various synaptic
proteins, such as GAD65, voltage-gated Ca channel (VGCC),
metabotropic glutamate receptor type 1 (
mGluR1), and
glutamate receptor delta (GluR delta) are auto-immune targets. Among them, the pathophysiological mechanisms underlying anti-VGCC, anti-mGluR1, and anti-GluR delta
antibodies remain unclear. Despite divergent auto-immune and clinical profiles, these subtypes show common clinical features of good prognosis with no or mild cerebellar
atrophy in non-
paraneoplastic syndrome. The favorable prognosis reflects functional
cerebellar disorders without neuronal death. Interestingly, these
autoantigens are all involved in molecular cascades for induction of long-term depression (LTD) of synaptic transmissions between parallel fibers (PFs) and Purkinje cells (PCs), a crucial mechanism of synaptic plasticity in the cerebellum. We suggest that anti-VGCC, anti-mGluR1, and anti-GluR delta Abs-associated
cerebellar ataxias share one common pathophysiological mechanism: a deregulation in PF-PC LTD, which results in impairment of restoration or maintenance of the internal model and triggers
cerebellar ataxias. The novel concept of LTDpathies could lead to improvements in clinical management and treatment of cerebellar patients who show these
antibodies.