[Current Perspective on Voltage-gated Potassium Channel Complex Antibody Associated Diseases]

Area of Science:

• Neuroimmunology
• Channelopathies
• Autoimmune Encephalitis

Background:

• Voltage-gated potassium channel (VGKC) complex autoantibodies were first identified in Isaacs' syndrome (IS), characterized by muscle cramps and neuromyotonia.
• These antibodies are also found in Morvan's syndrome (MoS) and limbic encephalopathy (LE), presenting with a spectrum of neurological and psychiatric symptoms including seizures and amnesia.
• Autoantibodies targeting LGI1 and Caspr2 are common in IS, MoS, and LE, but double-negative VGKC antibodies are detected in other conditions.

Purpose of the Study:

• To re-evaluate the classification and pathogenic potential of VGKC complex autoantibodies, particularly double-negative variants.
• To explore the novel mechanisms by which these antibodies disrupt physiological functions of target proteins.
• To understand the implications of LGI1 antibody-mediated disruption of LGI1-ADAM22 interaction on synaptic AMPA receptors and neuronal excitability.

Main Methods:

• Analysis of patient cohorts with VGKC complex autoantibodies, including those with LGI1/Caspr2 reactivity and double-negative cases.
• Immunological assays to characterize antibody targets, including extracellular and cytosolic epitopes.
• Functional studies investigating the impact of autoantibodies on protein interactions and receptor function.

Main Results:

• Double-negative VGKC complex antibodies, often targeting cytosolic epitopes, are found in diseases beyond IS, MoS, and LE, such as Creutzfeldt-Jakob disease and ALS.
• These antibodies should no longer be exclusively classified as neuronal-surface antibodies lacking pathogenic potential.
• LGI1 antibodies neutralize LGI1-ADAM22 interaction, reducing synaptic AMPA receptors and potentially causing amnesia and seizures, possibly via effects on inhibitory neurons.

Conclusions:

• VGKC complex autoantibodies, including double-negative types, possess pathogenic potential and require reclassification.
• The disruption of protein interactions, such as LGI1-ADAM22, represents a key mechanism of antibody-induced neurological dysfunction.
• Further research into the precise targets and mechanisms of these antibodies is crucial for understanding and treating associated autoimmune neurological disorders.