Diagnostic Tests

CLINICAL ASSOCIATIONS

Mitogen’s VGKC assay is an autoimmune diagnostic test that detects autoantibodies to contactin-associated protein 2 (CASPR2) & leucine-rich glioma-inactivated protein 1 (LGI1). CASPR2 (Contactin-associated protein 2 or CNTNAP2) is a protein that is encoded by one of the largest genes in the human genome. It is found in nerve cells between paranodes and internodes (juxtaparanodes). CASPR2 is associated with potassium channels and it functions in the nervous system as cell adhesion molecules and receptors. Autoantibodies to CASPR2 are associated with encephalitis, peripheral nerve hyperexcitability and in some patients with neuromyotonia. Clinical symptoms tend to be more diverse than those associated with classical limbic encephalitis due to the frequent co-occurrence of other autoantibodies.

LGI1 (Leucine-rich, glioma inactivated 1) is a transmembrane protein that contains leucine-rich repeats. LGI1 is predominantly expressed and translated in neural tissues / nerve cells in the brain. Decreased levels of LGI1 is found in brain tumors and malignant gliomas and has connections to epilepsy. In autoimmunity, when LGI1 is targeted by autoantibodies it results in the immunoprecipitation of voltage-gated potassium channel complexes from brain tissue. LGI1 antibodies are found in patients with limbic encephalitis and faciobrachial dystonic seizure (FBDS). FBDS is a subtle form of epilepsy which manifests as frequent seizures involving the arm and face for short durations. FBDS patients have better outcomes when treated with immunotherapy as opposed to anti-epileptic drugs.

LGI1 autoantibodies are a feature of some patients with limbic encephalopathy where some patients may present with rapidly progressive dementia and/or myoclonic-like movements that resembles Creutzfeldt-Jakob disease.

References:
HE Peery et al.. Autoimmun Rev. 11: 863, 2012.
“Entrez Gene: LGI1 leucine-rich, glioma inactivated 1”