Antibodies to Kv1 potassium channel-complex proteins leucine-rich, glioma inactivated 1 protein and contactin-associated protein-2 in limbic encephalitis, Morvan's syndrome and acquired neuromyotonia.
Antibodies that immunoprecipitate (125)I-alpha-dendrotoxin-labelled voltage-gated potassium channels extracted from mammalian brain tissue have been identified in patients with neuromyotonia, Morvan's syndrome, limbic encephalitis and a few cases of adult-onset epilepsy. These conditions often improve following immunomodulatory therapies. However, the proportions of the different syndromes, the numbers with associated tumours and the relationships with potassium channel subunit antibody specificities have been unclear. We documented the clinical phenotype and tumour associations in 96 potassium channel antibody positive patients (titres >400 pM). Five had thymomas and one had an endometrial adenocarcinoma. To define the antibody specificities, we looked for binding of serum antibodies and their effects on potassium channel currents using human embryonic kidney cells expressing the potassium channel subunits. Surprisingly, only three of the patients had antibodies directed against the potassium channel subunits. By contrast, we found antibodies to three proteins that are complexed with (125)I-alpha-dendrotoxin-labelled potassium channels in brain extracts: (i) contactin-associated protein-2 that is localized at the juxtaparanodes in myelinated axons; (ii) leucine-rich, glioma inactivated 1 protein that is most strongly expressed in the hippocampus; and (iii) Tag-1/contactin-2 that associates with contactin-associated protein-2. Antibodies to Kv1 subunits were found in three sera, to contactin-associated protein-2 in 19 sera, to leucine-rich, glioma inactivated 1 protein in 55 sera and to contactin-2 in five sera, four of which were also positive for the other antibodies. The remaining 18 sera were negative for potassium channel subunits and associated proteins by the methods employed. Of the 19 patients with contactin-associated protein-antibody-2, 10 had neuromyotonia or Morvan's syndrome, compared with only 3 of the 55 leucine-rich, glioma inactivated 1 protein-antibody positive patients (P < 0.0001), who predominantly had limbic encephalitis. The responses to immunomodulatory therapies, defined by changes in modified Rankin scores, were good except in the patients with tumours, who all had contactin-associated-2 protein antibodies. This study confirms that the majority of patients with high potassium channel antibodies have limbic encephalitis without tumours. The identification of leucine-rich, glioma inactivated 1 protein and contactin-associated protein-2 as the major targets of potassium channel antibodies, and their associations with different clinical features, begins to explain the diversity of these syndromes; furthermore, detection of contactin-associated protein-2 antibodies should help identify the risk of an underlying tumour and a poor prognosis in future patients.
Irani
Sarosh R
SR
Neurosciences Group, Department of Clinical Neurology, University of Oxford, John Radcliffe Hospital, Oxford, UK.
Alexander
Sian
S
Waters
Patrick
P
Kleopa
Kleopas A
KA
Pettingill
Philippa
P
Zuliani
Luigi
L
Peles
Elior
E
Buckley
Camilla
C
Lang
Bethan
B
Vincent
Angela
A
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000906:Antibodies / Q000097:blood* / Q000494:pharmacology; D000918:Antibody Specificity / Q000276:immunology; D002461:Cell Line, Transformed; D004546:Elapid Venoms / Q000493:pharmacokinetics; D005260:Female; D005786:Gene Expression Regulation / Q000235:genetics; D049452:Green Fluorescent Proteins / Q000235:genetics; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D047468:Immunoprecipitation / Q000379:methods; D007167:Immunotherapy / Q000379:methods; D047908:Intracellular Signaling Peptides and Proteins; D007456:Iodine Isotopes / Q000493:pharmacokinetics; D020386:Isaacs Syndrome / Q000097:blood* / Q000188:drug therapy / Q000276:immunology; D020363:Limbic Encephalitis / Q000097:blood* / Q000188:drug therapy / Q000276:immunology / Q000473:pathology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000235:genetics; D008565:Membrane Proteins / Q000276:immunology*; D008875:Middle Aged; D009419:Nerve Tissue Proteins / Q000276:immunology*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D018408:Patch-Clamp Techniques / Q000379:methods; D011485:Protein Binding / Q000187:drug effects / Q000502:physiology; D011506:Proteins; D012720:Severity of Illness Index; D051637:Shaker Superfamily of Potassium Channels / Q000276:immunology*; D013595:Syringomyelia / Q000097:blood* / Q000188:drug therapy / Q000276:immunology; D014162:Transfection / Q000379:methods; D016896:Treatment Outcome; D055815:Young Adult
D000906:Antibodies; C403049:CNTNAP2 protein, human; D004546:Elapid Venoms; D047908:Intracellular Signaling Peptides and Proteins; D007456:Iodine Isotopes; C116499:LGI1 protein, human; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D011506:Proteins; D051637:Shaker Superfamily of Potassium Channels; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins; C020273:dendrotoxin