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Combined pre- and postsynaptic action of IgG antibodies in Miller Fisher syndrome

From the Neurologische Klinik der Bayerischen Julius–Maximilians–Universität Würzburg, Germany; Neurologische Klinik der Technischen Universität München (Drs. Bufler and Pitz), Germany; "Giorgio Spagnol" Laboratory of Clinical Neuroimmunology (Drs. Carpo and Nobile–Orazio), Institute of Clinical Neurology, Centro Dino Ferrari, University of Milan, Italy; Neurologische Klinik der Medizinischen Hochschule Hannover (Dr. Heidenreich), Germany; and Physiologisches Institut der Technischen Universität München (Dr. Dudel), Germany.

Address correspondence and reprint requests to Dr. Brigitte Buchwald, Neurologische Klinik der Universität Würzburg, Josef-Schneider-Strasse 11, D-97080 Würzburg, Germany; e-mail: brigitte.buchwald{at}mail.uni-wuerzburg.de

BACKGROUND: Miller Fisher syndrome (MFS), a variant of the Guillain-Barré syndrome, is associated with the presence of neuromuscular blocking antibodies, some of which may be directed at the ganglioside GQ1b.

MATERIALS AND METHODS: The authors investigated the in vitro effects of serum and purified immunoglobulin (Ig) G in a total of 11 patients with typical MFS during active disease, and in three of those patients after recovery. From one patient’s serum, we prepared an IgG fraction enriched in anti-GQ1b antibodies by affinity chromatography. For combined pre- and postsynaptic analysis, endplate currents were recorded by a perfused macro-patch clamp electrode. Postsynaptic nicotinic acetylcholine receptor channels were investigated by an outside-out patch clamp technique in cultured mouse myotubes.

RESULTS: AllMFS-sera depressed evoked quantal release and reduced the amplitude of postsynaptic currents. Five of the 11 sera were additionally examined by outside-out patch clamp analysis and caused a concentration-dependent and reversible decrease in acetylcholine-induced currents. The time course of activation and desensitization of nicotinic acetylcholine receptor channels was not altered by MFS-IgG. Nine patients (82 %) were positive for anti-GQ1b antibodies in ELISA and dot–blot. The enriched anti-GQ1b antibody fraction had a similar effect as whole serum. After recovery from MFS, blocking activity was lost and sera originally positive for anti-GQ1b antibodies became negative.

CONCLUSION: Circulating IgG antibodies induce both pre- and postsynaptic blockade and may play a pathogenic role in acute MFS.

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