A comprehensive analysis of the epidemiology and clinical characteristics of anti-LRP4 in myasthenia gravis

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Anti-Aquaporin-1 Autoantibodies in Patients with Neuromyelitis Optica Spectrum Disorders

Autoantibodies against aquaporin-4 (AQP4), a water channel in CNS astrocytes, are detected in ∼50-80% of patients with neuromyelitis optica spectrum disorders (NMOsd), characterized by longitudinally extensive transverse myelitis (LETM) and/or optic neuritis. Although these autoantibodies present an invaluable biomarker for NMOsd and for the differential diagnosis of multiple sclerosis (MS), diagnosis of anti-AQP4-seronegative NMOsd remains challenging. We hypothesized that seronegative NMOsd patients might have autoantibodies against aquaporin-1 (AQP1), another water channel in CNS astrocytes. We initially developed a radioimmunoprecipitation assay to search for anti-AQP1 antibodies in sera from 632 individuals. Anti-AQP1 or anti-AQP4 autoantibodies were detected in 16.7% and 12%, respectively, of 348 patients with suspected NMOsd. Anti-AQP1 specificity was confirmed by competition, protein immunoblotting and ELISA assays, whereas epitope localization was studied by immunoadsorption on intact cells expressing AQP1 and peptide mapping experiments. Most anti-AQP1 autoantibodies were of the complement-activating IgG1 subclass and the majority bound to the extracellular domain of AQP1, suggesting a possible pathogenic role. Five out of 42 MS patients had anti-AQP1 antibodies, but 2 of them also had spinal cord lesions, while the anti-AQP1 antibodies in the other 3 bound to the cytoplasmic domain of AQP1. Anti-AQP1 antibodies were not detected in 100 healthy individuals or 142 patients with non-demyelinating neuroimmune diseases. Analysis of 17 anti-AQP1+/anti-AQP4- patients with suspected NMOsd showed that 5 had NMO and 11 had LETM. 12/17 of these sera bound predominantly to the extracellular AQP1 loop-Α. Overall, we found that anti-AQP1 autoantibodies are present in a subgroup of patients with chronic demyelination in the CNS and similarities with anti-AQP4-seronegative NMOsd, offering a novel potential biomarker for CNS demyelination disorders. © 2013 Tzartos et al

Double seronegative myasthenia gravis with low density lipoprotein-4 (LRP4) antibodies presenting with isolated ocular symptoms

The detection of low density lipoprotein-4 (LRP4) antibodies in double seronegative (dSN) myasthenia gravis (MG) patients has provided new insights in the diagnosis and treatment of MG. However, there are limited data regarding the clinical presentation and treatment response in dSN MG patients with LRP4-antibodies. We present a case series of three Caucasian dSN MG patients with positive LRP4-antibodies sharing a common ethnic background that presented with isolated ocular symptoms (MGFA I). The demographic and clinical characteristics, the diagnostic work-up as well as the treatment response during a follow-up period of 12-24 months are described in detail. All patients were treated successfully with acetylcholinesterase inhibitors (AcheI) and prednisone with two exhibiting full remission of their symptoms, while the remaining exhibited mild residual diplopia. Notably, we documented no signs of generalized disease progression, while no patient required immunosuppressive treatment. In conclusion, the distinct clinical phenotype of our patients highlights the clinical relevance of screening for LRP4-antibodies in patients presenting with isolated ocular MG independent of age and gender, since it may lead to the timely diagnosis of MG and prompt initiation of effective therapy with ACheI and corticosteroids. © 2014 Elsevier B.V. All rights reserved

MuSK-Ab positive myasthenia: Not always grave

Antibodies (Abs) to muscle-specific tyrosine kinase (MuSK) are detected in approximately 40% of generalized acetylcholine receptor antibody-negative myasthenia gravis (MG). Anti-MuSK Abs are nearly always associated with generalized symptoms, with prevalent involvement of craniobulbar, cervical and respiratory muscles and with a striking preponderance in women. The typical course of MuSK-MG is acute onset, rapid progression, brittle course in the first years, early respiratory crises and unprovoked relapses in spite of high-dose immunosuppression. Patients often require long-term management with multiple immunosuppressive (IS) agents and many of them remain dependent on IS treatment. The majority of anti-MuSK Abs are of the non-complement-binding IgG4 subclass. We report the case of a Greek female MuSK-MG patient with typical phenotype but clearly atypical clinical course during 12 years of follow-up. The patient received only corticosteroid treatment for one year and showed mild and stable MG symptoms under no treatment for the rest of the observation period, except for postpartum mild and short-lived exacerbation. In mildly symptomatic stable state, anti-MuSK Abs were of the IgG4 subclass and no other immunological peculiarity was detected. © 2013 Published by Elsevier B.V

Crystal structure of a human neuronal nAChR extracellular domain in pentameric assembly: Ligand-bound α2 homopentamer

In this study we report the X-ray crystal structure of the extracellular domain (ECD) of the human neuronal α2 nicotinic acetylcholine receptor (nAChR) subunit in complex with the agonist epibatidine at 3.2 Å. Interestingly, α2 was crystallized as a pentamer, revealing the intersubunit interactions in a wild type neuronal nAChR ECD and the full ligand binding pocket conferred by two adjacent α subunits. The pentameric assembly presents the conserved structural scaffold observed in homologous proteins, as well as distinctive features, providing unique structural information of the binding site between principal and complementary faces. Structure-guided mutagenesis and electrophysiological data confirmed the presence of the α2(+)/α2(-) binding site on the heteromeric low sensitivity α2β2 nAChR and validated the functional importance of specific residues in α2 and β2 nAChR subunits. Given the pathological importance of the α2 nAChR subunit and the high sequence identity with α4 (78%) and other neuronal nAChR subunits, our findings offer valuable information for modeling several nAChRs and ultimately for structure-based design of subtype specific drugs against the nAChR associated diseases. © 2016, National Academy of Sciences. All rights reserved

AChR-myasthenia gravis switching to double-seropositive several years after the onset

We report an early onset AChR-myasthenia gravis (MG) with biphasic clinical course. The clinical "switch" from AChR-MG to MuSK-MG emerged 16 years after the onset and 11 years after thymectomy. MuSK antibodies were detected only by cell-based assay and only upon clinical "switch", while AChR antibodies remained positive and at high titers during the whole disease course. Although the occurrence of AChR antibodies and MuSK antibodies in the same individual is rare, the re-assessment of the antibody status, using all available assays, is advisable when there is clinical indication. © 2013 Elsevier B.V