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1.  Aquaporin-4 autoantibodies in neuromyelitis optica spectrum disorders: comparison between tissue-based and cell-based indirect immunofluorescence assays 
Background
Neuromyelitis optica spectrum disorders (NMOSD) are severe central nervous system inflammatory demyelinating disorders (CNS IDD) characterized by monophasic or relapsing, longitudinally extensive transverse myelitis (LETM) and/or optic neuritis (ON). A significant proportion of NMOSD patients are seropositive for aquaporin-4 (AQP4) autoantibodies. We compared the AQP4 autoantibody detection rates of tissue-based indirect immunofluorescence assay (IIFA) and cell-based IIFA.
Methods
Serum of Chinese CNS IDD patients were assayed for AQP4 autoantibodies by tissue-based IIFA using monkey cerebellum and cell-based IIFA using transfected HEK293 cells which express human AQP4 on their cell membranes.
Results
In total, 128 CNS IDD patients were studied. We found that 78% of NMO patients were seropositive for AQP4 autoantibodies by cell-based IIFA versus 61% by tissue-based IFA (p = 0.250), 75% of patients having relapsing myelitis (RM) with LETM were seropositive by cell-based IIFA versus 50% by tissue-based IIFA (p = 0.250), and 33% of relapsing ON patients were seropositive by cell-based IIFA versus 22% by tissue-based IIFA (p = 1.000); however the differences were not statistically significant. All patients seropositive by tissue-based IIFA were also seropositive for AQP4 autoantibodies by cell-based IIFA. Among 29 NMOSD patients seropositive for AQP4 autoantibodies by cell-based IIFA, 20 (69%) were seropositive by tissue-based IIFA. The 9 patients seropositive by cell-based IIFA while seronegative by tissue-based IIFA had NMO (3), RM with LETM (3), a single attack of LETM (1), relapsing ON (1) and a single ON attack (1). Among 23 NMO or RM patients seropositive for AQP4 autoantibodies by cell-based IIFA, comparison between those seropositive (n = 17) and seronegative (n = 6) by tissue-based IIFA revealed no differences in clinical and neuroradiological characteristics between the two groups.
Conclusion
Cell-based IIFA is slightly more sensitive than tissue-based IIFA in detection of AQP4 autoantibodies, which are highly specific for NMOSD.
doi:10.1186/1742-2094-7-50
PMCID: PMC2941752  PMID: 20822515
2.  Cerebrospinal fluid antibodies to aquaporin-4 in neuromyelitis optica and related disorders: frequency, origin, and diagnostic relevance 
Background
In 70-80% of cases, neuromyelitis optica (NMO) is associated with highly specific serum auto-antibodies to aquaporin-4 (termed AQP4-Ab or NMO-IgG). Recent evidence strongly suggests that AQP4-Ab are directly involved in the immunopathogenesis of NMO.
Objective
To assess the frequency, syndrome specificity, diagnostic relevance, and origin of cerebrospinal fluid (CSF) AQP4-Ab in patients with NMO spectrum disorders (NMOSD).
Methods
87 CSF samples from 37 patients with NMOSD and 42 controls with other neurological diseases were tested for AQP4-Ab in a cell based assay using recombinant human AQP4. Twenty-three paired CSF and serum samples from AQP4-Ab seropositive NMOSD patients were further analysed for intrathecal IgG synthesis to AQP4.
Results
AQP4-Ab were detectable in 68% of CSF samples from AQP4-Ab seropositive patients with NMOSD, but in none of the CSF samples from AQP4-Ab seronegative patients with NMOSD and in none of the control samples. Acute disease relapse within 30 days prior to lumbar puncture, AQP4-Ab serum titres >1:250, and blood-CSF barrier dysfunction, but not treatment status, predicted CSF AQP4-Ab positivity. A positive AQP4-specific antibody index was present in 1/23 samples analysed.
Conclusions
AQP4-Ab are detectable in the CSF of most patients with NMOSD, mainly during relapse, and are highly specific for this condition. In the cohort analysed in this study, testing for CSF AQP4-Ab did not improve the sensitivity and specificity of the current diagnostic criteria for NMO. The substantial lack of intrathecal AQP4-Ab synthesis in patients with NMOSD may reflect the unique localisation of the target antigen at the blood brain barrier, and is important for our understanding of the immunopathogenesis of the disease.
doi:10.1186/1742-2094-7-52
PMCID: PMC2945323  PMID: 20825655
3.  Antibody to Aquaporin 4 in the Diagnosis of Neuromyelitis Optica 
PLoS Medicine  2007;4(4):e133.
Background
Neuromyelitis optica (NMO) is a demyelinating disease of the central nervous system (CNS) of putative autoimmune aetiology. Early discrimination between multiple sclerosis (MS) and NMO is important, as optimum treatment for both diseases may differ considerably. Recently, using indirect immunofluorescence analysis, a new serum autoantibody (NMO-IgG) has been detected in NMO patients. The binding sites of this autoantibody were reported to colocalize with aquaporin 4 (AQP4) water channels. Thus we hypothesized that AQP4 antibodies in fact characterize NMO patients.
Methods and Findings
Based on these observations we cloned human water channel AQP4, expressed the protein in a eukaryotic transcription/translation system, and employed the recombinant AQP4 to establish a new radioimmunoprecipitation assay (RIPA). Indeed, application of this RIPA showed that antibodies against AQP4 exist in the majority of patients with NMO (n = 37; 21 positive) as well as in patients with isolated longitudinally extensive transverse myelitis (n = 6; six positive), corresponding to a sensitivity of 62.8% and a specificity of 98.3%. By contrast, AQP4 antibodies were virtually absent in 291 other participants, which included patients with MS (n = 144; four positive), patients with other inflammatory and noninflammatory neurological diseases (n = 73; one positive), patients with systemic autoimmune diseases (n = 45; 0 positive), and healthy participants (n = 29; 0 positive).
Conclusions
In the largest series reported so far to our knowledge, we quantified AQP4 antibodies in patients with NMO versus various other diseases, and showed that the aquaporin 4 water channel is a target antigen in a majority of patients with NMO. The newly developed assay represents a highly specific, observer-independent, and easily reproducible detection method facilitating clinically relevant discrimination between NMO, MS, and other inflammatory diseases.
A newly developed method to detect antibodies to the aquaporin 4 water channel can help discriminate between neuromyelitis optica, multiple sclerosis, and other inflammatory diseases.
Editors' Summary
Background.
Neuromyelitis optica (NMO or Devic syndrome) is a rare disease in which the immune system destroys the myelin (fatty material that insulates nerve fibers so that the body and the brain can communicate using electrical messages) in the optic nerve and spinal cord. Myelin destruction (demyelination) in these parts of the central nervous system (CNS) causes pain and swelling (inflammation) of the optic nerve (optic neuritis) and spinal cord (myelitis). The resultant disruption of communication along these nerves means that patients with NMO experience temporary or permanent blindness in one or both eyes that is preceded or followed by limb weakness or paralysis and loss of bladder and bowel control. These two sets of symptoms can occur many months apart and may happen once during a person's lifetime or recur at intervals. There is no cure for NMO, but corticosteroids or plasmapheresis reduce inflammation during acute attacks and, because NMO is an autoimmune disease (one in which the immune system attacks the body's own tissues instead of foreign organisms), long-term immunosuppression may prevent further attacks.
Why Was This Study Done?
There are many inflammatory/demyelinating diseases of the CNS with clinical symptoms similar to those of NMO. It is particularly hard to distinguish between NMO and multiple sclerosis, an autoimmune disease that involves widespread demyelination. Neurologists need to make a correct diagnosis before starting any treatment and usually use clinical examination and magnetic resonance imaging (to detect sites of inflammation) to help them in this task. Recently, however, a biomarker for NMO was identified. Many patients with NMO make autoantibodies (proteins that recognize a component of a person's own tissues) called NMO-IgGs. These recognize aquaporin 4 (AQP4), a protein that allows water to move through cell membranes. It is not known how often patients with NMO or other demyelinating diseases make antibodies to AQP4, so it is unclear whether testing for these antibodies would help in the diagnosis of NMO. In this study, the researchers have developed a new assay for antibodies to AQP4 and then quantified the antibodies in patients with NMO and other demyelinating diseases.
What Did the Researchers Do and Find?
The researchers made radioactively labeled AQP4 in a test tube, then incubated samples of this with serum (the liquid portion of blood), added small beads coated with protein A (a bacterial protein that binds to antibodies) and allowed the beads to settle. The amount of radioactivity attached to the beads indicates the amount of antibody to AQP4 in the original serum. The researchers used this radioimmunoprecipitation assay to measure antibodies to AQP4 in sera from 37 patients with NMO and from six with another neurological condition, longitudinally extensive transverse myelitis (LETM), which is characterized by large demyelinated lesions across the width of the spinal cord but no optic neuritis; these patients often develop NMO. They also measured antibodies to AQP4 in the sera of nearly 300 other people including patients with multiple sclerosis, other neurological conditions, various autoimmune diseases, and healthy individuals. Nearly two-thirds of the patients with NMO and all those with LETM made antibodies against AQP4; very few of the other study participants made these antibodies. In particular, only four of the 144 patients with multiple sclerosis made AQP4 antibodies.
What Do These Findings Mean?
These findings indicate that testing for antibodies to AQP4 could help neurologists distinguish between NMO and multiple sclerosis and between NMO and other demyelinating diseases of the CNS. In addition, the new radioimmunoprecipitation assay provides a standardized, high-throughput way to quantitatively test for these antibodies, whereas the indirect immune fluorescence assay for measurement of unspecific NMO-IgG is observer-dependent and nonquantitative. Although these findings need to be confirmed in more patients and the assay's reliability demonstrated in different settings, the measurement of antibodies to AQP4 by radioimmunoprecipitation may become a standard part of the differential diagnosis of NMO. Additional research will determine whether AQP4 is the only protein targeted by autoantibodies in NMO and whether this targeting is a critical part of the disease process.
Additional Information.
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.0040133.
US National Institute of Neurological Disorders and Stroke has information for patients who have neuromyelitis optica, transverse myelitis, and multiple sclerosis
The Transverse Myelitis Association offers information and useful links for patients and their carers about transverse myelitis and neuromyelitis optica (in several languages, including English and Spanish)
Mayo Clinic information for patients on Devic's syndrome
Medline Plus encyclopedia pages discuss autoimmune disorders (in English and Spanish)
A brief overview of aquaporins is available from the University of Miami
The American MS Society has information on MS
doi:10.1371/journal.pmed.0040133
PMCID: PMC1852124  PMID: 17439296
4.  Anti-Aquaporin-1 Autoantibodies in Patients with Neuromyelitis Optica Spectrum Disorders 
PLoS ONE  2013;8(9):e74773.
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.
doi:10.1371/journal.pone.0074773
PMCID: PMC3781161  PMID: 24086369
5.  Distinction between MOG antibody-positive and AQP4 antibody-positive NMO spectrum disorders 
Neurology  2014;82(6):474-481.
Objective:
To evaluate clinical features among patients with neuromyelitis optica spectrum disorders (NMOSD) who have myelin oligodendrocyte glycoprotein (MOG) antibodies, aquaporin-4 (AQP4) antibodies, or seronegativity for both antibodies.
Methods:
Sera from patients diagnosed with NMOSD in 1 of 3 centers (2 sites in Brazil and 1 site in Japan) were tested for MOG and AQP4 antibodies using cell-based assays with live transfected cells.
Results:
Among the 215 patients with NMOSD, 7.4% (16/215) were positive for MOG antibodies and 64.7% (139/215) were positive for AQP4 antibodies. No patients were positive for both antibodies. Patients with MOG antibodies represented 21.1% (16/76) of the patients negative for AQP4 antibodies. Compared with patients with AQP4 antibodies or patients who were seronegative, patients with MOG antibodies were more frequently male, had a more restricted phenotype (optic nerve more than spinal cord), more frequently had bilateral simultaneous optic neuritis, more often had a single attack, had spinal cord lesions distributed in the lower portion of the spinal cord, and usually demonstrated better functional recovery after an attack.
Conclusions:
Patients with NMOSD with MOG antibodies have distinct clinical features, fewer attacks, and better recovery than patients with AQP4 antibodies or patients seronegative for both antibodies.
doi:10.1212/WNL.0000000000000101
PMCID: PMC3937859  PMID: 24415568
6.  Intractable Nausea and Vomiting from Autoantibodies Against a Brain Water Channel 
Background & Aims
Antibodies against the water channel protein aquaporin (AQP)-4 cause a spectrum of inflammatory, demyelinating, central nervous system disorders called neuromyelitis optica spectrum disorders (NMOSDs); these primarily affect the optic nerves and spinal cord, but also the brain. Symptoms of intractable nausea, vomiting and hiccups reflect involvement of AQP4 in the brainstem area postrema and account for gastroenterologic presentations. We investigated the frequency of intractable nausea, vomiting, or hiccups in patients with NMOSD who tested positive for immunoglobulin-G against AQP4 (AQP4-IgG). We also analyzed sera from patients with idiopathic nausea or vomiting for the presence of AQP4-IgG.
Methods
We reviewed the Mayo Clinic AQP4-IgG positive NMOSD database (n=70) to identify patients who presented with vomiting, focusing on results from gastroenterologic evaluations. We also tested serum samples (from the Gastroparesis Clinical Research Consortium repository) from patients who presented with idiopathic nausea or vomiting for AQP4-IgG (controls n=318 with gastroparesis and 117 without gastroparesis).
Results
Ten AQP4-IgG-positive patients diagnosed with NMOSD (14% of patients in the database) initially presented with intractable vomiting. Extensive gastroenterological evaluation was non-informative. AQP4-IgG was not detected in any of the controls.
Conclusions
Though NMOSDs are rare, tests for AQP4-IgG should be considered for patients that present with unexplained, intractable vomiting. Detection of the antibody before the development of optic neuritis or transverse myelitis allows patients to receive immunosuppressive therapy before the development of neurologic disabilities.
doi:10.1016/j.cgh.2012.11.021
PMCID: PMC3581743  PMID: 23211959
diagnosis; chronic nausea and vomiting; central nervous system; aquaporin-4 antibody
7.  Serologic diagnosis of NMO 
Neurology  2012;78(9):665-671.
Objectives:
Neuromyelitis optica (NMO) immunoglobulin G (IgG) (aquaporin-4 [AQP4] IgG) is highly specific for NMO and related disorders, and autoantibody detection has become an essential investigation in patients with demyelinating disease. However, although different techniques are now used, no multicenter comparisons have been performed. This study compares the sensitivity and specificity of different assays, including an in-house flow cytometric assay and 2 commercial assays (ELISA and transfected cell-based assay [CBA]).
Methods:
Six assay methods (in-house or commercial) were performed in 2 international centers using coded serum from patients with NMO (35 patients), NMO spectrum disorders (25 patients), relapsing-remitting multiple sclerosis (39 patients), miscellaneous autoimmune diseases (25 patients), and healthy subjects (22 subjects).
Results:
The highest sensitivities were yielded by assays detecting IgG binding to cells expressing recombinant AQP4 with quantitative flow cytometry (77; 46 of 60) or visual observation (CBA, 73%; 44 of 60). The fluorescence immunoprecipitation assay and tissue-based immunofluorescence assay were least sensitive (48%–53%). The CBA and ELISA commercial assays (100% specific) yielded sensitivities of 68% (41 of 60) and 60% (36 of 60), respectively, and sensitivity of 72% (43 of 60) when used in combination.
Conclusions:
The greater sensitivity and excellent specificity of second-generation recombinant antigen-based assays for detection of NMO-IgG in a clinical setting should enable earlier diagnosis of NMO spectrum disorders and prompt initiation of disease-appropriate therapies.
doi:10.1212/WNL.0b013e318248dec1
PMCID: PMC3286228  PMID: 22302543
8.  Clinical Efficacy of Plasmapheresis in Patients with Neuromyelitis Optica Spectrum Disorder and Effects on Circulating Anti-Aquaporin-4 Antibody Levels 
Background and Purpose
Although plasmapheresis is becoming standard practice as a rescue therapy for neuromyelitis optica (NMO), evidence for the therapeutic efficacy of plasmapheresis is limited, and the effect of plasmapheresis on anti-aquaporin-4 (AQP4) levels in patients with NMO has not been reported. Here, our objective was to evaluate the clinical efficacy of therapeutic plasmapheresis and its effect on anti-AQP4 antibody levels in patients with NMO spectrum disorder (NMOSD).
Methods
We retrospectively reviewed the medical records of 15 patients with NMOSD who had 18 acute attacks and received plasmapheresis because they did not respond to high-dose intravenous methylprednisolone (IVMP) therapy. Anti-AQP4 antibodies were measured before and after plasmapheresis. The primary outcomes were functional improvements immediately and 6 months after plasmapheresis, and the secondary outcome was the change in anti-AQP4 antibody serum levels following plasmapheresis.
Results
Plasmapheresis following IVMP therapy led to significant improvement in 50% of the 18 attacks in 15 patients immediately after the procedure was completed, and in 78% (14 attacks) after 6 months. Plasmapheresis was generally well tolerated in all patients. Anti-AQP4 antibody serum levels declined significantly following plasmapheresis, to a mean of 15% of the preplasmapheresis levels. Lower scores on the visual outcome scale recorded before an attack were associated with significant immediate improvement upon the completion of plasmapheresis (p=0.03).
Conclusions
Plasmapheresis following IVMP therapy effectively removed anti-AQP4 antibodies and was accompanied by a substantial improvement in the neurological disability of patients with NMOSD. Lower levels of pre-existing neurological damage may be associated with an improved acute response to plasmapheresis.
doi:10.3988/jcn.2013.9.1.36
PMCID: PMC3543908  PMID: 23346159
plasmapheresis; neuromyelitis optica; anti-aquaporin-4 antibody
9.  Contrasting disease patterns in seropositive and seronegative neuromyelitis optica: A multicentre study of 175 patients 
Background
The diagnostic and pathophysiological relevance of antibodies to aquaporin-4 (AQP4-Ab) in patients with neuromyelitis optica spectrum disorders (NMOSD) has been intensively studied. However, little is known so far about the clinical impact of AQP4-Ab seropositivity.
Objective
To analyse systematically the clinical and paraclinical features associated with NMO spectrum disorders in Caucasians in a stratified fashion according to the patients' AQP4-Ab serostatus.
Methods
Retrospective study of 175 Caucasian patients (AQP4-Ab positive in 78.3%).
Results
Seropositive patients were found to be predominantly female (p < 0.0003), to more often have signs of co-existing autoimmunity (p < 0.00001), and to experience more severe clinical attacks. A visual acuity of ≤ 0.1 during acute optic neuritis (ON) attacks was more frequent among seropositives (p < 0.002). Similarly, motor symptoms were more common in seropositive patients, the median Medical Research Council scale (MRC) grade worse, and MRC grades ≤ 2 more frequent, in particular if patients met the 2006 revised criteria (p < 0.005, p < 0.006 and p < 0.01, respectively), the total spinal cord lesion load was higher (p < 0.006), and lesions ≥ 6 vertebral segments as well as entire spinal cord involvement more frequent (p < 0.003 and p < 0.043). By contrast, bilateral ON at onset was more common in seronegatives (p < 0.007), as was simultaneous ON and myelitis (p < 0.001); accordingly, the time to diagnosis of NMO was shorter in the seronegative group (p < 0.029). The course of disease was more often monophasic in seronegatives (p < 0.008). Seropositives and seronegatives did not differ significantly with regard to age at onset, time to relapse, annualized relapse rates, outcome from relapse (complete, partial, no recovery), annualized EDSS increase, mortality rate, supratentorial brain lesions, brainstem lesions, history of carcinoma, frequency of preceding infections, oligoclonal bands, or CSF pleocytosis. Both the time to relapse and the time to diagnosis was longer if the disease started with ON (p < 0.002 and p < 0.013). Motor symptoms or tetraparesis at first myelitis and > 1 myelitis attacks in the first year were identified as possible predictors of a worse outcome.
Conclusion
This study provides an overview of the clinical and paraclinical features of NMOSD in Caucasians and demonstrates a number of distinct disease characteristics in seropositive and seronegative patients.
doi:10.1186/1742-2094-9-14
PMCID: PMC3283476  PMID: 22260418
Neuromyelitis optica; Devic disease; Devic syndrome; longitudinally extensive transverse myelitis; recurrent optic neuritis; NMO-IgG; aquaporin-4 (AQP4) antibody; epidemiology; clinical features; magnetic resonance imaging; cerebrospinal fluid
10.  Neuromyelitis Optica in Austria in 2011: To Bridge the Gap between Neuroepidemiological Research and Practice in a Study Population of 8.4 Million People 
PLoS ONE  2013;8(11):e79649.
Background
In 2008 the Austrian Task Force for Neuromyelitis Optica (NMO) started a nation-wide network for information exchange and multi-centre collaboration. Their aim was to detect all patients with NMO or NMO spectrum disorders (NMO-SD) in Austria and to analyse their disease courses and response to treatment.
Methods
(1) As of March 2008, 1957 serum samples (of 1557 patients) have been tested with an established cell based immunofluorescence aquaporin-4 antibody (AQP4-ab) assay with a high sensitivity and specificity (both >95%). All tests were performed in a single reference laboratory (Clinical Dept. of Neurology of the Innsbruck Medical University). (2) A nation-wide survey with several calls for participation (via email newsletters, articles in the official journal of the Austrian Society of Neurology, and workshops) was initiated in 2008. All collected data will be presented in a way that allows that every individual patient can be traced back in order to ensure transparency and to avoid any data distortion in future meta-analyses. The careful and detailed presentation allows the visualization and comparison of the different disease courses in real time span. Failure and response to treatment are made visible at one glance. Database closure was 31 December 2011. All co-operators were offered co-authorship.
Results
All 71 NMO- or NMO-SD patients with AQP4-ab positivity (age range 12.3 to 79.6 years) were analysed in detail. Sex ratio (m:f = 1:7) and the proportion of patients without oligoclonal bands in cerebrospinal fluid (86.6%) were in line with previously published results. All identified patients were Caucasians.
Conclusions
A nationwide collaboration amongst Austrian neurologists with good network communications made it possible to establish a database of 71 AQP4-ab positive patients with NMO/NMO-SD. This database is presented in detail and provides the basis for further studies and international cooperation in order to investigate this rare disease.
doi:10.1371/journal.pone.0079649
PMCID: PMC3818238  PMID: 24223985
11.  Myasthenia gravis and neuromyelitis optica spectrum disorder 
Neurology  2012;78(20):1601-1607.
Objective:
To describe 16 patients with a coincidence of 2 rare diseases: aquaporin-4 antibody (AQP4-Ab)–mediated neuromyelitis optica spectrum disorder (AQP4-NMOSD) and acetylcholine receptor antibody (AChR-Ab)–mediated myasthenia gravis (AChR-MG).
Methods:
The clinical details and antibody results of 16 patients with AChR-MG and AQP4-NMOSD were analyzed retrospectively.
Results:
All had early-onset AChR-MG, the majority with mild generalized disease, and a high proportion achieved remission. Fifteen were female; 11 were Caucasian. In 14/16, the MG preceded NMOSD (median interval: 16 years) and 11 of these had had a thymectomy although 1 only after NMOSD onset. In 4/5 patients tested, AQP4-Abs were detectable between 4 and 16 years prior to disease onset, including 2 patients with detectable AQP4-Abs prior to thymectomy. AChR-Abs decreased and the AQP4-Ab levels increased over time in concordance with the relevant disease. AChR-Abs were detectable at NMOSD onset in the one sample available from 1 of the 2 patients with NMOSD before MG.
Conclusions:
Although both conditions are rare, the association of MG and NMOSD occurs much more frequently than by chance and the MG appears to follow a benign course. AChR-Abs or AQP4-Abs may be present years before onset of the relevant disease and the antibody titers against AQP4 and AChR tend to change in opposite directions. Although most cases had MG prior to NMOSD onset, and had undergone thymectomy, NMOSD can occur first and in patients who have not had their thymus removed.
doi:10.1212/WNL.0b013e31825644ff
PMCID: PMC3348852  PMID: 22551731
12.  Evaluation of a Multiparametric Immunofluorescence Assay for Standardization of Neuromyelitis Optica Serology 
PLoS ONE  2012;7(6):e38896.
Background
Neuromyelitis optica (NMO) is a severely disabling autoimmune disorder of the central nervous system, which predominantly affects the optic nerves and spinal cord. In a majority of cases, NMO is associated with antibodies to aquaporin-4 (AQP4) (termed NMO-IgG).
Aims
In this study, we evaluated a new multiparametric indirect immunofluorescence (IIF) assay for NMO serology.
Methods
Sera from 20 patients with NMO, 41 patients with multiple sclerosis (MS), 30 healthy subjects, and a commercial anti-AQP4 IgG antibody were tested in a commercial composite immunofluorescence assay (“Neurology Mosaic 17”; Euroimmun, Germany), consisting of five different diagnostic substrates (HEK cells transfected with AQP4, non-transfected HEK cells, primate cerebellum, cerebrum, and optic nerve tissue sections).
Results
We identified AQP4 specific and non-specific fluorescence staining patterns and established positivity criteria. Based on these criteria, this kit yielded a high sensitivity (95%) and specificity (100%) for NMO and had a significant positive and negative likelihood ratio (LR+ = ∞, LR− = 0.05). Moreover, a 100% inter- and intra-laboratory reproducibility was found.
Conclusions
The biochip mosaic assay tested in this study is a powerful tool for NMO serology, fast to perform, highly sensitive and specific for NMO, reproducible, and suitable for inter-laboratory standardization as required for multi-centre clinical trials.
doi:10.1371/journal.pone.0038896
PMCID: PMC3373605  PMID: 22719979
13.  NMO-IgG Status in Fulminant Inflammatory CNS Demyelinating Disorders 
Archives of neurology  2009;66(8):964-966.
Background
The aquaporin-4-specific serum autoantibody, NMO-IgG, is a validated biomarker distinguishing neuromyelitis optica spectrum disorders (NMOSD) from multiple sclerosis (MS). Because fulminant attacks are more common in NMOSD than MS, some suggest that NMO-IgG may be a marker of destructive demyelination rather than a disease-specific biomarker. This study is the first to compare NMO-IgG serostatus among patients with fulminant CNS-inflammatory demyelinating disease (CNS-IDD).
Objective
To determine if NMO-IgG distinguishes NMOSD from other fulminant, steroid-refractory CNS-IDDs.
Design
Descriptive historical cohort
Setting
Neuroimmunology Laboratory and Neurology Practice, Mayo Clinic.
Patients and Methods
Sera from 74 patients plasmapheresed between 1993 and 2007 for a steroid-refractory CNS-IDD were tested for NMO-IgG (by indirect immunofluorescence assay). Two blinded observers scored sera (tested at 1:120 dilution). Clinical data were obtained by medical record review.
Results
Pre-plasmapheresis sera were available from 74 patients (F:M =2.5 ); mean time from blood draw to plasmapheresis was 13 days. At plasmapheresis, mean age was 46 years (range, 7 to 8 0); mean EDSS was 7 (range, 3.5 to 9.5) and diagnoses were NMO (14), longitudinally extensive transverse myelitis (LETM; ≥ 3 vertebral segments; 20), transverse myelitis (TM; < 3 vertebral segments; 8), acute disseminated encephalomyelitis (ADEM; 1), MS (definite, 18; probable, 11), and optic neuritis (ON; 2). NMO-IgG was detected in 20 patients (27%): 9 NMO, 10 LETM and one recurrent ON, and in no patient with fulminant ADEM, MS, TM or monophasic ON.
Conclusions
NMO-IgG is a specific biomarker for NMOSD and is not simply a marker of destructive CNS-IDD.
doi:10.1001/archneurol.2009.152
PMCID: PMC2742779  PMID: 19667216
14.  Aquaporin-4 Antibodies Are Not Related to HTLV-1 Associated Myelopathy 
PLoS ONE  2012;7(7):e39372.
Introduction
The seroprevalence of human T-cell leukemia virus type 1 (HTLV-1) is very high among Brazilians (∼1∶200). HTLV-1 associated myelopathy or tropical spastic paraparesis (HAM/TSP) is the most common neurological complication of HTLV-1 infection. HAM/TSP can present with an acute/subacute form of longitudinally extensive myelitis, which can be confused with lesions seen in aquaporin-4 antibody (AQP4-Ab) positive neuromyelitis optica spectrum disorders (NMOSD) on MRI. Moreover, clinical attacks in patients with NMOSD have been shown to be preceded by viral infections in around 30% of cases.
Objective
To evaluate the frequency of AQP4-Ab in patients with HAM/TSP. To evaluate the frequency of HTLV-1 infection in patients with NMOSD.
Patients and Methods
23 Brazilian patients with HAM/TSP, 20 asymptomatic HTLV-1+ serostatus patients, and 34 with NMOSD were tested for AQP4-Ab using a standardized recombinant cell based assay. In addition, all patients were tested for HTLV-1 by ELISA and Western blotting.
Results
20/34 NMOSD patients were positive for AQP4-Ab but none of the HAM/TSP patients and none of the asymptomatic HTLV-1 infected individuals. Conversely, all AQP4-Ab-positive NMOSD patients were negative for HTLV-1 antibodies. One patient with HAM/TSP developed optic neuritis in addition to subacute LETM; this patient was AQP4-Ab negative as well. Patients were found to be predominantly female and of African descent both in the NMOSD and in the HAM/TSP group; Osame scale and expanded disability status scale scores did not differ significantly between the two groups.
Conclusions
Our results argue both against a role of antibodies to AQP4 in the pathogenesis of HAM/TSP and against an association between HTLV-1 infection and the development of AQP4-Ab. Moreover, the absence of HTLV-1 in all patients with NMOSD suggests that HTLV-1 is not a common trigger of acute attacks in patients with AQP4-Ab positive NMOSD in populations with high HTLV-1 seroprevalence.
doi:10.1371/journal.pone.0039372
PMCID: PMC3393709  PMID: 22808032
15.  AQP4 antibody–positive Thai cases 
Neurology  2011;77(9):827-834.
Objective:
To evaluate the prevalence of aquaporin-4 (AQP4) antibody in Thai patients with idiopathic inflammatory demyelinating CNS diseases (IIDCDs) and to analyze the significance of the autoantibody to distinguish neuromyelitis optica (NMO) and other NMO spectrum disorders (ONMOSDs) from other IIDCDs, especially multiple sclerosis (MS).
Methods:
We retrospectively evaluated 135 consecutive patients with IIDCDs seen at the MS clinic at Siriraj Hospital, Bangkok, Thailand, and classified them into NMO, ONMOSDs, optic-spinal MS (OSMS), classic MS (CMS), and clinically isolated syndrome (CIS) groups in this order with accepted diagnostic criteria. The patients' coded sera were tested separately for AQP4 antibody. Then the relations between the clinical diagnosis and the AQP4 antibody serologic status were analyzed.
Results:
Among the 135 patients, 53 (39.3%) were AQP4 antibody–positive. Although the AQP4 antibody–positive group had features of NMO, such as female predominance, long cord lesions (>3 vertebral bodies), and CSF pleocytosis, only 18 patients (33% of 54) fully met Wingerchuk 2006 criteria except for AQP4 antibody–seropositive status. We also detected some AQP4 antibody–positive patients in the OSMS (4 of 7), CMS (11 of 46), and CIS (1 of 16) groups. These patients had been misdiagnosed with MS because they often had brain lesions and never underwent spinal cord MRI examination or lacked long cord lesions.
Conclusions:
AQP4 antibody was highly prevalent (almost 40%) in Thai patients with IIDCDs. Moreover, only one-third of AQP4 antibody–positive patients fully met Wingerchuk 2006 criteria, and many were misdiagnosed with MS. A sensitive AQP4 antibody assay is required in this region because the therapy for NMO is different from that for MS.
doi:10.1212/WNL.0b013e31822c61b1
PMCID: PMC3463102  PMID: 21813785
16.  Absence of cortical demyelination in neuromyelitis optica 
Neurology  2010;75(23):2103-2109.
Objective:
To asses the presence of cortical demyelination in brains of patients with neuromyelitis optica (NMO). NMO is an autoimmune inflammatory demyelinating disease that specifically targets aquaporin-4-rich regions of the CNS. Since aquaporin-4 is highly expressed in normal cortex, we anticipated that cortical demyelination may occur in NMO.
Methods:
This is a cross-sectional neuropathologic study performed on archival forebrain and cerebellar tissue sections from 19 autopsied patients with a clinically and/or pathologically confirmed NMO spectrum disorder.
Results:
Detailed immunohistochemical analyses of 19 archival NMO cases revealed preservation of aquaporin-4 in a normal distribution within cerebral and cerebellar cortices, and no evidence of cortical demyelination.
Conclusions:
This study provides a plausible explanation for the absence of a secondary progressive clinical course in NMO and shows that cognitive and cortical neuroimaging abnormalities previously reported in NMO cannot be attributed to cortical demyelination. Lack of cortical demyelination is another characteristic that further distinguishes NMO from MS.
GLOSSARY
= aquaporin-4;
= blood-brain barrier;
= immunoglobulin G;
= multiple sclerosis;
= neuromyelitis optica;
= neuromyelitis optica spectrum disorder.
doi:10.1212/WNL.0b013e318200d80c
PMCID: PMC2995539  PMID: 21135384
17.  Diagnostic utility of NMO/AQP4-IgG in evaluating CNS inflammatory disease in Thai Patients 
Journal of the neurological sciences  2012;320(1-2):118-120.
Epidemiological studies in Thailand have reported that inflammatory demyelinating diseases (IDDs) commonly affect the optic nerve and spinal cord. We investigated the diagnostic utility of aquaporin (AQP)-4-IgG testing in 31 consecutive patients evaluated for CNS IDDs in 3 academic Thai hospital neurology clinics between February 2008 and January 2009. Patients were classified into 3 clinical diagnostic groups: Neuromyelitis optica (NMO, n=10) multiple sclerosis (MS n=5) and unclassified IDD (n=16). All sera were tested blindly by cell binding (Euroimmun) assay (CBA). Sera were also tested by indirect immunofluorescence assay (IFA) and ELISA (RSR/Kronus). After initial screening by CBA, AQP4-IgG was detected in 6 NMO patients (60%); 3 of the 4 seronegative cases were receiving immunosuppressants. AQP4-IgG was detected in 13 unclassified IDD cases (81%), but in no MS cases. Cell binding assay and ELISA were more sensitive than IFA (p=0.0004). The 81% seropositivity rate in “unclassified” patients suggests that AQP4 autoimmunity accounts for a significant proportion of Thai CNS inflammatory demyelinating disease, especially those with optic neuritis or transverse myelitis, with or without abnormal brain MRI, in whom a specific diagnosis or clear-cut treatment approach is unclear.
doi:10.1016/j.jns.2012.07.014
PMCID: PMC3423321  PMID: 22831763
demyelinating disease; Devic’s syndrome; autoimmune diseases; neuromyelitis optica; aquaporin-4; autoantibodies; multiple sclerosis; assays; diagnosis; sensitivity
18.  Update on the diagnosis and treatment of neuromyelitis optica: Recommendations of the Neuromyelitis Optica Study Group (NEMOS) 
Journal of Neurology  2013;261:1-16.
Neuromyelitis optica (NMO, Devic’s syndrome), long considered a clinical variant of multiple sclerosis, is now regarded as a distinct disease entity. Major progress has been made in the diagnosis and treatment of NMO since aquaporin-4 antibodies (AQP4-Ab; also termed NMO-IgG) were first described in 2004. In this review, the Neuromyelitis Optica Study Group (NEMOS) summarizes recently obtained knowledge on NMO and highlights new developments in its diagnosis and treatment, based on current guidelines, the published literature and expert discussion at regular NEMOS meetings. Testing of AQP4-Ab is essential and is the most important test in the diagnostic work-up of suspected NMO, and helps to distinguish NMO from other autoimmune diseases. Furthermore, AQP4-Ab testing has expanded our knowledge of the clinical presentation of NMO spectrum disorders (NMOSD). In addition, imaging techniques, particularly magnetic resonance imaging of the brain and spinal cord, are obligatory in the diagnostic workup. It is important to note that brain lesions in NMO and NMOSD are not uncommon, do not rule out the diagnosis, and show characteristic patterns. Other imaging modalities such as optical coherence tomography are proposed as useful tools in the assessment of retinal damage. Therapy of NMO should be initiated early. Azathioprine and rituximab are suggested as first-line treatments, the latter being increasingly regarded as an established therapy with long-term efficacy and an acceptable safety profile in NMO patients. Other immunosuppressive drugs, such as methotrexate, mycophenolate mofetil and mitoxantrone, are recommended as second-line treatments. Promising new therapies are emerging in the form of anti-IL6 receptor, anti-complement or anti-AQP4-Ab biologicals.
doi:10.1007/s00415-013-7169-7
PMCID: PMC3895189  PMID: 24272588
Neuromyelitis optica; Differential diagnosis; Diagnostic tests; Therapy
19.  Aquaporin-4 Autoantibodies in Neuromyelitis Optica: AQP4 Isoform-Dependent Sensitivity and Specificity 
PLoS ONE  2013;8(11):e79185.
Neuromyelitis Optica (NMO) is an autoimmune demyelinating disease, characterized by the presence of autoantibody (NMO-IgG) to Aquaporin-4 (AQP4). NMO-IgG identification supports NMO diagnosis and several diagnostic tests have been developed, but their sensitivity is too variable, and some assay show low sensitivity. This impairs correct diagnosis of NMO. By cell based assay (CBA) we here evaluate the efficacy of different strategies to express AQP4 in mammalian cells in terms of: a) AQP4 translation initiation signals; b) AQP4 isoforms (M1 and M23) and fluorescent tag position; c) NMO serum concentration and AQP4 degradation. Our results demonstrate that when using AQP4-M1, the nucleotide in position −3 of the AUG greatly affects the AQP4-M1/M23 protein ratio, NMO-IgG binding, and consequently test sensitivity. Test sensitivity was highest with M23 expressing cells (97.5%) and only 27.5% with AQP4-M1. The fluorescent tag added to the N-terminus of AQP4-M23 considerably affected the NMO-IgG binding, and test sensitivity, due to disruption of AQP4 suprastructures. Furthermore, sera used at high concentration resulted in AQP4 degradation which affected test sensitivity. To further evaluate the reliability of the M23 based CBA test, samples of one NMO patient collected during about 2 years clinical follow-up were tested. The results of serum titer correlated with disease activity and treatment response. In conclusion, we provide a molecular explanation for the contrasting CBA test data reported and suggest the use of M23 with a C-terminus fluorescent tag as the proper test for NMO diagnosis.
doi:10.1371/journal.pone.0079185
PMCID: PMC3829826  PMID: 24260168
20.  Distinction of seropositive NMO spectrum disorder and MS brain lesion distribution 
Neurology  2013;80(14):1330-1337.
Objective:
Neuromyelitis optica and its spectrum disorder (NMOSD) can present similarly to relapsing-remitting multiple sclerosis (RRMS). Using a quantitative lesion mapping approach, this research aimed to identify differences in MRI brain lesion distribution between aquaporin-4 antibody–positive NMOSD and RRMS, and to test their diagnostic potential.
Methods:
Clinical brain MRI sequences for 44 patients with aquaporin-4 antibody–positive NMOSD and 50 patients with RRMS were examined for the distribution and morphology of brain lesions. T2 lesion maps were created for each subject allowing the quantitative comparison of the 2 conditions with lesion probability and voxel-wise analysis.
Results:
Sixty-three percent of patients with NMOSD had brain lesions and of these 27% were diagnostic of multiple sclerosis. Patients with RRMS were significantly more likely to have lesions adjacent to the body of the lateral ventricle than patients with NMOSD. Direct comparison of the probability distributions and the morphologic attributes of the lesions in each group identified criteria of “at least 1 lesion adjacent to the body of the lateral ventricle and in the inferior temporal lobe; or the presence of a subcortical U-fiber lesion; or a Dawson's finger-type lesion,” which could distinguish patients with multiple sclerosis from those with NMOSD with 92% sensitivity, 96% specificity, 98% positive predictive value, and 86% negative predictive value.
Conclusion:
Careful inspection of the distribution and morphology of MRI brain lesions can distinguish RRMS and NMOSD.
doi:10.1212/WNL.0b013e3182887957
PMCID: PMC3656462  PMID: 23486868
21.  Evaluation of Clinical Interest of Anti-Aquaporin-4 Autoantibody Followup in Neuromyelitis Optica 
Neuromyelitis optica (NMO) is an autoimmune disease in which a specific biomarker named NMO-IgG and directed against aquaporin-4 (AQP4) has been found. A correlation between disease activity and anti-AQP4 antibody (Ab) serum concentration or complement-mediated cytotoxicity has been reported, but the usefulness of longitudinal evaluation of these parameters remains to be evaluated in actual clinical practice. Thirty serum samples from 10 NMO patients positive for NMO-IgG were collected from 2006 to 2011. Anti-AQP4 Ab serum concentration and complement-mediated cytotoxicity were measured by flow cytometry using two quantitative cell-based assays (CBA) and compared with clinical parameters. We found a strong correlation between serum anti-AQP4 Ab concentration and complement-mediated cytotoxicity (P < 0.0001). Nevertheless, neither relapse nor worsening of impairment level was closely associated with a significant increase in serum Ab concentration or cytotoxicity. These results suggest that complement-mediated serum cytotoxicity assessment does not provide extra insight compared to anti-AQP4 Ab serum concentration. Furthermore, none of these parameters appears closely related to disease activity and/or severity. Therefore, in clinical practice, serum anti-AQP4 reactivity seems not helpful as a predictive biomarker in the followup of NMO patients as a means of predicting the onset of a relapse and adapting the treatment accordingly.
doi:10.1155/2013/146219
PMCID: PMC3655457  PMID: 23710199
22.  Brain Abnormalities in Neuromyelitis Optica Spectrum Disorder 
Neuromyelitis optica (NMO) is an idiopathic inflammatory syndrome of the central nervous system that is characterized by severe attacks of optic neuritis (ON) and myelitis. Until recently, NMO was considered a disease without brain involvement. However, since the discovery of NMO-IgG/antiaqaporin-4 antibody, the concept of NMO was broadened to NMO spectrum disorder (NMOSD), and brain lesions are commonly recognized. Furthermore, some patients present with brain symptoms as their first manifestation and develop recurrent brain symptoms without ON or myelitis. Brain lesions with characteristic locations and configurations can be helpful in the diagnosis of NMOSD. Due to the growing recognition of brain abnormalities in NMOSD, these have been included in the NMO and NMOSD diagnostic criteria or guidelines. Recent technical developments such as diffusion tensor imaging, MR spectroscopy, and voxel-based morphometry reveal new findings related to brain abnormalities in NMOSD that were not identified using conventional MRI. This paper focuses on the incidence and characteristics of the brain lesions found in NMOSD and the symptoms that they cause. Recent studies using advanced imaging techniques are also introduced.
doi:10.1155/2012/735486
PMCID: PMC3518965  PMID: 23259063
23.  New Insights into Neuromyelitis Optica 
Neuromyelitis optica (NMO) is an idiopathic inflammatory disorder of the central nervous system (CNS) that preferentially affects the optic nerves and spinal cord. In Asia, NMO has long been considered a subtype of multiple sclerosis (MS). However, recent clinical, pathological, immunological, and imaging studies have suggested that NMO is distinct from MS. This reconsideration of NMO was initially prompted by the discovery of a specific antibody for NMO (NMO-IgG) in 2004. NMO-IgG is an autoantibody that targets aquaporin-4 (AQP4), the most abundant water channel in the CNS; hence, it was named anti-AQP4 antibody. Since it demonstrated reasonable sensitivity and high specificity, anti-AQP4 antibody was incorporated into new diagnostic criteria for NMO.The spectrum of NMO is now known to be wider than was previously recognized and includes a proportion of patients with recurrent, isolated, longitudinally extensive myelitis or optic neuritis, and longitudinally extensive myelitis or optic neuritis associated with systemic autoimmune disease or with brain lesions typical of NMO. In this context, a new concept of "NMO spectrum disorders" was recently introduced. Furthermore, seropositivity for NMO-IgG predicts future relapses and is recognized as a prognostic marker for NMO spectrum disorders. Humoral immune mechanisms, including the activation of B-cells and the complement pathway, are considered to play important roles in NMO pathogenesis. This notion is supported by recent studies showing the potential pathogenic role of NMO-IgG as an initiator of NMO lesions. However, a demonstration of the involvement of NMO-IgG by the development of active immunization and passive transfer in animal models is still needed. This review focuses on the new concepts of NMO based on its pathophysiology and clinical characteristics. Potential management strategies for NMO in light of its pathomechanism are also discussed.
doi:10.3988/jcn.2011.7.3.115
PMCID: PMC3212597  PMID: 22087205
neuromyelitis optica; Devic's disease; neuromyelitis optica spectrum disorder; pathogenesis; diagnosis; management
24.  Patterns of Antibody Binding to Aquaporin-4 Isoforms in Neuromyelitis Optica 
PLoS ONE  2010;5(5):e10455.
Background
Neuromyelitis optica (NMO), a severe demyelinating disease, represents itself with optic neuritis and longitudinally extensive transverse myelitis. Serum NMO-IgG autoantibodies (Abs), a specific finding in NMO patients, target the water channel protein aquaporin-4 (AQP4), which is expressed as a long (M-1) or a short (M-23) isoform.
Methodology/Principal Findings
The aim of this study was to analyze serum samples from patients with NMO and controls for the presence and epitope specificity of IgG and IgM anti-AQP4 Abs using an immunofluorescence assay with HEK293 cells expressing M-1 or M-23 human AQP4. We included 56 patients with definite NMO (n = 30) and high risk NMO (n = 26), 101 patients with multiple sclerosis, 27 patients with clinically isolated syndromes (CIS), 30 patients with systemic lupus erythematosus (SLE) or Sjögren's syndrome, 29 patients with other neurological diseases and 47 healthy controls. Serum anti-AQP4 M-23 IgG Abs were specifically detected in 29 NMO patients, 17 patients with high risk NMO and two patients with myelitis due to demyelination (CIS) and SLE. In contrast, IgM anti-AQP4 Abs were not only found in some NMO and high risk patients, but also in controls. The sensitivity of the M-23 AQP4 IgG assay was 97% for NMO and 65% for high risk NMO, with a specificity of 100% compared to the controls. Sensitivity with M-1 AQP4 transfected cells was lower for NMO (70%) and high risk NMO (39%). The conformational epitopes of M-23 AQP4 are the primary targets of NMO-IgG Abs, whereas M-1 AQP4 Abs are developed with increasing disease duration and number of relapses.
Conclusions
Our results confirm M-23 AQP4-IgG Abs as reliable biomarkers in patients with NMO and high risk syndromes. M-1 and M-23 AQP4-IgG Abs are significantly associated with a higher number of relapses and longer disease duration.
doi:10.1371/journal.pone.0010455
PMCID: PMC2864757  PMID: 20463974
25.  Antibody to aquaporin-4 in the long-term course of neuromyelitis optica 
Brain  2008;131(11):3072-3080.
Neuromyelitis optica (NMO) is a severe inflammatory CNS disorder of putative autoimmune aetiology, which predominantly affects the spinal cord and optic nerves. Recently, a highly specific serum reactivity to CNS microvessels, subpia and Virchow–Robin spaces was described in patients with NMO [called NMO–IgG (NMO–immunoglobulin G)]. Subsequently, aquaporin-4 (AQP4), the most abundant water channel in the CNS, was identified as its target antigen. Strong support for a pathogenic role of the antibody would come from studies demonstrating a correlation between AQP4-Ab (AQP4-antibody) titres and the clinical course of disease. In this study, we determined AQP4-Ab serum levels in 96 samples from eight NMO–IgG positive patients (median follow-up 62 months) in a newly developed fluorescence-based immunoprecipitation assay employing recombinant human AQP4. We found that AQP4-Ab serum levels correlate with clinical disease activity, with relapses being preceded by an up to 3-fold increase in AQP4-Ab titres, which was not paralleled by a rise in other serum autoantibodies in one patient. Moreover, AQP4-Ab titres were found to correlate with CD19 cell counts during therapy with rituximab. Treatment with immunosuppressants such as rituximab, azathioprine and cyclophosphamide resulted in a marked reduction in antibody levels and relapse rates. Our results demonstrate a strong relationship between AQP4-Abs and clinical state, and support the hypothesis that these antibodies are involved in the pathogenesis of NMO.
doi:10.1093/brain/awn240
PMCID: PMC2577801  PMID: 18945724
Devic syndrome; neuromyelitis optica; longitudinally extensive transverse myelitis; NMO-IgG;  aquaporin-4 antibody; long-term follow-up

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