CSF-S100B Is a Potential Candidate Biomarker for Neuromyelitis Optica Spectrum Disorders

Blood-based inflammatory protein biomarker panel for the prediction of relapse and severity in patients with neuromyelitis optica spectrum disorder: A prospective cohort study

BACKGROUND

To date, most existing models for predicting neuromyelitis optica spectrum disorder (NMOSD) are based primarily on clinical characteristics. Blood-based NMOSD severity and prognostic predictive immune- and inflammation-related biomarkers are needed. We aimed to investigate the associations between plasma inflammatory biomarkers and relapse and attack severity in NMOSD.

METHODS

This two-step, single-center prospective cohort study included discovery and validation cohorts. We quantified 92 plasma inflammatory proteins by using Olink's proximity extension assay and identified differentially expressed proteins in the relapse group (relapse within 1 year of follow-up) and severe attack group. To define a new molecular prognostic model, we calculated the risk score of each patient based on the key protein signatures and validated the results in the validation cohort.

RESULTS

The relapse prediction model, including FGF-23, DNER, GDNF, and SLAMF1, predicted the 1-year relapse risk. The severe attack prediction model, including PD-L1 and MCP-2, predicted the severe clinical attack risk. Both the relapse and severe attack prediction models demonstrated good discriminative ability and high accuracy in the validation cohort.

CONCLUSIONS

Our discovered biomarker signature and prediction models may complement current clinical risk stratification approaches. These inflammatory biomarkers could contribute to the discovery of therapeutic interventions and prevent NMOSD progression.

Soluble biomarkers for Neuromyelitis Optica Spectrum Disorders: a mini review

The Neuromyelitis Optica Spectrum Disorders (NMOSD) constitute a spectrum of rare autoimmune diseases of the central nervous system characterized by episodes of transverse myelitis, optic neuritis, and other demyelinating attacks. Previously thought to be a subtype of multiple sclerosis, NMOSD is now known to be a distinct disease with unique pathophysiology, clinical course, and treatment options. Although there have been significant recent advances in the diagnosis and treatment of NMOSD, the field still lacks clinically validated biomarkers that can be used to stratify disease severity, monitor disease activity, and inform treatment decisions. Here we review many emerging NMOSD biomarkers including markers of cellular damage, neutrophil-to-lymphocyte ratio, complement, and cytokines, with a focus on how each biomarker can potentially be used for initial diagnosis, relapse surveillance, disability prediction, and treatment monitoring.

The relationship between serum astroglial and neuronal markers and AQP4 and MOG autoantibodies

BACKGROUND

Certain demyelinating disorders, such as neuromyelitis optica spectrum disorder (NMOSD) and myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD) exhibit serum autoantibodies against aquaporin-4 (αAQP4) and myelin oligodendrocyte glycoprotein (αMOG). The variability of the autoantibody presentation warrants further research into subtyping each case.

METHODS

To elucidate the relationship between astroglial and neuronal protein concentrations in the peripheral circulation with occurrence of these autoantibodies, 86 serum samples were analyzed using immunoassays. The protein concentration of glial fibrillary acidic protein (GFAP), neurofilament light chain (NFL) and tau protein was measured in 3 groups of subcategories of suspected NMOSD: αAQP4 positive (n = 20), αMOG positive (n = 32) and αMOG/αAQP4 seronegative (n = 34). Kruskal-Wallis analysis, univariate predictor analysis, and multivariate logistic regression with ROC curves were performed.

RESULTS

GFAP and NFL concentrations were significantly elevated in the αAQP4 positive group (p = 0.003; p = 0.042, respectively), and tau was elevated in the αMOG/αAQP4 seronegative group (p < 0.001). A logistic regression model to classify serostatus was able to separate αAQP4 seropositivity using GFAP + tau, and αMOG seropositivity using tau. The areas under the ROC curves (AUCs) were 0.77 and 0.72, respectively. Finally, a combined seropositivity versus negative status logistic regression model was generated, with AUC = 0.80.

CONCLUSION

The 3 markers can univariately and multivariately classify with moderate accuracy the samples with seropositivity and seronegativity for αAQP4 and αMOG.

Body fluid markers for multiple sclerosis and differential diagnosis from atypical demyelinating disorders

INTRODUCTION

Body fluid markers could be helpful to predict the conversion into clinically definite multiple sclerosis (MS) in people with a first demyelinating event of the central nervous system (CNS). Consequently, biomarkers such as oligoclonal bands, which are integrated in the current MS diagnostic criteria, could assist early MS diagnosis.

AREAS COVERED

This review examines existing knowledge on a broad spectrum of body fluid markers in people with a first CNS demyelinating event, explores their potential to predict conversion to MS, to assess MS disease activity, as well as their utility to differentiate MS from atypical demyelinating disorders such as neuromyelitis optica spectrum disorder and myelin oligodendrocyte glycoprotein associated disease.

EXPERT OPINION

This field of research has shown a dramatic increase of evidence, especially in the last decade. Some biomarkers are already established in clinical routine (e.g. oligoclonal bands) while others are currently implemented (e.g. kappa free light chains) or considered as breakthroughs (e.g. neurofilament light). Determination of biomarkers poses challenges for continuous monitoring, especially if exclusively detectable in cerebrospinal fluid. A handful of biomarkers are measurable in blood which holds a significant potential.

The relationship between serum astroglial and neuronal markers and AQP4 and MOG autoantibodies

Background

Certain demyelinating disorders, such as neuromyelitis optica spectrum disorder (NMOSD) and myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD) exhibit serum autoantibodies against aquaporin-4 (αAQP4) and myelin oligodendrocyte glycoprotein (αMOG). The variability of the autoantibody presentation warrants further research into subtyping each case.

Methods

To elucidate the relationship between astroglial and neuronal protein concentrations in the peripheral circulation with occurrence of these autoantibodies, 86 serum samples were analyzed using immunoassays. The protein concentration of glial fibrillary acidic protein (GFAP), neurofilament light chain (NFL) and tau protein was measured in 3 groups of subcategories of suspected NMOSD: αAQP4 positive (n = 20), αMOG positive (n = 32) and αMOG/αAQP4 seronegative (n = 34). Kruskal-Wallis analysis, univariate predictor analysis, and multivariate logistic regression with ROC curves were performed.

Results

GFAP and NFL concentrations were significantly elevated in the αAQP4 positive group (p = 0.003; p = 0.042, respectively), and tau was elevated in the αMOG/αAQP4 seronegative group (p < 0.001). A logistic regression model to classify serostatus was able to separate αAQP4 seropositivity using GFAP + tau, and αMOG seropositivity using tau. The areas under the ROC curves (AUCs) were 0.77 and 0.72, respectively. Finally, a combined seropositivity versus negative status logistic regression model was generated, with AUC = 0.80.

Conclusion

The 3 markers can univariately and multivariately classify with moderate accuracy the samples with seropositivity and seronegativity for αAQP4 and αMOG.

Patterns of Adult Neuromyelitis Optica Spectrum Disorder Patients Compared to Multiple Sclerosis: A Systematic Review and Meta-Analysis

Neuromyelitis optica spectrum disorders (NMOSDs) are central nervous system inflammatory conditions, now recognized to involve the brain, often identified by aquaporin-4 (AQP4) antibodies. We aimed to summarize the characteristics of adult NMOSD patients compared to multiple sclerosis (MS). A computerized search was conducted on MEDLINE via PubMed, Web of Science, and ProQuest using the relevant keywords. Three independent reviewers performed two-stage screening and data extraction. The Review Manager 5.4 program (Cochrane Collaboration, Windows, London, UK) was used for the analysis. The Joanna Briggs Institute (JIB) tool was used for the quality of included studies. Twenty-three articles were included. NMOSD patients were associated with older age at presentation and higher Expanded Disability Status Scale (MD = 3.88, 95% CI: 1.80 to 5.97, P = 0.0003) and (MD = 1.15, 95% CI: 0.58 to 1.72, P < 0.0001), respectively. The risk of NMOSD in females was significantly higher than MS (OR = 2.21, 95% CI: 1.41 to 3.46, P = 0.0005). Patients with NMOSD were associated with a lower risk of extrapyramidal symptoms (OR = 0.26, 95% CI: 0.11 to 0.60, P < 0.01), brainstem involvement symptoms (OR = 0.32, 95% CI: 0.16 to 0.64, P < 0.01), and developing brain lesions compared to MS (OR = 0.08, 95% CI: 0.03 to 0.18, P < 0.00001). The current evidence suggests that both NMOSD and MS have different demographic, clinical, and lesion characteristics. There is a need for additional validation of the identified differences compared with MS due to the lack of long-term systematic imaging investigations in NMOSD.

Double-negative neuromyelitis optica spectrum disorder

Most patients with neuromyelitis optica spectrum disorders (NMOSD) test positive for aquaporin-4 antibody (AQP4-IgG) or myelin oligodendrocyte glycoprotein antibodies (MOG-IgG). Those who are negative are termed double-negative (DN) NMOSD and may constitute a diagnostic and therapeutic challenge. DN NMOSD is a syndrome rather than a single disease, ranging from a (postinfectious) monophasic illness to a more chronic syndrome that can be indistinguishable from AQP4-IgG+ NMOSD or develop into other mimics such as multiple sclerosis. Thus, underlying disease mechanisms are likely to be heterogeneous. This topical review aims to (1) reappraise antibody-negative NMOSD definition as it has changed over time with the development of the AQP4 and MOG-IgG assays; (2) outline clinical characteristics and the pathophysiological nature of this rare entity by contrasting its differences and similarities with antibody-positive NMOSD; (3) summarize laboratory characteristics and magnetic resonance imaging findings of DN NMOSD; and (4) discuss the current treatment for DN NMOSD.

Granulocyte activation markers in cerebrospinal fluid differentiate acute neuromyelitis spectrum disorder from multiple sclerosis

BACKGROUND

Granulocyte invasion into the brain is a pathoanatomical feature differentiating neuromyelitis optica spectrum disorder (NMOSD) from multiple sclerosis (MS). We aimed to determine whether granulocyte activation markers (GAM) in cerebrospinal fluid (CSF) can be used as a biomarker to distinguish NMOSD from MS, and whether levels associate with neurological impairment.

METHODS

We quantified CSF levels of five GAM (neutrophil elastase, myeloperoxidase, neutrophil gelatinase-associated lipocalin, matrixmetalloproteinase-8, tissue inhibitor of metalloproteinase-1), as well as a set of inflammatory and tissue-destruction markers, known to be upregulated in NMOSD and MS (neurofilament light chain, glial fibrillary acidic protein, S100B, matrix metalloproteinase-9, intercellular adhesion molecule-1, vascular cellular adhesion molecule-1), in two cohorts of patients with mixed NMOSD and relapsing-remitting multiple sclerosis (RRMS).

RESULTS

In acute NMOSD, GAM and adhesion molecules, but not the other markers, were higher than in RRMS and correlated with actual clinical disability scores. Peak GAM levels occurred at the onset of NMOSD attacks, while they were stably low in MS, allowing to differentiate the two diseases for ≤21 days from onset of clinical exacerbation. Composites of GAM provided area under the curve values of 0.90-0.98 (specificity of 0.76-1.0, sensitivity of 0.87-1.0) to differentiate NMOSD from MS, including all anti-aquaporin-4 protein (aAQP4)-antibody-negative patients who were untreated.

CONCLUSIONS

GAM composites represent a novel biomarker to reliably differentiate NMOSD from MS, including in aAQP4- NMOSD. The association of GAM with the degree of concurrent neurological impairment provides evidence for their pathogenic role, in turn suggesting them as potential drug targets in acute NMOSD.

Decreased kynurenine in cerebrospinal fluid and potential role in neuromyelitis optica spectrum disorder

Tryptophan (Trp) metabolism has been implicated in neuroinflammatory and neurodegenerative disorders, but its relationship with neuromyelitis optica spectrum disorder (NMOSD) is unclear. In this pilot study, cerebrospinal fluid (CSF) was prospectively collected from 26 NMOSD patients in relapse and 16 controls with noninflammatory diseases and 6 neurometabolites in the tryptophan metabolic pathway, including 5-hydroxytryptamine (5-HT), kynurenine (KYN), melatonin (MLT), 5-hydroxyindoleacetic acid (5HIAA), 3-hydroxy-o-aminobenzoic acid (3-HAA), and kynurenic acid (KYA), were measured by ultrahigh-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). The association of Trp metabolites with NMOSD and its clinical parameters was evaluated. The role of KYN, which is a Trp metabolite involved in the binding of NMOSD-IgG antibody to aquaporin 4 (AQP4), was also evaluated in vitro. CSF KYN was significantly decreased in patients with relapsing NMOSD compared to controls, and CSF KYN was associated with CSF white blood cells in NMOSD. In vitro experiments showed that NMOSD-IgG specifically recognized KYN, which reversed the NMOSD-IgG-induced downregulation of AQP4 expression. Our results show that abnormal Trp metabolism occurs in NMOSD and that KYN might be a potential target for the treatment of AQP4-IgG-positive NMOSD patients.

Glial fibrillary acidic protein as a biomarker in neuromyelitis optica spectrum disorder: a current review

INTRODUCTION

Neuromyelitis optica spectrum disorder (NMOSD) is a relapsing, often debilitating neuroinflammatory disease, whose predominant clinical manifestations are longitudinally extensive transverse myelitis and optic neuritis. About 80% of the patients with an NMOSD phenotype have pathogenic autoantibodies against the astrocyte water channel aquaporin-4 (AQP4-IgG). While therapeutic options for NMOSD have greatly expanded in recent years, well-established biomarkers for prognosis or treatment response are still lacking. Glial fibrillary acidic protein (GFAP) is mainly expressed in astrocytes and can be detected in cerebrospinal fluid (CSF) and blood of patients with NMOSD.

AREAS COVERED

Here, we comprehensively review the current knowledge on GFAP as a biomarker in NMOSD.

EXPERT OPINION

In patients with AQP4-IgG⁺ NMOSD, GFAP levels are elevated in CSF and serum during acute attacks and correlate with disability, consistent with the pathophysiology of this antibody-mediated astrocytopathy. Serum GFAP levels tend to be higher in AQP4-IgG⁺ NMOSD than in its differential diagnoses, multiple sclerosis, and myelin oligodendrocyte antibody-associated disease. Importantly, serum GFAP levels in AQP4-IgG⁺ NMOSD during remission may be predictive of future disease activity. Serial serum GFAP measurements are emerging as a biomarker to monitor disease activity in AQP4-IgG⁺ NMOSD and could have the potential for application in clinical practice.

Novel CSF Biomarkers Tracking Autoimmune Inflammatory and Neurodegenerative Aspects of CNS Diseases

The accurate diagnosis of neuroinflammatory (NIDs) and neurodegenerative (NDDs) diseases and the stratification of patients into disease subgroups with distinct disease-related characteristics that reflect the underlying pathology represents an unmet clinical need that is of particular interest in the era of emerging disease-modifying therapies (DMT). Proper patient selection for clinical trials and identifying those in the prodromal stages of the diseases or those at high risk will pave the way for precision medicine approaches and halt neuroinflammation and/or neurodegeneration in early stages where this is possible. Towards this direction, novel cerebrospinal fluid (CSF) biomarker candidates were developed to reflect the diseased organ's pathology better. Μisfolded protein accumulation, microglial activation, synaptic dysfunction, and finally, neuronal death are some of the pathophysiological aspects captured by these biomarkers to support proper diagnosis and screening. We also describe advances in the field of molecular biomarkers, including miRNAs and extracellular nucleic acids known as cell-free DNA and mitochondrial DNA molecules. Here we review the most important of these novel CSF biomarkers of NIDs and NDDs, focusing on their involvement in disease development and emphasizing their ability to define homogeneous disease phenotypes and track potential treatment outcomes that can be mirrored in the CSF compartment.

Current view on the diagnosis and treatment of neuromyelitis optica spectrum disorders exacerbations

Irreversible neurological deficit and disability in neuromyelitis optica spectrum disorders (NOSD) are formed as a result of exacerbations, which are often life-threatening. Timely diagnosis and treatment of exacerbations is a key task in the management of this category of patients. A unified structured approach to the diagnosis and treatment of NOSD exacerbations has not been developed. The purpose of this article is to analyze the scientific literature data on this issue in order to optimize the diagnostics and treatment of NOSD exacerbations in everyday clinical practice. 

In utero exposure to maternal anti-aquaporin-4 antibodies alters brain vasculature and neural dynamics in male mouse offspring

The fetal brain is constantly exposed to maternal IgG before the formation of an effective blood-brain barrier (BBB). Here, we studied the consequences of fetal brain exposure to an antibody to the astrocytic protein aquaporin-4 (AQP4-IgG) in mice. AQP4-IgG was cloned from a patient with neuromyelitis optica spectrum disorder (NMOSD), an autoimmune disease that can affect women of childbearing age. We found that embryonic radial glia cells in neocortex express AQP4. These cells are critical for blood vessel and BBB formation through modulation of the WNT signaling pathway. Male fetuses exposed to AQP4-IgG had abnormal cortical vasculature and lower expression of WNT signaling molecules Wnt5a and Wnt7a. Positron emission tomography of adult male mice exposed in utero to AQP4-IgG revealed increased blood flow and BBB leakiness in the entorhinal cortex. Adult male mice exposed in utero to AQP4-IgG had abnormal cortical vessels, fewer dendritic spines in pyramidal and stellate neurons, and more S100β+ astrocytes in the entorhinal cortex. Behaviorally, they showed impairments in the object-place memory task. Neural recordings indicated that their grid cell system, within the medial entorhinal cortex, did not map the local environment appropriately. Collectively, these data implicate in utero binding of AQP4-IgG to radial glia cells as a mechanism for alterations of the developing male brain and adds NMOSD to the conditions in which maternal IgG may cause persistent brain dysfunction in offspring.

Serum and Cerebrospinal Fluid Biomarkers in Neuromyelitis Optica Spectrum Disorder and Myelin Oligodendrocyte Glycoprotein Associated Disease

The term neuromyelitis optica spectrum disorder (NMOSD) describes a group of clinical-MRI syndromes characterized by longitudinally extensive transverse myelitis, optic neuritis, brainstem dysfunction and/or, less commonly, encephalopathy. About 80% of patients harbor antibodies directed against the water channel aquaporin-4 (AQP4-IgG), expressed on astrocytes, which was found to be both a biomarker and a pathogenic cause of NMOSD. More recently, antibodies against myelin oligodendrocyte glycoprotein (MOG-IgG), have been found to be a biomarker of a different entity, termed MOG antibody-associated disease (MOGAD), which has overlapping, but different pathogenesis, clinical features, treatment response, and prognosis when compared to AQP4-IgG-positive NMOSD. Despite important refinements in the accuracy of AQP4-IgG and MOG-IgG testing assays, a small proportion of patients with NMOSD still remain negative for both antibodies and are called “seronegative” NMOSD. Whilst major advances have been made in the diagnosis and treatment of these conditions, biomarkers that could help predict the risk of relapses, disease activity, and prognosis are still lacking. In this context, a number of serum and/or cerebrospinal fluid biomarkers are emerging as potentially useful in clinical practice for diagnostic and treatment purposes. These include antibody titers, cytokine profiles, complement factors, and markers of neuronal (e.g., neurofilament light chain) or astroglial (e.g., glial fibrillary acidic protein) damage. The aim of this review is to summarize current evidence regarding the role of emerging diagnostic and prognostic biomarkers in patients with NMOSD and MOGAD.

Application of deep-learning to the seronegative side of the NMO spectrum

OBJECTIVES

To apply a deep-learning algorithm to brain MRIs of seronegative patients with neuromyelitis optica spectrum disorders (NMOSD) and NMOSD-like manifestations and assess whether their structural features are similar to aquaporin-4-seropositive NMOSD or multiple sclerosis (MS) patients.

PATIENTS AND METHODS

We analyzed 228 T2- and T1-weighted brain MRIs acquired from aquaporin-4-seropositive NMOSD (n = 85), MS (n = 95), aquaporin-4-seronegative NMOSD [n = 11, three with anti-myelin oligodendrocyte glycoprotein antibodies (MOG)], and aquaporin-4-seronegative patients with NMOSD-like manifestations (idiopathic recurrent optic neuritis and myelitis, n = 37), who were recruited from February 2010 to December 2019. Seventy-three percent of aquaporin-4-seronegative patients with NMOSD-like manifestations also had a clinical follow-up (median duration of 4 years). The deep-learning neural network architecture was based on four 3D convolutional layers. It was trained and validated on MRI scans of aquaporin-4-seropositive NMOSD and MS patients and was then applied to aquaporin-4-seronegative NMOSD and NMOSD-like manifestations. Assignment of unclassified aquaporin-4-seronegative patients was compared with their clinical follow-up.

RESULTS

The final algorithm differentiated aquaporin-4-seropositive NMOSD and MS patients with an accuracy of 0.95. All aquaporin-4-seronegative NMOSD and 36/37 aquaporin-4-seronegative patients with NMOSD-like manifestations were classified as NMOSD. Anti-MOG patients had a similar probability of being NMOSD or MS. At clinical follow-up, one unclassified aquaporin-4-seronegative patient evolved to MS, three developed NMOSD, and the others did not change phenotype.

CONCLUSIONS

Our findings support the inclusion of aquaporin4-seronegative patients into NMOSD and suggest a possible expansion to aquaporin-4-seronegative unclassified patients with NMOSD-like manifestations. Anti-MOG patients are likely to have intermediate brain features between NMOSD and MS.

The occurrence of myelin oligodendrocyte glycoprotein antibodies in aquaporin-4-antibody seronegative Neuromyelitis Optica Spectrum Disorder: A systematic review and meta-analysis

BACKGROUND

Despite inclusion in neuromyelitis optica spectrum disorders (NMOSD), myelin oligodendrocyte glycoprotein antibody (MOG-Ab)-associated diseases are increasingly recognized as an independent disease entity. In this study, we conducted a systematic review and meta-analysis to comprehensively update the rate of occurrence of MOG-Ab in Aquaporin4 (AQP4)-antibody seronegative NMOSD.

METHODS

We searched PubMed, EMBASE, and Cochrane databases for studies reporting the rates of patients with MOG-Ab in NMOSD. Fixed or random-effects models were used to pool results across studies.

RESULTS

Fourteen studies met the inclusion criteria. Overall, MOG-Abs positive patients comprised 9.3% of all NMO/NMOSD (95% confidence interval [CI] 7.9%-10.8%, I² = 13.1%), 32.5% of all AQP4-Ab seronegative NMO/NMOSD (95% CI 25.7%-39.3%, I² = 45.8%), and 41.6% of AQP4-Ab seronegative NMOSD cases diagnosed by IPND 2015 criteria (95% CI 35.1%-48.2%, I² = 0.0%). The pooled prevalence of MOG-Ab was 31.0% among Asian AQP4-Ab seronegative NMO/NMOSD patients (95% CI 22.1%-39.9% I²=54.1%) and 34.3% in European seronegative NMO/NMOSD (95% CI 21.9%-46.7%, I² = 51.9%).

CONCLUSIONS

This study shows that MOG-Abs represent a substantial proportion of AQP4-Ab seronegative NMOSD patients despite different underlying mechanisms, clinical manifestations, and treatment response, suggesting MOG-Ab screening in AQP4-Ab seronegative NMOSD patients can facilitate accurate diagnoses and treatments.

CSF levels of glutamine synthetase and GFAP to explore astrocytic damage in seronegative NMOSD

OBJECTIVE

To explore levels of astrocytopathy in neuromyelitis optica spectrum disorder (NMOSD) by measuring levels of the astrocytic enzyme glutamine synthetase (GS) and glial fibrillary acidic protein (GFAP), an established astrocytic biomarker known to be associated with disease activity in multiple sclerosis.

METHODS

Cerebrospinal fluid concentrations of GS and GFAP were measured by ELISA in patients with NMOSD (n=39, 28 aquaporin-4 (AQP4)-Ab-seropositive, 3 double-Ab-seronegative, 4 myelin oligodendrocyte glycoprotein (MOG)-Ab-seropositive and 4 AQP4-Ab-seronegative with unknown MOG-Ab-serostatus), multiple sclerosis (MS) (n=69), optic neuritis (n=5) and non-neurological controls (n=37).

RESULTS

GFAP and GS concentrations differed significantly across groups (both p<0.001), showing a similar pattern of elevation in patients with AQP4-Ab-seropositive NMOSD. GS and GFAP were significantly correlated, particularly in patients with AQP4-Ab-seropositive NMOSD (r_s=0.70, p<0.001). Interestingly, GFAP levels in some patients with double-Ab-seronegative NMOSD were markedly increased.

CONCLUSIONS

Our data indicate astrocytic injury occurs in some patients with double-Ab-seronegative NMOSD, which hints at the possible existence of yet undiscovered astrocytic autoimmune targets. We hypothesise that elevated GS and GFAP levels could identify those double-Ab-seronegative patients suitable to undergo in-depth autoimmune screening for astrocytic antibodies.