Differential Binding of Autoantibodies to MOG Isoforms in Inflammatory Demyelinating Diseases

Distinguishing Neuromyelitis Optica Spectrum Disorders Subtypes: A Study on AQP4 and C3d Epitope Expression in Cytokine-Primed Human Astrocytes

Neuromyelitis optica spectrum disorders (NMOSD) are severe autoimmune conditions affecting the central nervous system. In a subset of cases, no autoantibodies are detectable with the currently used routine assays. This study aimed to determine whether the levels of expression of aquaporin-4 (AQP4), excitatory amino acid transporter 2 (EAAT2), or complement C3/C3d and C5b-9 in human astrocytes following incubation with patient sera under inflammatory conditions differ between the various NMOSD subtypes and whether such differences can help to identify autoantibody-mediated cases of NMOSD. Levels of AQP4, EAAT2, complement C3/C3d and C5b-9 epitope expression on human astrocytes pretreated with various cytokines were quantitatively analyzed via indirect immunofluorescence after exposure to sera from patients with AQP4-IgG seropositive, MOG-IgG seropositive, and AQP4/MOG-IgG double seronegative NMOSD. Significant differences in AQP4 and C3d epitope expression were observed, with IL-17A, IL-10, and IL-6 pre-treatment notably influencing astrocytic responses. Using uniform manifold approximation and projection (UMAP), patients were classified into clusters corresponding to AQP4-IgG seropositive, MOG-IgG seropositive, or double seronegative NMOSD. These results demonstrate distinct astrocytic staining patterns across NMOSD subtypes, providing a potential diagnostic tool for distinguishing between autoantibody-mediated astrocytopathy and other cases. These findings suggest specific pathogenic mechanisms linked to each NMOSD subtype, which may have implications for tailoring therapeutic strategies based on cytokine involvement and astrocyte reactivity.

The MOG antibody non-P42 epitope is predictive of a relapsing course in MOG antibody-associated disease

BACKGROUND

Myelin oligodendrocyte glycoprotein (MOG) IgG seropositivity is a prerequisite for MOG antibody-associated disease (MOGAD) diagnosis. While a significant proportion of patients experience a relapsing disease, there is currently no biomarker predictive of disease course. We aim to determine whether MOG-IgG epitopes can predict a relapsing course in MOGAD patients.

METHODS

MOG-IgG-seropositive confirmed adult MOGAD patients were included (n=202). Serum MOG-IgG and epitope binding were determined by validated flow cytometry live cell-based assays. Associations between epitopes, disease course, clinical phenotype, Expanded Disability Status Scale and Visual Functional System Score at onset and last review were evaluated.

RESULTS

Of 202 MOGAD patients, 150 (74%) patients had MOG-IgG that recognised the immunodominant proline42 (P42) epitope and 115 (57%) recognised histidine103/serine104 (H103/S104). Fifty-two (26%) patients had non-P42 MOG-IgG and showed an increased risk of a relapsing course (HR 1.7; 95% CI 1.15 to 2.60, p=0.009). Relapse-freedom was shorter in patients with non-P42 MOG-IgG (p=0.0079). Non-P42 MOG-IgG epitope status remained unchanged from onset throughout the disease course and was a strong predictor of a relapsing course in patients with unilateral optic neuritis (HR 2.7, 95% CI 1.06 to 6.98, p=0.038), with high specificity (95%, 95% CI 77% to 100%) and positive predictive value (85%, 95% CI 45% to 98%).

CONCLUSIONS

Non-P42 MOG-IgG predicts a relapsing course in a significant subgroup of MOGAD patients. Patients with unilateral optic neuritis, the most frequent MOGAD phenotype, can reliably be tested at onset, regardless of age and sex. Early detection and specialised management in these patients could minimise disability and improve long-term outcomes.

Is there an immunological cross-reactivity of antibodies to the myelin oligodendrocyte glycoprotein and coronaviruses?

Recent reports indicated that myelin oligodendrocyte glycoprotein antibody-associated disease might be a rare complication after severe acute respiratory syndrome coronavirus 2 infection or vaccination. It is unclear whether this is an unspecific sequel of infection or vaccination or caused by possible immunological cross-reactivity of severe acute respiratory syndrome coronavirus 2 proteins and myelin oligodendrocyte glycoprotein. The aim of this study was therefore to elucidate whether there is an immunological cross-reactivity between severe acute respiratory syndrome coronavirus 2 spike or nucleocapsid proteins and myelin oligodendrocyte glycoprotein and to explore the relation of antibody responses against myelin oligodendrocyte glycoprotein and severe acute respiratory syndrome coronavirus 2 and other coronaviruses. We analysed serum samples from patients with severe acute respiratory syndrome coronavirus 2 infection and neurological symptoms with (myelin oligodendrocyte glycoprotein antibody-associated disease, n = 12) or without myelin oligodendrocyte glycoprotein-antibodies (n = 10); severe acute respiratory syndrome coronavirus 2 infection without neurological symptoms (n = 32); vaccinated patients with no history of severe acute respiratory syndrome coronavirus 2 infection and neurological symptoms with (myelin oligodendrocyte glycoprotein antibody-associated disease, n = 10) or without myelin oligodendrocyte glycoprotein-antibodies (n = 9); and severe acute respiratory syndrome coronavirus 2 negative/naïve unvaccinated patients with neurological symptoms with (myelin oligodendrocyte glycoprotein antibody-associated disease, n = 47) or without myelin oligodendrocyte glycoprotein-antibodies (n = 20). All samples were analysed for serum antibody responses to myelin oligodendrocyte glycoprotein, severe acute respiratory syndrome coronavirus 2, and other common coronaviruses (CoV-229E, CoV-HKU1, CoV-NL63 and CoV-OC43). Based on sample amount and antibody titres, 21 samples were selected for analysis of antibody cross-reactivity between myelin oligodendrocyte glycoprotein and severe acute respiratory syndrome coronavirus 2 spike and nucleocapsid proteins using affinity purification and pre-absorption. Whereas we found no association of immunoglobulin G and A myelin oligodendrocyte glycoprotein antibodies with coronavirus antibodies, infections with severe acute respiratory syndrome coronavirus 2 correlated with an increased immunoglobulin M myelin oligodendrocyte glycoprotein antibody response. Purified antibodies showed no cross-reactivity between severe acute respiratory syndrome coronavirus 2 spike protein and myelin oligodendrocyte glycoprotein. However, one sample of a patient with myelin oligodendrocyte glycoprotein antibody-associated disease following severe acute respiratory syndrome coronavirus 2 infection showed a clear immunoglobulin G antibody cross-reactivity to severe acute respiratory syndrome coronavirus 2 nucleocapsid protein and myelin oligodendrocyte glycoprotein. This patient was also seropositive for other coronaviruses and showed immunological cross-reactivity of severe acute respiratory syndrome coronavirus 2 and CoV-229E nucleocapsid proteins. Overall, our results indicate that an immunoglobulin G antibody cross-reactivity between myelin oligodendrocyte glycoprotein and severe acute respiratory syndrome coronavirus 2 proteins is rare. The presence of increased myelin oligodendrocyte glycoprotein-immunoglobulin M antibodies after severe acute respiratory syndrome coronavirus 2 infection may either be a consequence of a previous infection with other coronaviruses or arise as an unspecific sequel after viral infection. Furthermore, our data indicate that myelin oligodendrocyte glycoprotein-immunoglobulin A and particularly myelin oligodendrocyte glycoprotein-immunoglobulin M antibodies are a rather unspecific sequel of viral infections. Finally, our findings do not support a causative role of coronavirus infections for the presence of myelin oligodendrocyte glycoprotein-immunoglobulin G antibodies.

The pathogenesis of multiple sclerosis: a series of unfortunate events

Multiple sclerosis (MS) is characterized by the chronic inflammatory destruction of myelinated axons in the central nervous system. Several ideas have been put forward to clarify the roles of the peripheral immune system and neurodegenerative events in such destruction. Yet, none of the resulting models appears to be consistent with all the experimental evidence. They also do not answer the question of why MS is exclusively seen in humans, how Epstein-Barr virus contributes to its development but does not immediately trigger it, and why optic neuritis is such a frequent early manifestation in MS. Here we describe a scenario for the development of MS that unifies existing experimental evidence as well as answers the above questions. We propose that all manifestations of MS are caused by a series of unfortunate events that usually unfold over a longer period of time after a primary EBV infection and involve periodic weakening of the blood-brain barrier, antibody-mediated CNS disturbances, accumulation of the oligodendrocyte stress protein αB-crystallin and self-sustaining inflammatory damage.

Pathogenesis, Clinical Features, and Treatment of Patients with Myelin Oligodendrocyte Glycoprotein (MOG) Autoantibody-Associated Disorders Focusing on Optic Neuritis with Consideration of Autoantibody-Binding Sites: A Review

Although there is a substantial amount of data on the clinical characteristics, diagnostic criteria, and pathogenesis of myelin oligodendrocyte glycoprotein (MOG) autoantibody-associated disease (MOGAD), there is still uncertainty regarding the MOG protein function and the pathogenicity of anti-MOG autoantibodies in this disease. It is important to note that the disease characteristics, immunopathology, and treatment response of MOGAD patients differ from those of anti-aquaporin 4 antibody-positive neuromyelitis optica spectrum disorders (NMOSDs) and multiple sclerosis (MS). The clinical phenotypes of MOGAD are varied and can include acute disseminated encephalomyelitis, transverse myelitis, cerebral cortical encephalitis, brainstem or cerebellar symptoms, and optic neuritis. The frequency of optic neuritis suggests that the optic nerve is the most vulnerable lesion in MOGAD. During the acute stage, the optic nerve shows significant swelling with severe visual symptoms, and an MRI of the optic nerve and brain lesion tends to show an edematous appearance. These features can be alleviated with early extensive immune therapy, which may suggest that the initial attack of anti-MOG autoantibodies could target the structures on the blood-brain barrier or vessel membrane before reaching MOG protein on myelin or oligodendrocytes. To understand the pathogenesis of MOGAD, proper animal models are crucial. However, anti-MOG autoantibodies isolated from patients with MOGAD do not recognize mouse MOG efficiently. Several studies have identified two MOG epitopes that exhibit strong affinity with human anti-MOG autoantibodies, particularly those isolated from patients with the optic neuritis phenotype. Nonetheless, the relations between epitopes on MOG protein remain unclear and need to be identified in the future.

Depression and Hand-Grip: Unraveling the Association

This review article explores the association between hand-grip strength and depression. A total of 14 studies were carefully considered to provide a comprehensive analysis of the topic. The studies reveal a consistent association between low hand-grip strength and depressive symptoms, independent of age, gender, and chronic disease status. The evidence suggests that hand-grip strength assessment could be a useful tool for identifying individuals at risk of depression, particularly older adults and those with chronic diseases. Incorporating physical activity and strength training into treatment plans can contribute to better mental health outcomes. Hand-grip strength assessment can also be used as a monitoring tool to track changes in physical and mental health over time in individuals with depression. Healthcare professionals should consider the relationship between hand-grip strength and depression when evaluating patients and developing treatment plans. The findings from this comprehensive clinical review have important clinical implications and highlight the importance of considering physical health factors in the context of mental health.

Myelin Oligodendrocyte Glycoprotein as an Autoantigen in Inflammatory Demyelinating Diseases of the Central Nervous System

Demyelinating diseases of the central nervous system are caused by an autoimmune attack on the myelin sheath surrounding axons. Myelin structural proteins become antigenic, leading to the development of myelin lesions. The use of highly specialized laboratory diagnostic techniques for identification of specific antibodies directed against myelin components can significantly improve diagnostic approaches. Myelin oligodendrocyte glycoprotein (MOG) antibody-associated disease (MOGAD) currently includes demyelinating syndromes with known antigens. Based on the demonstrated pathogenic role of human IgG against MOG, MOGAD was classified as a distinct nosological entity. However, generation of multiple MOG isoforms by alternative splicing hinders antigen detection even with the most advanced immunofluorescence techniques. On the other hand, MOG conformational changes ensure the structural integrity of other myelin proteins and maintain human-specific mechanisms of immune autotolerance.

Dissection of complement and Fc-receptor-mediated pathomechanisms of autoantibodies to myelin oligodendrocyte glycoprotein

Autoantibodies against myelin oligodendrocyte glycoprotein (MOG) have recently been established to define a new disease entity, MOG-antibody-associated disease (MOGAD), which is clinically overlapping with multiple sclerosis. MOG-specific antibodies (Abs) from patients are pathogenic, but the precise effector mechanisms are currently still unknown and no therapy is approved for MOGAD. Here, we determined the contributions of complement and Fc-receptor (FcR)-mediated effects in the pathogenicity of MOG-Abs. Starting from a recombinant anti-MOG (mAb) with human IgG1 Fc, we established MOG-specific mutant mAbs with differential FcR and C1q binding. We then applied selected mutants of this MOG-mAb in two animal models of experimental autoimmune encephalomyelitis. First, we found MOG-mAb-induced demyelination was mediated by both complement and FcRs about equally. Second, we found that MOG-Abs enhanced activation of cognate MOG-specific T cells in the central nervous system (CNS), which was dependent on FcR-, but not C1q-binding. The identification of complement-dependent and -independent pathomechanisms of MOG-Abs has implications for therapeutic strategies in MOGAD.

The Potential Pathogenicity of Myelin Oligodendrocyte Glycoprotein Antibodies in the Optic Pathway

BACKGROUND

Myelin oligodendrocyte glycoprotein (MOG) antibody-associated disease (MOGAD) is an acquired inflammatory demyelinating disease with optic neuritis (ON) as the most frequent clinical symptom. The hallmark of the disease is the presence of autoantibodies against MOG (MOG-IgG) in the serum of patients. Whereas the role of MOG in the experimental autoimmune encephalomyelitis animal model is well-established, the pathogenesis of the human disease and the role of human MOG-IgG is still not fully clear.

EVIDENCE ACQUISITION

PubMed was searched for the terms "MOGAD," "optic neuritis," "MOG antibodies," and "experimental autoimmune encephalomyelitis" alone or in combination, to find articles of interest for this review. Only articles written in English language were included and reference lists were searched for further relevant papers.

RESULTS

B and T cells play a role in the pathogenesis of human MOGAD. The distribution of lesions and their development toward the optic pathway is influenced by the genetic background in animal models. Moreover, MOGAD-associated ON is frequently bilateral and often relapsing with generally favorable visual outcome. Activated T-cell subsets create an inflammatory environment and B cells are necessary to produce autoantibodies directed against the MOG protein. Here, pathologic mechanisms of MOG-IgG are discussed, and histopathologic findings are presented.

CONCLUSIONS

MOGAD patients often present with ON and harbor antibodies against MOG. Furthermore, pathogenesis is most likely a synergy between encephalitogenic T and antibody producing B cells. However, to which extent MOG-IgG are pathogenic and the exact pathologic mechanism is still not well understood.

More Efficient Complement Activation by Anti–Aquaporin-4 Compared With Anti–Myelin Oligodendrocyte Glycoprotein Antibodies

Background and Objectives

The objective was to study complement-mediated cytotoxicity induced by immunoglobulin G (IgG) anti–aquaporin-4 antibodies (AQP4-IgG) and anti–myelin oligodendrocyte glycoprotein antibodies (MOG-IgG) in human serum samples from patients suffering from the rare demyelinating diseases of the CNS neuromyelitis optica spectrum disorder (NMOSD) and MOG-IgG–associated disease (MOGAD).

Methods

A cell-based assay with HEK293A cells expressing different MOG isoforms (MOGα1-3β1-3) or AQP4-M23 was used. Cells were incubated with human MOG-IgG or AQP4-IgG–positive serum samples together with active or heat-inactivated human complement, and complement-dependent cytotoxicity (CDC) was measured with a lactate dehydrogenase assay. To further quantify antibody-mediated cell damage, formation of the terminal complement complex (TCC) was analyzed by flow cytometry. In addition, immunocytochemistry of the TCC and complement component 3 (C3) was performed.

Results

AQP4-IgG–positive serum samples induced higher CDC and TCC levels than MOG-IgG–positive sera. Notably, both showed a correlation between antibody titers and CDC and also between titers and TCC levels. In addition, all 6 MOG isoforms tested (MOGα1-3β1-3) could induce at least some CDC; however, the strongest MOG-IgG–induced CDC levels were found on MOGα1, MOGα3, and MOGβ1. Different MOG-IgG binding patterns regarding recognition of different MOG isoforms were investigated, and it was found that MOG-IgG recognizing all 6 isoforms again induced highest CDC levels on MOGα1and MOGβ1. Furthermore, surface staining of TCC and C3 revealed positive staining on all 6 MOG isoforms tested, as well as on AQP4-M23.

Discussion

Both MOG-IgG and AQP4-IgG are able to induce CDC in a titer-dependent manner. However, AQP4-IgG showed markedly higher levels of CDC compared with MOG in vitro on target cells. This further highlights the role of complement in AQP4-IgG–mediated disease and diminishes the importance of complement activation in MOG-IgG–mediated autoimmune disease.

A genetic correlation and bivariate genome-wide association study of grip strength and depression

Grip strength is an important biomarker reflecting muscle strength, and depression is a psychiatric disorder all over the world. Several studies found a significant inverse association between grip strength and depression, and there is also evidence for common physiological mechanisms between them. We used twin data from Qingdao, China to calculate genetic correlations, and we performed a bivariate GWAS to explore potential SNPs, genes, and pathways in common between grip strength and depression. 139 pairs of Dizygotic twins were used for bivariate GWAS. VEAGSE2 and PASCAL software were used for gene-based analysis and pathway enrichment analysis, respectively. And the resulting SNPs were subjected to eQTL analysis and pleiotropy analysis. The genetic correlation coefficient between grip strength and depression was -0.41 (-0.96, -0.15). In SNP-based analysis, 7 SNPs exceeded the genome-wide significance level (P<5×10-8) and a total of 336 SNPs reached the level of suggestive significance (P<1×10-5). Gene-based analysis and pathway-based analysis identified genes and pathways related to muscle strength and the nervous system. The results of eQTL analysis were mainly enriched in tissues such as the brain, thyroid, and skeletal muscle. Pleiotropy analysis shows that 9 of the 15 top SNPs were associated with both grip strength and depression. In conclusion, this bivariate GWAS identified potentially common pleiotropic SNPs, genes, and pathways in grip strength and depression.

Peripheral neuropathy and MOG-IgG: A clinical and neuropathological retrospective study

BACKGROUND

Myelin oligodendrocyte glycoprotein antibodies (MOG-Abs) may rarely be associated with peripheral nervous system involvement. We aimed to test MOG-Abs in patients with undetermined peripheral neuropathy (PN).

METHODS

Consecutive patients with available sural nerve biopsy and paired serum sample were retrospectively identified (January, 1st 2016-November, 1st 2021) and tested for MOG-Abs with live cell-based assay (CBA). Patients with antibody titre ≥1:160 (secondary H + L antibody) and selective MOG-IgG presence (IgG-Fc predominance) were considered MOG-IgG positive. All positive samples were analysed with immunohistochemistry and CBAs for antibodies against Neurofascin-155 and Contactin-1. Clinical and neuropathological data were collected through clinical reports.

RESULTS

Among 163 patients, 5 (3%) resulted positive for predominantly IgG MOG-Abs (median titer 1:320, range 1:160-1:5120), none showed other concomitant antibodies. Median age was 74 years-old (range 55-81), median disease duration was 60 months (range 1-167), 60% of patients were female. Of these, 4/5 cases had clinical features suggestive of acute (n = 1) or chronic (n = 3) inflammatory demyelinating neuropathy, 2/5 fulfilled the criteria of combined central and peripheral demyelination (CCPD) whilst 3/5 had isolated PNS involvement. Neuropathological findings showed mixed axonal-demyelinating features in 2/5, predominant demyelination in 3/5 cases. Other neuropathological hallmarks included paranodal demyelination (n = 3), myelin outfoldings (n = 4), slight inflammatory infiltrates (n = 3), onion bulbs (n = 3), and clusters of regeneration (n = 4).

DISCUSSION

MOG-IgG can be detected in patients with isolated PN or CCPD. Clinical and neuropathological features are suggestive for demyelination and slight inflammation. Further studies should include larger cohorts of patients to elucidate the utility of MOG-Abs testing in PN.

Diagnostik der Neuromyelitis-optica-Spektrum-Erkrankung (NMOSD) und der MOG-Antikörper-assoziierten Erkrankung (MOGAD)

Die Aquaporin-4-Antikörper-positive Neuromyelitis-optica-Spektrum-Erkrankung (engl. NMOSD) und die Myelin-Oligodendrozyten-Glykoprotein-Antikörper-assoziierte Erkrankung (engl. MOGAD) sind Autoimmunerkrankungen des zentralen Nervensystems. Typische Erstmanifestationen sind bei Erwachsenen Optikusneuritis und Myelitis. Eine Beteiligung auch von Hirn und Hirnstamm, spätestens im weiteren Verlauf, ist häufig. Während die NMOSD nahezu immer schubförmig verläuft, nimmt die MOGAD gelegentlich einen monophasischen Verlauf. Die Differenzialdiagnostik ist anspruchsvoll und stützt sich auf u. a. auf radiologische und serologische Befunde. Die Abgrenzung von der häufigeren neuroinflammatorischen Erkrankung, Multiple Sklerose (MS), ist von erheblicher Bedeutung, da sich Behandlung und langfristige Prognose von NMOSD, MOGAD und MS wesentlich unterscheiden. Die vielfältigen Symptome und die umfangreiche Diagnostik machen eine enge Zusammenarbeit zwischen Ophthalmologie, Neurologie und Radiologie erforderlich. Dieser Artikel gibt einen Überblick über typische MRT-Befunde und die serologische Antikörperdiagnostik bei NMOSD und MOGAD. Zwei illustrative Fallberichte aus der ärztlichen Praxis ergänzen die Darstellung.

Comparison on the effect of seven drugs to prevent relapses of neuromyelitis optica spectrum disorders: A modeling analysis of literature aggregate data

BACKGROUND

Neuromyelitis optica spectrum disorders (NMOSD) is an immune-mediated demyelinating disease of the central nervous system. This study aimed to perform a comprehensive comparison of the effect of seven drugs to prevent relapses of NMOSD.

METHOD

A literature search was conducted using public databases. Clinical studies on the seven drugs (eculizumab, inebilizumab, satralizumab, rituximab, tocilizumab, azathioprine, and mycophenolate mofetil) to prevent relapses of NMOSD were identified. A time-course model was established using the time to first relapse as the primary endpoint, in order to evaluate the long-term effect of each drug in preventing relapse.

RESULTS

Twenty-four trials, including 2207 patients, were included in the model analysis. The results showed that monoclonal antibody therapy could significantly prolong the time to first relapse. Among all seven drugs, eculizumab can most significantly prevent patient from relapse. The estimated proportion of relapse-free patients treated with eculizumab was 98.9% at 24 months.

CONCLUSION

Based on the construction of a time-course pharmacodynamic model, this study made a comprehensive quantitative comparison of seven drugs for the treatment of NMOSD for the first time. These results can not only serve as a quantitative supplement for the rational use of drugs in clinical practice but also provide a pharmacodynamic reference for clinical trial design and decision making in the future.

Testing for Antibodies Against Aquaporin-4 and Myelin Oligodendrocyte Glycoprotein in the Diagnosis of Patients With Suspected Autoimmune Myelopathy

Autoimmune myelopathies are immune-mediated disorders of the spinal cord that can cause significant neurologic disability. Discoveries of antibodies targeting aquaporin-4 (AQP4-IgG) and myelin oligodendrocyte glycoprotein (MOG-IgG) have facilitated the diagnosis of autoimmune myelopathies that were previously considered to be atypical presentations of multiple sclerosis (MS) or idiopathic, and represent major advancements in the field of autoimmune neurology. The detection of these antibodies can substantially impact patient diagnosis and management, and increasing awareness of this has led to a dramatic increase in testing for these antibodies among patients with suspected autoimmune myelopathy. In this review we discuss test methodologies used to detect these antibodies, the role of serum vs. cerebrospinal fluid testing, and the value of antibody titers when interpreting results, with the aim of helping laboratorians and clinicians navigate this testing when ordered as part of the diagnostic evaluation for suspected autoimmune myelopathy.

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.