Genome-wide Association Study Identifies 2 New Loci Associated With Anti-NMDAR Encephalitis

From immunobiology to intervention: Pathophysiology of autoimmune encephalitis

Autoimmune encephalitides (AEs) are neurological disorders caused by autoantibodies against neuronal and glial surface proteins. Nearly 20 years after their discovery, AE have evolved from being frequently misdiagnosed and untreated to a growing group of increasingly well-characterized conditions where patients benefit from targeted therapeutic strategies. This narrative review provides an immunological perspective on AE, focusing on NMDAR, CASPR2 and LGI1 encephalitis as the three most common forms of AE associated with anti-neuronal surface autoantibodies. We examine the autoreactive B cell subsets, the tolerance checkpoints that may fail, and the known triggers and predispositions contributing to disease. In addition, we discuss the roles of other immune cells, including T cells and microglia, in the pathogenesis of AE. By analyzing therapeutic strategies and treatment responses we draw insights into AE pathophysiology. Written at a time of transformative therapeutic advancements through cell therapies this work underscores the synergy between detailed immunological research and the development of innovative therapies.

Cerebrospinal fluid-specific oligoclonal bands in dogs with idiopathic epilepsy

BACKGROUND

In dogs with idiopathic epilepsy (IE), 33% develop resistance to conventional anti-seizure medication (ASM) despite adequate treatment. In human medicine, an immune-mediated etiology is suspected in a subset of ASM-resistant patients with epilepsy and cerebrospinal fluid (CSF)-specific immunoglobulin G (IgG)-type oligoclonal bands (OCBs) have been detected. In dogs, cases of autoimmune encephalitis recently were reported. Neuroinflammation may provide an additional explanation for the lack of response of certain dogs with IE to ASM.

HYPOTHESIS

Cerebrospinal fluid-specific OCBs are found in a subgroup of dogs with ASM-resistant IE.

ANIMALS

Eighty-four dogs with IE were recruited from 3 referral centers and classified based on their response to ASM treatment (responsive, n = 56; resistant, n = 28).

METHODS

Detection of OCBs was performed using isoelectric focusing (IEF) followed by immunoblotting. Associations of CSF-specific OCBs with seizure type, severity, and response to ASM were calculated using logistic regression models.

RESULTS

The overall frequency of CSF-specific OCBs in dogs with IE was 15.5% (95% confidence interval [CI], 8.5%-25%). In dogs with ASM-resistant IE, 21.4% (6/28) had CSF-specific OCBs compared with only 12.5% (7/56) in those responsive to ASM, but no evidence of an association was detected (odds ratio, 1.9; 95% CI, 0.57-6.35; P = .29).

CONCLUSIONS AND CLINICAL IMPORTANCE

Cerebrospinal fluid-specific OCBs were detected in a subgroup of dogs with IE. This finding could indicate that intrathecal IgG synthesis as a sign of neuroinflammation may play a role in disease pathogenesis.

Strategies to improve autoimmune neurological diseases treatment

There is a need to improve therapies in autoimmune neurologic conditions. Yet which strategic objectives are required, what are the barriers that stand before reaching them, and what are the options to address them? This article tries to summarize these objectives and their respective barriers. It discusses the difficulties in identifying molecular targets, biomarker-defined subgroups, the merits of upstream and downstream-targeted therapies, the need to develop autoreactivity-specific treatments in contrast to cell-type specific therapies, and the "evidence-bottleneck". Its focus is on autoantigen-specific autoimmunopathies in neurology. It also discusses the role of B- and T-cells in autoimmune neurology and how these can be exploited therapeutically. Finally, it argues for improved training of present and future neuroimmunologists.

Immune-mediated neurological syndromes associated with childhood cancers

The association of recognisable neurological conditions with an underlying malignancy is well described. In this review we explore the complex interplay of genetic, environmental and tumour factors which contribute to autoimmunity and paraneoplastic conditions. We review the current understanding of the pathogenesis of well recognised paraneoplastic conditions in children including Opsoclonus myoclonus ataxia syndrome, N-Methyl-D Aspartate receptor encephalitis and limbic encephalitis, and the broad approaches to treatment. Rapid advances in oncological treatment has expanded the arsenal of therapeutic modalities. We explore the broad spectrum of immune therapies in childhood cancer, and the potential neurological complications of these novel therapies, and discuss the fine balance of risk and benefit that these bring.

HLA and KIR genetic association and NK cells in anti-NMDAR encephalitis

Introduction

Genetic predisposition to autoimmune encephalitis with antibodies against N-methyl-D-aspartate receptor (NMDAR) is poorly understood. Given the diversity of associated environmental factors (tumors, infections), we hypothesized that human leukocyte antigen (HLA) and killer-cell immunoglobulin-like receptors (KIR), two extremely polymorphic gene complexes key to the immune system, might be relevant for the genetic predisposition to anti-NMDAR encephalitis. Notably, KIR are chiefly expressed by Natural Killer (NK) cells, recognize distinct HLA class I allotypes and play a major role in anti-tumor and anti-infection responses.

Methods

We conducted a Genome Wide Association Study (GWAS) with subsequent control-matching using Principal Component Analysis (PCA) and HLA imputation, in a multi-ethnic cohort of anti-NMDAR encephalitis (n=479); KIR and HLA were further sequenced in a large subsample (n=323). PCA-controlled logistic regression was then conducted for carrier frequencies (HLA and KIR) and copy number variation (KIR). HLA-KIR interaction associations were also modeled. Additionally, single cell sequencing was conducted in peripheral blood mononuclear cells from 16 cases and 16 controls, NK cells were sorted and phenotyped.

Results

Anti-NMDAR encephalitis showed a weak HLA association with DRB1*01:01~DQA1*01:01~DQB1*05:01 (OR=1.57, 1.51, 1.45; respectively), and DRB1*11:01 (OR=1.60); these effects were stronger in European descendants and in patients without an underlying ovarian teratoma. More interestingly, we found increased copy number variation of KIR2DL5B (OR=1.72), principally due to an overrepresentation of KIR2DL5B*00201. Further, we identified two allele associations in framework genes, KIR2DL4*00103 (25.4% vs. 12.5% in controls, OR=1.98) and KIR3DL3*00302 (5.3% vs. 1.3%, OR=4.44). Notably, the ligands of these KIR2DL4 and KIR3DL3, respectively, HLA-G and HHLA2, are known to act as immune checkpoint with immunosuppressive functions. However, we did not find differences in specific KIR-HLA ligand interactions or HLA-G polymorphisms between cases and controls. Similarly, gene expression of CD56dim or CD56bright NK cells did not differ between cases and controls.

Discussion

Our observations for the first time suggest that the HLA-KIR axis might be involved in anti-NMDAR encephalitis. While the genetic risk conferred by the identified polymorphisms appears small, a role of this axis in the pathophysiology of this disease appears highly plausible and should be analyzed in future studies.

Genetic predisposition to autoimmune encephalitis and paraneoplastic neurological syndromes

PURPOSE OF REVIEW

We summarize the recent discoveries on genetic predisposition to autoimmune encephalitis and paraneoplastic neurological syndromes (PNS), emphasizing clinical and pathophysiological implications.

RECENT FINDINGS

The human leukocyte antigen (HLA) is the most studied genetic factor in autoimmune encephalitis and PNS. The HLA haplotype 8.1, which is widely known to be related to systemic autoimmunity, has been only weakly associated with a few types of autoimmune encephalitis and PNS. However, the strongest and most specific associations have been reported in a subgroup of autoimmune encephalitis that comprises antileucine-rich glioma-inactivated 1 (LGI1) limbic encephalitis, associated with DRB1∗07 : 01 , anticontactin-associated protein-like 2 (CASPR2) limbic encephalitis, associated with DRB1∗11 : 01 , and anti-IgLON5 disease, associated with DRB1∗10 : 01∼DQA1∗01∼DQB1∗05 . Non-HLA genes have been poorly investigated so far in autoimmune encephalitis, mainly in those lacking HLA associations such as anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis, with only a few genome-wide association studies (GWAS) reporting equivocal results principally limited by small sample size.

SUMMARY

Genetic predisposition seems to be driven mostly by HLA in a group of autoimmune encephalitis characterized by being nonparaneoplastic and having predominantly IgG4 autoantibodies. The contribution of non-HLA genes, especially in those diseases lacking known or strong HLA associations, will require large cohorts enabling GWAS to be powerful enough to render meaningful results.

Comparative Study of Paraneoplastic and Nonparaneoplastic Autoimmune Encephalitis With GABABR Antibodies

BACKGROUND AND OBJECTIVES

While patients with paraneoplastic autoimmune encephalitis (AE) with gamma-aminobutyric-acid B receptor antibodies (GABABR-AE) have poor functional outcomes and high mortality, the prognosis of nonparaneoplastic cases has not been well studied.

METHODS

Patients with GABABR-AE from the French and the Dutch Paraneoplastic Neurologic Syndromes Reference Centers databases were retrospectively included and their data collected; the neurologic outcomes of paraneoplastic and nonparaneoplastic cases were compared. Immunoglobulin G (IgG) isotyping and human leukocyte antigen (HLA) genotyping were performed in patients with available samples.

RESULTS

A total of 111 patients (44/111 [40%] women) were enrolled, including 84 of 111 (76%) paraneoplastic and 18 of 111 (16%) nonparaneoplastic cases (cancer status was undetermined for 9 patients). Patients presented with seizures (88/111 [79%]), cognitive impairment (54/111 [49%]), and/or behavioral disorders (34/111 [31%]), and 54 of 111 (50%) were admitted in intensive care unit (ICU). Nonparaneoplastic patients were significantly younger (median age 54 years [range 19-88] vs 67 years [range 50-85] for paraneoplastic cases, p < 0.001) and showed a different demographic distribution. Nonparaneoplastic patients more often had CSF pleocytosis (17/17 [100%] vs 58/78 [74%], p = 0.02), were almost never associated with KTCD16-abs (1/16 [6%] vs 61/70 [87%], p < 0.001), and were more frequently treated with second-line immunotherapy (11/18 [61%] vs 18/82 [22%], p = 0.003). However, no difference of IgG subclass or HLA association was observed, although sample size was small (10 and 26 patients, respectively). After treatment, neurologic outcome was favorable (mRS ≤2) for 13 of 16 (81%) nonparaneoplastic and 37 of 84 (48%) paraneoplastic cases (p = 0.03), while 3 of 18 (17%) and 42 of 83 (51%) patients had died at last follow-up (p = 0.008), respectively. Neurologic outcome no longer differed after adjustment for confounding factors but seemed to be negatively associated with increased age and ICU admission. A better survival was associated with nonparaneoplastic cases, a younger age, and the use of immunosuppressive drugs.

DISCUSSION

Nonparaneoplastic GABABR-AE involved younger patients without associated KCTD16-abs and carried better neurologic and vital prognoses than paraneoplastic GABABR-AE, which might be due to a more intensive treatment strategy. A better understanding of immunologic mechanisms underlying both forms is needed.

Genome-Wide Association Study Identifies IFIH1 and HLA-DQB1*05:02 Loci Associated With Anti-NMDAR Encephalitis

BACKGROUND AND OBJECTIVES

Anti-N-methyl-d-aspartate receptor (NMDAR) encephalitis is a rare autoimmune neurologic disorder, the genetic etiology of which remains poorly understood. Our study aims to investigate the genetic basis of this disease in the Chinese Han population.

METHODS

We performed a genome-wide association study and fine-mapping study within the major histocompatibility complex (MHC) region of 413 Chinese patients with anti-NMDAR encephalitis recruited from 6 large tertiary hospitals and 7,127 healthy controls.

RESULTS

Our genome-wide association analysis identified a strong association at the IFIH1 locus on chromosome 2q24.2 (rs3747517, p = 1.06 × 10-8, OR = 1.55, 95% CI, 1.34-1.80), outside of the human leukocyte antigen (HLA) region. Furthermore, through a fine-mapping study of the MHC region, we discovered associations for 3 specific HLA class I and II alleles. Notably, HLA-DQB1*05:02 (p = 1.43 × 10-12; OR, 2.10; 95% CI 1.70-2.59) demonstrates the strongest association among classical HLA alleles, closely followed by HLA-A*11:01 (p = 4.36 × 10-7; OR, 1.52; 95% CI 1.29-1.79) and HLA-A*02:07 (p = 1.28 × 10-8; OR, 1.87; 95% CI 1.50-2.31). In addition, we uncovered 2 main HLA amino acid variation associated with anti-NMDAR encephalitis including HLA-DQβ1-126H (p = 1.43 × 10-12; OR, 2.10; 95% CI 1.70-2.59), exhibiting a predisposing effect, and HLA-B-97R (p = 3.40 × 10-8; OR, 0.63; 95% CI 0.53-0.74), conferring a protective effect. Computational docking analysis suggested a close relationship between the NR1 subunit of NMDAR and DQB1*05:02.

DISCUSSION

Our findings indicate that genetic variation in IFIH1, involved in the type I interferon signaling pathway and innate immunity, along with variations in the HLA class I and class II genes, has substantial implications for the susceptibility to anti-NMDAR encephalitis in the Chinese Han population.

Immune-mediated encephalitis

A neurological deterioration in a child presents a significant worry to the family and often a diagnostic challenge to the clinician. A dysregulated immune response is implicated in a wide and growing spectrum of neurological conditions. In this review we consider the current paradigms in which immune-mediated encephalopathies are considered; the development of paediatric specific diagnostic criteria that facilitate early consideration and treatment of immune-mediated conditions and the limitations and potential developments in diagnostic testing. We consider the expanding phenotype of myelin oligodendrocyte glycoprotein antibody, the spectrum of virus-associated encephalopathy syndromes, and the strategies that have been employed to build an evidence base for the management of these rare conditions. Looking forward we explore the potential for advanced molecular investigations to improve our understanding of immune-mediated encephalitides and guide future treatment strategies. Recently characterized immune-mediated central nervous system disorders include new antibodies causing previously recognized phenotypes. Aggregation of conditions with similar clinical triggers, and characterization of unique imaging features in virus-associated encephalopathy syndromes. Immune treatment iscurrently guided by meta-analysis of individualized patient data and/or multi-national consensus.

Teratoma pathology and genomics in anti-NMDA receptor encephalitis

INTRODUCTION

Ovarian teratoma is a common occurrence in patients with anti-NMDA receptor encephalitis (NMDARe), and its removal is crucial for a favorable prognosis. However, the initial pathogenesis of autoimmunity in the encephalitic teratoma remains unclear. In this study, we aimed to investigate the genomic landscape and microscopic findings by comparing NMDARe-associated teratomas and non-encephalitic control teratomas.

MATERIALS AND METHODS

A prospective consecutive cohort of 84 patients with NMDARe was recruited from January 2014 to April 2020, and among them, patients who received teratoma removal surgery at Seoul National University Hospital were enrolled. We conducted a comparison of whole-exome sequencing data and pathologic findings between NMDARe-associated teratomas and control teratomas.

RESULTS

We found 18 NMDARe-associated teratomas from 15 patients and compared them with 17 non-encephalitic control teratomas. Interestingly, the genomic analysis revealed no significant differences in mutations between encephalitic and non-encephalitic teratomas. Pathologic analysis showed no discrepancies in terms of the presence of neuronal tissue and lymphocytic infiltration between the encephalitic teratomas (n = 14) and non-encephalitic teratomas (n = 18). However, rituximab-naïve encephalitic teratomas exhibited a higher frequency of germinal center formation compared to non-encephalitic teratomas (80% vs. 16.7%, P = 0.017). Additionally, rituximab-treated encephalitic teratomas demonstrated a reduced number of CD20+ cells and germinal centers in comparison to rituximab-naïve encephalitic teratomas (P = 0.048 and 0.023, respectively).

DISCUSSION

These results suggest that the initiation of immunopathogenesis in NMDARe-associated teratoma is not primarily attributed to intrinsic tumor mutations, but rather to immune factors present in the encephalitic patient group, ultimately leading to germinal center formation within the teratoma.

General features, pathogenesis, and laboratory diagnostics of autoimmune encephalitis

Autoimmune encephalitis (AE) is a group of inflammatory conditions that can associate with the presence of antibodies directed to neuronal intracellular, or cell surface antigens. These disorders are increasingly recognized as an important differential diagnosis of infectious encephalitis and of other common neuropsychiatric conditions. Autoantibody diagnostics plays a pivotal role for accurate diagnosis of AE, which is of utmost importance for the prompt recognition and early treatment. Several AE subgroups can be identified, either according to the prominent clinical phenotype, presence of a concomitant tumor, or type of neuronal autoantibody, and recent diagnostic criteria have provided important insights into AE classification. Antibodies to neuronal intracellular antigens typically associate with paraneoplastic neurological syndromes and poor prognosis, whereas antibodies to synaptic/neuronal cell surface antigens characterize many AE subtypes that associate with tumors less frequently, and that are often immunotherapy-responsive. In addition to the general features of AE, we review current knowledge on the pathogenic mechanisms underlying these disorders, focusing mainly on the potential role of neuronal antibodies in the most frequent conditions, and highlight current theories and controversies. Then, we dissect the crucial aspects of the laboratory diagnostics of neuronal antibodies, which represents an actual challenge for both pathologists and neurologists. Indeed, this diagnostics entails technical difficulties, along with particularly interesting novel features and pitfalls. The novelties especially apply to the wide range of assays used, including specific tissue-based and cell-based assays. These assays can be developed in-house, usually in specialized laboratories, or are commercially available. They are widely used in clinical immunology and in clinical chemistry laboratories, with relevant differences in analytic performance. Indeed, several data indicate that in-house assays could perform better than commercial kits, notwithstanding that the former are based on non-standardized protocols. Moreover, they need expertise and laboratory facilities usually unavailable in clinical chemistry laboratories. Together with the data of the literature, we critically evaluate the analytical performance of the in-house vs commercial kit-based approach. Finally, we propose an algorithm aimed at integrating the present strategies of the laboratory diagnostics in AE for the best clinical management of patients with these disorders.

Paraneoplastic Neurologic Syndromes

OBJECTIVE

Progress is ongoing in understanding paraneoplastic neurologic disorders, with new syndromes and antibodies being described and more detailed evidence available to guide workup for diagnosis and treatment to improve outcomes. Many excellent reviews have summarized the molecular features of different antibodies, but this article emphasizes the clinical features of each syndrome that may help guide initial diagnosis and treatment, which often should occur before an antibody or cancer is found to confirm the diagnosis.

LATEST DEVELOPMENTS

Recent findings include updated diagnostic criteria with validated sensitivity and specificity, discovery of novel antibodies, and clinical findings that increase the likelihood of an underlying paraneoplastic disorder. Suggestive syndromes that have been recently identified include faciobrachial dystonic seizures and pilomotor auras in anti-leucine-rich glioma inactivated protein 1 encephalitis, extreme delta brush on EEG in N-methyl-d-aspartate (NMDA)-receptor encephalitis, déjà vu aura in anti-glutamic acid decarboxylase 65 (GAD65) encephalitis, and sleep disturbances in several disorders. In addition, there is confirmed utility of brain positron emission tomography (PET) and CSF markers, including carcinoembryonic antigen and oligoclonal bands, as well as improved tests for the presence of leptomeningeal cancer cells in CSF. Associations of cancer immunotherapies with paraneoplastic syndromes and herpes simplex virus encephalitis (and COVID-19) with NMDA-receptor encephalitis have been described.

ESSENTIAL POINTS

All neurologists should be aware of advances regarding paraneoplastic neurologic syndromes, as patients can present with a wide variety of neurologic symptoms and earlier diagnosis and treatment can improve outcomes.

Pediatric anti-NMDA-receptor autoimmune encephalitis in siblings: Developmental, Electrophysiologic, and Genetic Implications

BACKGROUND

Anti-NMDAR encephalitis is a leading cause of autoimmune encephalitis in children. Untreated disease can lead to long-term neurological disability.

CASE REPORT

We present siblings with pediatric-onset anti-NMDAR encephalitis. One was treated early, while the other's diagnosis and treatment were delayed by several years. Developmental, electrophysiologic, and genetic implications are discussed.

CONCLUSION

Anti-NMDAR encephalitis is a severely debilitating disease that often requires prompt initiation and early escalation in treatment. Delayed treatment may lead to irreversible neurological sequalae. Further studies exploring associations between timing and tier of treatment initiation and longitudinal outcomes are needed.

Cerebrospinal fluid proteomics indicates immune dysregulation and neuronal dysfunction in antibody associated autoimmune encephalitis

Autoimmune Encephalitis (AE) spans a group of non-infectious inflammatory conditions of the central nervous system due to an imbalanced immune response. Aiming to elucidate the pathophysiological mechanisms of AE, we applied an unsupervised proteomic approach to analyze the cerebrospinal fluid (CSF) protein profile of AE patients with autoantibodies against N-methyl-d-aspartate receptor (NMDAR) (n = 9), leucine-rich glioma-inactivated protein 1 (LGI1) (n = 9), or glutamate decarboxylase 65 (GAD65) (n = 8) compared to 9 patients with relapsing-remitting multiple sclerosis as inflammatory controls, and 10 patients with somatic symptom disorder as non-inflammatory controls. We found a dysregulation of the complement system, a disbalance between pro-inflammatory and anti-inflammatory proteins on the one hand, and dysregulation of proteins involved in synaptic transmission, synaptogenesis, brain connectivity, and neurodegeneration on the other hand to a different extent in all AE subtypes compared to non-inflammatory controls. Furthermore, elevated levels of several proteases and reduction in protease inhibitors could be detected in all AE subtypes compared to non-inflammatory controls. Moreover, the different AE subtypes showed distinct protein profiles compared to each other and inflammatory controls which may facilitate future identification of disease-specific biomarkers. Overall, CSF proteomics provides insights into the complex pathophysiological mechanisms of AE, including immune dysregulation, neuronal dysfunction, neurodegeneration, and altered protease function.

Clinical Characteristics of Children With Anti-N-Methyl-d-Aspartate Receptor Encephalitis After Japanese Encephalitis

BACKGROUND

Viral encephalitis is an important trigger for anti-N-methyl-d-aspartate receptor (NMDAR) encephalitis. We analyzed the clinical characteristics of anti-NMDAR encephalitis after Japanese encephalitis (JE) in children.

METHODS

Clinical data of 185 children with anti-NMDAR encephalitis were retrospectively reviewed. Patients with a history of viral encephalitis other than JE or who were identified with other autoantibodies were excluded.

RESULTS

Twenty children with anti-NMDAR encephalitis after JE were enrolled with a median age of 6 years and 10 months (interquartile range [IQR]: 3 years to 11 years and 5 months). The median time from JE to anti-NMDAR encephalitis was 29 (IQR: 25 to 32) days. At 12 months, most patients (17 of 18) recovered to at least their baseline modified Rankin scale (mRS) scores caused by JE. One hundred forty two children with classical anti-NMDAR encephalitis were enrolled. Compared with classical anti-NMDAR encephalitis, patients after JE had significantly more decreased level of consciousness (50% vs 18.3%, P = 0.003), more autonomic dysfunction (30.0% vs 9.9%, P = 0.021), fewer psychiatric or behavioral symptoms (70.0% vs 90.8%, P = 0.016), fewer seizures (25.0% vs 68.3%, P < 0.001), lesser improvement 4 weeks after immunotherapy (35.0% vs 73.2%, P = 0.001), and worse outcomes at 12 months (median mRS: 1 vs 0, P < 0.001).

CONCLUSIONS

Anti-NMDAR encephalitis after JE in children mainly occurred within two months. Their clinical manifestation may differ from classical anti-NMDAR encephalitis. The prognosis of children with anti-NMDAR encephalitis after JE probably depends on the neurological sequelae after JE.

A protein with broad functions: damage-specific DNA-binding protein 2

Damage-specific DNA-binding protein 2 (DDB2) was initially identified as a component of the damage-specific DNA-binding heterodimeric complex, which cooperates with other proteins to repair UV-induced DNA damage. DDB2 is involved in the occurrence and development of cancer by affecting nucleotide excision repair (NER), cell apoptosis, and premature senescence. DDB2 also affects the sensitivity of cancer cells to radiotherapy and chemotherapy. In addition, a recent study found that DDB2 is a pathogenic gene for hepatitis and encephalitis. In recent years, there have been few relevant literature reports on DDB2, so there is still room for further research about it. In this paper, the molecular mechanisms of different biological processes involving DDB2 are reviewed in detail to provide theoretical support for research on drugs that can target DDB2.

Current Status of Biomarkers in Anti-N-Methyl-D-Aspartate Receptor Encephalitis

The discovery of biomarkers in rare diseases is of paramount importance to allow a better diagnosis, improve predictions of outcomes, and prompt the development of new treatments. Anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis is a rare autoimmune disorder associated with the presence of antibodies targeting the GluN1 subunit of the NMDAR. Since it was discovered in 2007, large efforts have been made towards the identification of clinical, paraclinical, and molecular biomarkers to better understand the immune mechanisms that govern the course of the disease as well as to define predictors of treatment response and long-term outcomes. However, most of these biomarkers are still in an exploratory phase, with only a few candidates reaching the final phases of the always-complex process of biomarker development, mainly due to the low incidence of the disease and its recent description. Clinical and paraclinical markers are probably the most widely explored in anti-NMDAR encephalitis, five of them combined in a clinical score to predict 1 year outcome. On the contrary, soluble molecules, such as persistent antibody positivity, antibody titers, cytokines, and other inflammatory mediators, have been proposed as biomarkers of clinical activity, inflammation, prognosis, and treatment response, but further studies are required for their clinical validation including larger and more homogenous cohorts of patients. Similarly, genetic susceptibility biomarkers are still in the exploratory phase and, therefore, weak conclusions can for now only be achieved. Thus, further studies are warranted to define biomarkers and unravel the underlying mechanisms driving rare diseases such as anti-NMDAR encephalitis. Future international collaborative studies with prospective designs that enable the enrollment of large cohorts will allow for the identification and validation of novel biomarkers for clinical decision-making.