Features of Isoforms of Human Soluble TACI.

The BAFF/APRIL-system with the two cytokines BAFF and APRIL and their three receptors, transmembrane activator and CAML interactor (TACI), BAFF receptor, and B-cell maturation Ag, is important for B cell maintenance. The BAFF/APRIL system is a therapeutic target in B cell-derived malignancies and autoimmune diseases. However, unexpected outcomes of clinical trials with atacicept (TACI-Fc) underline our incomplete understanding of this system. Shedding of the three receptors is one important regulatory element. In humans, TACI exists in two isoforms generated through alternative splicing in their extracellular portion: TACI-long (l) has two cysteine-rich domains, whereas TACI-short (s) lacks the first low-affinity one. In this study, we discriminated soluble (s) forms of TACI-l and TACI-s with newly generated mAbs and found that both were spontaneously released from activated human B cells, with a predominance of sTACI-l. Furthermore, sTACI-l was also the dominant isoform in human serum. Vaccination with the mRNA vaccine from BioNTech does not significantly affect the serum levels of sTACI-l. Both TACI-s and TACI-l were shed by a disintegrin and metalloproteinase domain-containing protein 10. TACI-l and TACI-s formed homo- and hetero-oligomers in soluble and membrane-bound forms. Both sTACI-l and sTACI-s acted as decoy receptors for BAFF, but only sTACI-l also efficiently inhibited APRIL. Dimerization of sTACI-l enhanced its decoy functions only slightly. Together, we extend our knowledge of the complexity of the BAFF/APRIL system by identifying and characterizing the two soluble isoforms of TACI.

Clinical, serological and genetic predictors of response to immunotherapy in anti-IgLON5 disease.

Anti-IgLON5 disease is a newly defined clinical entity characterized by a progressive course with high disability and mortality rate. While precise pathogenetic mechanisms remain unclear, features characteristic of both autoimmune and neurodegenerative diseases were reported. Data on immunotherapy are limited, and its efficacy remains controversial. In this study, we retrospectively investigated an anti-IgLON5 disease cohort with special focus on clinical, serological and genetic predictors of the immunotherapy response and long-term outcome. Patients were recruited from the GENERATE (German Network for Research on Autoimmune Encephalitis) registry. Along with clinical parameters, anti-IgLON5 immunoglobulin (Ig)G in serum and CSF, anti-IgLON5 IgG1-4, IgA and IgM in serum, neurofilament light chain and glial fibrillary acidic protein in serum as well as human leukocyte antigen-genotypes were determined. We identified 53 patients (symptom onset 63.8 ± 10.3 years, female:male 1:1.5). The most frequent initial clinical presentations were bulbar syndrome, hyperkinetic syndrome or isolated sleep disorder [at least one symptom present in 38% (20/53)]. At the time of diagnosis, the majority of patients had a generalized multi-systemic phenotype; nevertheless, 21% (11/53) still had an isolated brainstem syndrome and/or a characteristic sleep disorder only. About one third of patients [28% (15/53)] reported subacute disease onset and 51% (27/53) relapse-like exacerbations during the disease course. Inflammatory CSF changes were evident in 37% (19/51) and increased blood-CSF-barrier permeability in 46% (21/46). CSF cell count significantly decreased, while serum anti-IgLON5 IgG titre increased with disease duration. The presence of human leukocyte antigen-DRB1*10:01 [55% (24/44)] was associated with higher serum anti-IgLON5 IgG titres. Neurofilament light chain and glial fibrillary acidic protein in serum were substantially increased (71.1 ± 103.9 pg/ml and 126.7 ± 73.3 pg/ml, respectively). First-line immunotherapy of relapse-like acute-to-subacute exacerbation episodes resulted in improvement in 41% (11/27) of patients and early initiation within the first 6 weeks was a predictor for therapy response. Sixty-eight per cent (36/53) of patients were treated with long-term immunotherapy and 75% (27/36) of these experienced no further disease progression (observation period of 20.2 ± 15.4 months). Long-term immunotherapy initiation during the first year after onset and low pre-treatment neurofilament light chain were significant predictors for a better outcome. In conclusion, subacute disease onset and early inflammatory CSF changes support the primary role of autoimmune mechanisms at least at initial stages of anti-IgLON5 disease. Early immunotherapy, prior to advanced neurodegeneration, is associated with a better long-term clinical outcome. Low serum neurofilament light chain at treatment initiation may serve as a potential biomarker of the immunotherapy response.

B-Cell Maturation Antigen (BCMA) as a Biomarker and Potential Treatment Target in Systemic Lupus Erythematosus.

The BAFF-APRIL system is crucial for the pathogenesis of systemic lupus erythematosus (SLE) by promoting B cell survival, differentiation and the maintenance of humoral autoimmunity. Here, we investigated the relationship of BCMA expression on B cell subsets with its ligands BAFF and APRIL, together with soluble BCMA, and with clinical and serologic variables in a cohort of 100 SLE patients (86 under conventional and 14 under belimumab therapy) and 30 healthy controls (HCs) using multicolor flow cytometry and ELISA. We found that BCMA expression in SLE patients was significantly increased on all B cell subsets compared to HCs, with all examined components of the BAFF-APRIL system being upregulated. BCMA expression was significantly increased on switched and unswitched memory B cells compared to naïve B cells, both in HCs and SLE. BCMA expression on B cells correlated with plasmablast frequencies, serum anti-dsDNA antibodies and complement consumption, while soluble BCMA correlated with plasmablast frequency, highlighting its potential as a clinical biomarker. Belimumab treatment significantly reduced BCMA expression on most B cell subsets and soluble TACI and contributed to the inhibition of almost the entire BAFF-APRIL system and restoration of B cell homeostasis. These results provide insights into the complex dysregulation of the BAFF-APRIL system in SLE and highlight the therapeutic potential of targeting its components, particularly BCMA, in addition to its use as a biomarker for disease activity.

Shedding of BAFF/APRIL Receptors Controls B Cells.

Proteolytic shedding of the receptors BCMA, TACI, and BAFFR reduces their cell-surface expression and ligand-mediated survival of B cell subsets. This shedding is executed by protease γ-secretase or by metalloproteases, and is partially dependent on ligand binding and receptor interactions. Shed receptors may serve as biomarkers for autoimmunity and lymphoma.

Abundant glutamic acid decarboxylase (GAD)-reactive B cells in gad-antibody-associated neurological disorders.

High levels of antibodies against glutamic acid decarboxylase (GAD) are observed in patients with different neurological disorders, but cells producing these autoantibodies are largely unexplored. We detect circulating GAD-reactive B cells in peripheral blood that readily differentiate into antibody-producing cells. These cells are highly elevated in most patients with GAD-antibody-associated disorders (n = 15) compared to controls (n = 19). They mainly produce GAD65 antibodies of the IgG1 and IgG4 subclasses and are as abundant as B cells reactive for common recall antigens. Bone marrow cells represent an additional source of GAD antibodies. The identification of GAD-antibody-producing cells has implications for the selection of cell-specific biologics. ANN NEUROL 2019;85:448-454.

Pathogenicity of human antibodies against myelin oligodendrocyte glycoprotein.

OBJECTIVE: Autoantibodies against myelin oligodendrocyte glycoprotein (MOG) occur in a proportion of patients with inflammatory demyelinating diseases of the central nervous system (CNS). We analyzed their pathogenic activity by affinity-purifying these antibodies (Abs) from patients and transferring them to experimental animals. METHODS: Patients with Abs to MOG were identified by cell-based assay. We determined the cross-reactivity to rodent MOG and the recognized MOG epitopes. We produced the correctly folded extracellular domain of MOG and affinity-purified MOG-specific Abs from the blood of patients. These purified Abs were used to stain CNS tissue and transferred in 2 models of experimental autoimmune encephalomyelitis. Animals were analyzed histopathologically. RESULTS: We identified 17 patients with MOG Abs from our outpatient clinic and selected 2 with a cross-reactivity to rodent MOG; both had recurrent optic neuritis. Affinity-purified Abs recognized MOG on transfected cells and stained myelin in tissue sections. The Abs from the 2 patients recognized different epitopes on MOG, the CC' and the FG loop. In both patients, these Abs persisted during our observation period of 2 to 3 years. The anti-MOG Abs from both patients were pathogenic upon intrathecal injection in 2 different rat models. Together with cognate MOG-specific T cells, these Abs enhanced T-cell infiltration; together with myelin basic protein-specific T cells, they induced demyelination associated with deposition of C9neo, resembling a multiple sclerosis type II pathology. INTERPRETATION: MOG-specific Abs affinity purified from patients with inflammatory demyelinating disease induce pathological changes in vivo upon cotransfer with myelin-reactive T cells, suggesting that these Abs are similarly pathogenic in patients. Ann Neurol 2018;84:315-328.

Human Plasmacytoid Dendritic Cells Display and Shed B Cell Maturation Antigen upon TLR Engagement.

The BAFF-APRIL system is best known for its control of B cell homeostasis, and it is a target of therapeutic intervention in autoimmune diseases and lymphoma. By analyzing the expression of the three receptors of this system, B cell maturation Ag (BCMA), transmembrane activator and CAML interactor, and BAFF receptor, in sorted human immune cell subsets, we found that BCMA was transcribed in plasmacytoid dendritic cells (pDCs) in both blood and lymphoid tissue. Circulating human pDCs contained BCMA protein without displaying it on the cell surface. After engagement of TLR7/8 or TLR9, BCMA was detected also on the cell surface of pDCs. The display of BCMA on the surface of human pDCs was accompanied by release of soluble BCMA (sBCMA); inhibition of γ-secretase enhanced surface expression of BCMA and reduced the release of sBCMA by pDCs. In contrast with human pDCs, murine pDCs did not express BCMA, not even after TLR9 activation. In this study, we extend the spectrum of BCMA expression to human pDCs. sBCMA derived from pDCs might determine local availability of its high-affinity ligand APRIL, because sBCMA has been shown to function as an APRIL-specific decoy. Further, therapeutic trials targeting BCMA in patients with multiple myeloma should consider possible effects on pDCs.

Reversible cerebral vasoconstriction syndrome and posterior reversible encephalopathy syndrome associated with intracranial hypotension.

BACKGROUND: Reversible cerebral vasoconstriction syndrome (RCVS) and posterior reversible encephalopathy syndrome (PRES) are both rare disorders. The pathophysiology of both diseases is not yet fully understood. METHODS: We report the unique case of a 19-year-old comatose woman who was brought to the ER after a series of generalized tonic-clonic seizures 6 days post peridural anesthesia for cesarean section. Vital signs and initial laboratory testing including urine analysis and drug screening were unremarkable. Initial cranial CT scan showed an acute small subdural hematoma (17 mm length × 6 mm width × 30 mm height), cerebral edema with slit ventricles, and slight cerebellar tonsillar herniation as signs of intracranial hypotension. CT angiography depicted narrowing of the proximal intracranial vessels consistent with RCVS. MR imaging was also suggestive of both intracranial hypotension and RCVS and showed, in addition, vasogenic edema consistent with PRES. An extensive CSF leakage involving T1 to L2/L3 was confirmed by spinal MRI. RESULTS: The patient underwent conservative therapy for intracranial hypotension (e.g., head-down position) as well as epidural blood patch, which led to regression of the clinical symptoms within a few days. Follow-up MRI showed complete resolution of all radiological changes. CONCLUSIONS: In summary, our patient developed clinical and neuroradiological signs of intracranial hypotension and a combination of PRES and RCVS associated with a CSF leakage caused by peridural anesthesia; by treating the intracranial hypotension, the other syndromes resolved. From a clinical point of view, it is important to look for CSF leakage as a treatable possible cause of PRES and/or RCVS triggered by intracranial hypotension as in our patient postpartum. Moreover, it is vital to obtain a good history as, in cases of suspected CSF leakage with classic postural headache, a recent spinal/cranial procedure is typically present.

Early Neuroaxonal Damage in Neurologic Disorders Associated With GAD65 Antibodies.

OBJECTIVES: Neurodegeneration is considered a relevant pathophysiologic feature in neurologic disorders associated with antibodies against glutamic acid decarboxylase 65 (GAD65). In this study, we investigate surrogates of neuroaxonal damage in relation to disease duration and clinical presentation. METHODS: In a multicentric cohort of 50 patients, we measured serum neurofilament light chain (sNfL) in relation to disease duration and disease phenotypes, applied automated MRI volumetry, and analyzed clinical characteristics. RESULTS: In patients with neurologic disorders associated with GAD65 antibodies, we detected elevated sNfL levels early in the disease course. By contrast, this elevation of sNfL levels was less pronounced in patients with long-standing disease. Increased sNfL levels were observed in patients presenting with cerebellar ataxia and limbic encephalitis, but not in those with stiff person syndrome. Using MRI volumetry, we identified atrophy predominantly of the cerebellar cortex, cerebellar superior posterior lobe, and cerebral cortex with similar atrophy patterns throughout all clinical phenotypes. DISCUSSION: Together, our data provide evidence for early neuroaxonal damage and support the need for timely therapeutic interventions in GAD65 antibody-associated neurologic disorders.

Case report: Anti septin-5-encephalitis as a treatable cause of cerebellar ataxia and psychiatric symptoms.

Objectives: Anti-septin-5 encephalitis is a rare disease with only few published cases, mainly based on retrospective CSF and serum analyses. Predominant symptoms are cerebellar ataxia and oculomotor abnormalities. Due to the rareness of the disease, treatment recommendations are scarce. Herein, we prospectively describe the clinical course of a female patient with anti-septin-5 encephalitis. Methods: We describe diagnostic workup, treatment and follow-up of a 54-year-old patient presenting with vertigo, unsteady gait, lack of drive and behavioral changes. Results: Clinical examination revealed severe cerebellar ataxia, saccadic smooth pursuit, upbeat-nystagmus, and dysarthria. Additionally, the patient presented with a depressive syndrome. MRI of the brain and spinal cord were normal. CSF analysis showed lymphocytic pleocytosis (11 cells/µl). Extensive antibody testing revealed anti septin-5 IgG in both CSF and serum without coexisting anti-neuronal antibodies. PET/CT detected no signs of malignancy. Corticosteroids, plasma exchange, and rituximab led to transient clinical improvement followed by relapse. Re-applied treatment with plasma exchange followed by bortezomib resulted in moderate but sustained clinical improvement. Discussion: Anti septin-5 encephalitis represents a rare but treatable and therefore relevant differential diagnosis in patients with cerebellar ataxia. Psychiatric symptoms can be observed in anti septin-5 encephalitis. Immunosuppressive treatment including bortezomib is moderately effective.

Antibodies Against Glutamic Acid Decarboxylase 65 Are Locally Produced in the CSF and Arise During Affinity Maturation.

BACKGROUND AND OBJECTIVES: Antibodies (Abs) against the cytoplasmic protein glutamic acid decarboxylase 65 (GAD65) are detected in patients with neurologic syndromes together referred to as GAD65-Ab spectrum disorders. The response of some of these patients to plasma exchange or immunoglobulins indicates that GAD65-Abs could contribute to disease pathogenesis at least at some stages of disease. However, the involvement of GAD65-reactive B cells in the CNS is incompletely understood. METHODS: We studied 7 patients with high levels of GAD65-Abs and generated monoclonal Abs (mAbs) derived from single cells in the CSF. Sequence characteristics, reactivity to GAD65, and the role of somatic hypermutations of the mAbs were analyzed. RESULTS: Twelve CSF-derived mAbs were generated originating from 3 patients with short disease duration, and 7/12 of these mAbs (58%) were GAD65 reactive in at least 1 detection assay. Four of 12 (33%) were definitely positive in all 3 detection assays. The intrathecal anti-GAD65 response was polyclonal. GAD65-Abs were mostly of the IgG1 subtype and had undergone affinity maturation. Reversion of 2 GAD65-reactive mAbs to their corresponding germline-encoded unmutated common ancestors abolished GAD65 reactivity. DISCUSSION: GAD65-specific B cells are present in the CNS and represent a sizable fraction of CSF B cells early in the disease course. The anti-GAD65 response in the CSF is polyclonal and shows evidence of antigen-driven affinity maturation required for GAD65 recognition. Our data support the hypothesis that the accumulation of GAD65-specific B cells and plasma cells in the CSF is an important feature of early disease stages.

Glutamic acid decarboxylase antibody-associated neurological syndromes: Clinical and antibody characteristics and therapy response.

BACKGROUND: Antibodies against glutamic acid decarboxylase (GAD-abs) at high serum levels are associated with diverse autoimmune neurological syndromes (AINS), including cerebellar ataxia, epilepsy, limbic encephalitis and stiff-person syndrome. The impact of low serum GAD-ab levels in patients with suspected AINS remains controversial. Specific intrathecal GAD-ab synthesis may serve as a marker for GAD-ab-associated nervous system autoimmunity. We present characteristics of a multicentric patient cohort with suspected AINS associated with GAD antibodies (SAINS-GAD+) and explore the relevance of serum GAD-ab levels and intrathecal GAD-ab synthesis. METHODS: All patients with SAINS-GAD+ included in the registry of the German Network for Research on Autoimmune Encephalitis (GENERATE) from 2011 to 2019 were analyzed. High serum GAD-ab levels were defined as RIA>2000 U/mL, ELISA>1000 U/mL, or as a positive staining pattern on cell-based assays. RESULTS: One-hundred-one patients were analyzed. In descending order they presented with epilepsy/limbic encephalitis (39%), cerebellar ataxia (28%), stiff person syndrome (22%), and overlap syndrome (12%). Immunotherapy was administered in 89% of cases with improvements in 46%. 35% of SAINS-GAD+ patients had low GAD-ab serum levels. Notably, unmatched oligoclonal bands in CSF but not in serum were more frequent in patients with low GAD-ab serum levels. GAD-ab-levels (high/low) and intrathecal GAD-ab synthesis (present or not) did not impact clinical characteristics and outcome. CONCLUSIONS: Overall, immunotherapy in SAINS-GAD+ was moderately effective. Serum GAD-ab levels and the absence or presence of intrathecal GAD-ab synthesis did not predict clinical characteristics or outcomes in SAINS-GAD+. The detection of unmatched oligoclonal bands might outweigh low GAD-ab serum levels.

Intrathecal Antibody Production Against Epstein-Barr, Herpes Simplex, and Other Neurotropic Viruses in Autoimmune Encephalitis.

BACKGROUND AND OBJECTIVES: Neurotropic viruses are suspected to play a role in the pathogenesis of autoimmune diseases of the CNS such as the association between the Epstein-Barr virus (EBV) and multiple sclerosis (MS). A group of autoimmune encephalitis (AE) is linked to antibodies against neuronal cell surface proteins. Because CNS infection with the herpes simplex virus can trigger anti-NMDA receptor (NMDAR) encephalitis, a similar mechanism for EBV and other neurotropic viruses could be postulated. To investigate for previous viral infections of the CNS, intrathecally produced virus-specific antibody synthesis was determined in patients with AE. METHODS: Antibody-specific indices (AIs) against EBV and measles, rubella, varicella zoster, herpes simplex virus, and cytomegalovirus were determined in 27 patients having AE (anti-NMDAR encephalitis, n = 21, and LGI1 encephalitis, n = 6) and in 2 control groups comprising of 30 patients with MS and 21 patients with noninflammatory CNS diseases (NIND), which were sex and age matched. RESULTS: An intrathecal synthesis of antibodies against EBV was found in 5/27 (19%) patients with AE and 2/30 (7%) of the patients with MS. All these patients had also at least 1 additional elevated virus-specific AI. In contrast, in none of the patients with NIND, an elevated virus-specific AI was detected. DISCUSSION: Intrathecally produced antibodies against EBV can be found in patients with AE and MS but only together with antibodies against different neurotropic viruses. Evidence of these antibodies is the result of a polyspecific immune response similar yet distinct from MS response rather than an elapsed infection of the CNS.

Rituximab Treatment and Long-term Outcome of Patients With Autoimmune Encephalitis: Real-world Evidence From the GENERATE Registry.

BACKGROUND AND OBJECTIVES: To determine the real-world use of rituximab in autoimmune encephalitis (AE) and to correlate rituximab treatment with the long-term outcome. METHODS: Patients with NMDA receptor (NMDAR)-AE, leucine-rich glioma-inactivated-1 (LGI1)- AE, contactin-associated protein-like-2 (CASPR2)-AE, or glutamic acid decarboxylase 65 (GAD65) disease from the GErman Network for Research on AuToimmune Encephalitis who had received at least 1 rituximab dose and a control cohort of non-rituximab-treated patients were analyzed retrospectively. RESULTS: Of the 358 patients, 163 (46%) received rituximab (NMDAR-AE: 57%, CASPR2-AE: 44%, LGI1-AE: 43%, and GAD65 disease: 37%). Rituximab treatment was initiated significantly earlier in NMDAR- and LGI1-AE (median: 54 and 155 days from disease onset) compared with CASPR2-AE or GAD65 disease (median: 632 and 1,209 days). Modified Rankin Scale (mRS) scores improved significantly in patients with NMDAR-AE, both with and without rituximab treatment. Although being more severely affected at baseline, rituximab-treated patients with NMDAR-AE more frequently reached independent living (mRS score ≤2) (94% vs 88%). In LGI1-AE, rituximab-treated and nontreated patients improved, whereas in CASPR2-AE, only rituximab-treated patients improved significantly. No improvement was observed in patients with GAD65 disease. A significant reduction of the relapse rate was observed in rituximab-treated patients (5% vs 13%). Detection of NMDAR antibodies was significantly associated with mRS score improvement. A favorable outcome was also observed with early treatment initiation. DISCUSSION: We provide real-world data on immunosuppressive treatments with a focus on rituximab treatment for patients with AE in Germany. We suggest that early and short-term rituximab therapy might be an effective and safe treatment option in most patients with NMDAR-, LGI1-, and CASPR2-AE. CLASS OF EVIDENCE: This study provides Class IV evidence that rituximab is an effective treatment for some types of AE.

CSF Findings in Acute NMDAR and LGI1 Antibody-Associated Autoimmune Encephalitis.

BACKGROUND AND OBJECTIVES: CSF in antibody-defined autoimmune encephalitis (AE) subtypes shows subtype-dependent degrees of inflammation ranging from rare and often mild to frequent and often robust. AEs with NMDA receptor antibodies (NMDAR-E) and leucine-rich glioma-inactivated protein 1 antibodies (LGI1-E) represent opposite ends of this spectrum: NMDAR-E with typically frequent/robust and LGI1-E with rare/mild CSF inflammation. For a more in-depth analysis, we characterized CSF findings in acute, therapy-naive NMDAR-E and LGI1-E in a multicentric, retrospective, cross-sectional setting. METHODS: Eighty-two patients with NMDAR-E and 36 patients with LGI1-E from the GErman NEtwork for Research of AuToimmune Encephalitis (GENERATE) with lumbar puncture within 90 days of onset and before immunotherapy were included. CSF parameters comprised leukocytes, oligoclonal bands (OCBs), and CSF/serum ratios for albumin, immunoglobulin G (IgG), A (IgA), and M (IgM), the latter 3 converted to Z scores according to Reiber formulas. The MRZ reaction was tested in 14 patients with NMDAR-E and 6 patients with LGI1-E, respectively. RESULTS: CSF was abnormal in 94% of NMDAR-E but only in 36% of LGI1-E patients. Robust quantitative intrathecal immunoglobulin synthesis (IIS, IgG > IgM >> IgA) was characteristic for NMDAR-E, but absent in LGI-E. In NMDAR-E, CSF leukocytes were higher when IIS was present or more pronounced. In addition, in NMDAR-E, CSF leukocytes were lower and IIS occurred less often and if so to a lesser degree at older age. Patients with NMDAR-E with severe functional impairment more often had positive OCBs. In CSF obtained later than 3 weeks of onset, leukocytes were lower. In parallel, the correlation of leukocytes with IIS disappeared as IIS was partially independent of disease duration. The MRZ reaction was positive in 5 (36%) patients with NMDAR-E. All these associations were completely absent in LGI1-E. Here, younger patients showed more blood-CSF barrier dysfunction. In LGI1-E, but not in NMDAR-E, the blood-CSF barrier was more dysfunctional when CSF leukocytes were higher. DISCUSSION: NMDAR-E and LGI-E differ in their typical extent of CSF inflammation. In addition, the patterns formed by the different inflammatory CSF parameters and their relationship with disease severity, age, and disease duration are subtype-characteristic. Moreover, signs for multiple sclerosis-like chronic inflammation are present in a subgroup of patients with NMDAR-E. These CSF patterns might be markers for the different immunopathogeneses of LGI1-E and NMDAR-E.

Frequency and Characterization of Movement Disorders in Anti-IgLON5 Disease.

OBJECTIVE: Anti-IgLON5 disease is a recently described neurological disease that shares features of autoimmunity and neurodegeneration. Abnormal movements appear to be frequent and important but have not been characterized and are under-reported. Here we describe the frequency and types of movement disorders in a series of consecutive patients with this disease. METHODS: In this retrospective, observational study, the presence and phenomenology of movement disorders were assessed with a standardized clinical questionnaire. Available videos were centrally reviewed by three experts in movement disorders. RESULTS: Seventy two patients were included. In 41 (57%) the main reason for initial consultation was difficulty walking along with one or several concurrent movement disorders. At the time of anti-IgLON5 diagnosis, 63 (87%) patients had at least one movement disorder with a median of three per patient. The most frequent abnormal movements were gait and balance disturbances (52 patients, 72%), chorea (24, 33%), bradykinesia (20, 28%), dystonia (19, 26%), abnormal body postures or rigidity (18, 25%), and tremor (15, 21%). Other hyperkinetic movements (myoclonus, akathisia, myorhythmia, myokymia, or abdominal dyskinesias) occurred in 26 (36%) patients. The craniofacial region was one of the most frequently affected by multiple concurrent movement disorders (23 patients, 32%) including dystonia (13), myorhythmia (6), chorea (4) or myokymia (4). Considering any body region, the most frequent combination of multiple movement disorders consisted of gait instability or ataxia associated with craniofacial dyskinesias or generalized chorea observed in 31(43%) of patients. In addition to abnormal movements, 87% of patients had sleep alterations, 74% bulbar dysfunction, and 53% cognitive impairment. Fifty-five (76%) patients were treated with immunotherapy, resulting in important and sustained improvement of the movement disorders in only seven (13%) cases. CONCLUSIONS: Movement disorders are a frequent and leading cause of initial neurological consultation in patients with anti-IgLON5 disease. Although multiple types of abnormal movements can occur, the most prevalent are disorders of gait, generalized chorea, and dystonia and other dyskinesias that frequently affect craniofacial muscles. Overall, anti-IgLON5 disease should be considered in patients with multiple movement disorders, particularly if they occur in association with sleep alterations, bulbar dysfunction, or cognitive impairment.

Possible link of genetic variants to autoimmunity in GAD-antibody-associated neurological disorders.

OBJECTIVE: In patients with GAD-antibody (ab) associated neurological disorders coexistence of other autoimmune disorders is observed. METHODS: In this exploratory study we analysed variations in 33 candidate genes involved in autoimmunity or representing immunological check-points using next-generation sequencing. We performed haplotype-analysis of HLA-DRB1 and HLA-DQB1. Additionally, we analysed levels of sFasL, IL10, and IL18 in serum of patients and healthy controls. RESULTS: 19 patients (3 males, 16 females; mean age at onset: 46.4 years) with positive GAD-ab and the following neurological phenotypes were included: n = 8 cerebellar ataxia, n = 6 limbic encephalitis, n = 4 stiff person syndrome, n = 1 demyelinating CNS disease with recurrent optic neuritis. 15 patients exhibited at least one other autoimmune disorder and/or showed other auto-ab. We identified several variations in genes linked to autoimmunity or representing check-point proteins. Most frequently (14/19 patients, allele frequency: 42.1%), we observed an amino acid exchange in the cytotoxic T-lymphocyte-associated protein 4 (CTLA4) gene. Two of the observed variants are known to cause alterations of protein function (Y446C in caspase-10, K750N in protein-tyrosin-phosphatase, non-receptor type 22). These latter variants were detected in two related patients (mother and daughter) who both present with GAD-ab-associated neurological disorders but with different clinical phenotypes. The rare haplotype DRB1*15:01:01 ~ DQA1*01:02:01 ~ DQB1*05:02:01 previously described in patients with GAD-ab-associated neurological disorders was not observed in any of our patients. No elevated serum levels of sFasL, IL18 or IL10 were observed in patients indicating no typical phenotype of autoimmune lymphoproliferate syndrome. CONCLUSIONS: These findings suggest genetic risk factors in patients with GAD-ab-associated neurological disorders.

Oligodendrocyte myelin glycoprotein as a novel target for pathogenic autoimmunity in the CNS.

Autoimmune disorders of the central nervous system (CNS) comprise a broad spectrum of clinical entities. The stratification of patients based on the recognized autoantigen is of great importance for therapy optimization and for concepts of pathogenicity, but for most of these patients, the actual target of their autoimmune response is unknown. Here we investigated oligodendrocyte myelin glycoprotein (OMGP) as autoimmune target, because OMGP is expressed specifically in the CNS and there on oligodendrocytes and neurons. Using a stringent cell-based assay, we detected autoantibodies to OMGP in serum of 8/352 patients with multiple sclerosis, 1/28 children with acute disseminated encephalomyelitis and unexpectedly, also in one patient with psychosis, but in none of 114 healthy controls. Since OMGP is GPI-anchored, we validated its recognition also in GPI-anchored form. The autoantibodies to OMGP were largely IgG1 with a contribution of IgG4, indicating cognate T cell help. We found high levels of soluble OMGP in human spinal fluid, presumably due to shedding of the GPI-linked OMGP. Analyzing the pathogenic relevance of autoimmunity to OMGP in an animal model, we found that OMGP-specific T cells induce a novel type of experimental autoimmune encephalomyelitis dominated by meningitis above the cortical convexities. This unusual localization may be directed by intrathecal uptake and presentation of OMGP by meningeal phagocytes. Together, OMGP-directed autoimmunity provides a new element of heterogeneity, helping to improve the stratification of patients for diagnostic and therapeutic purposes.

Identification of circulating MOG-specific B cells in patients with MOG antibodies.

OBJECTIVE: To identify circulating myelin oligodendrocyte glycoprotein (MOG)-specific B cells in the blood of patients with MOG antibodies (Abs) and to determine whether circulating MOG-specific B cells are linked to levels and epitope specificity of serum anti-MOG-Abs. METHODS: We compared peripheral blood from 21 patients with MOG-Abs and 26 controls for the presence of MOG-specific B cells. We differentiated blood-derived B cells in vitro in separate culture wells to Ab-producing cells via engagement of Toll-like receptors 7 and 8. We quantified the anti-MOG reactivity with a live cell-based assay by flow cytometry. We determined the recognition of MOG epitopes with a panel of mutated variants of MOG. RESULTS: MOG-Ab-positive patients had a higher frequency of MOG-specific B cells in blood than controls, but MOG-specific B cells were only detected in about 60% of these patients. MOG-specific B cells in blood showed no correlation with anti-MOG Ab levels in serum, neither in the whole group nor in the untreated patients. Epitope analysis of MOG-Abs secreted from MOG-specific B cells cultured in different wells revealed an intraindividual heterogeneity of the anti-MOG autoimmunity. CONCLUSIONS: This study shows that patients with MOG-Abs greatly differ in the abundance of circulating MOG-specific B cells, which are not linked to levels of MOG-Abs in serum suggesting different sources of MOG-Abs. Identification of MOG-specific B cells in blood could be of future relevance for selecting patients with MOG-Abs for B cell-directed therapy.