Paraneoplastic Calmodulin Kinase-Like Vesicle-Associated Protein (CAMKV) Autoimmune Encephalitis.

OBJECTIVES: To report an autoimmune paraneoplastic encephalitis characterized by immunoglobulin G (IgG) antibody targeting synaptic protein calmodulin kinase-like vesicle-associated (CAMKV). METHODS: Serum and cerebrospinal fluid (CSF) samples harboring unclassified antibodies on murine brain-based indirect immunofluorescence assay (IFA) were screened by human protein microarray. In 5 patients with identical cerebral IFA staining, CAMKV was identified as top-ranking candidate antigen. Western blots, confocal microscopy, immune-absorption, and mass spectrometry were performed to substantiate CAMKV specificity. Recombinant CAMKV-specific assays (cell-based [fixed and live] and Western blot) provided additional confirmation. RESULTS: Of 5 CAMKV-IgG positive patients, 3 were women (median symptom-onset age was 59 years; range, 53-74). Encephalitis-onset was subacute (4) or acute (1) and manifested with: altered mental status (all), seizures (4), hyperkinetic movements (4), psychiatric features (3), memory loss (2), and insomnia (2). Paraclinical testing revealed CSF lymphocytic pleocytosis (all 4 tested), electrographic seizures (3 of 4 tested), and striking MRI abnormalities in all (mesial temporal lobe T2 hyperintensities [all patients], caudate head T2 hyperintensities [3], and cortical diffusion weighted hyperintensities [2]). None had post-gadolinium enhancement. Cancers were uterine adenocarcinoma (3 patients: poorly differentiated or neuroendocrine-differentiated in 2, both demonstrated CAMKV immunoreactivity), bladder urothelial carcinoma (1), and non-Hodgkin lymphoma (1). Two patients developed encephalitis following immune checkpoint inhibitor cancer therapy (atezolizumab [1], pembrolizumab [1]). All treated patients (4) demonstrated an initial response to immunotherapy (corticosteroids [4], IVIG [2]), though 3 died from cancer. INTERPRETATION: CAMKV-IgG is a biomarker of immunotherapy-responsive paraneoplastic encephalitis with temporal and extratemporal features and uterine cancer as a prominent oncologic association. ANN NEUROL 2024;96:21-33.

Septin-5 and -7-IgGs: Neurologic, Serologic, and Pathophysiologic Characteristics.

BACKGROUND AND OBJECTIVES: We sought to determine clinical significance of neuronal septin autoimmunity and evaluate for potential IgG effects. METHODS: Septin-IgGs were detected by indirect immunofluorescence assays (IFAs; mouse tissue and cell based) or Western blot. IgG binding to (and internalization of) extracellular septin epitopes were evaluated for by live rat hippocampal neuron assay. The impact of purified patient IgGs on murine cortical neuron function was determined by recording extracellular field potentials in a multielectrode array platform. RESULTS: Septin-IgGs were identified in 23 patients. All 8 patients with septin-5-IgG detected had cerebellar ataxia, and 7 had prominent eye movement disorders. One of 2 patients with co-existing septin-7-IgG had additional psychiatric phenotype (apathy, emotional blunting, and poor insight). Fifteen patients had septin-7 autoimmunity, without septin-5-IgG detected. Disorders included encephalopathy (11; 2 patients with accompanying myelopathy, and 2 were relapsing), myelopathy (3), and episodic ataxia (1). Psychiatric symptoms (≥1 of agitation, apathy, catatonia, disorganized thinking, and paranoia) were prominent in 6 of 11 patients with encephalopathic symptoms. Eight of 10 patients with data available (from 23 total) improved after immunotherapy, and a further 2 patients improved spontaneously. Staining of plasma membranes of live hippocampal neurons produced by patient IgGs (subclasses 1 and 2) colocalized with pre- and post-synaptic markers. Decreased spiking and bursting behavior in mixed cultures of murine glutamatergic and GABAergic cortical neurons produced by patient IgGs were attributable to neither antigenic crosslinking and internalization nor complement activation. INTERPRETATION: Septin-IgGs are predictive of distinct treatment-responsive autoimmune central nervous system (CNS) disorders. Live neuron binding and induced electrophysiologic effects by patient IgGs may support septin-specific pathophysiology. ANN NEUROL 2022;92:1090-1101.

Autoantibody-induced internalization of CNS AQP4 water channel and EAAT2 glutamate transporter requires astrocytic Fc receptor.

Aquaporin-4 (AQP4) water channel-specific IgG distinguishes neuromyelitis optica (NMO) from multiple sclerosis and causes characteristic immunopathology in which central nervous system (CNS) demyelination is secondary. Early events initiating the pathophysiological outcomes of IgG binding to astrocytic AQP4 are poorly understood. CNS lesions reflect events documented in vitro following IgG interaction with AQP4: AQP4 internalization, attenuated glutamate uptake, intramyelinic edema, interleukin-6 release, complement activation, inflammatory cell recruitment, and demyelination. Here, we demonstrate that AQP4 internalization requires AQP4-bound IgG to engage an astrocytic Fcγ receptor (FcγR). IgG-lacking Fc redistributes AQP4 within the plasma membrane and induces interleukin-6 release. However, AQP4 endocytosis requires an activating FcγR's gamma subunit and involves astrocytic membrane loss of an inhibitory FcγR, CD32B. Interaction of the IgG-AQP4 complex with FcγRs triggers coendocytosis of the excitatory amino acid transporter 2 (EAAT2). Requirement of FcγR engagement for internalization of two astrocytic membrane proteins critical to CNS homeostasis identifies a complement-independent, upstream target for potential early therapeutic intervention in NMO.

Glial fibrillary acidic protein immunoglobulin G as biomarker of autoimmune astrocytopathy: Analysis of 102 patients.

OBJECTIVE: A novel autoimmune central nervous system (CNS) disorder with glial fibrillary acidic protein (GFAP)-IgG as biomarker was recently characterized. Here, 102 patients with GFAP-IgG positivity are described. METHODS: The 102 included patients had: (1) serum, cerebrospinal fluid (CSF), or both that yielded a characteristic astrocytic pattern of mouse tissue immunostaining; (2) confirmation of IgG reactive with specific GFAP isoforms (α, ɛ, or κ) by cell-based assays; and (3) clinical data available. Control specimens (n = 865) were evaluated by tissue (n = 542) and cell-based (n = 323) assays. RESULTS: Median symptom onset age was 44 years (range = 8-103), and 54% were women. The predominant phenotype (83 patients; 81%) was inflammation of meninges, brain, spinal cord, or all 3 (meningoencephalomyelitis). Among patients, highest specificity for those phenotypes was observed for CSF testing (94%), and highest sensitivity was for the GFAPα isoform (100%). Rare GFAP-IgG positivity was encountered in serum controls by tissue-based assay (0.5%) or cell-based assay (1.5%), and in CSF controls by cell-based assay (0.9%). Among patients, striking perivascular radial enhancement was found on brain magnetic resonance imaging in 53%. Although cases frequently mimicked vasculitis, angiography was uniformly negative, and spinal imaging frequently demonstrated longitudinally extensive myelitic lesions. Diverse neoplasms encountered were found prospectively in 22%. Ovarian teratoma was most common and was predicted best when both N-methyl-D-aspartate receptor-IgG and aquaporin-4-IgG coexisted (71%). Six patients with prolonged follow-up had brisk corticosteroid response, but required additional immunosuppression to overcome steroid dependency. INTERPRETATION: GFAPα-IgG, when detected in CSF, is highly specific for an immunotherapy-responsive autoimmune CNS disorder, sometimes with paraneoplastic cause. Ann Neurol 2017;81:298-309.

Molecular outcomes of neuromyelitis optica (NMO)-IgG binding to aquaporin-4 in astrocytes.

The astrocytic aquaporin-4 (AQP4) water channel is the target of pathogenic antibodies in a spectrum of relapsing autoimmune inflammatory central nervous system disorders of varying severity that is unified by detection of the serum biomarker neuromyelitis optica (NMO)-IgG. Neuromyelitis optica is the most severe of these disorders. The two major AQP4 isoforms, M1 and M23, have identical extracellular residues. This report identifies two novel properties of NMO-IgG as determinants of pathogenicity. First, the binding of NMO-IgG to the ectodomain of astrocytic AQP4 has isoform-specific outcomes. M1 is completely internalized, but M23 resists internalization and is aggregated into larger-order orthogonal arrays of particles that activate complement more effectively than M1 when bound by NMO-IgG. Second, NMO-IgG binding to either isoform impairs water flux directly, independently of antigen down-regulation. We identified, in nondestructive central nervous system lesions of two NMO patients, two previously unappreciated histopathological correlates supporting the clinical relevance of our in vitro findings: (i) reactive astrocytes with persistent foci of surface AQP4 and (ii) vacuolation in adjacent myelin consistent with edema. The multiple molecular outcomes identified as a consequence of NMO-IgG interaction with AQP4 plausibly account for the diverse pathological features of NMO: edema, inflammation, demyelination, and necrosis. Differences in the nature and anatomical distribution of NMO lesions, and in the clinical and imaging manifestations of disease documented in pediatric and adult patients, may be influenced by regional and maturational differences in the ratio of M1 to M23 proteins in astrocytic membranes.

Clinical and serological insights into paraneoplastic brachial amyotrophic diplegia.

BACKGROUND: Brachial amyotrophic diplegia (BAD) is typically linked to a neurodegenerative etiology such as amyotrophic lateral sclerosis (ALS). Clinical and serological characterizations of paraneoplastic neurologic syndromes resembling BAD are limited. METHODS: A retrospective chart review of patients with BAD-like presentations was conducted. Clinical/paraclinical features of paraneoplastic BAD and neurodegenerative BAD cases were compared. RESULTS: Between 2017 and 2023, 13 cases of BAD were identified, of these 10 were neurodegenerative BAD (ALS variant), and 3 cases associated with paraneoplastic autoimmunity. An additional paraneoplastic BAD case diagnosed in 2005 was included. LUZP4-IgG was detected in all four paraneoplastic cases, with coexisting KLHL11-IgG in three cases and ANNA1 (anti-Hu)-IgG in one case. Out of the four paraneoplastic cases, two patients had seminoma, while the remaining two had limited cancer investigation. Three patients exhibited bi-brachial weakness as the initial symptom before the onset of brainstem symptoms or seizures. Compared to BAD patients with a neurodegenerative etiology, a higher proportion of paraneoplastic cases had ataxia (75% vs 0%, p = 0.011). Other clinical features only detected in the paraneoplastic BAD group were vertigo (n = 2), hearing loss (n = 2) and ophthalmoplegia (n = 2). Electrodiagnostic studies in these patients revealed cervical myotome involvement, supportive of motor neuronopathy. All paraneoplastic cases but none of the neurodegenerative BAD cases exhibited inflammatory cerebrospinal fluid (CSF) findings (lymphocytic pleocytosis and/or supernumerary oligoclonal bands; p = 0.067). Despite the administration of immunotherapy and/or cancer treatment, none of the paraneoplastic patients reported clinical improvement. DISCUSSION: BAD or bi-brachial neurogenic weakness is a rare phenotypic presentation associated with paraneoplastic autoimmunity. Co-existing features of brainstem dysfunction or cerebellar ataxia should prompt further paraneoplastic evaluation. Common serological and cancer associations among these cases include LUZP4-IgG and KLHL11-IgG, along with testicular germ cell tumors, respectively.

Astrocytic autoantibody of neuromyelitis optica (NMO-IgG) binds to aquaporin-4 extracellular loops, monomers, tetramers and high order arrays.

The principal central nervous system (CNS) water channel, aquaporin-4 (AQP4), is confined to astrocytic and ependymal membranes and is the target of a pathogenic autoantibody, neuromyelitis optica (NMO)-IgG. This disease-specific autoantibody unifies a spectrum of relapsing CNS autoimmune inflammatory disorders of which NMO exemplifies the classic phenotype. Multiple sclerosis and other immune-mediated demyelinating disorders of the CNS lack a distinctive biomarker. Two AQP4 isoforms, M1 and M23, exist as homotetrameric and heterotetrameric intramembranous particles (IMPs). Orthogonal arrays of predominantly M23 particles (OAPs) are an ultrastructural characteristic of astrocytic membranes. We used high-titered serum from 32 AQP4-IgG-seropositive patients and 85 controls to investigate the nature and molecular location of AQP4 epitopes that bind NMO-IgG, and the influence of supramolecular structure. NMO-IgG bound to denatured AQP4 monomers (68% of cases), to native tetramers and high order arrays (90% of cases), and to AQP4 in live cell membranes (100% of cases). Disease-specific epitopes reside in extracellular loop C more than in loops A or E. IgG binding to intracellular epitopes lacks disease specificity. These observations predict greater disease sensitivity and specificity for tissue-based and cell-based serological assays employing "native" AQP4 than assays employing denatured AQP4 and fragments. NMO-IgG binds most avidly to plasma membrane surface AQP4 epitopes formed by loop interactions within tetramers and by intermolecular interactions within high order structures. The relative abundance and localization of AQP4 high order arrays in distinct CNS regions may explain the variability in clinical phenotype of NMO spectrum disorders.

IgG marker of optic-spinal multiple sclerosis binds to the aquaporin-4 water channel.

Neuromyelitis optica (NMO) is an inflammatory demyelinating disease that selectively affects optic nerves and spinal cord. It is considered a severe variant of multiple sclerosis (MS), and frequently is misdiagnosed as MS, but prognosis and optimal treatments differ. A serum immunoglobulin G autoantibody (NMO-IgG) serves as a specific marker for NMO. Here we show that NMO-IgG binds selectively to the aquaporin-4 water channel, a component of the dystroglycan protein complex located in astrocytic foot processes at the blood-brain barrier. NMO may represent the first example of a novel class of autoimmune channelopathy.

Evaluation of cell-based and tissue-based immunofluorescent assays for detection of glial fibrillary acidic protein autoantibodies in the cerebrospinal fluid of dogs with meningoencephalitis of unknown origin and other central nervous system disorders.

OBJECTIVE: To evaluate whether cell-based and tissue-based immunofluorescent assays (IFAs) run in parallel could be used to detect glial fibrillary acidic protein (GFAP) autoantibodies in the CSF of dogs with meningoencephalitis of unknown origin (MUO) and other CNS disorders. ANIMALS: 15 CSF samples obtained from dogs with presumed MUO (n = 5), CNS disease other than MUO (5), and idiopathic epilepsy (5). PROCEDURES: All CSF samples underwent parallel analysis with a cell-based IFA that targeted the α isoform of human GFAP and a tissue-based IFA that involved mouse brain cryosections. Descriptive data were generated. RESULTS: Only 1 CSF sample yielded mildly positive results on the cell-based IFA; that sample was from 1 of the dogs with presumed MUO. The remaining 14 CSF samples tested negative on the cell-based IFA. All 15 CSF samples yielded negative results on the tissue-based IFA. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that concurrent use of a cell-based IFA designed to target the human GFAP-α isoform and a tissue-based IFA that involved mouse tissue cryosections was inadequate for detection of GFAP autoantibodies in canine CSF samples. Given that GFAP autoantibodies were likely present in the CSF samples analyzed, these findings suggested that epitopes differ substantially between canine and human GFAP and that canine GFAP autoantibody does not bind to mouse GFAP. Without a positive control, absence of GFAP autoantibody in this cohort cannot be ruled out. Further research is necessary to develop a noninvasive and sensitive method for diagnosis of MUO in dogs.

GTPase Regulator Associated with Focal Adhesion Kinase 1 (GRAF1) Immunoglobulin-Associated Ataxia and Neuropathy.

BACKGROUND: To date, 10 patients with GTPase Regulator Associated with Focal Adhesion Kinase 1/Rho GTPase Activating Protein 26-Immunoglobulin (GRAF1/ARHGAP26-IgG) associated neurological disorders have been described, most with ataxia. OBJECTIVE: To report the clinical, oncological, and radiological associations of GRAF1 autoantibodies. METHODS: We identified 17 patients whose serum and/or cerebrospinal fluid IgG was confirmed to target GRAF1/ARHGAP26-IgG by both tissue-based immunofluorescence and transfected cell-based assay. Clinical information was available on 14 patients. RESULTS: The median age at neurological symptom onset was 51 years, and 8 (47%) were men. The predominant clinical features were subacute progressive cerebellar ataxia (13) or peripheral neuropathy (2). Magnetic resonance imaging brain (7 available) showed cerebellar atrophy (4, 1 also cerebrum and brainstem atrophy). Of 7 cerebrospinal fluids available for testing, 5 showed pleocytosis with oligoclonal bands in 3. Squamous cell carcinoma was observed in 3 patients (head and neck [2], lung [1]). CONCLUSION: GTPase Regulator Associated with Focal Adhesion Kinase 1 autoimmunity manifests commonly with subacute ataxia and cerebellar degeneration with a potential association with squamous cell carcinoma. Peripheral neuropathy may also be encountered. Cases in this series responded poorly to immunotherapy.

Clinical utility of AQP4-IgG titers and measures of complement-mediated cell killing in NMOSD.

OBJECTIVE: To investigate whether aquaporin-4-immunoglobulin G (AQP4-IgG) titers and measures of complement-mediated cell killing are clinically useful to predict the occurrence of relapse, relapse severity, and/or disability in neuromyelitis optica spectrum disorder (NMOSD). METHODS: We studied 336 serial serum specimens from 82 AQP4-lgG-seropositive patients. NMOSD activity at blood draw was defined as preattack (24 [7.1%], drawn within 30 days preceding an attack), attack (108 [32.1%], drawn on attack onset or within 30 days after), or remission (199 [59.2%], drawn >90 days after attack onset and >30 days preceding a relapse). For each specimen, we documented the attack type and severity and immunotherapy status. Complement-mediated cell killing was quantitated by flow cytometry using an M23-AQP4 cell-based assay. RESULTS: The estimated logarithmic means of AQP4-IgG titers in preattack, attack, and remission samples were 3.302, 3.657, and 3.458, respectively, p = 0.21. Analyses of 81 attack/remission pairs in 42 patients showed no significant titer differences (3.736 vs 3.472, p = 0.15). Analyses of 13 preattack/attack pairs in 9 patients showed no significant titer differences (3.994 vs 3.889, p = 0.67). Of 5 patients who converted to seronegative status, 2 continued to have attacks. Titers for major and minor attacks (n = 70) were not significantly different (3.905 vs 3.676, p = 0.47). Similarly, measures (titers) of complement-mediated cell killing were not significantly associated with disease course, attack severity, or disability at 5 years. CONCLUSIONS AND RELEVANCE: AQP4-IgG titer and complement-mediated cell killing lack significant prognostic or predictive utility in NMOSD. Although titers may drop in the setting of immunotherapy, seroconversion to negative status does not preclude ongoing clinical attacks. CLASSIFICATION OF EVIDENCE: This study provides Class II evidence that in patients with NMOSD, AQP4-IgG titers and measures of complement-mediated cell killing activity do not predict relapses, relapse severity, or disability.

Expanded Clinical Phenotype, Oncological Associations, and Immunopathologic Insights of Paraneoplastic Kelch-like Protein-11 Encephalitis.

Importance: Recognizing the presenting and immunopathological features of Kelch-like protein-11 immunoglobulin G seropositive (KLHL11 IgG+) patients may aid in early diagnosis and management. Objective: To describe expanding neurologic phenotype, cancer associations, outcomes, and immunopathologic features of KLHL11 encephalitis. Design, Setting, and Participants: This retrospective tertiary care center study, conducted from October 15, 1998, to November 1, 2019, prospectively identified 31 KLHL11 IgG+ cases in the neuroimmunology laboratory. Eight were identified by retrospective testing of patients with rhomboencephalitis (confirmed by tissue-based-immunofluorescence and transfected-cell-based assays). Main Outcomes and Measures: Outcome variables included modified Rankin score and gait aid use. Results: All 39 KLHL11 IgG+ patients were men (median age, 46 years; range, 28-73 years). Initial clinical presentations were ataxia (n = 32; 82%), diplopia (n = 22; 56%), vertigo (n = 21; 54%), hearing loss (n = 15; 39%), tinnitus (n = 14; 36%), dysarthria (n = 11; 28%), and seizures (n = 9; 23%). Atypical neurologic presentations included neuropsychiatric dysfunction, myeloneuropathy, and cervical amyotrophy. Hearing loss or tinnitus preceded other neurologic deficits by 1 to 8 months in 10 patients (26%). Among patients screened for malignancy (n = 36), testicular germ-cell tumors (n = 23; 64%) or testicular microlithiasis and fibrosis concerning for regressed germ cell tumor (n = 7; 19%) were found in 83% of the patients (n = 30). In 2 patients, lymph node biopsy diagnosed metastatic lung adenocarcinoma in one and chronic lymphocytic leukemia in the other. Initial brain magnetic resonance imaging revealed T2 hyperintensities in the temporal lobe (n = 12), cerebellum (n = 9), brainstem (n = 3), or diencephalon (n = 3). Among KLHL11 IgG+ patients who underwent HLA class I and class II genotyping (n = 10), most were found to have HLA-DQB1*02:01 (n = 7; 70%) and HLA-DRB1*03:01 (n = 6; 60%) associations. A biopsied gadolinium-enhancing temporal lobe lesion demonstrated T cell-predominant inflammation and nonnecrotizing granulomas. Cerebellar biopsy (patient with chronic ataxia) and 2 autopsied brains demonstrated Purkinje neuronal loss and Bergmann gliosis, supporting early active inflammation and later extensive neuronal loss. Compared with nonautoimmune control peripheral blood mononuclear cells, cluster of differentiation (CD) 8+ and CD4+ T cells were significantly activated when patient peripheral blood mononuclear cells were cultured with KLHL11 protein. Most patients (58%) benefitted from immunotherapy and/or cancer treatment (neurological disability stabilized [n = 10] or improved [n = 9]). Kaplan-Meier curve demonstrated significantly higher probability of wheelchair dependence among patients without detectable testicular cancer. Long-term outcomes in KLHL11-IgG+ patients were similar to Ma2 encephalitis. Conclusions and Relevance: Kelch-like protein-11 IgG is a biomarker of testicular germ-cell tumor and paraneoplastic neurologic syndrome, often refractory to treatment. Described expanded neurologic phenotype and paraclinical findings may aid in its early diagnosis and treatment.

Autoimmune gait disturbance accompanying adaptor protein-3B2-IgG.

OBJECTIVE: To describe phenotypes, treatment response, and outcomes of autoimmunity targeting a synaptic vesicle coat protein, the neuronal (B2) form of adaptor protein-3 (AP3). METHODS: Archived serum and CSF specimens (from 616,025 screened) harboring unclassified synaptic antibodies mimicking amphiphysin-immunoglobulin G (IgG) on tissue-based indirect immunofluorescence assay (IFA) were re-evaluated for novel IgG staining patterns. Autoantigens were identified by western blot and mass spectrometry. Recombinant western blot and cell-binding assay (CBA) were used to confirm antigen specificity. Clinical data were obtained retrospectively. RESULTS: Serum (10) and CSF (6) specimens of 10 patients produced identical IFA staining patterns throughout mouse nervous system tissues, most prominently in cerebellum (Purkinje neuronal perikarya, granular layer synapses, and dentate regions), spinal cord gray matter, dorsal root ganglia, and sympathetic ganglia. The antigen revealed by mass spectrometry analysis and confirmed by recombinant assays (western blot and CBA) was AP3B2 in all. Of 10 seropositive patients, 6 were women; median symptom onset age was 42 years (range 24-58). Clinical information was available for 9 patients, all with subacute onset and rapidly progressive gait ataxia. Neurologic manifestations were myeloneuropathy (3), peripheral sensory neuropathy (2), cerebellar ataxia (2), and spinocerebellar ataxia (2). Five patients received immunotherapy; none improved, but they did not worsen over the follow-up period (median 36 months; range 3-94). Two patients (both with cancer) died. One of 50 control sera was positive by western blot only (but not by IFA or CBA). CONCLUSION: AP3B2 (previously named ß-neuronal adaptin-like protein) autoimmunity appears rare, is accompanied by ataxia (sensory or cerebellar), and is potentially treatable.

Neurochondrin neurological autoimmunity.

OBJECTIVES: To describe the neurologic spectrum and treatment outcomes for neurochondrin-IgG positive cases identified serologically in the Mayo Clinic Neuroimmunology Laboratory. METHODS: Archived serum and CSF specimens previously scored positive for IgGs that stained mouse hippocampal tissue in a nonuniform synaptic pattern by immunofluorescence assay (89 among 616,025 screened, 1993-2019) were reevaluated. Antibody characterization experiments revealed specificity for neurochondrin, confirmed by recombinant protein assays. RESULTS: IgG in serum (9) or CSF (4) from 8 patients yielded identical neuron-restricted CNS patterns, most pronounced in hippocampus (stratum lucidum in particular), cerebellum (Purkinje cells and molecular layer), and amygdala. All were neurochondrin-IgG positive. Five were women; median symptom onset age was 43 years (range, 30-69). Of 7 with clinical data, 6 presented with rapidly progressive cerebellar ataxia, brainstem signs, or both; 1 had isolated unexplained psychosis 1 year prior. Five of 6 had cerebellar signs, 4 with additional brainstem symptoms or signs (eye movement abnormalities, 3; dysphagia, 2; nausea and vomiting, 1). One patient with brainstem signs (vocal cord paralysis and VII nerve palsy) had accompanying myelopathy (longitudinally extensive abnormality on MRI; aquaporin-4-IgG and myelin oligodendrocyte glycoprotein-IgG negative). The 7th patient had small fiber neuropathy only. Just 1 of 7 had contemporaneous cancer (uterine). Six patients with ataxia or brainstem signs received immunotherapy, but just 1 remained ambulatory. At last follow-up, 5 had MRI evidence of severe cerebellar atrophy. CONCLUSION: In our series, neurochondrin autoimmunity was usually accompanied by a nonparaneoplastic rapidly progressive rhombencephalitis with poor neurologic outcomes. Other phenotypes and occasional paraneoplastic causes may occur.

Paraneoplastic neuronal intermediate filament autoimmunity.

OBJECTIVE: To describe paraneoplastic neuronal intermediate filament (NIF) autoimmunity. METHODS: Archived patient and control serum and CSF specimens were evaluated by tissue-based indirect immunofluorescence assay (IFA). Autoantigens were identified by Western blot and mass spectrometry. NIF specificity was confirmed by dual tissue section staining and 5 recombinant NIF-specific HEK293 cell-based assays (CBAs, for α-internexin, neurofilament light [NfL], neurofilament medium, or neurofilament heavy chain, and peripherin). NIF-immunoglobulin Gs (IgGs) were correlated with neurologic syndromes and cancers. RESULTS: Among 65 patients, NIF-IgG-positive by IFA and CBAs, 33 were female (51%). Median symptom onset age was 62 years (range 18-88). Patients fell into 2 groups, defined by the presence of NfL-IgG (21 patients, who mostly had ≥4 NIF-IgGs detected) or its absence (44 patients, who mostly had ≤2 NIF-IgGs detected). Among NfL-IgG-positive patients, 19/21 had ≥1 subacute onset CNS disorders: cerebellar ataxia (11), encephalopathy (11), or myelopathy (2). Cancers were detected in 16 of 21 patients (77%): carcinomas of neuroendocrine lineage (10) being most common (small cell [5], Merkel cell [3], other neuroendocrine [2]). Two of 257 controls (0.8%, both with small cell carcinoma) were positive by both IFA and CBA. Five of 7 patients with immunotherapy data improved. By comparison, the 44 NfL-IgG-negative patients had findings of unclear significance: diverse nervous system disorders (p = 0.006), as well as limited (p = 0.003) and more diverse (p < 0.0001) cancer accompaniments. CONCLUSIONS: NIF-IgG detection by IFA, with confirmatory CBA testing that yields a profile including NfL-IgG, defines a paraneoplastic CNS disorder (usually ataxia or encephalopathy) accompanying neuroendocrine lineage neoplasia.

Glycine receptor modulating antibody predicting treatable stiff-person spectrum disorders.

BACKGROUND: Glycine receptor alpha-1 subunit (GlyRα1)-immunoglobulin G (IgG) is diagnostic of stiff-person syndrome (SPS) spectrum but has been reported detectable in other neurologic diseases for which significance is less certain. METHODS: To assess GlyRα1-IgGs as biomarkers of SPS spectrum among patients and controls, specimens were tested using cell-based assays (binding [4°C] and modulating [antigen endocytosing, 37°C]). Medical records of seropositive patients were reviewed. RESULTS: GlyRα1-IgG (binding antibody) was detected in 21 of 247 patients with suspected SPS spectrum (8.5%) and in 8 of 190 healthy subject sera (4%) but not CSF. Among 21 seropositive patients, 20 had confirmed SPS spectrum clinically, but 1 was later determined to have a functional neurologic disorder. Sera from 9 patients with SPS spectrum , but not 7 controls, nor the functional patient, caused GlyRα1 modulation (100% specificity). SPS spectrum phenotypes included progressive encephalomyelitis with rigidity and myoclonus (PERM) (8), classic SPS (5), stiff limb (5), stiff trunk (1), and isolated exaggerated startle (hyperekplexia, 1). Neuropsychiatric symptoms present in 12 patients (60%) were anxiety (11), depression (6), and delirium (3). Anxiety was particularly severe in 3 patients with PERM. Objective improvements in SPS neurologic symptoms were recorded in 16 of 18 patients who received first-line immunotherapy (89%, 9/10 treated with corticosteroids, 8/10 treated with IVIg, 3/4 treated with plasma exchange, and 1 treated with rituximab). Treatment-sparing maintenance strategies were successful in 4 of 7 patients (rituximab [2/3], azathioprine [1/1], and mycophenolate [1/3]). CONCLUSIONS: GlyRα1-modulating antibody improves diagnostic specificity for immunologically treatable SPS spectrum disorders. CLASSIFICATION OF EVIDENCE: This study provides Class IV evidence that GlyRα1-modulating antibody accurately identifies patients with treatable SPS spectrum disorders.

Autoimmune GFAP astrocytopathy: Prospective evaluation of 90 patients in 1 year.

In this prospective evaluation of serum and CSF samples, all but two CSF GFAPα-IgG positive patients had autoimmune meningoencephalomyelitis while serum GFAPα-IgG positivity alone was less specific. Phenotypes were diverse among patients that were serum positive only. Adult and pediatric clinical presentations were similar. Most patients were immunotherapy responsive. Co-existing NMDA-R-IgG and cancer were associated with lack of response to first-line immunotherapy. Among patients with follow-up information, 18% had relapses. This study demonstrates CSF GFAPα-IgG is a specific autoimmune meningoencephalomyelitis biomarker, with favorable corticosteroid response. Lack of response should prompt evaluation for co-existing NMDA-R-IgG or malignancy.

Functional evaluation and cancer risk assessment of BRCA2 unclassified variants.

The influence of germ line BRCA2 unclassified variants (UCV), including missense mutations and in-frame deletions and insertions on BRCA2 function and on cancer risk, has not been defined although these mutations account for 43% of all identified BRCA2 sequence alterations. To investigate the effects of UCVs on BRCA2 function, we compared mutant and wild-type forms of BRCA2 using assays of cellular survival and viability, homologous recombination repair, and genome instability. We confirm that the effects of known deleterious mutations can be distinguished from neutral polymorphisms and wild-type BRCA2 in these assays, and we characterize the influence of a series of UCVs on BRCA2 function. We also describe how the results from the assays can be combined with data from analysis of cosegregation of the UCVs with cancer, co-occurrence of the UCVs with other deleterious mutations, and interspecies sequence variation in a comprehensive framework in an effort to better distinguish between disease predisposing and neutral UCVs. This combined approach represents a useful means of addressing the functional significance and cancer relevance of UCVs in BRCA2.

IgLON5 antibody: Neurological accompaniments and outcomes in 20 patients.

OBJECTIVE: To describe the phenotypes, treatment response, and outcome of IgLON5 autoimmunity. METHODS: Archived serum and CSF specimens from 367 patients known to harbor unclassified antibodies which stained neural synapses diffusely (mimicking amphiphysin-IgG) were reevaluated by indirect immunofluorescence assay (IFA) using a composite of mouse tissues and recombinant IgLON5-transfected cell-based assay (CBA, Euroimmun). RESULTS: Available specimens (serum, 25; CSF, 9) from 26/367 patients (7%) had identical IFA appearance and robust IgLON5 CBA positivity. Clinical information was available for 20/26 patients; 13 were women. Median disease-onset age was 62 years (range, 46-75 years). Most patients had insidious onset and progression of neurological symptoms affecting movement and sleep predominantly. Sleep disorders were sleep-disordered breathing (11) and parasomnias (3). Brainstem disorders were gait instability (14), dysphagia (10), abnormal eye movements (7), respiratory dysfunction (6), ataxia (5), craniocervical dystonia (3), and dysarthria (3). Findings compatible with hyperexcitability included myoclonus (3), cramps (3), fasciculations (2), and exaggerated startle (2). Neuropsychiatric disorders included cognitive dysfunction (6), psychiatric symptoms (5), and seizures (1). Dysautonomia, in 9, affected bladder function (7), gastrointestinal motility (3), thermoregulation (3), and orthostatic tolerance (1). Just 2 patients had coexisting autoimmune disease. Brain MRI findings were nonspecific and CSF was noninflammatory in all tested. Seven of 9 immunotherapy-treated patients improved: 6 of those 7 were stable at last follow-up. Three untreated patients died. Each IgLON5-IgG subclass (1-4) was readily detectable in ≥80% of specimens using CBA. CONCLUSIONS: IgLON5-IgG is diagnostic of a potentially treatable neurological disorder, where autoimmune clues are otherwise lacking.