GABAA Receptor Antibodies Research Articles

Anti-GABA-A Receptor Antibody-Mediated Epilepsia Partialis Continua After Treatment With Alemtuzumab: A Case Report.

Patients with anti-GABA-A receptor encephalitis characteristically experience therapy-refractory epileptic seizures. General anesthesia is often required to terminate refractory status epilepticus. The immunologic mechanisms leading to antibody formation remain to be elucidated. Described triggers of anti-GABA-A autoimmunity are tumors, mainly thymomas, and herpes simplex encephalitis. We present a young woman with prediagnosis of relapse remitting multiple sclerosis (MS), treated with interferons, natalizumab, and alemtuzumab. Six months after one and only cycle of alemtuzumab, speech arrest and behavioral changes with aggressive and anxious traits appeared. She showed increasing motor convulsions resulting in focal status epilepticus. Anti-GABA-A receptor antibodies in CSF and serum were confirmed in different external laboratories, in a more extensive analysis after antibodies against NMDAR, CASPR2, LGI1, GABABR, and AMPAR were ruled out during in-house examination. Clinical condition improved temporarily with cortisone therapy, plasmapheresis, and IVIG but deteriorated rapidly after steroid discontinuation, resulting in brain biopsy. On histopathologic confirmation consistent with anti-GABA-A receptor antibody-associated CNS inflammation, completing the first rituximab cycle, continuing oral corticosteroids and supplementing immunosuppression with cyclosporine A led to quick recovery. Our case describes a severe autoantibody-induced encephalitis in a young patient with MS, with alemtuzumab as a potential trigger for anti-GABA-A receptor encephalitis.

The potential role of astroglial GABAA receptors in autoimmune encephalitis associated with GABAA receptor antibodies and seizures.

The γ-aminobutyric acid (GABA) is the main inhibitory transmitter in the central nervous system and GABA receptors mediate the inhibitory synaptic transmission. GABA binding to neuronal GABAA R leads to a rapid hyperpolarization and a higher excitation threshold due to an increase in membrane Cl- permeability. The synaptic GABAA R is mostly composed of two α(1-3), two β, and one γ subunit with the most abundant configuration α1β2γ2. Recently, antibodies (Abs) against α1, β3, and γ2 subunits of GABAA R were detected in a severe form of autoimmune encephalitis with refractory seizures, status epilepticus, and multifocal brain lesions, affecting gray and white matter. Experimental studies confirmed multiple mechanisms and direct functional effects of GABAA R Abs on neurons with decreased GABAergic synaptic transmission and increased neuronal excitability. The expression of GABAA R on astrocytes is well established. However, extensive studies about the effects of autoimmune GABAA R Abs on astrocytic GABAA R are missing. We hypothesize that GABAA R Abs may lead additionally to blocking astrocytic GABAA Rs with impaired Ca2+ homeostasis/spreading, astrocytic Cl- imbalance, dysfunction of astrocyte-mediated gliotransmission (e.g., decreased adenosine levels) and accumulation of excitatory neurotransmission, all this contributing to seizures, variable clinical/MRI presentations, and severity. The most abundant expressed GABAA R subunits in rodent astrocytes are α1, α2, β1, β3, and γ1 localized in both white and gray matter. Data about GABAA R subunits in human astrocytes are even more limited, comprising α2, β1, and γ1. Overlapping binding of GABAA R Abs to neuronal and astroglial receptors is still possible. In vitro and in vivo animal models can be helpful to test the effects of GABAA R Abs on glia. This is from an epileptological point of view relevant because of the increasing evidence, confirming the glial involvement in the pathogenesis of epilepsy. Taken together, autoimmune disorders are complex and multiple mechanisms including glia could contribute to the pathogenesis of GABAA R encephalitis with seizures.

Contribution of parasol-magnocellular pathway ganglion cells to foveal retina in macaque monkey

Parasol-magnocellular pathway ganglion cells form an important output stream of the primate retina and make a major contribution to visual motion detection. They are known to comprise ON and OFF type response polarities but the relative numbers of ON and OFF parasol cells, and the overall contribution of parasol cells to high-acuity foveal vision are not well understood. Here we use antibodies against carbonic anhydrase 8 (CA8) and intracellular injections of the liphilic dye DiI to show that CA8 selectively labels OFF parasol cells in macaque retina. By combined labeling with CA8 antibodies and a previously-described marker for parasol cells (GABAA receptor antibodies), we show that ON and OFF parasol cells each comprise ∼ 6% of all ganglion cells in central retina (each peak density ∼ 3000 cells/mm2 at 5 deg.), and each population comprises ∼ 10% of all ganglion cells in peripheral temporal retina. Thus, the spatial density of parasol cells in central retina is greater than reported by previous anatomical studies, and the central-peripheral gradient in parasol cell density is shallower than previously reported. The data nevertheless predict decline in spatial acuity with visual field eccentricity for both midget-parvocellular pathway and parasol-magnocellular pathway mediated visual functions. The spatial resolving power of the OFF parasol array (peak ∼ 7 cpd) falls short of macaque behavioral grating acuity by at least a factor of three throughout the retina.

Catatonia with GABAA receptor antibodies

A 22-year-old African woman developed acute behavioural change, against a background of sickle cell disease with strokes requiring a ventriculoperitoneal shunt. She alternated between mutism with prolonged staring and posturing,...

38.2 NEURONAL AUTOANTIBODIES IN PSYCHOSIS: ENOUGH ABOUT PREVALENCE, WHAT’S THE RELEVANCE?

BackgroundOne source of controversy in the emerging field of autoimmune psychiatry concerns varying prevalence estimates of neuronal surface autoantibodies (NSAbs) in psychiatric disorders, particularly psychotic disorders. Differences in assay methodology and patient selection may contribute to varying case-control estimates.I will argue that the field needs to move beyond small n prevalence studies, to address the question of the relevance of NSAbs in psychotic disorders, and namely the following questions:1) Does the presence of NSAbs offer any aetiopathological insights into psychosis i.e. by associating with other disease-relevant biomarkers?2) Do NSAbs shape the clinical phenotype of psychotic disorders?3) Do NSAbs have a predictive role in psychotic disorders, in terms of treatment response or course of illness?MethodsTo address this issue, we have undertaken measurement of NSAbs using multiple immunoassays in a cohort of individuals at ultra-high risk for psychosis, and another first episode psychosis cohort. Associations between NSAb seropositivity and phenotype, outcome and biomarkers including structural MRI were explored.ResultsNSAbs were detected at rates of between 1% and 9% of cases in both cohorts, depending on assay used. Live CBAs detected significantly more NMDAR and GABA-AR IgG antibodies than did fixed CBAs. Rates in cases were not significantly different from controls, regardless of assay.Nevertheless in UHR subjects NSAbs, and NMDAR Abs in particular, showed clear aetiopathological and phenotypic relevance, associating with cognitive function (poorer verbal memory and IQ), more severe psychopathology and increased volumes of key limbic areas. Significant interactions with a marker of blood-brain barrier integrity offered further aetiopathological insights. NSAbs detected by both fixed and live CBAs demonstrated phenotypic associations and interactions with BBB status, suggesting both assays can detect phenotypically relevant antibodies in the UHR context. In FEP subjects, no such associations were noted. GABA-A receptor antibodies, which have been proposed as NSAbs with emerging disease-relevance, showed no phenotypic associations.Data on the predictive utility of NSAbs in UHR and FEP subjects will be presented.DiscussionWith appropriately fine-grained phenotyping and careful consideration of moderating biological factors and assay variation, clear disease-relevance of NSAbs could be established in UHR subjects but not in FEP subjects. In particular, NMDAR antibodies may have important biomarker potential in the at-risk mental state.The failure to establish clear disease-relevance in previous psychiatric cohorts may reflect a genuinely irrelevant antibody but could also be due any of the following:1) Inadequately fine-grained phenotyping of subjects2) Ignoring the important moderating role of BBB permeability3) Choosing subjects at ‘too late’ a stage of illness4) Inadequately sensitive antibody detection assays

Thymoma-associated panencephalitis: a newly emerging paraneoplastic neurologic syndrome.

Recently, a few case reports of thymoma-associated panencephalitis (TAPE) have brought to light a disease entity that has not been fully characterized. Literature review of TAPE reveals an array of associated neuronal antibodies, with varied responses to thymomectomy with or without immunotherapy. This report describes a case of TAPE and proposes that the GABAA receptor antibody is a potential target antigen driving the immune process in this disease entity. Treatment-wise, early thymomectomy consistently improves the overall course of disease. Further study of such cases will be critical in clarifying the mechanisms of disease, improving early diagnosis, and developing targeted approaches to treatment.

GABAA receptor and LGI1 antibody encephalitis in a patient with thymoma.

Autoimmune encephalitis related to antibodies against neuronal cell surface and synaptic proteins is a new category of disorders in which the targets are well-known proteins and receptors involved in synaptic transmission and neuronal excitability. GABAA receptor is one of the latest identified antigens within this category.1 High-titer serum and CSF GABAA receptor antibodies were recently reported in 6 patients with autoimmune encephalitis associated with seizures or status epilepticus, 4 of them requiring pharmacologic-induced coma. Patients' brain MRIs showed characteristic multiple cortical and subcortical abnormalities with fluid-attenuated inversion recovery (FLAIR)/T2 hyperintensity. Antibodies to LGI1 are associated with limbic encephalitis previously attributed to voltage-gated potassium channels (VGKC).2 Coexistence of these antibodies is rare and intriguing.

Encephalitis with refractory seizures, status epilepticus, and antibodies to the GABAA receptor: a case series, characterisation of the antigen, and analysis of the effects of antibodies

Increasing evidence suggests that seizures and status epilepticus can be immune-mediated. We aimed to describe the clinical features of a new epileptic disorder, and to establish the target antigen and the effects of patients' antibodies on neuronal cultures. In this observational study, we selected serum and CSF samples for antigen characterisation from 140 patients with encephalitis, seizures or status epilepticus, and antibodies to unknown neuropil antigens. The samples were obtained from worldwide referrals of patients with disorders suspected to be autoimmune between April 28, 2006, and April 25, 2013. We used samples from 75 healthy individuals and 416 patients with a range of neurological diseases as controls. We assessed the samples using immunoprecipitation, mass spectrometry, cell-based assay, and analysis of antibody effects in cultured rat hippocampal neurons with confocal microscopy. Neuronal cell-membrane immunoprecipitation with serum of two index patients revealed GABAA receptor sequences. Cell-based assay with HEK293 expressing α1/β3 subunits of the GABAA receptor showed high titre serum antibodies (>1:160) and CSF antibodies in six patients. All six patients (age 3-63 years, median 22 years; five male patients) developed refractory status epilepticus or epilepsia partialis continua along with extensive cortical-subcortical MRI abnormalities; four patients needed pharmacologically induced coma. 12 of 416 control patients with other diseases, but none of the healthy controls, had low-titre GABAA receptor antibodies detectable in only serum samples, five of them also had GAD-65 antibodies. These 12 patients (age 2-74 years, median 26.5 years; seven male patients) developed a broader spectrum of symptoms probably indicative of coexisting autoimmune disorders: six had encephalitis with seizures (one with status epilepticus needing pharmacologically induced coma; one with epilepsia partialis continua), four had stiff-person syndrome (one with seizures and limbic involvement), and two had opsoclonus-myoclonus. Overall, 12 of 15 patients for whom treatment and outcome were assessable had full (three patients) or partial (nine patients) response to immunotherapy or symptomatic treatment, and three died. Patients' antibodies caused a selective reduction of GABAA receptor clusters at synapses, but not along dendrites, without altering NMDA receptors and gephyrin (a protein that anchors the GABAA receptor). High titres of serum and CSF GABAA receptor antibodies are associated with a severe form of encephalitis with seizures, refractory status epilepticus, or both. The antibodies cause a selective reduction of synaptic GABAA receptors. The disorder often occurs with GABAergic and other coexisting autoimmune disorders and is potentially treatable. The National Institutes of Health, the McKnight Neuroscience of Brain Disorders, the Fondo de Investigaciones Sanitarias, Fundació la Marató de TV3, the Netherlands Organisation for Scientific Research (Veni-incentive), the Dutch Epilepsy Foundation.

A new encephalitis with GABAA receptor antibodies

In the past decade, several autoimmune neurological syndromes have been identified. Many of these syndromes, especially those responsive to immunotherapy, involve antibodies to cell-surface antigens, such as the NMDA receptor, LGI1, and the GABAB receptor. 1 Bien CG Vincent A Barnett MH et al. Immunopathology of autoantibody-associated encephalitides: clues for pathogenesis. Brain. 2012; 135: 1622-1638 Crossref PubMed Scopus (416) Google Scholar , 2 Davis R Dalmau J Autoimmunity, seizures, and status epilepticus. Epilepsia. 2013; 54: 46-49 Crossref PubMed Scopus (63) Google Scholar Detailed investigations have led to the recognition of distinct features that aid in early diagnosis. For example, faciobrachial dystonic seizures—very brief (<3 seconds) contractions of the arm and usually the ipsilateral face—are highly suggestive of the non-paraneoplastic, autoimmune syndrome associated with anti-voltage-gated potassium channel complex antibodies, specifically the anti-LGI1 variant. 3 Irani SR Michell AW Lang B et al. Faciobrachial dystonic seizures precede Lgi1 antibody limbic encephalitis. Ann Neurol. 2011; 69: 892-900 Crossref PubMed Scopus (613) Google Scholar This is a treatable disorder with an excellent prognosis when recognised early. The faciobrachial dystonic seizures usually precede the rest of the syndrome, which consists of hyponatraemia and limbic encephalitis. Treatment with immunotherapy, especially corticosteroids, in the early phase can not only lead to improvement but can prevent the limbic encephalitis. 4 Irani SR Stagg CJ Schott JM et al. Faciobrachial dystonic seizures: the influence of immunotherapy on seizure control and prevention of cognitive impairment in a broadening phenotype. Brain. 2013; 136: 3151-3162 Crossref PubMed Scopus (292) Google Scholar Similarly, the clinical features of anti-NMDA receptor encephalitis are quite distinct, with psychiatric presentation, followed by rapid deterioration, including central apnoea requiring ventilatory support, and prominent dyskinesias, often in young women, and often in those with ovarian teratomas. 5 Titulaer MJ McCracken L Gabilondo I et al. Treatment and prognostic factors for long-term outcome in patients with anti-NMDA receptor encephalitis: an observational cohort study. Lancet Neurol. 2013; 12: 157-165 Summary Full Text Full Text PDF PubMed Scopus (1857) Google Scholar Extreme delta brushes on EEG might also be suggestive of this syndrome. 6 Schmitt SE Pargeon K Frechette ES Hirsch LJ Dalmau J Friedman D Extreme delta brush: a unique EEG pattern in adults with anti-NMDA receptor encephalitis. Neurology. 2012; 79: 1094-1100 Crossref PubMed Scopus (482) Google Scholar Identification of the antibodies to cell-surface antigens in these syndromes not only suggests good response to immunotherapy but also raises suspicion of specific yet-to-be-detected underlying malignancies—eg, small-cell lung cancer is present in half of patients with limbic encephalitis with GABAB (metabotropic) receptor antibodies. 7 Höftberger R Titulaer MJ Sabater L et al. Encephalitis and GABAB receptor antibodies: novel findings in a new case series of 20 patients. Neurology. 2013; 81: 1500-1506 Crossref PubMed Scopus (313) Google Scholar Encephalitis with refractory seizures, status epilepticus, and antibodies to the GABAA receptor: a case series, characterisation of the antigen, and analysis of the effects of antibodiesHigh titres of serum and CSF GABAA receptor antibodies are associated with a severe form of encephalitis with seizures, refractory status epilepticus, or both. The antibodies cause a selective reduction of synaptic GABAA receptors. The disorder often occurs with GABAergic and other coexisting autoimmune disorders and is potentially treatable. Full-Text PDF

GABA and GABA(A) receptor antagonists alter developing cone photoreceptor development in neonatal rabbit retina.

Gamma aminobutyric acid (GABA) has been established as an important developmental signal in a number of regions of the central nervous system (CNS), including retina. Our previous studies have shown that GABAergic horizontal cells act as the initial synaptic target for developing cone photoreceptors in neonatal rabbit retina. Since intraocular injections of the GABA(A) receptor antagonists, picrotoxin or bicuculline, disrupt cone synaptogenesis in vivo, GABA released from horizontal cells may provide a necessary signal for cone axon growth and/or synapse formation. In the current report, we have used cultured retinal explants to examine the effects of GABA(A) receptor antagonists on other aspects of developing cones. These include the distribution pattern of cone cell bodies across the outer surface of the retina and the expression of GABA(A) receptors within both cone cell bodies and axonal processes. Peanut agglutinin (PNA), a plant lectin that specifically labels cone plasma membrane and extracellular matrix, was used to monitor cone development, and a GABA(A) receptor antibody against the beta2/3 subunits of the protein was used to label GABA(A) receptors. Results showed that cones maintained in the explant culture express GABA(A) receptors in a temporal and spatial pattern similar to that observed in vivo, namely a low expression of receptors on cone cell bodies at postnatal day 1 (P1), peaking around P3 and diminishing by P7. Neonatal retinal explants exposed to the GABA(A) receptor antagonists, bicuculline (10 microM) or SR95531 (5 microM), for 24 h in culture showed disruption of the normal distribution of cone cell bodies. When GABA (100 microM) was added along with either antagonist, cone cell bodies appeared normal. Neither bicuculline nor SR95531 alone had any effect on the general morphology of other retinal layers, suggesting that these GABA(A) receptor antagonists at the concentrations used were not acting as nonspecific disruption agents. The effects of GABA antagonists were confined to the first week after birth with no disruption seen in P9 or adult explant cultures. These data provide a direct demonstration of the necessity for GABAergic input to cones during active synaptogenesis. As we have previously shown, GABA(A) receptor activation causes a substantial increase in intracellular calcium concentrations in cones and thereby could provide a mechanism by which GABA regulates cone maturation.

Expression of gabaa receptors by reactive astrocytes in explant and primary cultures of rat cns

The presence of GABAA-receptors on astrocytes was studied in explant and primary cultures of rat cerebellum, hippocampus and spinal cord by means of immunohistochemistry. For these studies we have used the monoclonal antibody bd 17 against the β2- and β3-subunits of GABAA-receptor. In explant cultures many neurones were intensely stained with the GABAA-receptor antibody whereas adjacent astrocytes revealed little or no immunoreactivity. In the far outgrowth zone of explant culture, however, many immunostained astrocytes were observed. In primary astrocyte cultures, only a few cells were stained by the antibody. Astrocytes which became reactive after producing an artificial scar or after addition of certain compounds such as dibutyryl cyclic AMP, interleukin-6, basic fibroblast growth factor and kainic acid, also revealed GABAA-receptor immunoreactivity. Furthermore, these astrocytes were intensely stained for glial fibrillary acidic protein and vimentin. From our studies we conclude that only a subpopulation of normal astrocytes are immunopositive for the GABAA-receptor antibody whereas astrocytes which become reactive following injury of the tissue or after addition of dibutyryl cyclic AMP, the cytokine interleukin-6, fibroblast growth factor or the neurotoxin kainic acid express GABAA-sites.

GABAA receptors in the retina of the cat: an immunohistochemical study of wholemounts, sections, and dissociated cells.

Gamma-aminobutyric acid (GABA) is an inhibitory neurotransmitter used by many neurons of the mammalian retina. To identify the synaptic targets of these cells, we undertook an immunohistochemical study with a monoclonal antibody that recognizes the GABAA receptors (62-3G1, generously donated by A. de Blas). This antibody labels the somata of at least one group of amacrine cells in the inner nuclear layer. It also labels two groups of somata in the ganglion cell layer; one small and the other much larger. The small cells are likely to be displaced amacrine cells based on their size, although some could be gamma ganglion cells. The much larger receptor-positive cells are clearly ganglion cells, based both on their size and the antibody labeling of the initial portion of their axon. In the peripheral retina, the size of these large somata suggests that many are beta ganglion cells. However, at any point across the retina the density of these cells never exceeded 50% of the density of beta cells as a whole. The antibody also labels a dense plexus of processes that extends throughout the inner plexiform layer (IPL), with a marked concentration in the inner third of the layer. This is the portion of the IPL in which the rod bipolar cells terminate. It is difficult to recognize processes of individual cells in the IPL, so retinae were dissociated. The rod bipolar cells were identified by protein kinase C immunoreactivity (Negishi et al., 1988; Karschin & Wäsle, 1990). They were not labeled by the GABAA receptor antibody. This is surprising in light of tight-seal, whole cell voltage-clamp recordings that have shown that the rod bipolars express functional GABAA receptors. One possible explanation is that the antibody recognizes only a subset of the GABAA receptors.