Autoimmunity to glutamic acid decarboxylase (GAD) in Stiff-Man syndrome and insulin-dependent diabetes mellitus.

Stiff-Man syndrome (SMS) is a disorder of the CNS, characterized by rigidity of the body musculature, which has been hypothesized to result from an impairment of GABAergic neurotransmission. GABA is the main inhibitory neurotransmitter of the brain. It is also a putative signal molecule in the pancreas, where it is produced by beta cells (insulin-secreting cells)--the autoimmune target in insulin-dependent diabetes mellitus (IDDM). Autoantibodies to the GABA-synthesizing enzyme glutamic acid decarboxylase (GAD) have been found in SMS and in IDDM. This review summarizes evidence suggesting that SMS may be an autoimmune disease and discusses the possible significance of the autoimmune response to GAD in SMS and IDDM.     

Autoantibodies to glutamic acid decarboxylase in patients with therapy-resistant epilepsy

BACKGROUND: Autoantibodies to glutamic acid decarboxylase (GAD-A) are present in type 1 diabetes and stiff man syndrome (SMS), and have also been reported in cerebellar ataxia. Epilepsy was present in 4 of 19 patients with SMS and GAD-A, implying that epilepsy sometimes is associated with anti-GAD autoimmunity. METHODS: The authors investigated the prevalence of GAD-A in patients with therapy-resistant localization-related epilepsy (n = 51) and generalized epilepsy (n = 49) by a radiobinding assay. The positive samples were confirmed by immunohistochemistry and immunoblotting of recombinant human GAD65. RESULTS: GAD-A were found in eight patients with localization-related epilepsy, whereas none of the patients with generalized epilepsy, other neurologic disorders (n = 38), or the control subjects (n = 48) had GAD-A. Two patients had high levels of GAD-A, similar to SMS, whereas six patients had significantly lower titers, characteristic of type 1 diabetes. The two patients with high levels of GAD-A had GAD-A both in serum and CSF by immunohistochemistry and immunoblotting. Both of them had longstanding therapy-resistant temporal lobe epilepsy but did not have diabetes. One had a history of autoimmune disease, whereas the other had serologic evidence of multiple autoantibodies without any clinical signs of autoimmune disease. CONCLUSIONS: GAD autoimmunity may be associated with refractory localization-related epilepsy.     

难治性癫痫中谷氨酸脱羧酶抗体的测定

目的　研究难治性癫痫与血清谷氨酸脱羧酶抗体 (GAD-A)水平的关系 ,探讨难治性癫痫的发病机制。方法　应用酶联免疫吸附法 (EL ISA)测定了 3 0例难治性癫痫和 3 0例完全缓解的癫痫患者血清 GAD-A水平。结果　难治性癫痫患者和完全缓解癫痫患者血清 GAD-A水平无显著性差异 (P>0 .0 5) ,并且 ,各种类型癫痫患者其 GAD-A亦无明显差异 (P>0 .0 5)。结论　 GAD-A与难治性癫痫无明确的相关性 ,需要进一步扩大规模研究难治性癫痫中的谷氨酸脱羧酶抗体的变化     

Opsoclonus-myoclonus-ataxia syndrome with autoantibodies to glutamic acid decarboxylase

Opsoclonus-myoclonus-ataxia syndrome (OMS) is a rare neurological disorder of probably autoimmune origin. Most cases are associated with a remote neoplasm or a viral infection; however in some instances no underlying aetiology can be demonstrated. We report the presence of anti-glutamic acid decarboxylase antibodies (anti-GAD Abs) in the serum and CSF of a patient with idiopathic OMS. Treatment with intravenous immunoglobulin led to a remarkable clinical improvement with parallel reduction of anti-GAD titers. Anti-GAD Abs have been associated with several neurological syndromes. They could also be responsible for the clinical triad of OMS, by impairing GABAergic transmission in specific brainstem and cerebellar circuits. We propose that testing for anti-GAD Abs should be performed in OMS, especially when no other aetiological association can be demonstrated.     

Clinical significance of glutamic acid decarboxylase antibodies in patients with epilepsy

Purpose: Glutamic acid decarboxylase antibodies (GADAs) have been detected in patients with epilepsy, but the clinical determinants of epilepsy associated with GADA have not been defined. Methods: We analyzed GADA with a radioimmunoassay in sera of 253 well‐characterized patients with epilepsy and 200 control subjects. The positive samples were confirmed by immunohistochemistry and western blotting (WB). Sera were screened for other autoantibodies. Results: GADA were detected in 15 patients (5.9%) and in three control subjects (1.5%) (p = 0.026). Seven patients (2.8%) had high GADA titers [≥1,000 relative units (RUs)/ml], six of whom had temporal lobe epilepsy (TLE). All three GADA‐positive control subjects had low titers. Two of the five patients with high GADA titers and available cerebrospinal fluid (CSF) samples had intrathecal synthesis (IS) of GADA; one patient had CSF oligoclonal bands. The prevalence of increased levels of GADA tended to be higher in patients with TLE than in patients with extra‐TLE [odds ratio (OR) 1.32, 95% confidence interval (CI) 0.39–4.42; p = 0.657]. The patients with high GADA titers had significantly higher number of other autoantibodies compared to the patients with low GADA titers (p = 0.001) and the patients with normal GADA (p < 0.001). Discussion: High GADA titers were present in a subgroup of patients; close to 90% had TLE. The immunologic profile of these patients suggests that the most probable origin of their epilepsy is autoimmune. A positive IS of GADA may be a marker of an ongoing immune response that could identify those patients in whom a trial with immunosuppressive therapy might be warranted.     

Autoantibodies to glutamic acid decarboxylase in downbeat nystagmus

The cause of downbeat nystagmus (DBN) remains undiagnosed in about 40% of patients. This paper reports the presence of antiglutamic acid decarboxylase antibodies (GAD-Ab) in a patient with DBN. Antibodies against GABAergic neurons located in the vestibular complex may induce chemical denervation of the floccular neurons, which normally suppress the peripheral imbalance between vertical semicircular canal systems, thereby causing DBN. Testing for GAD-Ab may be indicated in DBN patients without an identifiable anatomical brain lesion.     

Cerebellar ataxia with glutamic acid decarboxylase autoantibodies

Degenerative cerebellar ataxia with autoantibodies against glutamic acid decarboxylase (GAD) is a rare disorder and may represent a subset of ataxias previously classified as idiopathic. The authors report a patient with progressive cerebellar ataxia, insulin-dependent diabetes mellitus, and GAD antibodies who responded to i.v. immunoglobulins.     

重组大鼠谷氨酸脱羧酶载体的构建和功能分析(英文)

目的谷氨酸脱羧酶2 (glutamic acid decarboxylase 2,GAD65) 是γ-氨基丁酸(gamma-aminobutyric acid, GABA)的合成酶。本研究拟构建重组大鼠GAD65基因的慢病毒载体(recombinant lentivirus-rGAD65,rLV-rGAD65),并在体内外分析其功能。方法用RT-PCR法克隆大鼠GAD65基因的cDNA 并亚克隆至慢病毒载体上,形成重组慢病毒质粒(rLV-GFP-rGAD65)。在包装质粒的帮助下,获得重组慢病毒颗粒(rLV-rGAD65)并检测其滴度。用rLV-rGAD65感染原代培养的大鼠肺成纤维细胞,并用免疫细胞化学和蛋白印迹法检测rGAD65在成纤维细胞中的表达,用高效液相法(high-performance liquid chromatograph, HPLC)检测培养上清中GABA的含量。在体内, rLV-rGAD65 定点注射到Sprague-Dawley大鼠的丘脑底核(subthalamic nucleus,STN)。用免疫组织化学和蛋白印迹法检测GAD65基因在STN中的表达水平,HPLC检测黑质网状部(su...     

Autoantibodies to glutamic acid decarboxylase in palatal myoclonus and epilepsy

We report the presence of serum autoantibodies directed aginst glutamic acid decarboxylase in a patient with epilepsy and palatal myoclonus not associated with brain lesions. Glutamic acid decarboxylase antibody reactivity was dependent on the presence of carboxy-terminal amino acids, similar to that reported in patients with stiff-man syndrome. Marked reduction in the frequency of epileptic attacks and improvement in palatal myoclonus occurred when benzodiazepine was administered and phenytoin was gradually tapered. Testing for antiglutamic acid decarboxylase antibodies may be indicated in patients with palatal myoclonus and with convulsive disorders refractory to therapy.     

Autoantibodies to glutamic acid decarboxylase in patients with epilepsy are associated with low cortical GABA levels

Antibodies to glutamic acid decarboxylase (GAD), the major pathway for the synthesis of γ‐aminobutyric acid (GABA) in humans, are found at elevated levels in a subgroup of patients with chronic epilepsy. To test whether the antibodies were associated with changes in cortical GABA levels we used magnetic resonance spectroscopy. Four patients with epilepsy and high serum GAD antibody levels (107–6,200 units/ml) and 10 healthy controls were recruited. A 3T GABA‐optimized spectrum was obtained from a reproducible voxel in the cortex. Compared to the control group, the patient group had significantly lower GABA concentrations within the cortex. Demonstration of an association between high serum GAD antibodies and low cortical GABA levels in patients with epilepsy suggests that GAD antibodies are, at least, a marker of a specific disease process and support a role for immune‐mediated GABAergic dysfunction.     

Limbic encephalitis with antibodies to glutamic acid decarboxylase presenting with brainstem symptoms

Limbic encephalitis (LE) is a neurological syndrome that may present in association with cancer, infection, or as an isolate clinical condition often accompanying autoimmune disorders. LE associated with glutamic acid decarboxylase antibodies (anti-GAD) is rare in children. Here, we characterized the clinical and laboratory features of a patient presenting with brainstem involvement with non-paraneoplastic LE associated with anti-GAD antibodies. In our patient, after plasma exchange, we determined a dramatic improvement of the neurological deficits.     

Differential hippocampal expression of glutamic acid decarboxylase 65 and 67 messenger RNA in bipolar disorder and schizophrenia

BACKGROUND: Expression of messenger RNA (mRNA) for the gamma-aminobutyric acid (GABA)-synthesizing enzyme, glutamic acid decarboxylase (GAD), in the prefrontal cortex and the number of GABAergic neurons in the hippocampus are reduced in schizophrenia and bipolar disorder. We tested the hypothesis that the expression of the 2 isoforms, one 65 kd (GAD(65)) and the other 67 kd (GAD(67)), is differentially affected in the hippocampus in schizophrenia and bipolar disorder. METHODS: Hippocampal sections from 15 subjects in 3 groups (control subjects and subjects with schizophrenia and bipolar disorder) were studied using an in situ hybridization protocol with sulfur 35-labeled complementary riboprobes for GAD(65) and GAD(67) mRNA. Emulsion-dipped slides were analyzed for the density of GAD mRNA-positive neurons in 4 sectors of the hippocampus and for the cellular expression level of both GAD mRNAs. RESULTS: The density of GAD(65) and GAD(67) mRNA-positive neurons was decreased by 45% and 43%, respectively, in subjects with bipolar disorder, but only 14% and 4%, respectively, in subjects with schizophrenia. The decreased density of GAD(65) mRNA-positive neurons in subjects with bipolar disorder was significant in sectors CA2/3 and dentate gyrus, and that of GAD(67) mRNA-positive neurons was significant in CA4, but not other hippocampal sectors. Cellular GAD(65) mRNA expression was significantly decreased in subjects with bipolar disorder, particularly in CA4, but not in schizophrenic subjects. Cellular GAD(67) mRNA expression was normal in both groups. CONCLUSION: We have found a region-specific deficit of GAD(65) and GAD(67) mRNA expression in bipolar disorder.     

Sequential antibodies to potassium channels and glutamic acid decarboxylase in neuromyotonia

A patient with thymoma-associated neuromyotonia and voltage-gated potassium channel (Kv1.2 and Kv1.6) antibodies by immunoprecipitation and rat brain immunolabeling was treated successfully with immunoadsorption and cyclophosphamide. Curiously, glutamic acid decarboxylase antibodies, absent at onset, appeared later. Stiff-person syndrome was absent, but fast blink reflex recovery suggested enhanced brainstem excitability. The range of antibodies produced in thymoma-associated neuromyotonia is richer, and the timing of antibody appearance more complex, than previously suspected.     

Characterization of the proteins purified with monoclonal antibodies to glutamic acid decarboxylase

Immunoaffinity columns are prepared from the monoclonal antibody (MAb) GAD-1. These columns are used to enrich glutamic acid decarboxylase (GAD) from the cytosolic fraction of rat brain homogenates and from Triton X-100 extracts of the brain membrane fraction. In each case enzyme activity is enriched over 400-fold. The immunopurified fractions were analyzed by SDS-PAGE. Fractions purified from the cytosol consisted of a quantitatively major band of 59 kDa, and one band of 63 kDa, as well as a group centered around 55 kDa. Fractions purified from membranes consisted primarily of the 59 and 63 kDa components; only traces of the lower-molecular-weight components were present. The entire set of proteins purified on GAD-1 immunoaffinity columns is strongly recognized by 2 widely used antisera to GAD, those described in Saito et al. (1974) and Oertel et al. (1981). The 59 kDa protein from the cytosolic fraction was purified to homogeneity by preparative SDS-PAGE; a partial amino acid sequence of this protein was obtained. The 59 kDa protein has a high degree of sequence homology with the deduced amino acid sequence of the protein that was coded for by a cDNA for feline GAD (Kaufman et al., 1986; Kobayashi et al., 1987). Thus, these proteins are either products of a single gene that diverged during the evolution of rat and cat from a common ancestor, or are members of a closely related set of genes found in both species. The MAb GAD-6 recognizes the 59 kDa band and the group of bands centered around 55 kDa on Western blots. Therefore, these proteins are immunochemically related. GAD-6 does not recognize the 63 kDa band. In Western blots of unfractionated homogenates of the whole brain, the only band recognized by GAD-6 is a 59 kDa band.(ABSTRACT TRUNCATED AT 250 WORDS)