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

Autoimmune Processes in the Central Nervous System

In this chapter we discuss the factors that contribute to the unique immunological environment of the central nervous system and the mechanisms that may account for the development of autoimmunity within the CNS, including infectious agents as inducers of autoimmune disease. Consideration is given to a variety of human neurological diseases of autoimmune or presumed autoimmune etiology: autism, neuromyelitis optica, neuromyotonia, schizophrenia, lethargic encephalitis and stiff‐man syndrome. Also, we discuss autoimmunity as a possible mediator of CNS repair and examples of the protective effects of bacterial and helminth infections on CNS disease. Multiple sclerosis and models of multiple sclerosis are discussed with special attention given to the Theiler's virus‐induced demyelination model.

Stiff-person syndrome with acute recurrent peripheral vertigo: possible evidence of gamma aminobutyric acid as a neurotransmitter in the vestibular periphery

OBJECTIVE

We report a case of a 58-year-old man suffering from stiff-person syndrome and recurrent peripheral vertigo.

METHOD

A case report and a review of the recent literature on stiff-person syndrome are presented.

RESULTS

The patient presented with recurrent episodes of vertigo with a pure peripheral pattern and with concomitant episodes of burning muscle pain, muscle twitching, weight gain and fatigue, worsening with tension or stress that also occurred in periods without vertigo. Cochlear examinations only showed presbyacusis-like hearing loss. The diagnosis of stiff-person syndrome was made with electromyographic examination and from findings in the blood and cerebrospinal fluid of high titres of anti-glutamic acid decarboxylase (GAD67) autoantibodies. In a two-year follow-up period, therapy for stiff-person syndrome abolished episodes of both stiffness and vertigo.

CONCLUSION

As far as we know, no other clinical case of acute vestibular damage with a possible correlation with anti-glutamic acid decarboxylase antibodies has been described. Peripheral vertigo possibly related to a lack of gamma aminobutyric acid underlines a possible role of gamma aminobutyric acid as a neurotransmitter in the peripheral vestibular system.

Rigidity and spasms from autoimmune encephalomyelopathies: stiff-person syndrome

Stiff-person syndrome (SPS) is a disorder characterized by progressive muscle rigidity with superimposed painful muscle spasms and gait impairment due to continuous motor activity. Evidence has accumulated in favor of SPS representing an autoimmune, predominantly encephalomyelopathic disorder resulting from B-cell-mediated clonal production of autoantibodies against presynaptic inhibitory epitopes on the enzyme glutamic acid decarboxylase (GAD) and the synaptic membrane protein amphiphysin. Recognition of the clinical spectrum of SPS is important, particularly the upper-limb, cervical, and cranial nerve involvement that occurs in paraneoplastic variants. The correlation between antibody levels and severity of disease offers evidence for a pathogenic role for the anti-GAD and anti-amphiphysin autoantibodies. The scarcity of neuropathological correlates stand in sharp contrast with the severity of the disability in affected individuals and suggests that functional impairment of inhibitory circuits without structural damage is sufficient to develop the full clinical spectrum of SPS. The rarity of this condition limits the feasibility of controlled clinical trials in the treatment of SPS, but the available evidence suggest that drugs that increase cortical and spinal inhibition such as benzodiazepines and drugs that provide immune modulation such as intravenous immunoglobulin, plasmapheresis, and prednisone are effective treatments.

Analysis of GAD65 autoantibodies in Stiff-Person syndrome patients

Autoantibodies to the 65-kDa isoform of glutamate decarboxylase GAD65 (GAD65Ab) are strong candidates for a pathological role in Stiff-Person syndrome (SPS). We have analyzed the binding specificity of the GAD65Ab in serum and cerebrospinal fluid (CSF) of 12 patients with SPS by competitive displacement studies with GAD65-specific rFab-derived from a number of human and mouse mAbs specific for different determinants on the Ag. We demonstrate considerable differences in the epitope specificity when comparing paired serum and CSF samples, suggesting local stimulation of B cells in the CSF compartment of these patients. Moreover, these autoantibodies strongly inhibit the enzymatic activity of GAD65, thus blocking the formation of the neurotransmitter gamma-aminobutyric acid. The capacity of the sera to inhibit the enzymatic activity of GAD65 correlated with their binding to a conformational C-terminal Ab epitope. Investigation of the inhibitory mechanism revealed that the inhibition could not be overcome by high concentrations of glutamate or the cofactor pyridoxal phosphate, suggesting a noncompetitive inhibitory mechanism. Finally, we identified a linear epitope on amino acids residues 4-22 of GAD65 that was recognized solely by autoantibodies from patients with SPS but not by serum from type 1 diabetes patients. A mAb (N-GAD65 mAb) recognizing this N-terminal epitope was successfully humanized to enhance its potential therapeutic value by reducing its overall immunogenicity.

Structural and functional analysis of cysteine residues in human glutamate decarboxylase 65 (GAD65) and GAD67

Previously, we have shown that brain glutamate decarboxylase (GAD) is greatly inhibited by sulfhydryl reactive reagent suggesting cysteine residue(s) may play an important role in GAD function. In this report, we determined the role of cysteine residues in the recombinant human 65-kDa GAD isoform (hGAD65) and 67-kDa GAD isoform (hGAD67), using a combination of matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry and site-directed mutagenesis. Here, we report that cysteine 446 (C446) in hGAD65 is important for its activity and is present as free sulfhydryl group. This conclusion is based on the following observations: (i) mutation of C446 in hGAD65 to alanine reduced hGAD65 activity by more than 90%, (ii) MALDI-TOF analysis of the non-reduced, trypsin-digested GAD65 revealed that C446 is present as a free sulfhydryl group as indicated by a peak at m/z (mass/charge) 647.3446 (peptide 443-448) and, when GAD65 was treated with sulfhydryl reagent, N-ethylmaleimide (NEM), the peak is shifted to m/z 772.3702,a mass increase of 125.1 daltons (Da) as a result of modification of cysteine by NEM. Parallel studies have also been conducted with hGAD67. Cysteine 455 was found to be important for GAD67 activity.

Analysis of SNAP-25 immunoreactivity in hippocampal inhibitory neurons during development in culture and in situ

Synaptosomal associated protein of 25 kDa (SNAP-25) is a component of the soluble N-ethylmaleimide-sensitive fusion protein (NSF) attachment protein receptor (SNARE) complex which plays a central role in synaptic vesicle exocytosis. We have previously demonstrated that adult rat hippocampal GABAergic synapses, both in culture and in brain, are virtually devoid of SNAP-25 immunoreactivity and are less sensitive to the action of botulinum toxin type A, which cleaves this SNARE protein [Neuron 41 (2004) 599]. In the present study, we extend our findings to the adult mouse hippocampus and we also provide demonstration that hippocampal inhibitory synapses lacking SNAP-25 labeling belong to parvalbumin-, calretinin- and cholecystokinin-positive interneurons. A partial colocalization between SNAP-25 and glutamic acid decarboxylase is instead detectable in developing mouse hippocampus at P0 and, at a lesser extent, at P5. In rat embryonic hippocampal cultures at early developmental stages, SNAP-25 immunoreactivity is detectable in a percentage of GABAergic neurons, which progressively reduces with time in culture. Consistent with the presence of the substrate, botulinum toxin type A is partially effective in inhibiting synaptic vesicle recycling in immature GABAergic neurons. Since SNAP-25, beside its role as a SNARE protein, is involved in additional processes, such as neurite outgrowth and regulation of calcium dynamics, the presence of higher levels of the protein at specific stages of neuronal differentiation may have implications for the construction and for the functional properties of brain circuits.

Epitope analysis of GAD65Ab using fusion proteins and rFab

The identification of disease-specific autoantibodies to the 65-kDa isoform of glutamate decarboxylase (GAD65Ab) epitopes in type 1 diabetes has been hampered by their conformational nature. Here, we compared two methods of GAD65Ab epitope analysis: GAD65/67 fusion proteins and competition assays using GAD65-specific recombinant fraction antigen binding (rFab). Sera from newly diagnosed type 1 diabetes patients (n=61) were studied using both approaches. Competition of GAD65 binding by an rFab to a specific epitope did not correlate with binding to the fusion protein that represented this epitope. Conversely, samples that bound to specific fusion proteins were not necessarily competed with rFab specific to determinants in the same region. We conclude that epitopes of different characteristics are detected by fusion proteins and by competition with rFab. Fusion proteins allow the definition of large epitope regions; however, some conformational GAD65Ab epitopes, especially those residing in the middle region, are destroyed or distorted in the fusion proteins. Competition studies using rFab allow the identification of conformational epitopes. However, monoclonal rFab may only reflect a limited proportion of the epitopes recognized by polyclonal sera. A combined analysis using both approaches may therefore be necessary to gain best understanding of autoantibody characteristics and affinity maturation.

Evaluation of hyponatremia: a little physiology goes a long way

Hyponatremia is common in hospitalized patients. By taking a careful and logical approach, one can promptly recognize the causative factor or factors in nearly all cases. Most cases of hyponatremia are due to impaired renal water excretion, and recognizing the cause and pathophysiologic process makes it possible to provide focused individualized care and avoid mistreatment.

Autoantibody testing

Recent advances in neuroimmunology have led to improvements in the pathogenesis, diagnosis, prognosis, and treatment of many neuromuscular disorders. The value of autoantibody testing is increasing steadily in neurologic practice. Not all antibodies have a high yield in diagnosis. In some disorders, such as generalized adult onset of myasthenia gravis, Lambert-Eaton myasthenic syndrome,Miller Fisher syndrome, and multifocal motor neuropathy,autoantibody tests provide accurate diagnosis and can be considered biologic markers of these disorders.

Stiff-Person Syndrome

BACKGROUND

Stiff-person syndrome (SPS) is a rare neurologic disorder with autoimmune features. It is characterized by progressive, severe muscle rigidity or stiffness most prominently affecting the spine and lower extremities.

REVIEW SUMMARY

Superimposed muscle spasms result in simultaneous contraction of agonist and antagonist muscles which are detectable by electromyography (EMG) and relieved by administration of benzodiazepines. The exacerbation of SPS by emotional stressors often results in the referral of these patients for psychiatric assessment although this was more common before the discovery of an association with antibodies to glutamic acid decarboxylase (GAD antibodies). Formerly known as stiff-man syndrome, the female to male ratio is 2:1 and the principle paraneoplastic variant is associated with breast cancer. Although rare, this is a disease of middle age that severely curtails the functional capacity of those it strikes. It is frequently associated with diabetes and other autoimmune diseases. IVIg is recently demonstrated to be effective in the treatment of SPS; diazepam remains useful in managing the symptoms.

CONCLUSIONS

This article summarizes the history of SPS, describes important clinical features, discusses management, touches upon areas of uncertainty, and postulates some avenues for research.

GABA, gamma-hydroxybutyric acid, and neurological disease

gamma-Aminobutyric acid (GABA) is the primary inhibitory neurotransmitter in the central nervous system. GABA is converted from glutamic acid by the action of glutamic acid decarboxylase (GAD) of which two isoforms exist GAD65 and GAD67. GABA then is broken down, both within the cell and in the synaptic cleft by GABA transaminase to form succinic semialdehyde. In turn, succinic semialdehyde is converted either to succinic acid by succinic semialdehyde dehydrogenase or into gamma-hydroxybutyric acid (GHB) by succinic semialdehyde reductase. Because GABA modulates the majority of inhibition that is ongoing in the brain, perturbations in GABAergic inhibition have the potential to result in seizures. Therefore, the most common disorder in which GABA is targeted as a treatment is epilepsy. However, other disorders such as psychiatric disease, spasticity, and stiff-person syndrome all have been related to disorders of GABAergic function in the brain. This review covers the roles of GABAergic neurotransmission in epilepsy, anxiety disorders, schizophrenia, stiff-person syndrome, and premenstrual dysphoric disorder. In the final section of this review, the GABA metabolite GHB is discussed in terms of its physiological significance and its role in epilepsy, sleep disorders, drug and alcohol addiction, and an inborn error of GABA metabolism, succinic semialdehyde dehydrogenase deficiency.

Dual impairment of GABAA- and GABAB-receptor-mediated synaptic responses by autoantibodies to glutamic acid decarboxylase

Anti-glutamate decarboxylase autoantibodies (GAD-A) are associated with a group of patients with progressive cerebellar ataxia. We reported previously that cerebellar GABA(A)-mediated synaptic transmission was presynaptically depressed by GAD-A in the cerebrospinal fluid (CSF). Using whole-cell recording of rat cerebellar slices, we found in the present study that CSF immunoglobulins from ataxic patients reduced gamma-aminobutyric acid (GABA) release from cerebellar interneurons, thereby attenuating presynaptic inhibition on neighboring excitatory synapses through GABA(B) receptors (GABA(B)Rs). Our results suggest that in in vitro slices, GAD-A elicited the pathophysiological action of reduction in GABA release, which subsequently resulted in dual synaptic impairment in the cerebellar circuit, by depression of GABA(A) receptor (GABA(A)R)-mediated inhibitory synaptic transmissions, and attenuation of GABA(B) receptor-mediated inhibition of excitatory transmissions.

Progressive encephalomyelitis with rigidity presenting as a stiff-person syndrome

Diagnosis criteria of stiff-person syndrome (SPS) include progressive, fluctuating muscular rigidity and spasms with normal neurological examination. The presence of unusual features such as prominent limb rigidity with segmental signs and contracture, evidence of brainstem dysfunction, profound autonomic disturbances, CSF pleiocytosis or MRI abnormalities in patients with SPS presentation allows to classify these patients as progressive encephalomyelitis with rigidity (PER). We report a 50 year-old woman suffering from severe painful spasms of abdominal wall and limb muscles. Neurological examination showed pyramidal signs. EMG disclosed continuous muscle activity with superimposed discharges. Treatment with high doses of diazepam and baclofen led to moderate improvement of generalised stiffness. However, the right arm became more rigid with oedema and vasomotor changes. Subsequently, bilateral nystagmus and internuclear opthalmplegia appeared. There was mild CSF pleiocytosis. Associated auto-immune thyroiditis was found with positive anti-microsome antibodies and decreased thyroid hormones. Search for profound neoplasm was negative. The patient had three subacute bouts then she improved with methylprednisolone. The initial clinical presentation mimicking a SPS with subsequent diffuse involvement of the central nervous system and a striking localisation of a severe rigidity to one arm allowed to suspect the diagnosis of PER. The relationship between SPS and PER remains unclear because of the rarity of these disorders. The observation reported in this paper gives evidence that both the disorders are probably two clinical presentations of the same pathogenic process.

Molecular mechanisms of neurotransmitter release

The release of neurotransmitter from neurons represents one of the pivotal events in synaptic transmission. Neurotransmitters are released from synaptic vesicles in presynaptic neurons in response to neural activity, diffuse across the synaptic cleft, and bind specific receptors in order to bring about changes in postsynaptic neurons. Some of the molecular processes that govern neurotransmitter release are now becoming better understood. The steps involved can be broken down into two partially overlapping presynaptic cycles, the neurotransmitter cycle and the synaptic vesicle cycle. The neurotransmitter cycle involves transmitter biosynthesis, storage, reuptake, and degradation. The synaptic vesicle cycle involves targeting to the nerve terminal, docking, fusion, endocytosis, and recycling. Biochemical and structural studies have yielded important insight into our understanding of each of these two cycles. Further, both pharmacological and genetic interference with either of these cycles results in profound alterations in synaptic transmission and behavior, demonstrating the crucial role of neurotransmitter release.

Plasma exchange in stiff-man syndrome

Stiff-man syndrome (STS) is a rare neurological disorder characterized by involuntary axial and proximal limb rigidity and continuous motor unit activity on electromyography (EMG). Autoantibodies to glutamic acid decarboxylase (GAD) present in 60% of the patients are implicated. We report on the use of plasma exchange (PE) in 2 patients with STS whose serum and cerebrospinal fluid were negative for GAD autoantibodies. One patient showed minimal clinical improvement following PE while the second reported subjective improvement, but not any different from that with medications. Based on the results of PE in our patients, it seems that those who are autoantibody negative are less likely to respond. Whether a more aggressive approach to PE will be beneficial remains speculative.

Motor cortex excitability in stiff-person syndrome

Muscle stiffness in stiff-person syndrome (SPS) is produced by continuous, involuntary firing of motor units that is thought to be caused by an autoimmune mediated dysfunction of GABA-ergic inhibitory neurones. We have postulated that the loss of GABA-ergic inputs from spinal interneurones alone is insufficient to produce tonic firing of motor neurones and that excessive supraspinal excitation could also play a role. To determine whether SPS is associated with dysfunction in supraspinal GABA-ergic neurones, we assessed the excitability of the motor cortex with transcranial magnetic stimulation (TMS) in seven SPS patients and seven age-matched healthy volunteers. SPS patients had normal central motor conduction times, normal thresholds for motor evoked potentials (MEPs) in leg muscles, and a normal MEP stimulus versus response recruitment curve with increasing TMS intensities in resting hand and leg muscles. Cortical silent periods were shortened in leg muscles. Intracortical inhibition and excitation were assessed while recording from the abductor pollicis brevis, using a paired pulse TMS paradigm with subthreshold conditioning stimuli. Patients had decreased inhibition and markedly increased facilitation at short intervals. Using paired suprathreshold TMS, patients exhibited increased facilitation at 20- and 40-ms intervals. These results point to a hyperexcitability of the motor cortex in SPS, which could be explained by impairment of supraspinal GABA-ergic neurones, leading to an impaired balance between inhibitory and excitatory intracortical circuitry.

Structure of the mouse glutamate decarboxylase 65 gene and its promoter: preferential expression of its promoter in the GABAergic neurons of transgenic mice

GABA is synthesized by glutamate decarboxylase (GAD), which has two forms, GAD65 and GAD67. To elucidate the molecular mechanisms of mouse GAD65 (mGAD65) gene expression, we isolated and characterized the mGAD65 gene. The mGAD65 gene was found to be divided into 16 exons and spread over 75 kb. The sequence of the first exon and the 5'-flanking region indicated the presence of potential neuron-specific cis-regulatory elements. We used transgenic mice to examine the expression pattern conferred by a 9.2-kb promoter-proximal DNA fragment of the mGAD65 gene fused to the bacterial lacZ reporter gene. Transgenic mice showed high beta-galactosidase activity specifically in brain and testis. They also showed characteristic patterns of transgene expression in olfactory bulb, cerebellar cortex, and spinal cord, a similar expression pattern to that of endogenous mGAD65. However, no transgene expression was observed in the ventral thalamus or hypothalamus, in which high mGAD65 gene expression levels have been observed. These results suggest that the 9.2-kb DNA fragment of the mGAD65 gene is associated with its tissue-specific expression and its targeted expression in GABAergic neurons of specific brain regions but that additional regulatory elements are necessary to obtain fully correct expression.

Domain-restricted expression of two glutamic acid decarboxylase genes in midgestation mouse embryos

Glutamic acid decarboxylase (GAD) is the biosynthetic enzyme for gamma-aminobutyric acid (GABA), the major inhibitory neurotransmitter in the central nervous system (CNS) of vertebrates. In addition to the adult CNS, GABA and GAD also have been detected in embryos, although their precise localization and specific functions in embryonic development have not been elucidated. In this paper, the authors studied the cellular distribution of two GAD isoforms, GAD65 and GAD67, in midgestation mouse embryos by in situ hybridization histochemistry. With few exceptions, it was found that GAD65 and GAD67 mRNAs are localized in overlapping cellular domains of the embryonic CNS that later develop into regions with a strong GABAergic contribution. The GAD-expressing cells are situated in the differentiating zone of the embryonic day 10.5 (E10.5) through E11.5 CNS and in the subventricular zone and the mantle zone of the E12.5 CNS, which suggests that they are committed neuronal precursors. By using a specific serum for GABA, a similar pattern of distribution was obtained, indicating that GAD mRNAs are translated efficiently into enzymatically active GAD, which produces embryonic GABA. The expression domains of GAD overlap with those of genes that are known to be involved in the patterning of the embryonic CNS. The two GAD mRNAs also are detected outside of the embryonic CNS in various cell types, mainly those of placodal and neural crest origin. This pattern of expression is consistent with the notion that GAD and its product, GABA, play a signaling role during development.

Autoimmunity to gephyrin in Stiff-Man syndrome

Stiff-Man syndrome (SMS) is a rare disease of the central nervous system (CNS) characterized by chronic rigidity, spasms, and autoimmunity directed against synaptic antigens, most often the GABA-synthesizing enzyme glutamic acid decarboxylase (GAD). In a subset of cases, SMS has an autoimmune paraneoplastic origin. We report here the identification of high-titer autoantibodies directed against gephyrin in a patient with clinical features of SMS and mediastinal cancer. Gephyrin is a cytosolic protein selectively concentrated at the postsynaptic membrane of inhibitory synapses, where it is associated with GABA(A) and glycine receptors. Our findings provide new evidence for a close link between autoimmunity directed against components of inhibitory synapses and neurological conditions characterized by chronic rigidity and spasms.

Presynaptic impairment of cerebellar inhibitory synapses by an autoantibody to glutamate decarboxylase

Glutamic acid decarboxylase (GAD), the enzyme responsible for converting glutamate to gamma-aminobutyric acid (GABA), is a target of humoral autoimmunity in stiff-man syndrome and subacute cerebellar ataxia. Recently, we found that an anti-GAD autoantibody in the CSF of an ataxic patient selectively suppressed GABA-mediated transmission on cerebellar Purkinje cells without affecting glutamate-mediated transmission. Here, we examine the mechanism by which the autoantibody impaired the inhibitory transmission, using immunohistochemistry and whole-cell recording in rat cerebellar slices. The present results indicate that CSF immunoglobulins prepared from an ataxic patient acted on the presynaptic terminals of GABAergic interneurons and decreased GABA release onto Purkinje cells.

A novel method for expression and large-scale production of human brain l-glutamate decarboxylase

l-Glutamate decarboxylase (GAD; EC 4.1.1.15) is the rate-limiting enzyme involved in the synthesis of gamma-aminobutyric acid (GABA), the major inhibitory neurotransmitter in the mammalian brain. Imbalance in the conversion of glutamate to GABA has been implicated in a host of human diseases. Studies on the structure, function, and therapeutic use of GAD have been precluded by insufficient quantities of purified active enzyme. Here we report a novel methodology for the expression and large-scale production of enzymatically active, pure, recombinant human GAD65 and GAD67. This method circumvents the sequestering of expressed protein into insoluble inclusion bodies and reduces production of truncated proteins. The availability of sufficient quantities of purified HGAD65 and HGAD67 has allowed for the production of specific polyclonal antibodies that discriminate between the two isoforms. This methodology, in addition to providing key human brain enzymes, may be generally applicable to other systems.

Comparative analysis of epitope recognition of glutamic acid decarboxylase (GAD) by autoantibodies from different autoimmune disorders

Autoantibodies to GAD, an important marker of the autoimmune process in type I or insulin-dependent diabetes mellitus (IDDM), are also found in non-diabetic individuals with autoimmune polyendocrine syndrome type 1 (APS1), APS2, and stiff man syndrome (SMS). Most IDDM sera contain two distinct GAD antibody specificities, one of which targets an epitope region in the middle-third of GAD65 (IDDM-E1; amino acids 221-359) and one of which targets the carboxy-third of GAD65 (IDDM-E2; amino acids 453-569). Using 11 chimeric GAD65/GAD67 proteins to maintain conformation-dependent epitopes of GAD65, we compared the humoral repertoire of IgG antibodies from an individual with APS2-like disease (b35, b78, and b96) and MoAbs from an IDDM patient (MICA-2, MICA-3, and MICA-4). Neither the APS2 IgG antibodies nor the IDDM MoAbs bind the amino-terminal third of GAD65, but instead target the carboxy-terminal two-thirds of GAD65. Amino acids 270-359 (IDDM-E1) are targeted by one APS2 IgG antibody and MICA-4, while two other APS2 IgG antibodies, MICA-2 and MICA-3, target amino acids 443-585 (IDDM-E2). Using GAD65/67 chimera that span the IDDM-E2 region, we found that MICA-2 binds amino acids 514-528 of GAD65, but two APS2 IgG antibodies require this region and amino acids 529-570. In contrast, the binding of MICA-3 requires two discontinuous amino acid segments of GAD65 (452-513 and 528-569), but not amino acids 514-528. These results indicate that there are both similarities and differences in the humoral response to GAD65 in APS2 and IDDM.

Epitope-specific glutamic acid decarboxylase-65 autoantibodies in intravenous immunoglobulin preparations

Intravenous immunoglobulin (IVIG) has been used to treat many autoimmune disorders including Stiff-Man Syndrome (SMS). SMS is a neurological disorder associated with an immune-mediated deficiency of gamma-aminobutyric acid (GABA) due to autoantibodies against the GABA synthesizing enzyme glutamic acid decarboxylase-65 (GAD65). GAD65 autoantibodies are present among 1-2% of healthy individuals. It can therefore not be excluded that GAD65 autoantibodies may be present in IVIG, which is prepared from multiple blood donors. We report here that GAD65 but not IA-2 autoantibodies were present in commercial IVIG preparations. The presence of autoantibodies may affect the outcome of IVIG treatment and screening commercial preparations of IVIG for GAD65 autoantibodies is therefore recommended before treating patients.

The epsins define a family of proteins that interact with components of the clathrin coat and contain a new protein module

Epsin (epsin 1) is an interacting partner for the EH domain-containing region of Eps15 and has been implicated in conjunction with Eps15 in clathrin-mediated endocytosis. We report here the characterization of a similar protein (epsin 2), which we have cloned from human and rat brain libraries. Epsin 1 and 2 are most similar in their NH(2)-terminal region, which represents a module (epsin NH(2) terminal homology domain, ENTH domain) found in a variety of other proteins of the data base. The multiple DPW motifs, typical of the central region of epsin 1, are only partially conserved in epsin 2. Both proteins, however, interact through this central region with the clathrin adaptor AP-2. In addition, we show here that both epsin 1 and 2 interact with clathrin. The three NPF motifs of the COOH-terminal region of epsin 1 are conserved in the corresponding region of epsin 2, consistent with the binding of both proteins to Eps15. Epsin 2, like epsin 1, is enriched in brain, is present in a brain-derived clathrin-coated vesicle fraction, is concentrated in the peri-Golgi region and at the cell periphery of transfected cells, and partially colocalizes with clathrin. High overexpression of green fluorescent protein-epsin 2 mislocalizes components of the clathrin coat and inhibits clathrin-mediated endocytosis. The epsins define a new protein family implicated in membrane dynamics at the cell surface.

The stiff-person syndrome: an autoimmune disorder affecting neurotransmission of gamma-aminobutyric acid

The stiff-person syndrome, a rare and disabling disorder, is characterized by muscle rigidity and episodic spasms that involve axial and limb musculature. Continuous contraction of agonist and antagonist muscles caused by involuntary motor-unit firing at rest are the hallmark clinical and electrophysiologic signs of the disease. Except for global muscle stiffness, results of neurologic examination are usually normal. Results of conventional computed tomography and magnetic resonance imaging of the brain are also normal. The cause of the stiff-person syndrome is unknown; however, an autoimmune pathogenesis is suspected because of 1) the presence of antibodies against glutamic acid decarboxylase (GAD), the rate-limiting enzyme for the synthesis of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA); 2) the association of the disease with other autoimmune conditions; 3) the presence of various autoantibodies; and 4) a strong immunogenetic association. Anti-GAD antibodies, which are found in high titers in most patients, seem to be directed against conformational forms of GAD. New evidence suggests that these antibodies may be pathogenic because they interfere with the synthesis of GABA. In addition, a reduction in brain levels of GABA, which is prominent in the motor cortex, has been demonstrated with magnetic resonance spectroscopy in patients with the stiff-person syndrome. The stiff-person syndrome is clinically elusive but potentially treatable and should be considered in patients with unexplained stiffness and spasms. Drugs that enhance GABA neurotransmission, such as diazepam, vigabatrin, and baclofen, provide mild to modest relief of clinical symptoms. Immunomodulatory agents, such as steroids, plasmapheresis, and intravenous immunoglobulin, seem to offer substantial improvement. Results of an ongoing controlled trial will elucidate the role of these agents in the treatment of the disease.

Role of synaptic vesicle proton gradient and protein phosphorylation on ATP-mediated activation of membrane-associated brain glutamate decarboxylase

Previously, we have shown that the soluble form of brain glutamic acid decarboxylase (GAD) is inhibited by ATP through protein phosphorylation and is activated by calcineurin-mediated protein dephosphorylation (Bao, J., Cheung, W. Y., and Wu, J. Y. (1995) J. Biol. Chem. 270, 6464-6467). Here we report that the membrane-associated form of GAD (MGAD) is greatly activated by ATP, whereas adenosine 5'-[beta,gamma-imido]triphosphate (AMP-PNP), a non-hydrolyzable ATP analog, has no effect on MGAD activity. ATP activation of MGAD is abolished by conditions that disrupt the proton gradient of synaptic vesicles, e.g. the presence of vesicular proton pump inhibitor, bafilomycin A1, the protonophore carbonyl cyanide m-chorophenylhydrazone or the ionophore gramicidin, indicating that the synaptic vesicle proton gradient is essential in ATP activation of MGAD. Furthermore, direct incorporation of (32)P from [gamma-(32)P]ATP into MGAD has been demonstrated. In addition, MGAD (presumably GAD65, since it is recognized by specific monoclonal antibody, GAD6, as well as specific anti-GAD65) has been reported to be associated with synaptic vesicles. Based on these results, a model linking gamma-aminobutyric acid (GABA) synthesis by MGAD to GABA packaging into synaptic vesicles by proton gradient-mediated GABA transport is presented. Activation of MGAD by phosphorylation appears to be mediated by a vesicular protein kinase that is controlled by the vesicular proton gradient.

A model for a glutamate receptor agonist antibody-binding site

A combination of mutagenesis, computer modeling and immunoreactivity has been used to develop a structural model of a segment of the glutamate receptor (GluR), termed GluR3B, which is bound by receptor-activating autoantibodies. In this model, the GluR3B epitope is located in a reverse hairpin loop that places key residues important for antibody recognition and receptor activation in a linear arrangement on the solvent-exposed surface. The conformation of the loop is stabilized by a hydrophobic core which is critical for functional integrity of the epitope. The proximity of the amino- and carboxy-terminal residues suggested that the GluR3B peptide could be cyclized without diminishing immunoreactivity through replacement of these residues with cysteines and formation of a disulfide bond. This prediction was confirmed experimentally since the cyclized peptide retained full immunoreactivity. The model provides insight into GluR subunit-specific functional diversity and the role of autoantibodies to this region in neurological disease.

Radioimmunoassay for glutamic acid decarboxylase (GAD65) autoantibodies as a diagnostic aid for stiff-man syndrome and a correlate of susceptibility to type 1 diabetes mellitus

OBJECTIVE

To establish and validate a double-antibody radioimmunoassay (RIA) for detecting serum auto-antibodies against glutamic acid decarboxylase (GAD65). This enzyme catalyzes synthesis of the neurotransmitter gamma-aminobutyric acid in neurons and pancreatic islet cells.

MATERIAL AND METHODS

We compared the frequency of GAD65 and other "thyrogastric" autoantibodies in adult patients with stiff-man (Moersch-Woltman) syndrome, type 1 diabetes, or polyendocrine disorders and in healthy subjects. The frequency of pancreatic islet cell antibody (ICA) detection was also assessed. The GAD65 RIA was validated by testing blinded samples, by confirming the specificity of low-titered positive results by "cold" antigen inhibition, and by comparing the RIA results with results of a kit assay incorporating staphylococcal protein A as immunoprecipitant. Recombinant GAD65 protein labeled with 125I was used as antigen, and a combination of anti-human IgG and IgM was used as immunoprecipitant. Seropositivity was determined for ICA and gastric parietal cell antibodies by indirect immunofluorescence assays and for thyroid peroxidase (microsome) and thyroglobulin antibodies by agglutination assays.

RESULTS

We detected GAD65-specific antibodies in all but 1 of 46 local patients with stiff-man syndrome (98%); 16 had evidence of diabetes. Positive values exceeded 20 nmol/L in 96%, and 89% were ICA-positive; 76% had additional thyrogastric antibodies. Of 41 patients with type 1 diabetes (17 local and 24 workshop serum specimens), 33 were GAD65 antibody-positive (80%); 85% of these positive values were 20 nmol/L or lower. Only 18% of sera from patients with type 1 diabetes were ICA-positive, but 59% had other thyrogastric autoantibodies. Of 20 patients with autoimmune endocrinopathies without diabetes or stiff-man syndrome, 35% were GAD65 antibody-positive, 5% were ICA-positive, and 90% were thyrogastric antibody-positive. Of 117 healthy control subjects, 8% were GAD65 antibody-positive, and a third of those had other thyrogastric antibodies (14% overall); none was ICA-positive.

CONCLUSION

Seropositivity in the double-antibody RIA for GAD65 autoantibody is a sensitive and specific marker of predisposition to type 1 diabetes and related organ-specific autoimmune disorders. As such, this RIA is complemented by assays for thyroid and gastric parietal cell autoantibodies.

A monoclonal antibody-based characterization of autoantibodies against glutamic acid decarboxylase in adults with latent autoimmune diabetes

Autoantibodies to glutamic acid decarboxylase (GAD) are an important marker of the autoimmune-mediated beta-cell destruction in insulin-dependent (Type I) diabetes. However, these autoantibodies are also found in patients with Stiff-man syndrome (SMS) without onset of diabetes and some diabetic patients who initially present as non-insulin dependent (Type II) diabetes later becoming insulin-dependent, called as latent autoimmune diabetes in adults (LADA). To study the immune response to GAD in these LADA patients a competitive radiobinding assay based on murine monoclonal antibodies recognizing three different GAD regions was performed. The monoclonal antibodies against GAD recognize two different linear epitopes localized at the N- (amino acids 4-17) and C-terminus (amino acids 572-585) and one conformation-dependent epitope region (amino acids 221-442 IDDM-E1) known to be immunodominant for diabetes-associated autoantibodies. All LADA sera (20/20) reduced substantially the 125I-GAD binding of the monoclonal antibodies reactive with the conformation-dependent epitope region IDDM-E1 and only 20% of these sera additionally diminished the 125I-GAD65 binding by those monoclonals reactive with the both linear epitopes. The SMS sera completely abolished the GAD binding of all three monoclonals, reflecting a broader repertoire including an immune response against the IDDM-E1, a conformation-dependent GAD65 epitope region, also revealed if the SMS sera are diluted to equivalent antibody concentrations. In summary, our results show that diabetes-associated GAD autoantibodies even in adult patients with a late autoimmune process preferentially recognize a conformation-dependent middle GAD65 region. An immune response to all three GAD epitope regions is seldom in these LADA patients and only detectable in association with high antibody titres.

Widespread expression of an autoantigen-GAD65 transgene does not tolerize non-obese diabetic mice and can exacerbate disease

Glutamic acid decarboxylase (GAD)65 is a pancreatic beta cell autoantigen implicated as a target of T cells that initiate and sustain insulin-dependent diabetes mellitus (IDDM) in humans and in non-obese diabetic (NOD) mice. In an attempt to establish immunological tolerance toward GAD65 in NOD mice, and thereby to test the importance of GAD in IDDM, we generated three lines transgenic for murine GAD65 driven by a major histocompatibility complex class I promoter. However, despite widespread transgene expression in both newborn and adult mice, T cell tolerance was not induced. Mononuclear cell infiltration of the islets (insulitis) and diabetes were at least as bad in transgenic mice as in nontransgenic NOD mice, and in mice with the highest level of GAD65 expression, disease was exacerbated. In contrast, the same transgene introduced into mouse strain, FvB, induced neither insulitis nor diabetes, and T cells were tolerant to GAD. Thus, the failure of NOD mice to develop tolerance toward GAD65 reflects at minimum a basic defect in central tolerance, not seen in animals not predisposed to IDDM. Hence, it may not be possible experimentally to induce full tolerance toward GAD65 in prediabetic individuals. Additionally, the fact that autoimmune infiltration in GAD65 transgenic NOD mice remained largely restricted to the pancreas, indicates that the organ-specificity of autoimmune disease is dictated by tissue-specific factors in addition to those directing autoantigen expression.

Peptide specificity of high-titer anti-glutamic acid decarboxylase (GAD)65 autoantibodies

To study systematically the linear epitope specificity of anti-glutamic acid decarboxylase (GAD) autoantibodies associated with insulin-dependent diabetes mellitus (IDDM), we produced 93 overlapping 12-residue synthetic peptides derived from the sequence of the human GAD65 protein and covering the entire length of the protein. These peptides were used as antigens in an enzyme immunoassay to screen the sera from 10 IDDM patients, all of which contained at high level autoantibodies directed against GAD65. Three out of ten (30%) IDDM patients had antibodies that reacted with one or more of the synthetic peptides. Two of the peptide-reactive IDDM sera, which also bound denatured recombinant GAD65 on western blots, had the highest titers of anti-GAD antibodies in ELISA assay. Moreover, the anti-GAD antibodies-GAD complexes formed with these sera were characterized by low dissociation rates, indicative of their good stability. A fine specificity analysis, using analogs of antigen peptide 1 (residues 1-12), allowed us to identify the residues at positions 5-9 (GSGFW) as critical for antibody recognition.

A pharmacologic analysis of mechanical hyperalgesia in streptozotocin/diabetic rats

This study used streptozotocin (STZ; 50 mg/kg i.p.) diabetic rats and monitored weekly thermal and mechanical nociceptive thresholds for 8 weeks diabetes. Rats developed mechanical hyperalgesia as soon as 2 weeks after STZ injection. Thermal nociceptive threshold was not altered up to 8 weeks after STZ injection. Four week-diabetic rat mechanical hyperalgesia showed reduced sensitivity to the antinociceptive effect of morphine (5-20 mg/kg i.p.). Furthermore, a reduced sensitivity to the antinociceptive effect of the GABA(B) agonist, (+/-)baclofen, was observed. A dose as high as 16 mg/kg i.p. of (+/-)baclofen was necessary to reverse 4 week-diabetic rat hyperalgesia, whereas in control rats the highest antinociceptive dose devoid of muscle-relaxant effect was 4 mg/kg i.p. The non-peptide antagonist for the substance P, neurokinin, (NK1) receptor, RP 67580 (3-9 mg/kg i.p.) was not effective in reversing the mechanical hyperalgesia associated with 4 week-diabetes. A six day-treatment with an antagonist for the N-methyl-D-aspartate (NMDA) receptor for glutamate, (+)MK-801 (0.1 mg/kg i.p. twice a day), gradually but completely reversed 4 week-diabetes-induced mechanical hyperalgesia. These data suggest that diabetes-induced hyperalgesia may be the consequence of increased activity of primary afferent fibres leading to an increased excitatory tone within the spinal cord. An increased release of glutamate and activation of the NMDA receptor, would maintain the hyperalgesic state. Reduced activity of both opioidergic and GABA(B)ergic inhibitory systems, might exacerbate the increased excitation thus contributing to the ongoing pain. It is suggested that NMDA receptor antagonists may constitute an alternative therapy for diabetic neuropathic pain.

Stiff-leg syndrome: a focal form of stiff-man syndrome

We report on 2 patients who presented stiffness and spasms similar to those of stiff-man syndrome (SMS) that were limited to one leg for up to 11 years. Patients had serum glutamic acid decarboxylase (GAD) autoantibodies in high titer, clinical evidence of organ-specific autoimmunity, and electromyographic pattern of continuous motor unit activity with abnormally enhanced exteroceptive reflexes. The clinical and immunological profile suggests that this disorder may be a focal form of SMS.

Stiff-persons' syndrome associated with thymoma and subsequent myasthenia gravis

We report the first case of stiff-persons' (-man) syndrome in the setting of a histologically proven thymoma. Muscular hyperactivity was abolished under general anesthesia and the symptoms of stiffness resolved after thymectomy and three courses of intravenous immunoglobulins. After thymectomy, the patient developed ocular myasthenia gravis which later resolved spontaneously. We suggest that thymoma be sought for in cases with neuromuscular hyperactivity syndromes. Myasthenia gravis may develop subsequently in these cases.

Two glutamate decarboxylase forms corresponding to the mammalian GAD65 and GAD67 are expressed during development of the chick telencephalon

The gamma-aminobutyric acid (GABA)-synthesizing enzyme glutamate decarboxylase (GAD) was studied during development of the chick telencephalon. By means of reverse-phase HPLC analysis, we showed that GABA indeed accumulates during embryogenesis, whereas the levels of glutamate, the substrate for GAD, are more or less unchanged up to later developmental stages. The enzyme activity increased approximately 25-fold from embryonic day 3 to embryonic day 17. Immunoblotting data revealed that two GAD proteins, of approximately 65 and 67 kDa, were present during the period investigated. Furthermore, Northern blot analysis with probes obtained from rat cDNA sequences, as well as a chicken-specific probe for GAD65 generated by means of reverse transcriptase-polymerase chain reaction (RT-PCR), strengthened the interpretation that the chick embryo expresses genes corresponding to GAD65 and GAD67. The rat probes recognized transcript sizes of 3.9 kb (GAD65) and 5.6 kb (GAD67), sizes which are different from those of the rat brain (Erlander et al., Neuron, 7, 91-100, 1991). Sequencing of the RT-PCR products revealed a high level of homology (82% at the nucleotide level) between the mammalian and chick GAD65 genes. Taken together, these findings suggest that the chick embryo expresses two GAD genes during embryogenesis. The functional properties of each gene product remain to be investigated.

Murine monoclonal glutamic acid decarboxylase (GAD)65 antibodies recognize autoimmune-associated GAD epitope regions targeted in patients with type 1 diabetes mellitus and stiff-man syndrome

To study the immune response to glutamic acid decarboxylase (GAD) in insulin-dependent diabetes mellitus, monoclonal GAD antibodies after fusion of splenocytes from a nondiabetes-susceptible BALB/c mouse immunized with human recombinant GAD65 were generated. Of the 44 monoclonals, 35 are specific for the GAD65 isoform, whereas 9 also react with GAD67. Some 37 monoclonals, including all GAD65/67 reactive antibodies, react with GAD by Western blot analysis. The remaining 7 GAD65 monoclonals bind GAD only in an immunoprecipitation assay, which implies that they target epitopes dependent on the conformation of the GAD molecule. The 125I-GAD binding of the GAD65 monoclonals reactive on Western blotting was significantly diminished by all 3 sera from Stiff-man syndrome patients but only by 3/30 (10%) sera from type 1 diabetic patients. In contrast, the 7 monoclonal antibodies reactive with a conformation-dependent GAD epitope were competitive with 83% of GAD-autoantibody-positive sera from these diabetic patients. Using chimeric GAD65/67 proteins, the epitope region targeted by these monoclonals was mapped to the middle of GAD65 (amino acids 221-442). This central conformation-dependent GAD region was also targeted by sera from patients with type 1 diabetes. In conclusion, our data show that even after common immunization of a nondiabetes-susceptible mouse strain, monoclonal were obtained which preferentially react with the GAD65 linear amino-terminus (amino acids 4-17) and a conformation-dependent region located in the middle of GAD targeted by autoantibodies, indicating that this GAD region is not restricted to the autoimmune response associated with the Stiff-man syndrome and the beta-cell destruction in type 1 diabetes mellitus.

The insulin-dependent diabetes mellitus-associated ICA 105 autoantigen in stiff-man syndrome patients

The pathogenetic role of anti-glutamic acid decarboxylase (GAD) antibodies found in up to 60% of patients with stiff-man syndrome (SMS) is still controversial. GAD, in fact, is also one of the major target antigen of insulin-dependent diabetes mellitus (IDDM), a disease affecting one third of anti-GAD antibody-positive patients with SMS. To better define the role of autoimmunity in SMS we looked for molecular and immunological evidence of an autoimmune recognition of a second IDDM-associated autoantigen, the pancreatic 37/40 kDa IDDM-autoantigen, whose gene called ICA 105 has been recently cloned. By Northern blot analysis we found that tissue distribution of human ICA 105 is restricted to pancreas and brain and within the central nervous system (CNS) its distribution is similar to GAD. We also measured anti-ICA 105 antibodies in 11 SMS patients and 56 control patients with other neurological diseases (OND). Anti-ICA 105 antibodies were found in 4/11 (36%) patients with SMS (a frequency similar to that of anti-GAD-antibodies in our SMS population) but in only 2/56 (3%) patients with OND (P < 0.001). Anti-ICA 105 and anti-GAD antibodies were associated in 3/4 (75%) patients with SMS but in none of the 2 anti-ICA 105 antibody-positive OND patients. Among anti-ICA 105 antibody-positive patients with SMS, only 1 suffered also from IDDM. In contrast, the only 2 anti-ICA 105 antibody-positive with OND had IDDM. Our results indicate that ICA 105 represents another putative neuroendocrine autoantigen in SMS. The presence of circulating anti-GAD and/or anti-ICA 105 antibodies might help the diagnosis of SMS. The absence, however, of antibodies recognising specific CNS autoantigens (e.g. GAD, ICA 105) does not rule out SMS.

Comparison of the islet cell antibody pattern of monoclonal glutamic acid decarboxylase antibodies recognizing linear and conformational epitopes

In order to compare the reactivity of glutamic acid decarboxylase (GAD) antibodies recognizing linear and conformational epitopes as islet cell cytoplasmic antibodies (ICA), monoclonal antibodies were generated. An ELISA displacement test using two biotinylated monoclonals recognizing a linear (M61/7E11) or a conformational GAD65 epitope (M65/6B12) was performed to identify epitope regions recognized by monoclonal GAD antibodies. The GAD binding by monoclonal GAD antibodies was tested by immunofluorescence on fixed and unfixed pancreatic sections of human, rat, and mouse, and by Dot-blot experiments. 16/23 (69.6%) of the monoclonals were specifically reactive with GAD65 and 7/23 (30.4%) were reactive with both GAD isoforms. 8/16 (50%) of monoclonal GAD65 antibodies recognized a linear GAD epitope located at the N-terminus (pattern 1). 5/16 (31.3%) displaced M65/6B12, indicating the recognition of a conformational GAD epitope (pattern 2). Monoclonals belonging to patterns 1 and 2 showed strong ICA binding. 3/16 (18.8%) of monoclonals specific for GAD65 with weak or no immunostaining of pancreatic islets (pattern 3) did not inhibit the binding of both biotinylated antibodies in the displacement test, indicating other epitope specificities. In conclusion, GAD antibodies recognizing both conformational and linear epitopes of the GAD65 molecule are involved in ICA binding with strong reactivity. Furthermore, results obtained with monoclonals of pattern 3 suggest the occurrence of GAD65 epitopes partly inaccessible on cryosections, which may result in an ICA-negative test of GAD65 autoantibody positive sera.

Activation of a recombinant petunia glutamate decarboxylase by calcium/calmodulin or by a monoclonal antibody which recognizes the calmodulin binding domain

To date, only plants have been shown to possess a form of glutamate decarboxylase (GAD) that binds calmodulin. In the present study, a recombinant calmodulin-binding 58-kDa petunia GAD produced in Escherichia coli was purified to homogeneity using calmodulin-affinity chromatography, and its responsiveness to calcium and calmodulin was examined in vitro. At pH 7.0-7.5, the purified recombinant enzyme was essentially inactive in the absence of calcium and calmodulin, but it could be stimulated to high levels of activity (Vmax = 30 micromol of CO2 min-1 mg of protein-1) by the addition of exogenous calmodulin (K0.5 = 15 nM) in the presence of calcium (K0.5 = 0.8 microM). Neither calcium nor calmodulin alone had any effect on GAD activity. Recombinant GAD displayed hyperbolic kinetics at pH 7.3 (Km = 8.2 mM). A monoclonal antibody directed against the carboxyl-terminal region, which contains the calmodulin-binding domain of GAD, was able to fully activate GAD in a dose-dependent manner in the absence of calcium and calmodulin, whereas an antibody recognizing an epitope outside of this region was unable to activate GAD. This study provides the first evidence that the activity of the purified 58-kDa GAD polypeptide is essentially calcium/calmodulin-dependent at physiological pH. Furthermore, activation of GAD by two different proteins that interact with the calmodulin-binding domain, a monoclonal antibody or calcium/calmodulin, suggests that this domain plays a major role in the regulation of plant GAD activity.

The clinical significance of an autoimmune response against glutamic acid decarboxylase

Glutamic acid decarboxylase is attracting much interest because of its putative involvement in two clinical disorders: stiffman syndrome and insulin-dependent diabetes. Here we discuss the clinical significance of an autoimmune response against GAD and consider how such information may help identify the disease mechanisms of these disorders.

The role of autoimmunity to glutamate receptors in neurological disease

Understanding and experimentally approaching the processes that underlie the origin and progression of many severe neurological disorders presents a challenge to both clinical and basic researchers. We have found that the origin of some neurological diseases, including a rare form of childhood epilepsy and a neurodegenerative disease associated with peripheral cancers, may be related to production of physiologically active autoantibodies that are directed towards excitatory ionotropic glutamate receptors of the brain. This suggests that some neurological diseases may result from dysfunction of the immune system.

Stiff-man syndrome: case report

Stiff-man syndrome is a rare neurologic disorder characterized by progressive, fluctuating muscle rigidity with painful muscle contractions affecting predominantly the back and proximal extremities. In the ED, the diagnosis can be easily overlooked and misdiagnosed as acute or chronic low back pain and muscle spasm. This syndrome is often associated with diabetes, autoimmune diseases, and cancer. This report describes an illustrative case of a 39-year-old woman who presented to the ED with a two-year history of right leg spasms and low back pain that had become so severe in the preceding two days that she was unable to ambulate. Clues to the patient's proper diagnosis coincide with the diagnostic criteria for stiff-man syndrome: the presence of a slowly progressive stiffness of the axial muscles and proximal limb muscles, making ambulation difficult; hyperlordosis of the lumbar spine; episodic spasms precipitated by jarring or sudden movement; a normal intellectual, sensory, and motor examination when not in spasm; and a marked amelioration of symptoms with the IV administration of diazepam. High-dose oral diazepam is the maintenance drug of choice.

A convulsant, 3-mercaptopropionic acid, decreases the level of GABA and GAD in rat pancreatic islets and brain

To investigate the properties of the gamma-aminobutyric acid (GABA) synthesizing enzyme, glutamate decarboxylase (GAD), in the brain and the pancreatic islets of the rat, GABA concentration in the brain and the pancreatic islets was measured after intraperitoneal administration of 3-mercaptopropionic acid (3-MP) at 25 mg/kg. 60 min after the administration of 3-MP, GABA concentration in the hypothalamus, the superior colliculus and the hippocampus of the brain decreased by 20-30% and in the pancreatic islets by 35%. The concentration in the pancreatic acini did not change. Western blotting showed that GAD activity in the pancreatic islets decreased after administration of 3-MP compared to the control. The activity of GAD in the pancreatic islets as well as brain can be modified by a convulsant, in this case 3-MP. These results suggest the properties of GAD may be similar in the pancreatic islets and brain.

Stiff man syndrome: neurophysiological findings in eight patients

The neurophysiological findings in eight patients with the stiff man syndrome (SMS), including four of six tested with autoantibodies against glutamic acid decarboxylase, are presented. Neurophysiological findings did not make it possible to discriminate between patients with and those without autoimmunity against GABAergic neurons. Investigation of mono- and polysynaptic reflexes revealed abnormal results in a variable number of SMS patients, the abnormalities largely corresponding to those seen in spastic paresis. A stereotyped motor response to electrical stimulation of peripheral nerves was recorded from the trunk muscles of all patients investigated. This response was termed spasmodic reflex myoclonus and consisted of a sequence of 1-3 synchronous myoclonic bursts, 60-70 ms after median nerve stimulation, followed by a tonic decrescendo activity over a number of seconds. The recruitment order of muscles along the neuraxis in spasmodic reflex myoclonus suggested that the latter was generated in the spinal cord and conveyed via propriospinal tracts. It is thought that spasmodic reflex myoclonus may serve not only as a diagnostic tool, but also as a key to understanding some aspects of the pathophysiology of both spasms and stiffness in SMS. It is speculated that stiffness is a fragment of spasms, both being generated by common neuronal mechanisms tentatively ascribed to interneurons in the spinal grey matter.

Autoimmunity. Is antigen-specific suppression now unsuppressed?

Recent studies suggest that putative regulatory lymphocytes can effect antigen-specific down-regulation of autoimmunity. But we have yet to see how much this improves our picture of autoimmune disease progression.