Rasmussen's encephalitis with concomitant cortical dysplasia: the role of GluR3

Focal cortical dysplasia is a frequent coexistent pathology in patients with Rasmussen's encephalitis

INTRODUCTION

Rasmussen's encephalitis (RE) is a rare, predominantly pediatric epilepsy disorder of unknown etiology. It classically affects one of the cerebral hemispheres and histologically shows cortical chronic inflammation, gliosis, and neuronal loss. The etiopathogenesis of RE remains unknown, with genetic, infectious, and autoimmune factors all speculated to play a role. Although the histologic findings in RE are well described, few studies have investigated a large cohort of cases looking for the coexistence of RE with focal cortical dysplasia (FCD).

DESIGN

The study is a retrospective review of RE patients who underwent surgical resection of brain tissue between 1979 and 2021. Relevant patient history was retrieved, and available histologic slides were reviewed. The histologic severity of RE was described according to the Pardo criteria. In cases where FCD was present, the observed patterns of FCD (namely Ia, Ib, IIa, IIb, etc.) were described using the International League Against Epilepsy (ILAE) classification.

RESULTS

Thirty-eight resection specimens from 31 patients formed the study cohort. Seventeen patients (54.8 %) were male; average age at surgery was 8 years (range: 2-28 years). Twenty-seven resection specimens (71.1 %) from 23 patients (74 %) showed evidence of coexistent FCD. Most cases with FCD resembled the ILAE type Ib (n = 23) pattern. Cases of RE that did not show FCD were either Pardo stage 1 (n = 5) or 4 (n = 6), with all Pardo stage 2 and 3 cases demonstrating FCD.

CONCLUSIONS

FCD was found in most patients with RE (74 %). The most observed pattern of FCD was ILAE Ib.

Rasmussen's encephalitis: mechanisms update and potential therapy target

Rasmussen’s encephalitis (RE) is rare neurological diseases characterized as epilepsia partialis continua, invariably hemiparesis, and cognitive impairment. This disease is encountered frequently in childhood and presents with progressive atrophy of the unilateral hemisphere, and there are also sustained neurological complications. Owing to uncertain pathogenesis, the most effective way to limit the influence of seizures currently is cerebral hemispherectomy. In this review, we focus on four main lines of pathogenesis: virus infection, antibody-mediated, cell-mediated immunity, and microglia activation. Although one or more antigenic epitopes may give rise to infiltrating T cell responses in RE brain tissue, no exact antigen was confirmed as the definite cause of the disease. On the other hand, the appearance of antibodies related with RE seem to be a secondary pathological process. Synthetic studies have suggested an adaptive immune mechanism mediated by CD8⁺ T cells and an innate immune mechanism mediated by activated microglia and neuroglia. Accordingly, opinions have been raised that immunomodulatory treatments aimed at initial damage to the brain that are induced by cytotoxic CD8⁺ T cell lymphocytes and microglia in the early stage of RE slow down disease progression. However, systematic exploration of the theory behind these therapeutic effects based on multicenter and large sample studies are needed. In addition, dysfunction of the adenosine system, including the main adenosine removing enzyme adenosine kinase and adenosine receptors, has been demonstrated in RE, which might provide a novel therapeutic target for treatment of RE in future.

Understanding Childhood Neuroimmune Diseases of the Central Nervous System

Immune-mediated diseases of the central nervous system (CNS) in childhood are a heterogeneous group of rare conditions sharing the inflammatory involvement of the CNS. This review highlights the growing knowledge of childhood neuroimmune diseases that primarily affect the CNS, outlining the clinical and diagnostic features, the pathobiological mechanisms and genetics, current treatment options, and emerging challenges. The clinical spectrum of these conditions is increasingly expanded, and the underlying mechanisms of dysregulation of the immune system could vary widely. Cell-mediated and antibody-mediated disorders, infection-triggered and paraneoplastic conditions, and genetically defined mechanisms can occur in previously healthy children and can contribute to different stages of the disease. The careful evaluation of the clinical presentation and temporal course of symptoms, the specific neuroimaging and immunological findings, and the exclusion of alternative causes are mandatory in clinical practice for the syndromic diagnosis. A common feature of these conditions is that immunotherapeutic agents could modulate the clinical course and outcomes of the disease. Furthermore, specific symptomatic treatments and comprehensive multidisciplinary care are needed in the overall management. We focus on recent advances on immune-mediated demyelinating CNS disorders, autoimmune encephalitis, interferonopathies, and possible neuroimmune disorders as Rasmussen encephalitis. Better knowledge of these conditions could allow prompt diagnosis and targeted immunotherapy, to decrease morbidity and mortality as well as to improve clinical outcomes, reducing the burden of the disease due to possible long-term neuropsychiatric sequelae. Persisting controversies remain in the rigorous characterization of each specific clinical entity because of the relative rarity in children; moreover, in a large proportion of suspected neuroimmune diseases, the immune "signature" remains unidentified; treatment guidelines are mostly based on retrospective cohort studies and expert opinions; then advances in specific molecular therapies are required. In the future, a better characterization of specific immunological biomarkers may provide a useful understanding of the underlying pathobiological mechanisms of these conditions in order to individualize more tailored therapeutic options and paradigms. Multicenter collaborative research on homogeneous groups of patients who may undergo immunological studies and therapeutic trials could improve the characterization of the underlying mechanisms, the specific phenotypes, and tailored management.

A Case Series of Adult-Onset Rasmussen's Encephalitis: Diagnostic and Therapeutic Challenges

Rasmussen’s encephalitis (RE) is a rare neurologic disorder characterized by progressive cerebral hemiatrophy and medically refractory epilepsy. The majority of current literature on this topic is focused on the pediatric population. In this case series, we will review three cases of adult-onset RE, as defined by fulfillment of the 2005 Bien criteria. The diagnostic challenge of characterizing this rare disease will be highlighted by the extensive serum, CSF, and pathologic sampling in all three patients. MR imaging and EEG data will be examined over time to characterize hallmark findings as well as progression. In addition, we will review the various forms of therapy attempted in these three patients, namely anti-epileptic drug therapy and immunomodulatory therapy. We will also utilize this case series to critically evaluate the broader context of atypical presentations of this disease and the value of current diagnostic criteria.

Neuropathology of epilepsy

Epilepsy is one of the most common neurologic disorders, affecting about 50 million people worldwide. The disease is characterized by recurrent seizures, which are due to aberrant neuronal networks resulting in synchronous discharges. The term epilepsy encompasses a large spectrum of syndromes and diseases with different etiopathogenesis. The recent development of imaging and epilepsy surgery techniques is now enabling the identification of structural abnormalities that are part of the epileptic network, and the removal of these lesions may result in control of seizures. Access of this clinically well-characterized neurosurgical material has provided neuropathologists with the opportunity to study a variety of structural brain abnormalities associated with epilepsy, by combining traditional routine histopathologic methods with molecular genetics and functional analysis of the resected tissue. This approach has contributed greatly to a better diagnosis and classification of these structural lesions, and has provided important new insights into their pathogenesis and epileptogenesis. The present chapter provides a detailed description of the large spectrum of histopathologic findings encountered in epilepsy surgery patients, addressing in particular the nonneoplastic pathologies, including hippocampal sclerosis, malformations of cortical development, Sturge-Weber syndrome, and Rasmussen encephalitis, and reviews current knowledge regarding the underlying molecular pathomechanisms and cellular mechanisms mediating hyperexcitability.

Evidence for Resident Memory T Cells in Rasmussen Encephalitis

Rasmussen encephalitis (RE) is a rare pediatric neuroinflammatory disease of unknown etiology characterized by intractable seizures, and progressive atrophy usually confined to one cerebral hemisphere. Surgical removal or disconnection of the affected cerebral hemisphere is currently the only intervention that effectively stops the seizures. Histopathological evaluation of resected brain tissue has shown that activated brain resident macrophages (microglia) and infiltrating T cells are involved in the inflammatory reaction. Here, we report that T cells isolated from seven RE brain surgery specimens express the resident memory T cell (T_RM) marker CD103. CD103 was expressed by >50% of CD8⁺ αβ T cells and γδ T cells irrespective of the length of time from seizure onset to surgery, which ranged from 0.3 to 8.4 years. Only ~10% of CD4⁺ αβ were CD103⁺, which was consistent with the observation that few CD4⁺ T cells are found in RE brain parenchyma. Clusters of T cells in brain parenchyma, which are a characteristic of RE histopathology, stained for CD103. Less than 10% of T cells isolated from brain specimens from eight surgical cases of focal cortical dysplasia (FCD), a condition that is also characterized by intractable seizures, were CD103⁺. In contrast to the RE cases, the percent of CD103⁺ T cells increased with the length of time from seizure onset to surgery. In sections of brain tissue from the FCD cases, T cells were predominantly found around blood vessels, and did not stain for CD103. The presence of significant numbers of T_RM cells in RE brain irrespective of the length of time between clinical presentation and surgical intervention supports the conclusion that a cellular immune response to an as yet unidentified antigen(s) occurs at an early stage of the disease. Reactivated T_RM cells may contribute to disease progression.

Rasmussen encephalitis with dual pathology in a patient without seizures: case report and literature review

PURPOSE

Rasmussen encephalitis without seizures is rare. We report a case of Rasmussen encephalitis and cortical dysplasia without epilepsy as well as describe the imaging, pathology, and clinical course and review the literature to investigate whether this may represent a rare subset of Rasmussen encephalitis.

CASE REPORT

We report the case of a 12-year-old girl with a history of cognitive decline and right arm weakness. Magnetic resonance imaging demonstrated diffuse left hemispheric cortical and subcortical atrophy suggestive of Rasmussen encephalitis. The patient had no clinical history of seizures, and electroencephalography did not demonstrate epileptiform abnormalities. Craniotomy for open brain biopsy was performed, and histopathologic evaluation identified Rasmussen encephalitis with cortical dysplasia (dual pathology).

CONCLUSIONS

To the best of our knowledge, this is the third case of Rasmussen encephalitis diagnosed by both imaging and histopathology that had no clinical or electroencephalographic evidence of seizures and is the only case of Rasmussen encephalitis with cortical dysplasia without epilepsy.

Evidence for the involvement of gamma delta T cells in the immune response in Rasmussen encephalitis

Background

Rasmussen encephalitis (RE) is a rare neuroinflammatory disease characterized by intractable seizures and progressive atrophy on one side of the cerebrum. Perivascular cuffing and clusters of T cells in the affected cortical hemisphere are indicative of an active cellular immune response.

Methods

Peripheral blood mononuclear cells (PBMCs) and brain-infiltrating lymphocytes (BILs) were isolated from 20 RE surgery specimens by standard methods, and CD3⁺ T cell populations were analyzed by flow cytometry. Gamma delta T cell receptor spectratyping was carried out by nested PCR of reversed transcribed RNA extracted from RE brain tissue, followed by high resolution capillary electrophoresis. A MiSeq DNA sequencing platform was used to sequence the third complementarity determining region (CDR3) of δ1 chains.

Results

CD3⁺ BILs from all of the RE brain specimens comprised both αβ and γδ T cells. The median αβ:γδ ratio was 1.9 (range 0.58–5.2) compared with a median ratio of 7.7 (range 2.7–40.8) in peripheral blood from the same patients. The αβ T cells isolated from brain tissue were predominantly CD8⁺, and the majority of γδ T cells were CD4⁻ CD8⁻. Staining for the early activation marker CD69 showed that a fraction of the αβ and γδ T cells in the BILs were activated (median 42 %; range 13–91 %, and median 47 %; range 14–99 %, respectively). Spectratyping T cell receptor (TCR) Vδ1-3 chains from 14 of the RE brain tissue specimens indicated that the γδ T cell repertoire was relatively restricted. Sequencing δ1 chain PCR fragments revealed that the same prevalent CDR3 sequences were found in all of the brain specimens. These CDR3 sequences were also detected in brain tissue from 15 focal cortical dysplasia (FCD) cases.

Conclusion

Neuroinflammation in RE involves both activated αβ and γδ T cells. The presence of γδ T cells with identical TCR δ1 chain CDR3 sequences in all of the brain specimens examined suggests that a non-major histocompatibility complex (MHC)-restricted immune response to the same antigen(s) is involved in the etiology of RE. The presence of the same δ1 clones in CD brain implies the involvement of a common inflammatory pathway in both diseases.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-015-0352-2) contains supplementary material, which is available to authorized users.

Prednisolone as an Effective Treatment for Epilepsy

Rasmussen encephalitis is a chronic inflammatory disease commonly seen in children. Hemispheric atrophy, intellectual disability, and hemiparesis are characteristics of this rare disease. The main pathological findings are chronic meningeal and parenchymal inflammation attributed to T lymphocytes. Plasmapheresis, immunomodulators, and immunosuppressives are commonly used for treatment. In this article, a patient suffering from Rasmussen encephalitis whose seizures were treated with prednisolone is discussed according to the literature.

Rasmussen's encephalitis presenting as focal cortical dysplasia

Rasmussen's encephalitis is a rare syndrome characterized by intractable seizures, often associated with epilepsia partialis continua and symptoms of progressive hemispheric dysfunction. Seizures are usually the hallmark of presentation, but antiepileptic drug treatment fails in most patients and is ineffective against epilepsia partialis continua, which often requires surgical intervention. Co-occurrence of focal cortical dysplasia has only rarely been described and may have implications regarding pathophysiology and management. We describe a rare case of dual pathology of Rasmussen's encephalitis presenting as a focal cortical dysplasia (FCD) and discuss the literature on this topic.

Dual Pathology in Rasmussen's Encephalitis: A Report of Coexistent Focal Cortical Dysplasia and Review of the Literature

Rasmussen's encephalitis is a well-established, albeit rare cause of medically intractable epilepsy. In a small number of Rasmussen's cases, a second pathology is identified, which independently can cause medically intractable seizures (dual pathology). This paper documents a case of a 13-year-old male who presented with medically intractable epilepsy. The patient underwent a series of surgical resections, early on resulting in a diagnosis of focal cortical dysplasia and later yielding a diagnosis of coexistent Rasmussen's encephalitis, marked by chronic inflammation, microglial nodules, and focal cortical atrophy, combined with focal cortical dysplasia (Palmini et al. type IIA, ILAE type IIA). The literature on dual pathology in the setting of Rasmussen's encephalitis is reviewed.

The role of gap junction channels during physiologic and pathologic conditions of the human central nervous system

Gap junctions (GJs) are expressed in most cell types of the nervous system, including neuronal stem cells, neurons, astrocytes, oligodendrocytes, cells of the blood brain barrier (endothelial cells and astrocytes) and under inflammatory conditions in microglia/macrophages. GJs connect cells by the docking of two hemichannels, one from each cell with each hemichannel being formed by 6 proteins named connexins (Cx). Unapposed hemichannels (uHC) also can be open on the surface of the cells allowing the release of different intracellular factors to the extracellular space. GJs provide a mechanism of cell-to-cell communication between adjacent cells that enables the direct exchange of intracellular messengers, such as calcium, nucleotides, IP(3), and diverse metabolites, as well as electrical signals that ultimately coordinate tissue homeostasis, proliferation, differentiation, metabolism, cell survival and death. Despite their essential functions in physiological conditions, relatively little is known about the role of GJs and uHC in human diseases, especially within the nervous system. The focus of this review is to summarize recent findings related to the role of GJs and uHC in physiologic and pathologic conditions of the central nervous system.

Epileptic encephalitis: the role of the innate and adaptive immune system

Seizures are a prominent clinical feature of encephalitis. Recent data suggest the adaptive as well as innate immune system to be involved directly in the pathomechanism of epileptogenesis. Cytotoxic T-cells and antibody-mediated complement activation are major components of the adaptive immune system, which can induce neurodegeneration, thereby probably contributing to epileptic encephalitis. The innate immune system operates via interleukin-1 and toll-like receptor-associated mechanisms and was shown to play a direct role in epileptogenesis. Here, we review neuropathology hallmarks of various encephalitis conditions such as Rasmussen encephalitis (RE) but also introduce the more recently discovered antibody-associated voltage-gated potassium channel complex (VGKC), N-methyl-D-aspartate receptor (NMDAR) or glutamic acid decarboxylase (GAD) 65 encephalitides. Neuropathological investigations are used to determine specific cellular components and molecular mechanisms used by the immune system to provoke neurodegeneration and to promote epileptogenesis. Based on recent findings, we propose concepts for the stratification of epileptic encephalitis. Knowledge of the role of the innate immunity has already translated into clinical treatment strategies and may help to discover novel drug targets for these epileptic disorders.

Dual pathology in Rasmussen's encephalitis: a study of seven cases and review of the literature

Dual pathology has previously been reported in less than 10% of cases of Rasmussen's encephalitis (RE). Given the rarity of RE, it appears unlikely that dual pathology in RE is merely a coincidence. We therefore reviewed all cases of RE experienced in our institution to assess for an additional/associated pathology. A total of seven patients with RE were identified in our archives. Seven children (4 boys and 3 girls, age range: 3-16 years, mean: 9.5 years) with medically refractory epilepsy underwent surgical resection for intractable seizures. The surgical specimens were examined with routine neurohistological techniques, and immunohistochemistry was performed with an extensive panel of antibodies for viruses, lymphocytes, microglia/macrophages, human leukocyte antigen (HLA)-DR, astrocytes, and neurons. Relevant literature was reviewed. Microscopically, all seven cases demonstrated the inflammatory pathology of RE in the cortex and white matter with leptomeningeal and perivascular lymphocytic infiltration, microglial nodules with/without neuronophagia, neuronal loss and gliosis. The HLA-DR antibody was extremely helpful in highlighting the extent of microglial cell proliferation/activation that was not appreciable with standard histology. An unexpected finding in all seven cases was the presence of cortical dysplasia. In our series of seven cases, there was co-occurrence of the inflammatory/destructive pathology of RE with malformative/dysplastic features in cortical architecture in 100% of cases, raising questions about the possible relationships between the two entities. Awareness of the possibility of dual pathology in RE is important for clinical and pathological diagnosis, and may affect the management and outcome of these patients. Immunohistochemistry is very helpful to make a definitive diagnosis of both pathologies.

Late onset Rasmussen's encephalitis with triple pathology

Rasmussen's encephalitis is a devastating illness characterized by intractable focal seizures due to chronic localised encephalitis. We report on a rare variant of delayed onset Rasmussen's encephalitis with triple pathology. A 27-year-old male, who was initially diagnosed with seizures when he was 16 years old, presented with focal seizures that became refractory to multiple anticonvulsants. Multiple investigations, including subdural electrode monitoring, revealed foci of onset in the right frontotemporal region. The patient underwent right front-temporal lobectomy. Post-operatively, the seizures became more severe and he developed new epilepsia partialis continua. Treatment with intravenous immunoglobulin was unsuccessful. He subsequently underwent a right hemispherectomy that rendered him seizure free. The three pathologies identified were old ischemic changes, type II cortical dysplasia and stage II Rasmussen's encephalitis.

Focal Chronic Inflammatory Epileptic Encephalopathy in a Patient with Malformations of Cortical Development, with a Review of the Spectrum of Chronic Inflammatory Epileptic Encephalopathy

PURPOSE

Chronic cellular inflammation closely associated with epilepsy without an active infection is a hallmark of Rasmussen encephalitis (RE). RE has typical and defining features lacking in other rare epilepsy patients who also have neocortical lymphocytes without an identifiable cause. A patient with malformations of cortical development had an abrupt change in frequency and epileptic focus after 22 years of a stable seizure disorder. Functional neurosurgery yielded a specimen showing a mixed cellular meningoencephalitis in the absence of a demonstrable infection.

METHODS

Historical, neurologic, electroencephalographic, pathologic, and literature data were correlated.

RESULTS

There was a subarachnoid mixed infiltrate including evidence of dendritic cells in our patient and also cytotoxic T lymphocytes adjacent to karyolytic neurons that corresponded to cells previously demonstrated to damage neurons in RE. Literature review disclosed 42 other cases similar to RE but with heterogeneous findings. The course was more protracted and often more benign than in RE. The inflammation that would have markedly decreased or disappeared in RE over that period was generally still well represented.

CONCLUSIONS

Our patient has heterogeneous features similar to, yet with differences from, RE. Literature review of chronic cellular inflammatory epileptic encephalopathy cases also similar to RE discloses important differences that may reflect idiosyncratic reactions and pace of the disease rather than a different disease. Comorbidity factors, genetic population traits, and secondary effects of the seizure disorder may lead to an expansion of the initial site of damage by an autoimmune reaction. These cases might best be grouped, probably along with RE, as secondary autoimmune diseases.

Rasmussen's encephalitis in a 58-year-old female: still a variant?

BACKGROUND

We report the case of a 58-year-old female with clinical, radiological, and histopathological evidence of Rasmussen's encephalitis, representing the oldest confirmed case to date.

CASE SUMMARY

The patient presented with complex partial seizures characterized by numbness of the left face and staring spells. These progressed to a state of epilepsia partialis continua with jerking of the left face, as well as severe cognitive impairment and loss of all communication. The patient responded well to Intravenous Immunoglobulin (IVIG) therapy despite early complications and with ongoing treatment is living independently with minimal cognitive impairment.

CONCLUSIONS

This represents the oldest confirmed case of Rasmussen's encephalitis and suggests that this diagnosis should be considered in patients of any age with an appropriate clinical picture. We recommend IVIG as a first line therapy for adult cases of Rasmussen's encephalitis.

Brain inflammation in epilepsy: experimental and clinical evidence

Inflammatory reactions occur in the brain in various CNS diseases, including autoimmune, neurodegenerative, and epileptic disorders. Proinflammatory and antiinflammatory cytokines and related molecules have been described in CNS and plasma, in experimental models of seizures and in clinical cases of epilepsy. Inflammation involves both the innate and the adaptive immune systems and shares molecules and pathways also activated by systemic infection. Experimental studies in rodents show that inflammatory reactions in the brain can enhance neuronal excitability, impair cell survival, and increase the permeability of the blood-brain barrier to blood-borne molecules and cells. Moreover, some antiinflammatory treatments reduce seizures in experimental models and, in some instances, in clinical cases of epilepsy. However, inflammatory reactions in brain also can be beneficial, depending on the tissue microenvironment, the inflammatory mediators produced in injured tissue, the functional status of the target cells, and the length of time the tissue is exposed to inflammation. We provide an overview of the current knowledge in this field and attempt to bridge experimental and clinical evidence to discuss critically the possibility that inflammation may be a common factor contributing, or predisposing, to the occurrence of seizures and cell death, in various forms of epilepsy of different etiologies. The elucidation of this aspect may open new perspectives for the pharmacologic treatment of seizures.

Neue Erkenntnis zur Rasmussen-Enzephalitis

Rasmussen encephalitis (RE) is a severe and at the same time pathophysiologically fascinating condition. The chronic inflammation affects one of the two cerebral hemispheres and destroys it during the disease process that lasts from months to years. The patients -- mostly children -- suffer from frequent pharmacoresistant seizures, often in the form of epilepsia partialis continua. In parallel to the atrophy of the affected hemisphere, the neurological functions associated with it decline continuously. This results in a final stage with a usually high-grade sensorimotor hemisyndrome, hemianopia, cognitive impairment and -- if the language-dominant hemisphere is affected -- aphasia. Research results in the last 5 years have contributed to a deeper understanding of the pathogenesis of this condition. Formal diagnostic criteria have been proposed, and new therapeutic options have emerged by which the disease progression can be slowed or stopped. This article summarizes the current research results on the background of older data and gives recommendations regarding diagnostic and therapeutic procedures in RE patients.

Myasthenia Gravis and Hypothyroidism in a Dog With Meningomyelitis

A 12-year-old, spayed female miniature poodle was evaluated because of a 4-day history of paraparesis, dysuria, and tenesmus. Neurological assessment suggested peripheral nervous system dysfunction, predominantly pelvic limb weakness with a possible concurrent sixth lumbar (L6) to second sacral (S2) myelopathy. Further studies supported the diagnoses of myasthenia gravis, hypothyroidism, and meningomyelitis. To the authors’ knowledge, this is the first reported case of concurrent myasthenia gravis and meningomyelitis in the dog. It was unclear whether the identified conditions evolved from a shared etiopathogenesis or were merely coincidental.

Rasmussen's Encephalitis

When the diagnosis of Rasmussen's encephalitis is being considered, it is important to rapidly exclude other causes of epilepsia partialis continua and hemiparesis. Although there is no good data from randomized trials of different immune-related therapies, treatment with immunoglobulin G (IgG), steroids, or plasmapheresis is advocated as first-line therapy. It is not unreasonable to institute at least two treatment options (eg, IgG followed by plasmapheresis) if response to the first treatment is poor. Functional hemispherectomy and its variants are associated with a lower long-term complication rate.

Glutamate uptake

Brain tissue has a remarkable ability to accumulate glutamate. This ability is due to glutamate transporter proteins present in the plasma membranes of both glial cells and neurons. The transporter proteins represent the only (significant) mechanism for removal of glutamate from the extracellular fluid and their importance for the long-term maintenance of low and non-toxic concentrations of glutamate is now well documented. In addition to this simple, but essential glutamate removal role, the glutamate transporters appear to have more sophisticated functions in the modulation of neurotransmission. They may modify the time course of synaptic events, the extent and pattern of activation and desensitization of receptors outside the synaptic cleft and at neighboring synapses (intersynaptic cross-talk). Further, the glutamate transporters provide glutamate for synthesis of e.g. GABA, glutathione and protein, and for energy production. They also play roles in peripheral organs and tissues (e.g. bone, heart, intestine, kidneys, pancreas and placenta). Glutamate uptake appears to be modulated on virtually all possible levels, i.e. DNA transcription, mRNA splicing and degradation, protein synthesis and targeting, and actual amino acid transport activity and associated ion channel activities. A variety of soluble compounds (e.g. glutamate, cytokines and growth factors) influence glutamate transporter expression and activities. Neither the normal functioning of glutamatergic synapses nor the pathogenesis of major neurological diseases (e.g. cerebral ischemia, hypoglycemia, amyotrophic lateral sclerosis, Alzheimer's disease, traumatic brain injury, epilepsy and schizophrenia) as well as non-neurological diseases (e.g. osteoporosis) can be properly understood unless more is learned about these transporter proteins. Like glutamate itself, glutamate transporters are somehow involved in almost all aspects of normal and abnormal brain activity.

Disorders of membrane channels or channelopathies

OBJECTIVE

To review the structure and function of membrane ion channels with special emphasis on inherited nervous system channel disorders or channelopathies.

RESULTS

Channels are pores in the cell membrane. Through these pores ions flow across the membrane and depolarize or hyperpolarize the cell. Channels can be classified into 3 types: non-gated, directly gated and second messenger gated channels. Among the important directly gated channels are voltage gated (Na(+), K(+), Ca(2+), Cl(-)) and ligand gated (ACh, Glutamate, GABA, Glycine) channels. Channels are macromolecular protein complexes within the lipid membrane. They are divided into distinct protein units called subunits. Each subunit has a specific function and is encoded by a different gene. The following inherited channelopathies are described. (1) Sodium channelopathies: familial generalized epilepsy with febrile seizures plus, hyperkalemic periodic paralysis, paramyotonias, hypokalemic periodic paralysis; (2) potassium channelopathies: benign infantile epilepsy, episodic ataxia type 1; (3) calcium channelopathies: episodic ataxia type 2, spinocerebellar ataxia type 6, familial hemiplegic migraine, hypokalemic periodic paralysis, central core disease, malignant hyperthermia syndrome, congenital stationary night blindness; (4) chloride channelopathies: myotonia congenitas; (5) ACh receptor channelopathies: autosomal dominant frontal lobe nocturnal epilepsy, congenital myasthenic syndromes; (6) glycine receptor channelopathies: hyperekplexia.

CONCLUSIONS

Studies of human inherited channelopathies have clarified the functions of many ion channels. More than one gene may regulate a function in a channel, thus different genetic mutations may manifest with the same disorder. The complex picture of the genetic and molecular structures of channels will require frequent updates.

[Probable Rasmussen's syndrome. Case report]

The syndrome of chronic encephalitis with epilepsy (Rasmussen's syndrome) typically occurs in children and is characterized by the development of intractable focal seizures, progressive hemiparesis and intellectual deterioration. The etiology is unknown, and the pathological abnormalities vary. We report the case of a 17-year-old boy, presenting with clinical features typical of probable Rasmussen's syndrome. We discuss the etiology and treatment for this pathology.