Frequency of CNKSR2 mutation in the X‐linked epilepsy‐aphasia spectrum

Synaptic proteins are critical to neuronal function in the brain, and their deficiency can lead to seizures and cognitive impairments. CNKSR2 (connector enhancer of KSR2) is a synaptic protein involved in Ras signaling‐mediated neuronal proliferation, migration and differentiation. Mutations in the X‐linked gene CNKSR2 have been described in patients with seizures and neurodevelopmental deficits, especially those affecting language. In this study, we sequenced 112 patients with phenotypes within the epilepsy‐aphasia spectrum (EAS) to determine the frequency of CNKSR2 mutation within this complex set of disorders. We detected a novel nonsense mutation (c.2314 C>T; p.Arg712*) in one Ashkenazi Jewish family, the male proband of which had a severe epileptic encephalopathy with continuous spike‐waves in sleep (ECSWS). His affected brother also had ECSWS with better outcome, whereas the sister had childhood epilepsy with centrotemporal spikes. This mutation segregated in the three affected siblings in an X‐linked manner, inherited from their mother who had febrile seizures. Although the frequency of point mutation is low, CNKSR2 sequencing should be considered in families with suspected X‐linked EAS because of the specific genetic counseling implications.     

Cnksr2 Loss in Mice Leads to Increased Neural Activity and Behavioral Phenotypes of Epilepsy-Aphasia Syndrome

Epilepsy Aphasia Syndromes (EAS) are a spectrum of childhood epileptic, cognitive, and language disorders of unknown etiology. CNKSR2 is a strong X-linked candidate gene implicated in EAS; however, there have been no studies of genetic models to dissect how its absence may lead to EAS. Here we develop a novel Cnksr2 KO mouse line and show that male mice exhibit increased neural activity and have spontaneous electrographic seizures. Cnksr2 KO mice also display significantly increased anxiety, impaired learning and memory, and a progressive and dramatic loss of ultrasonic vocalizations. We find that Cnksr2 is expressed in cortical, striatal, and cerebellar regions and is localized at both excitatory and inhibitory postsynapses. Proteomics analysis reveals Cnksr2 anchors key binding partners at synapses, and its loss results in significant alterations of the synaptic proteome, including proteins implicated in epilepsy disorders. Our results validate that loss of CNKSR2 leads to EAS and highlights the roles of Cnksr2 in synaptic organization and neuronal network activity.SIGNIFICANCE STATEMENT Epilepsy Aphasia Syndromes (EAS) are at the severe end of a spectrum of cognitive-behavioral symptoms seen in childhood epilepsies, and they remain an inadequately understood disorder. The prognosis of EAS is frequently poor, and patients have life-long language and cognitive disturbances. Here we describe a genetic mouse model of EAS, based on the KO of the EAS risk gene Cnksr2. We show that these mice exhibit electrophysiological and behavioral phenotypes similar to those of patients, providing an important new model for future studies of EAS. We also provide insights into the molecular disturbances downstream of Cnksr2 loss by using in vivo quantitative proteomics tools.     

Synaptic dysfunction in genetic models of Parkinson's disease: a role for autophagy?

The past decade in Parkinson's disease (PD) research has been punctuated by numerous advances in understanding genetic factors that contribute to the disease. Common to most of the genetic models of Parkinsonian neurodegeneration are pathologic mechanisms of mitochondrial dysfunction, secretory vesicle dysfunction and oxidative stress that likely trigger common cell death mechanisms. Whereas presynaptic function is implicated in the function/dysfunction of α-synuclein, the first gene shown to contribute to PD, synaptic function has not comprised a major focus in most other genetic models. However, recent advances in understanding the impact of mutations in parkin and LRRK2 have also yielded insights into synaptic dysfunction as a possible early pathogenic mechanism. Autophagy is a common neuronal response in each of these genetic models of PD, participating in the clearance of protein aggregates and injured mitochondria. However, the potential consequences of autophagy upregulation on synaptic structure and function remain unknown. In this review, we discuss the evidence that supports a role for synaptic dysfunction in the neurodegenerative cascade in PD, and highlight unresolved questions concerning a potential role for autophagy in either pathological or compensatory synaptic remodeling. This article is part of a Special Issue entitled "Autophagy and protein degradation in neurological diseases."     

Impaired regulation of synaptic actin cytoskeleton in Alzheimer's disease

Representing the most common cause of dementia, Alzheimer's disease (AD) has dramatically impacted the neurological and economic health of our society. AD is a debilitating neurodegenerative disease that produces marked cognitive decline. Much evidence has accumulated over the past decade to suggest soluble oligomers of beta-amyloid (Aβ) have a critical role in mediating AD pathology early in the disease process by perturbing synaptic efficacy. Here we critically review recent research that implicates synapses as key sites of early pathogenesis in AD. Most excitatory synapses in the brain rely on dendritic spines as the sites for excitatory neurotransmission. The structure and function of dendritic spines are dynamically regulated by cellular pathways acting on the actin cytoskeleton. Numerous studies analyzing human postmortem tissue, animal models and cellular paradigms indicate that AD pathology has a deleterious effect on the pathways governing actin cytoskeleton stability. Based on the available evidence, we propose the idea that a contributing factor to synaptic pathology in early AD is an Aβ oligomer-initiated collapse of a "synaptic safety net" in spines, leading to dendritic spine degeneration and synaptic dysfunction. Spine stabilizing pathways may thus represent efficacious therapeutic targets for combating AD pathology.     

Mechanisms underlying NMDA receptor synaptic/extrasynaptic distribution and function

Research over the last few decades has shaped our understanding of the crucial involvement of the N-methyl-D-aspartate receptor (NMDAR) in mediating excitatory synaptic neurotransmission, neuronal development and learning and memory. The complexity of NMDAR modulation has escalated with the knowledge that receptors can traffic between synaptic and extrasynaptic sites, and that location on the plasma membrane profoundly affects the physiological function of NMDARs. Moreover, mechanisms that regulate NMDAR subcellular localization and function, such as protein-protein interactions, phosphorylation, palmitoylation, ubiquitination and receptor proteolytic cleavage, may differ for synaptic and extrasynaptic NMDARs. Recent studies suggest that NMDAR mislocalization is a dominant contributing factor to glutamatergic dysfunction and pathogenesis in neurological disorders such as Huntington's disease, Alzheimer's disease and ischemia. Therapeutic approaches that specifically rectify receptor mislocalization or target resulting downstream apoptotic signaling could be beneficial for preventing disease onset or progression across many disorders that are commonly caused by NMDAR dysfunction. This review will summarize the molecular mechanisms that regulate synaptic and extrasynaptic NMDAR localization in both physiologic and pathogenic states.     

Mitochondrial trafficking and the provision of energy and calcium buffering at excitatory synapses

Neuronal postsynaptic currents consume most of the brain's energy supply. Delineating how neurons control the distribution, morphology and function of the energy-producing mitochondria that fuel synaptic communication is therefore important for our understanding of nervous system function and pathology. Here we review recent insights into the molecular mechanisms that control activity-dependent regulation of mitochondrial trafficking, morphology and activity at excitatory synapses. We also consider some implications of this regulation for synaptic function and plasticity and discuss how this may contribute to synaptic dysfunction and signalling in neurological disease, with a focus on Alzheimer's disease.     

阿尔茨海默病中突触结构的损伤

神经突触具有高度可塑性,突触的形成和重塑是神经元活性依赖性的,是学习记忆、认知功能的基础。包括阿尔茨海默病（AD）在内的多种表现出认知缺陷的神经疾病。均存在突触结构或者功能的异常。AD病程缓慢,临床早期表现为单纯的记忆功能损伤,随病程深入,AD认知障碍进行性加重,并出现明显的神经退行性病变。其中新皮质、海马的联合区的突触密度下降,在AD的早期即出现,并且与认知功能下降呈现最显著的相关性。年龄似乎并不是突触丢失的促因。本文将回顾AD中突触损伤的相关研究,并讨论脑内神经连接下降后的可能代偿机制。     

Modeling synaptogenesis in schizophrenia and autism using human iPSC derived neurons

Schizophrenia (SCZ) and autism spectrum disorder (ASD) are genetically and phenotypically complex disorders of neural development. Human genetic studies, as well as studies examining structural changes at the cellular level, have converged on glutamatergic synapse formation, function, and maintenance as common pathophysiologic substrates involved in both disorders. Synapses as basic functional units of the brain are continuously modified by experience throughout life, therefore they are particularly attractive candidates for targeted therapy. Until recently we lacked a system to evaluate dynamic changes that lead to synaptic abnormalities. With the development of techniques to generate induced pluripotent stem cells (iPSCs) from patients, we are now able to study neuronal and synaptic development in cells from individual patients in the context of genetic changes conferring disease susceptibility. In this review, we discuss recent studies focusing on neural cells differentiated from SCZ and ASD patient iPSCs. These studies support a central role for glutamatergic synapse formation and function in both disorders and demonstrate that iPSC derived neurons offer a potential system for further evaluation of processes leading to synaptic dysregulation and for the design and screening of future therapies.     

Impaired cognition, sensorimotor gating, and hippocampal long-term depression in mice lacking the prostaglandin E2 EP2 receptor

Cyclooxygenase-2 (COX-2) is a neuronal immediate early gene that is regulated by N-methyl d aspartate (NMDA) receptor activity. COX-2 enzymatic activity catalyzes the first committed step in prostaglandin synthesis. Recent studies demonstrate an emerging role for the downstream PGE₂ EP2 receptor in diverse models of activity-dependent synaptic plasticity and a significant function in models of neurological disease including cerebral ischemia, Familial Alzheimer's disease, and Familial amyotrophic lateral sclerosis. Little is known, however, about the normal function of the EP2 receptor in behavior and cognition. Here we report that deletion of the EP2 receptor leads to significant cognitive deficits in standard tests of fear and social memory. EP2−/− mice also demonstrated impaired prepulse inhibition (PPI) and heightened anxiety, but normal startle reactivity, exploratory behavior, and spatial reference memory. This complex behavioral phenotype of EP2−/− mice was associated with a deficit in long-term depression (LTD) in hippocampus. Our findings suggest that PGE₂ signaling via the EP2 receptors plays an important role in cognitive and emotional behaviors that recapitulate some aspects of human psychopathology related to schizophrenia.     

Recent advances in the understanding of the role of synaptic proteins in Alzheimer's Disease and other neurodegenerative disorders

Synaptic damage is an early pathological event common to many neurodegenerative disorders such as Alzheimer's disease (AD) and is the best correlate to the cognitive impairment. Several molecules involved in AD and in other neurodegenerative disorders play an important role in synaptic function and when misfolded aggregate and form amyloid fibrils. Synaptic proteins with an amyloid domain include amyloid beta-protein precursor, prion protein, huntingtin, ataxin-1 and alpha-synuclein. Two of the possible mechanisms by which alterations in synaptic proteins lead to synapse damage are: 1) misfolded or aggregated synaptic molecules have lost their normal function and/or 2) they have gained a toxic capacity. Recent studies support the possibility that while oligomers are toxic, polymers might be inactive. The mechanisms by which oligomers trigger synapse loss could be related to their ability to triggers stress signals once they enter the nucleus and/or accumulate at the endoplasmic reticulum.     

M-channels: neurological diseases,neuromodulation, and drug development

Efforts in basic neuroscience and studies of rare hereditary neurological diseases are partly motivated by the hope that such work can lead to better understanding of and treatments for the common neurological disorders. An example is the progress that has resulted from identification of the genes that cause benign familial neonatal convulsions (BFNCs). Benign familial neonatal convulsions is a rare idiopathic, generalized epilepsy syndrome. In 1998, geneticists discovered that BFNC is caused by mutations in a novel potassium channel subunit, KCNQ2. Further work quickly revealed the sequences of 3 related brain channel genes KCNQ3, KCNQ4, and KCNQ5. Mutations in 2 of these genes were shown to cause BFNC (KCNQ3) and hereditary deafness (KCNQ4). Physiologists soon discovered that the KCNQ genes encoded subunits of the M-channel, a widely expressed potassium channel that mediates effects of modulatory neurotransmitters and controls repetitive neuronal discharges. Finally, pharmacologists discovered that the biological activities of 3 classes of compounds in development as treatments for Alzheimer disease, epilepsy, and stroke were mediated in part by effects on brain KCNQ channels. Cloned human KCNQ channels can now be used for high-throughput screening of additional drug candidates. Ongoing studies in humans and animal models will refine our understanding of KCNQ channel function and may reveal additional targets for therapeutic manipulation.     

Increased AβPP processing in familial Danish dementia patients

An autosomal dominant mutation in the BRI2/ITM2B gene causes Familial Danish Dementia (FDD). We have generated a mouse model of FDD, called FDDKI, genetically congruous to the human disease. These mice carry one mutant and one wild type Bri2/Itm2b allele, like FDD patients. Analysis of FDDKI mice and samples from human patients has shown that the Danish mutation causes loss of Bri2 protein. FDDKI mice show synaptic plasticity and memory impairments. BRI2 is a physiological interactor of amyloid-β protein precursor (AβPP), a gene associated with Alzheimer's disease, which inhibits processing of AβPP. AβPP/Bri2 complexes are reduced in synaptic membranes of FDDKI mice. Consequently, AβPP metabolites derived from processing of AβPP by β-, α-, and γ-secretases are increased in Danish dementia mice. AβPP haplodeficiency prevents memory and synaptic dysfunctions, consistent with a role for AβPP-metabolites in the pathogenesis of memory and synaptic deficits. This genetic suppression provides compelling evidence that AβPP and BRI2 functionally interact. Here, we have investigated whether AβPP processing is altered in FDD patients' brain samples. We find that the levels of several AβPP metabolites, including Aβ, are significantly increased in the brain sample derived from an FDD patient. Our data are consistent with the findings in FDDKI mice, and support the hypothesis that the neurological effects of the Danish form of BRI2 are caused by toxic AβPP metabolites, suggesting that Familial Danish and Alzheimer's dementias share common pathogenic mechanisms.     

Swallowing dysfunction in Wilson's disease: a scintigraphic study

Abstract  Although dysphagia is a common complaint of patients with Wilson's disease (WD) and pneumonia is an important cause of death in these patients, swallowing function remains an underinvestigated field in this condition. The aim of this study was to characterize swallowing dynamics in WD patients. Eight WD patients and 15 age-matched controls underwent scintigraphic evaluation of oral and pharyngeal deglutition. Patients had significantly slower oral transit ( P  = 0.008) and a greater percentage of oral residue ( P  = 0.006) when compared to controls. Two of eight patients were free of neurological symptoms at time of examination. Impaired oropharyngeal function was found in patients without dysphagia and without neurological symptoms. Our findings indicate that WD may present with objective swallowing dysfunction, even in the absence of neurological manifestations. Further studies are necessary to investigate the impact of this dysfunction on morbidity and mortality in WD.     

Expanding the clinical and EEG spectrum of CNKSR2-related encephalopathy with status epilepticus during slow sleep (ESES)

ObjectiveTo investigate the clinical and EEG features of Encephalopathy with Status Epilepticus during slow Sleep (ESES) related to CNKSR2 pathogenic variants.MethodsDetailed clinical history, repeated wakefulness/overnight sleep EEGs, brain MRI were collected in five patients, including one female, with CNKSR2-related ESES.ResultsNeurodevelopment in infancy was normal in two patients, delayed in three. Epilepsy onset (age range: 2–6 years) was associated with appearance or aggravation of cognitive impairment, language regression and/or behavioral disorders. Worsening of epilepsy and of cognitive/behavioral disturbances paralleled by enhancement of non-rapid eye movement (NREM) sleep-related, frontally predominant, EEG epileptic discharges [spike-wave-index (SWI): range 60–96%] was consistent with ESES. In three patients, episodes of absence status epilepticus or aggravation of atypical absences occurred, in this latter case associated with striking increment of awake SWI. Speech/oro-motor dyspraxia was diagnosed in four patients. In two patients, long-term follow-up showed epilepsy remission and persistence of mild/moderate cognitive disorders and behavioral disturbances into adulthood.ConclusionsNovel findings of our study are occurrence also in females, normal neurodevelopment before epilepsy onset, epilepsy aggravation associated with enhanced awake SWI, mild/moderate evolution in adulthood and language disorder due to speech/oro-motor dyspraxia.SignificanceOur findings expand the phenotypic spectrum of CNKSR2-related ESES.     

Autoimmune and paraneoplastic channelopathies

Thirty years ago, antibodies against the muscle acetylcholine receptor (AChR) were recognized as the cause of myasthenia gravis. Since then, there has been great interest in identifying other neurological disorders associated with auto-antibodies. Several other antibody-mediated neuromuscular disorders have been identified, each associated with an antibody against a ligand- or voltage-gated ion channel. The Lambert-Eaton syndrome is caused by antibodies against voltage-gated calcium channels and often occurs in patients with small cell lung cancer. Acquired neuromyotonia is caused by voltage-gated potassium channel antibodies, and autoimmune autonomic ganglionopathy is caused by antibodies against the neuronal AChR in autonomic ganglia. There is good evidence that antibodies in these disorders cause changes in synaptic function r neuronal excitability by directly inhibiting ion channel function. More recently, studies have identified ion channel antibodies in patients with certain CNS disorders, such as steroid-responsive encephalitis and paraneoplastic cerebellar ataxia. It remains unclear if antibodies can gain access to the CNS and directly cause ion channel dysfunction. Treatment of autoimmune channelopathies includes drugs that help restore normal neuronal function and treatments to remove pathogenic antibodies (plasma exchange) or modulate the immune response (steroids or immunosuppressants). These disabling neurological disorders may be dramatically responsive to immunomodulatory therapy. Future studies will likely lead to identification of other ion channel antibodies and other autoimmune channelopathies.     

Cyclooxygenases, lipoxygenases, and epoxygenases in CNS: their role and involvement in neurological disorders

Three enzyme systems, cyclooxygenases that generate prostaglandins, lipoxygenases that form hydroxy derivatives and leukotrienes, and epoxygenases that give rise to epoxyeicosatrienoic products, metabolize arachidonic acid after its release from neural membrane phospholipids by the action of phospholipase A(2). Lysophospholipids, the other products of phospholipase A(2) reactions, are either reacylated or metabolized to platelet-activating factor. Under normal conditions, these metabolites play important roles in synaptic function, cerebral blood flow regulation, apoptosis, angiogenesis, and gene expression. Increased activities of cyclooxygenases, lipoxygenases, and epoxygenases under pathological situations such as ischemia, epilepsy, Alzheimer's disease, Parkinson disease, amyotrophic lateral sclerosis, and Creutzfeldt-Jakob disease produce neuroinflammation involving vasodilation and vasoconstriction, platelet aggregation, leukocyte chemotaxis and release of cytokines, and oxidative stress. These are closely associated with the neural cell injury which occurs in these neurological conditions. The metabolic products of docosahexaenoic acid, through these enzymes, generate a new class of lipid mediators, namely docosatrienes and resolvins. These metabolites antagonize the effect of metabolites derived from arachidonic acid. Recent studies provide insight into how these arachidonic acid metabolites interact with each other and other bioactive mediators such as platelet-activating factor, endocannabinoids, and docosatrienes under normal and pathological conditions. Here, we review present knowledge of the functions of cyclooxygenases, lipoxygenases, and epoxygenases in brain and their association with neurodegenerative diseases.     

Ageing and the nigrostriatal dopaminergic system

BACKGROUND: Brain dopamine has been the focus of numerous studies owing to its crucial role in motor function and in neurological and psychiatric disease processes. Whilst early work relied on postmortem data, functional imaging has allowed a more sophisticated approach to the quantification of receptor density, affinity and functional capacity. This review aims to summarise changes in the nigrostriatal dopaminergic system which accompany normal ageing. METHODS: A literature search focussed on postmortem and neuroimaging studies of normal ageing within the nigrostriatal dopaminergic tract. The functional significance of age-related effects was also considered. RESULTS: There are significant reductions in pre- and post-synaptic markers of brain dopamine activity during normal ageing: However the rate of decline (linear or exponential), the effects of gender and heterogeneity and the mechanisms by which these changes occur remain undetermined. Limited data suggest there is a significant association between postsynaptic receptor density and specific aspects of motor and cognitive function. CONCLUSION: The identification of strategies to improve dopaminergic transmission may delay the onset of motor and cognitive deficits associated with normal ageing. In order to develop effective preventative strategies, the causative mechanisms underlying age-related changes and the interaction between synaptic structure and function need to be more clearly elucidated.     

Autonomic ganglia, acetylcholine receptor antibodies, and autoimmune ganglionopathy

Nicotinic acetylcholine receptors (AChR) are ligand-gated cation channels that are present throughout the nervous system. The ganglionic (alpha3-type) neuronal AChR mediates fast synaptic transmission in sympathetic, parasympathetic and enteric autonomic ganglia. Autonomic ganglia are an important site of neural integration and regulation of autonomic reflexes. Impaired cholinergic ganglionic synaptic transmission is one important cause of autonomic failure. Ganglionic AChR antibodies are found in many patients with autoimmune autonomic ganglionopathy (AAG). These antibodies recognize the alpha3 subunit of the ganglionic AChR, and thus do not bind non-specifically to other nicotinic AChR. Patients with high levels of ganglionic AChR antibodies typically present with rapid onset of severe autonomic failure, with orthostatic hypotension, gastrointestinal dysmotility, anhidrosis, bladder dysfunction and sicca symptoms. Impaired pupillary light reflex is often seen. Like myasthenia gravis, AAG is an antibody-mediated neurological disorder. Antibodies from patients with AAG inhibit ganglionic AChR currents and impair transmission in autonomic ganglia. An animal model of AAG in the rabbit recapitulates the important clinical features of the human disease and provides additional evidence that AAG is an antibody-mediated disorder caused by impairment of synaptic transmission in autonomic ganglia.     

Synaptic learning rules, cortical circuits, and visual function.

Sensory experience is essential for the refinement of neuronal circuits during development and for learning and memory in the adult brain. Such experience-dependent plasticity is largely mediated by activity-dependent synaptic modification. In this review, we focus on a spike timing-dependent synaptic learning rule, in which the direction and magnitude of synaptic modification depend on the relative spike timing of presynaptic and postsynaptic neurons. We discuss a series of recent studies exploring the functional implications of this learning rule in the visual system. These studies show that temporally patterned visual stimuli can cause rapid changes in visual circuits, neuronal receptive fields, and visual perception, with a temporal specificity of tens of milliseconds. Particularly, motion stimuli that are common in natural scenes may interact strongly with the spike timing-dependent learning rule, leaving distinct marks in the perceptual function of the mature brain.