Pathways to Drug Development for Autism Spectrum Disorders

Drug Treatments for Neurodevelopmental Disorders: Targeting Signaling Pathways and Homeostasis

PURPOSE OF THE REVIEW

Preclinical and clinical evidence support the notion that neurodevelopmental disorders (NDDs) are synaptic disorders, characterized by excitatory-inhibitory imbalance. Despite this, NDD drug development programs targeting glutamate or gamma-aminobutyric acid (GABA) receptors have been largely unsuccessful. Nonetheless, recent drug trials in Rett syndrome (RTT), fragile X syndrome (FXS), and other NDDs targeting other mechanisms have met their endpoints. The purpose of this review is to identify the basis of these successful studies.

RECENT FINDINGS

Despite increasing evidence of disruption in synaptic homeostasis, most genetic variants associated with NDDs implicate proteins involved in cell regulation and not in neurotransmission. Metabolic processes, in particular mitochondrial function, appear to play a role in NDD pathophysiology. NDDs are also characterized by distinctive cell signaling abnormalities, which link cellular and synaptic homeostasis. Recent successful trials in NDDs, including those of trofinetide, the first drug specifically approved for one of these disorders (i.e., RTT), implicate the targeting of downstream processes (i.e., signaling pathways) rather than neurotransmitter receptors. Recent positive drug studies in NDDs and their underlying mechanisms, in conjunction with new knowledge on the pathophysiology of these disorders, support the concept that targeting signaling and cellular and synaptic homeostasis may be a preferred approach for ameliorating synaptic abnormalities in many NDDs.

Prenatal exposure to valproic acid reduces synaptic δ-catenin levels and disrupts ultrasonic vocalization in neonates

Valproic acid (VPA) is an effective and commonly prescribed drug for epilepsy and bipolar disorder. However, children born from mothers treated with VPA during pregnancy exhibit an increased incidence of autism spectrum disorder (ASD). Although VPA may impair brain development at the cellular level, the mechanism of VPA-induced ASD has not been completely addressed. A previous study has found that VPA treatment strongly reduces δ-catenin mRNA levels in cultured human neurons. δ-catenin is important for the control of glutamatergic synapses and is strongly associated with ASD. VPA inhibits dendritic morphogenesis in developing neurons, an effect that is also found in neurons lacking δ-catenin expression. We thus hypothesize that prenatal exposure to VPA significantly reduces δ-catenin levels in the brain, which impairs glutamatergic synapses to cause ASD. Here, we found that prenatal exposure to VPA markedly reduced δ-catenin levels in the brain of mouse pups. VPA treatment also impaired dendritic branching in developing mouse cortical neurons, which was partially reversed by elevating δ-catenin expression. Prenatal VPA exposure significantly reduced synaptic α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor levels and postsynaptic density 95 (PSD95) in the brain of mouse pups, indicating dysfunctions in glutamatergic synaptic transmission. VPA exposure also significantly altered ultrasonic vocalization (USV) in newly born pups when they were isolated from their nest. Moreover, VPA-exposed pups show impaired hypothalamic response to isolation, which is required to produce animals' USVs following isolation from the nest. Therefore, these results suggest that VPA-induced ASD pathology can be mediated by the loss of δ-catenin functions.

Mast Cells in Autism Spectrum Disorder-The Enigma to Be Solved?

Autism Spectrum Disorder (ASD) is a disturbance of neurodevelopment with a complicated pathogenesis and unidentified etiology. Many children with ASD have a history of "allergic symptoms", often in the absence of mast cell (MC)-positive tests. Activation of MCs by various stimuli may release molecules related to inflammation and neurotoxicity, contributing to the development of ASD. The aim of the present paper is to enrich the current knowledge on the relationship between MCs and ASD by discussing key molecules and immune pathways associated with MCs in the pathogenesis of autism. Cytokines, essential marker molecules for MC degranulation and therapeutic targets, are also highlighted. Understanding the relationship between ASD and the activation of MCs, as well as the involved molecules and interactions, are the main points contributing to solving the enigma. Key molecules, associated with MCs, may provide new insights to the discovery of drug targets for modeling inflammation in ASD.

Prenatal exposure to valproic acid reduces synaptic δ-catenin levels and disrupts ultrasonic vocalization in neonates

Valproic acid (VPA) is an effective and commonly prescribed drug for epilepsy and bipolar disorder. However, children born from mothers treated with VPA during pregnancy exhibit an increased incidence of autism spectrum disorder (ASD). Although VPA may impair brain development at the cellular level, the mechanism of VPA-induced ASD has not been completely addressed. A previous study has found that VPA treatment strongly reduces δ-catenin mRNA levels in cultured human neurons. δ-catenin is important for the control of glutamatergic synapses and is strongly associated with ASD. VPA inhibits dendritic morphogenesis in developing neurons, an effect that is also found in neurons lacking δ-catenin expression. We thus hypothesize that prenatal exposure to VPA significantly reduces δ-catenin levels in the brain, which impairs glutamatergic synapses to cause ASD. Here, we found that prenatal exposure to VPA markedly reduced δ-catenin levels in the brain of mouse pups. VPA treatment also impaired dendritic branching in developing mouse cortical neurons, which was reversed by elevating δ-catenin expression. Prenatal VPA exposure significantly reduced synaptic AMPA receptor levels and postsynaptic density 95 (PSD95) in the brain of mouse pups, indicating dysfunctions in glutamatergic synaptic transmission. VPA exposure also significantly altered ultrasonic vocalization (USV) in newly born pups when they were isolated from their nest. Moreover, VPA-exposed pups show impaired hypothalamic response to isolation, which is required to produce animals' USVs following isolation from the nest. Therefore, these results suggest that VPA-induced ASD pathology can be mediated by the loss of δ-catenin functions.

Highlights

Prenatal exposure of valproic acid (VPA) in mice significantly reduces synaptic δ-catenin protein and AMPA receptor levels in the pups' brains.VPA treatment significantly impairs dendritic branching in cultured cortical neurons, which is reversed by increased δ-catenin expression.VPA exposed pups exhibit impaired communication such as ultrasonic vocalization.Neuronal activation linked to ultrasonic vocalization is absent in VPA-exposed pups.The loss of δ-catenin functions underlies VPA-induced autism spectrum disorder (ASD) in early childhood.

The anterior insular cortex processes social recognition memory

Impaired social abilities are characteristics of a variety of psychiatric disorders such as schizophrenia, autism spectrum disorder, and bipolar disorder. Studies consistently implicated the relationship between the anterior insular cortex (aIC) and social ability, however, how the aIC involves in processing specific subtypes of social ability was uninvestigated. We, therefore, investigated whether the absence or presence of the aIC affects the social behaviors of mice. We found that electrolytic lesions of the aIC specifically impaired mice's ability to recognize a novel stranger mouse, while the sociability of the aIC-lesioned mice was intact. Interestingly, the aIC-lesioned mice were still distinguished between a mouse that had been housed together before the aIC lesion and a novel mouse, supporting that retrieval of social recognition memory may not involve the aIC. Additional behavioral tests revealed that this specific social ability impairment induced by the aIC lesion was not due to impairment in olfaction, learning and memory, locomotion, or anxiety levels. Together our data suggest that the aIC is specifically involved in processing social recognition memory, but not necessarily involved in retrieving it.

Profile of psychotropic agents used in autism spectrum disorder according to comorbidities in Turkey: A 4-year evaluation

It is known that the use of psychotropic pharmaceuticals is common in comorbidities seen in autism spectrum disorder (ASD). We have very limited knowledge about which psychotropic drugs are prescribed when comorbidities are diagnosed in patients with ASD. It is aimed to determine the profile of psychotropic agents in patients diagnosed with ASD associated with comorbidities between the ages of 0-24 in Turkey over 4 years. Data belonging to ASD in Prescription Information System (PIS) was obtained from the 'Turkish Medicines and Medical Devices Agency'. A total of 34 066 prescriptions including 45 624 psychotropic drugs were analyzed. A total of psychotropic drugs prescribed for patients with ASD was 75.4%. The following psychotropic drugs were prescribed for the patients with ASD and its comorbidities; risperidone (28.6%), aripiprazole (13.7%), and valproic acid (11.3%) are the most preferred psychotropics. The percentage of pharmaceuticals containing psychotropic active substances in prescriptions with ASD and its comorbidities is 7.5%. This study is the first research in which psychotropics used in ASD were evaluated over a wide period and nationwide. Antipsychotics were most commonly prescribed with the diagnosis of ASD. In the presence of ASD and its comorbidities, risperidone was most frequently prescribed.

The autism-associated loss of δ-catenin functions disrupts social behaviors

δ-catenin is expressed in excitatory synapses and functions as an anchor for the glutamatergic AMPA receptor (AMPAR) GluA2 subunit in the postsynaptic density. The glycine 34 to serine (G34S) mutation in the δ-catenin gene is found in autism spectrum disorder (ASD) patients and induces loss of δ-catenin functions at excitatory synapses, which is presumed to underlie ASD pathogenesis in humans. However, how the G34S mutation causes loss of δ-catenin functions to induce ASD remains unclear. Here, using neuroblastoma cells, we discover that the G34S mutation generates an additional phosphorylation site for glycogen synthase kinase 3β (GSK3β). This promotes δ-catenin degradation and causes the reduction of δ-catenin levels, which likely contributes to the loss of δ-catenin functions. Synaptic δ-catenin and GluA2 levels in the cortex are significantly decreased in mice harboring the δ-catenin G34S mutation. The G34S mutation increases glutamatergic activity in cortical excitatory neurons while it is decreased in inhibitory interneurons, indicating changes in cellular excitation and inhibition. δ-catenin G34S mutant mice also exhibit social dysfunction, a common feature of ASD. Most importantly, inhibition of GSK3β activity reverses the G34S-induced loss of δ-catenin function effects in cells and mice. Finally, using δ-catenin knockout mice, we confirm that δ-catenin is required for GSK3β inhibition-induced restoration of normal social behaviors in δ-catenin G34S mutant animals. Taken together, we reveal that the loss of δ-catenin functions arising from the ASD-associated G34S mutation induces social dysfunction via alterations in glutamatergic activity and that GSK3β inhibition can reverse δ-catenin G34S-induced synaptic and behavioral deficits.

Significance Statement

δ-catenin is important for the localization and function of glutamatergic AMPA receptors at synapses in many brain regions. The glycine 34 to serine (G34S) mutation in the δ-catenin gene is found in autism patients and results in the loss of δ-catenin functions. δ-catenin expression is also closely linked to other autism-risk genes involved in synaptic structure and function, further implying that it is important for the autism pathophysiology. Importantly, social dysfunction is a key characteristic of autism. Nonetheless, the links between δ-catenin functions and social behaviors are largely unknown. The significance of the current research is thus predicated on filling this gap by discovering the molecular, cellular, and synaptic underpinnings of the role of δ-catenin in social behaviors.

Altered Expression and In Vivo Activity of mGlu5 Variant a Receptors in the Striatum of BTBR Mice: Novel Insights Into the Pathophysiology of Adult Idiopathic Forms of Autism Spectrum Disorders

BACKGROUND

mGlu5 metabotropic glutamate receptors are considered as candidate drug targets in the treatment of "monogenic" forms of autism spectrum disorders (ASD), such as Fragile- X syndrome (FXS). However, despite promising preclinical data, clinical trials using mGlu5 receptor antagonists to treat FXS showed no beneficial effects.

OBJECTIVE

Here, we studied the expression and function of mGlu5 receptors in the striatum of adult BTBR mice, which model idiopathic forms of ASD, and behavioral phenotype.

METHODS

Behavioral tests were associated with biochemistry analysis including qPCR and western blot for mRNA and protein expression. In vivo analysis of polyphosphoinositides hydrolysis was performed to study the mGlu5-mediated intracellular signaling in the striatum of adult BTBR mice under basal conditions and after MTEP exposure.

RESULTS

Expression of mGlu5 receptors and mGlu5 receptor-mediated polyphosphoinositides hydrolysis were considerably high in the striatum of BTBR mice, sensitive to MTEP treatment. Changes in the expression of genes encoding for proteins involved in excitatory and inhibitory neurotransmission and synaptic plasticity, including Fmr1, Dlg4, Shank3, Brd4, bdnf-exon IX, Mef2c, and Arc, GriA2, Glun1, Nr2A, and Grm1, Grm2, GriA1, and Gad1 were also found. Behaviorally, BTBR mice showed high repetitive stereotypical behaviors, including self-grooming and deficits in social interactions. Acute or repeated injections with MTEP reversed the stereotyped behavior and the social interaction deficit. Similar effects were observed with the NMDA receptor blockers MK-801 or ketamine.

CONCLUSION

These findings support a pivotal role of mGlu5 receptor abnormal expression and function in idiopathic ASD adult forms and unveil novel potential targets for therapy.

Pten heterozygosity restores neuronal morphology in fragile X syndrome mice

Genetic studies of hippocampal granule neuron development have been used to elucidate cellular functions of Pten and Fmr1. While mutations in each gene cause neurodevelopmental disorders such as autism and fragile X syndrome, how Pten and Fmr1 function alone or together during normal development is not known. Moreover, Pten mRNA is bound by the fragile X mental retardation protein (FMRP) RNA binding protein, but how this physical interaction impinges on phosphatase and tensin homolog protein (PTEN) expression is not known. To understand the interaction of PTEN and FMRP, we investigated the dentate gyrus granule neuron development in Pten and Fmr1 knockout (KO) mice. Interestingly, heterozygosity of Pten restored Fmr1 KO cellular phenotypes, including dendritic arborization, and spine density, while PTEN protein expression was significantly increased in Fmr1 KO animals. However, complete deletion of both Pten and Fmr1 resulted in a dramatic increase in dendritic length, spine density, and spine length. In addition, overexpression of PTEN in Fmr1 KO Pten heterozygous background reduced dendritic length, arborization, spine density, and spine length including pS6 levels. Our findings suggest that PTEN levels are negatively regulated by FMRP, and some Fmr1 KO phenotypes are caused by dysregulation of PTEN protein. These observations provide evidence for the genetic interaction of PTEN and FMRP and a possible mechanistic basis for the pathogenesis of Fmr1-related fragile X neurodevelopmental disorders.

Autism and Emotion: A Narrative Review

Autism spectrum disorder (ASD) includes a variety of childhood-onset and lifelong neurodevelopmental condition with an enduring impact on multiple domains of functioning characterized by persistent deficits in social communication, restricted and repetitive behavior interest, and activities. They often find it hard to recognize and control emotions but their emotional expression can be improved by various intervention techniques that in turn can help them understand and respond more appropriately to other people. Problems in the area on emotional reciprocity among individual with ASD involve recognizing, understanding, expressing, and regulating emotions. Their ability in emotional reciprocity is often improved with a comprehensive treatment approach, especially by focused emotional enhancement intervention. In this review, we followed the standard IMRAD (Introduction, Methods, Results, and Discussion) structure to critically examine the condition of autism and its relation with genetic mechanism, and how theories of emotion and theory of mind associated with persons with ASD, some of the widely used assessment tools and future research direction in the emotional development of individuals diagnosed with ASD by using the narrative review method. Records collected through research databases such as Scopus, PubMed, Web of Science, Medline, EBSCO and published books with ISBN (International Standard Book Number), and published test manuals were evaluated in-depth and summarized based on the subtopic of the proposed title. A critical theoretical analysis of the genetic mechanism of emotions, theories of emotions, and theory of mind was explained in connection with ASD.

Helminth therapy for autism under gut-brain axis- hypothesis

Autism is a neurodevelopmental disease included within Autism Syndrome Disorder (ASD) spectrum. ASD has been linked to a series of genes that play a role in immune response function and patients with autism, commonly suffer from immune-related comorbidities. Despite the complex pathophysiology of autism, Gut-brain axis is gaining strength in the understanding of several neurological disorders. In addition, recent publications have shown the correlation between immune dysfunctions, gut microbiota and brain with the behavioral alterations and comorbid symptoms found in autism. Gut-brain axis acts as the "second brain", in a communication network established between neural, endocrine and the immunological systems. On the other hand, Hygiene Hypothesis suggests that the increase in the incidence of autoimmune diseases in the modern world can be attributed to the decrease of exposure to infectious agents, as parasitic nematodes. Helminths induce modulatory and protective effects against several inflammatory disorders, maintaining gastrointestinal homeostasis and modulating brain functions. Helminthic therapy has been previously performed in diseases such as ulcerative colitis, Crohn's disease, diabetes, multiple sclerosis, asthma, rheumatoid arthritis, and food allergies. Considering gut-brain axis, Hygiene Hypothesis, and the modulatory effects of helminths I hypothesized that a treatment with Trichuris suis soluble products represents a feasible holistic treatment for autism, and the key for the development of novel treatments. Preclinical studies are required to test this hypothesis.

The Application of Adeno-Associated Viral Vector Gene Therapy to the Treatment of Fragile X Syndrome

Viral vector-mediated gene therapy has grown by leaps and bounds over the past several years. Although the reasons for this progress are varied, a deeper understanding of the basic biology of the viruses, the identification of new and improved versions of viral vectors, and simply the vast experience gained by extensive testing in both animal models of disease and in clinical trials, have been key factors. Several studies have investigated the efficacy of adeno-associated viral (AAV) vectors in the mouse model of fragile X syndrome where AAVs have been used to express fragile X mental retardation protein (FMRP), which is missing or highly reduced in the disorder. These studies have demonstrated a range of efficacies in different tests from full correction, to partial rescue, to no effect. Here we provide a backdrop of recent advances in AAV gene therapy as applied to central nervous system disorders, outline the salient features of the fragile X studies, and discuss several key issues for moving forward. Collectively, the findings to date from the mouse studies on fragile X syndrome, and data from clinical trials testing AAVs in other neurological conditions, indicate that AAV-mediated gene therapy could be a viable strategy for treating fragile X syndrome.

Defining the hidden evidence in autism research. Forty per cent of rigorously designed clinical trials remain unpublished - a cross-sectional analysis

Autism spectrum disorders (ASD) have a prevalence of up to 2.7% and show significant rates of comorbidities. Pharmacological treatment can be difficult. New treatment options are needed, several are currently under investigation. Publication bias presents a major problem in current clinical research. This study was designed to quantify publication bias in rigorously designed ASD research. The database at ClinicalTrials.gov was searched for all completed randomized controlled clinical trials investigating interventions in ASD and their results made public. If results could neither be retrieved through search of the database, nor of scientific databases nor by enquiries of the responsible parties or sponsors listed, a trial was defined as not published. The search delivered N = 30 (60%) trials were published, N = 20 (40%) remained unpublished, N = 2,421 (59%) patients were enrolled in the published trials, N = 1,664 (41%) patients in the unpublished trials, time to publication was 21.4 months [standard deviation (SD) = 18.48; range = -5 to 80 months]. Results of N = 22 trials were available through ClinicalTrials.gov. Characteristics of published compared to unpublished trials did not show apparent differences. The majority of trials investigated drugs. The results emphasize the serious issue of publication bias. The large proportion of unpublished results precludes valuable information and has the potential to distort evidence for treatment approaches in ASD.

Updated report on tools to measure outcomes of clinical trials in fragile X syndrome

OBJECTIVE

Fragile X syndrome (FXS) has been the neurodevelopmental disorder with the most active translation of preclinical breakthroughs into clinical trials. This process has led to a critical assessment of outcome measures, which resulted in a comprehensive review published in 2013. Nevertheless, the disappointing outcome of several recent phase III drug trials in FXS, and parallel efforts at evaluating behavioral endpoints for trials in autism spectrum disorder (ASD), has emphasized the need for re-assessing outcome measures and revising recommendations for FXS.

METHODS

After performing an extensive database search (PubMed, Food and Drug Administration (FDA)/National Institutes of Health (NIH)'s www.ClinicalTrials.gov, etc.) to determine progress since 2013, members of the Working Groups who published the 2013 Report evaluated the available outcome measures for FXS and related neurodevelopmental disorders using the COSMIN grading system of levels of evidence. The latter has also been applied to a British survey of endpoints for ASD. In addition, we also generated an informal classification of outcome measures for use in FXS intervention studies as instruments appropriate to detect shorter- or longer-term changes.

RESULTS

To date, a total of 22 double-blind controlled clinical trials in FXS have been identified through www.ClinicalTrials.gov and an extensive literature search. The vast majority of these FDA/NIH-registered clinical trials has been completed between 2008 and 2015 and has targeted the core excitatory/inhibitory imbalance present in FXS and other neurodevelopmental disorders. Limited data exist on reliability and validity for most tools used to measure cognitive, behavioral, and other problems in FXS in these trials and other studies. Overall, evidence for most tools supports a moderate tool quality grading. Data on sensitivity to treatment, currently under evaluation, could improve ratings for some cognitive and behavioral tools. Some progress has also been made at identifying promising biomarkers, mainly on blood-based and neurophysiological measures.

CONCLUSION

Despite the tangible progress in implementing clinical trials in FXS, the increasing data on measurement properties of endpoints, and the ongoing process of new tool development, the vast majority of outcome measures are at the moderate quality level with limited information on reliability, validity, and sensitivity to treatment. This situation is not unique to FXS, since reviews of endpoints for ASD have arrived at similar conclusions. These findings, in conjunction with the predominance of parent-based measures particularly in the behavioral domain, indicate that endpoint development in FXS needs to continue with an emphasis on more objective measures (observational, direct testing, biomarkers) that reflect meaningful improvements in quality of life. A major continuous challenge is the development of measurement tools concurrently with testing drug safety and efficacy in clinical trials.

Neurobiologically-based treatments in Rett syndrome: opportunities and challenges

Introduction: Rett syndrome (RTT) is an X-linked neurodevelopmental disorder that primarily affects females, typically resulting in a period of developmental regression in early childhood followed by stabilization and severe chronic cognitive, behavioral, and physical disability. No known treatment exists beyond symptomatic management, and while insights into the genetic cause, pathophysiology, neurobiology, and natural history of RTT have been gained, many challenges remain. Areas covered: Based on a comprehensive survey of the primary literature on RTT, this article describes and comments upon the general and unique features of the disorder, genetic and neurobiological bases of drug development, and the history of clinical trials in RTT, with an emphasis on drug trial design, outcome measures, and implementation. Expert opinion: Neurobiologically based drug trials are the ultimate goal in RTT, and due to the complexity and global nature of the disorder, drugs targeting both general mechanisms (e.g., growth factors) and specific systems (e.g., glutamate modulators) could be effective. Trial design should optimize data on safety and efficacy, but selection of outcome measures with adequate measurement properties, as well as innovative strategies, such as those enhancing synaptic plasticity and use of biomarkers, are essential for progress in RTT and other neurodevelopmental disorders.

FMRP Expression Levels in Mouse Central Nervous System Neurons Determine Behavioral Phenotype

Fragile X mental retardation protein (FMRP) is absent or highly reduced in Fragile X Syndrome, a genetic disorder causing cognitive impairment and autistic behaviors. Previous proof-of-principle studies have demonstrated that restoring FMRP in the brain using viral vectors can improve pathological abnormalities in mouse models of fragile X. However, unlike small molecule drugs where the dose can readily be adjusted during treatment, viral vector–based biological therapeutic drugs present challenges in terms of achieving optimal dosing and expression levels. The objective of this study was to investigate the consequences of expressing varying levels of FMRP selectively in neurons of Fmr1 knockout and wild-type (WT) mice. A wide range of neuronal FMRP transgene levels was achieved in individual mice after intra-cerebroventricular administration of adeno-associated viral vectors coding for FMRP. In all treated knockout mice, prominent FMRP transgene expression was observed in forebrain structures, whereas lower levels were present in more caudal regions of the brain. Reduced levels of the synaptic protein PSD-95, elevated levels of the transcriptional modulator MeCP2, and abnormal motor activity, anxiety, and acoustic startle responses in Fmr1 knockout mice were fully or partially rescued after expression of FMRP at about 35–115% of WT expression, depending on the brain region examined. In the WT mouse, moderate FMRP over-expression of up to about twofold had little or no effect on PSD-95 and MeCP2 levels or on behavioral endophenotypes. In contrast, excessive over-expression in the Fmr1 knockout mouse forebrain (approximately 2.5–6-fold over WT) induced pathological motor hyperactivity and suppressed the startle response relative to WT mice. These results delineate a range of FMRP expression levels in the central nervous system that confer phenotypic improvement in fragile X mice. Collectively, these findings are pertinent to the development of long-term curative gene therapy strategies for treating Fragile X Syndrome and other neurodevelopmental disorders.

Antipsychotic Use Trends in Youth With Autism Spectrum Disorder and/or Intellectual Disability: A Meta-Analysis

OBJECTIVE

Although irritability and aggression are relevant treatment targets in autism spectrum disorders (ASDs) and intellectual disability (ID) that may prompt antipsychotic use, antipsychotic prescribing patterns in such youth have not been systematically reviewed.

METHOD

We systematically searched PubMed/MEDLINE/PsycInfo until March 2015 for studies reporting data on the frequency of youth diagnosed with ASDs and/or ID among antipsychotic-treated youth, as well as antipsychotic use in youth with ASD/ID, conducting a meta-analysis and meta-regression analysis of potential moderators, including publication year, study time point, country, setting, sample size, age, sex, and race/ethnicity.

RESULTS

A total of 39 studies were meta-analyzed (n = 365,449, age = 11.4 ± 6.2 years, males = 70.0% ± 10.0%). Among 27 studies (n = 273,139, age = 11.9 ± 8.0 years, males = 67.0% ± 12.9%) reporting on antipsychotic-treated youth, 9.5% (95% CI = 7.8%-11.5%) were diagnosed with ASD/ID. In 20 studies (n = 209,756) reporting data separately for ASD, 7.9% (95% CI = 6.2%-9.9%) had an ASD diagnosis. In 5 longitudinal studies, the proportion of antipsychotic-treated youth with ASD did not change significantly from 1996 to 2011 (6.7% to 5.8%, odds ratio = 0.9, 95% CI = 0.8-1.0, p =.17). However, later study time point moderated greater ASD/ID proportions (β = 0.12, p < .00001). In 13 studies (n = 96,688, age = 9.8 ± 1.2 years, males = 78.6% ± 2.0%) reporting on antipsychotic use in ASD samples, 17.5% (95% CI = 13.7%-22.1%) received antipsychotics. Again, later study time point moderated higher antipsychotic use among patients with ASD (β = 0.10, p = .004).

CONCLUSION

Almost 1 in 10 antipsychotic-treated youth were diagnosed with ASD and/or ID, and 1 in 6 youth with ASD received antipsychotics. Both proportions increased in later years; however, clinical reasons and outcomes of antipsychotic use in ASD/ID require further study.

Autism spectrum disorders and neuropathology of the cerebellum

The cerebellum contains the largest number of neurons and synapses of any structure in the central nervous system. The concept that the cerebellum is solely involved in fine motor function has become outdated; substantial evidence has accumulated linking the cerebellum with higher cognitive functions including language. Cerebellar deficits have been implicated in autism for more than two decades. The computational power of the cerebellum is essential for many, if not most of the processes that are perturbed in autism including language and communication, social interactions, stereotyped behavior, motor activity and motor coordination, and higher cognitive functions. The link between autism and cerebellar dysfunction should not be surprising to those who study its cellular, physiological, and functional properties. Postmortem studies have revealed neuropathological abnormalities in cerebellar cellular architecture while studies on mouse lines with cell loss or mutations in single genes restricted to cerebellar Purkinje cells have also strongly implicated this brain structure in contributing to the autistic phenotype. This connection has been further substantiated by studies investigating brain damage in humans restricted to the cerebellum. In this review, we summarize advances in research on idiopathic autism and three genetic forms of autism that highlight the key roles that the cerebellum plays in this spectrum of neurodevelopmental disorders.

Persistent astrocyte activation in the fragile X mouse cerebellum

BACKGROUND

Fragile X Syndrome, the most common single gene cause of autism, results from loss of the RNA-binding protein FMRP. Although FMRP is highly expressed in neurons, it has also recently been identified in glia. It has been postulated that in the absence of FMRP, abnormal function of non-neuronal cells may contribute to the pathogenesis of the disorder. We previously demonstrated reduced numbers of oligodendrocyte precursor cells and delayed myelination in the cerebellum of fragile X (Fmr1) knockout mice.

METHODS

We used quantitative western blotting and immunocytochemistry to examine the status of astrocytes and microglia in the cerebellum of Fmr1 mice during development and in adulthood.

RESULTS

We report increased expression of the astrocyte marker GFAP in the cerebellum of Fmr1 mice starting in the second postnatal week and persisting in to adulthood. At 2 weeks postnatal, expression of Tumor Necrosis Factor Receptor 2 (TNFR2) and Leukemia Inhibitory Factor (LIF) were elevated in the Fmr1 KO cerebellum. In adults, expression of TNFR2 and the glial marker S100β were also elevated in Fmr1 knockouts, but LIF expression was not different from wild-type mice. We found no evidence of microglial activation or neuroinflammation at any age examined.

CONCLUSIONS

These findings demonstrate an atypical pattern of astrogliosis in the absence of microglial activation in Fmr1 knockout mouse cerebellum. Enhanced TNFR2 and LIF expression in young mice suggests that changes in the expression of astrocytic proteins may be an attempt to compensate for delayed myelination in the developing cerebellum of Fmr1 mice.

Use of transcranial magnetic stimulation in autism spectrum disorders

The clinical, social and financial burden of autism spectrum disorder (ASD) is staggering. We urgently need valid and reliable biomarkers for diagnosis and effective treatments targeting the often debilitating symptoms. Transcranial magnetic stimulation (TMS) is beginning to be used by a number of centers worldwide and may represent a novel technique with both diagnostic and therapeutic potential. Here we critically review the current scientific evidence for the use of TMS in ASD. Though preliminary data suggests promise, there is simply not enough evidence yet to conclusively support the clinical widespread use of TMS in ASD, neither diagnostically nor therapeutically. Carefully designed and properly controlled clinical trials are warranted to evaluate the true potential of TMS in ASD.

Prevalence of antimitochondrial antibodies in autism spectrum subjects

ABSTRACT 

Objective: Autism is a neurodevelopmental disorder characterized by impairment in verbal and nonverbal communication, repetitive and stereotypic behavior. Dysregulated immune system has a role in the pathogenesis of Autism. This study was designed to measure the prevalence of antimitochondrial (AM) antibodies in a group of autistic children. Methods: AM antibodies subtype 2 (AMA-M2) were evaluated by indirect solid phase enzyme immunoassay in 62 autistic children and 14 age-matched healthy controls. Autistic activity was assessed by using the Childhood Autism Rating Scale. Results: Significantly elevated levels of AMA-M2 were observed in the sera of autistic children (n = 54, 0.221 ± 0.029 IU/ml [mean ± SEM]) compared with healthy controls (n = 14, 0.111 ± 0.010 IU/ml [mean ± SEM], p = 0.0008) and there was no significant difference in patients with moderate to severe autism (p = 0.49). AM antibodies in autistic patients have no correlation with Childhood Autism Rating Scale score. Conclusion: The current study demonstrated significantly high levels of AMA-M2 in autistic subjects when compared with healthy controls. Further large-scale studies are required to dissect any pathogenic role of these antibodies in the development of autism.

Sensitivity of the modified Children’s Yale–Brown Obsessive Compulsive Scale to detect change: Results from two multi-site trials

Repetitive behavior is a core feature of autism spectrum disorder. We used 8-week data from two federally funded, multi-site, randomized trials with risperidone conducted by the Research Units on Pediatric Psychopharmacology Autism Network to evaluate the sensitivity of the Children’s Yale–Brown Obsessive Compulsive Scale modified for autism spectrum disorder to detect change with treatment. Study 1 included 52 subjects assigned to placebo and 49 subjects to risperidone under double-blind conditions. In Study 2, 49 subjects received risperidone only and 75 subjects received risperidone plus parent training. The combined sample consisted of 187 boys and 38 girls (aged 4–17 years). At the medication-free baseline, the internal consistency on the Children’s Yale–Brown Obsessive Compulsive Scale modified for autism spectrum disorder total score was excellent (Cronbach’s alpha = 0.84) and the mean scores were similar across the four groups. Compared to placebo in Study 1, all three active treatment groups showed significant improvement (effect sizes: 0.74–0.88). There were no differences between active treatment groups. These results indicate that the Children’s Yale–Brown Obsessive Compulsive Scale modified for autism spectrum disorder has acceptable test–retest as evidenced by the medium to high correlations in the placebo group and demonstrated sensitivity to change with treatment.

Pharmacogenomic medicine in autism: challenges and opportunities

Autism spectrum disorder (ASD) affects 1 in 68 children in the US and is distinguished by core deficits in social interactions. Developing pharmacologic treatments for ASD is complicated by clinical and genetic heterogeneity. Although pharmacological treatments have not been shown to be effective in treating the core symptoms of ASD (i.e., social deficits), there is evidence that the burden of emotional and behavioral problems can be reduced with pharmacotherapy. Numerous randomized clinical trials of treatments for the core ASD deficits have been conducted; however, most have provided inconclusive results due to the substantial variation in treatment response. Variation also exists in the considerable metabolic side effects of many of the current treatments. Some of this variation may be explained by differences in the underlying genetic pathways. Exploiting the link between genetic heterogeneity and clinical variation associated with behavioral problems may provide an opportunity for targeted treatment of ASD. In this review, we summarize the recent findings from pharmacogenomics studies of ASD and suggest further how understanding how genetic liability modifies the effect of drugs may present an opportunity to address the challenges of personalized medicine in autism.

Reduced phenotypic severity following adeno-associated virus-mediated Fmr1 gene delivery in fragile X mice

Fragile X syndrome (FXS) is a neurodevelopmental disorder caused by a trinucleotide repeat expansion in the FMR1 gene that codes for fragile X mental retardation protein (FMRP). To determine if FMRP expression in the central nervous system could reverse phenotypic deficits in the Fmr1 knockout (KO) mouse model of FXS, we used a single-stranded adeno-associated viral (AAV) vector with viral capsids from serotype 9 that contained a major isoform of FMRP. FMRP transgene expression was driven by the neuron-selective synapsin-1 promoter. The vector was delivered to the brain via a single bilateral intracerebroventricular injection into neonatal Fmr1 KO mice and transgene expression and behavioral assessments were conducted 22-26 or 50-56 days post injection. Western blotting and immunocytochemical analyses of AAV-FMRP-injected mice revealed FMRP expression in the striatum, hippocampus, retrosplenial cortex, and cingulate cortex. Cellular expression was selective for neurons and reached ∼ 50% of wild-type levels in the hippocampus and cortex at 56 days post injection. The pathologically elevated repetitive behavior and the deficit in social dominance behavior seen in phosphate-buffered saline-injected Fmr1 KO mice were reversed in AAV-FMRP-injected mice. These results provide the first proof of principle that gene therapy can correct specific behavioral abnormalities in the mouse model of FXS.

The utility of patient specific induced pluripotent stem cells for the modelling of Autistic Spectrum Disorders

Until now, models of psychiatric diseases have typically been animal models. Whether they were to be used to further understand the pathophysiology of the disorder, or as drug discovery tools, animal models have been the choice of preference in mimicking psychiatric disorders in an experimental setting. While there have been cellular models, they have generally been lacking in validity. This situation is changing with the advent of patient-specific induced pluripotent stem cells (iPSCs). In this article, we give a methodological evaluation of the current state of the iPS technology with reference to our own work in generating patient-specific iPSCs for the study of autistic spectrum disorder (ASD). In addition, we will give a broader perspective on the validity of this technology and to what extent it can be expected to complement animal models of ASD in the coming years.

Disruption of the ASTN2/TRIM32 locus at 9q33.1 is a risk factor in males for autism spectrum disorders, ADHD and other neurodevelopmental phenotypes

Rare copy number variants (CNVs) disrupting ASTN2 or both ASTN2 and TRIM32 have been reported at 9q33.1 by genome-wide studies in a few individuals with neurodevelopmental disorders (NDDs). The vertebrate-specific astrotactins, ASTN2 and its paralog ASTN1, have key roles in glial-guided neuronal migration during brain development. To determine the prevalence of astrotactin mutations and delineate their associated phenotypic spectrum, we screened ASTN2/TRIM32 and ASTN1 (1q25.2) for exonic CNVs in clinical microarray data from 89 985 individuals across 10 sites, including 64 114 NDD subjects. In this clinical dataset, we identified 46 deletions and 12 duplications affecting ASTN2. Deletions of ASTN1 were much rarer. Deletions near the 3' terminus of ASTN2, which would disrupt all transcript isoforms (a subset of these deletions also included TRIM32), were significantly enriched in the NDD subjects (P = 0.002) compared with 44 085 population-based controls. Frequent phenotypes observed in individuals with such deletions include autism spectrum disorder (ASD), attention deficit hyperactivity disorder (ADHD), speech delay, anxiety and obsessive compulsive disorder (OCD). The 3'-terminal ASTN2 deletions were significantly enriched compared with controls in males with NDDs, but not in females. Upon quantifying ASTN2 human brain RNA, we observed shorter isoforms expressed from an alternative transcription start site of recent evolutionary origin near the 3' end. Spatiotemporal expression profiling in the human brain revealed consistently high ASTN1 expression while ASTN2 expression peaked in the early embryonic neocortex and postnatal cerebellar cortex. Our findings shed new light on the role of the astrotactins in psychopathology and their interplay in human neurodevelopment.

Is a subtype of autism an allergy of the brain?

BACKGROUND

Autism spectrum disorders (ASDs) are characterized by deficits in social communication and language and the presence of repetitive behaviors that affect as many as 1 in 50 US children. Perinatal stress and environmental factors appear to play a significant role in increasing the risk for ASDs. There is no definitive pathogenesis, which therefore significantly hinders the development of a cure.

OBJECTIVE

We aimed to identify publications using basic or clinical data that suggest a possible association between atopic symptoms and ASDs, as well as evidence of how such an association could lead to brain disease, that may explain the pathogenesis of ASD.

METHODS

PubMed was searched for articles published since 1995 that reported any association between autism and/or ASDs and any one of the following terms: allergy, atopy, brain, corticotropin-releasing hormone, cytokines, eczema, food allergy, food intolerance, gene mutation, inflammation, mast cells, mitochondria, neurotensin, phenotype, stress, subtype, or treatment.

RESULTS

Children with ASD respond disproportionally to stress and also present with food and skin allergies that involve mast cells. Brain mast cells are found primarily in the hypothalamus, which participates in the regulation of behavior and language. Corticotropin-releasing hormone is secreted from the hypothalamus under stress and, together with neurotensin, stimulates brain mast cells that could result in focal brain allergy and neurotoxicity. Neurotensin is significantly increased in serum of children with ASD and stimulates mast cell secretion of mitochondrial adenosine triphosphate and DNA, which is increased in these children; these mitochondrial components are misconstrued as innate pathogens, triggering an autoallergic response in the brain. Gene mutations associated with higher risk of ASD have been linked to reduction of the phosphatase and tensin homolog, which inhibits the mammalian target of rapamycin (mTOR). These same mutations also lead to mast cell activation and proliferation. Corticotropin-releasing hormone, neurotensin, and environmental toxins could further trigger the already activated mTOR, leading to superstimulation of brain mast cells in those areas responsible for ASD symptoms. Preliminary evidence indicates that the flavonoid luteolin is a stronger inhibitor of mTOR than rapamycin and is a potent mast cell blocker.

CONCLUSION

Activation of brain mast cells by allergic, environmental, immune, neurohormonal, stress, and toxic triggers, especially in those areas associated with behavior and language, lead to focal brain allergies and subsequent focal encephalitis. This possibility is more likely in the subgroup of patients with ASD susceptibility genes that also involve mast cell activation.

Psychopharmacological treatment in children and adolescents with autism spectrum disorders in Germany

Data on psychopharmacological treatment of individuals with autism spectrum disorder (ASD) are scarce, especially for European countries. This study evaluated psychopharmacotherapy utilisation in children and adolescents with a diagnosis of ASD in Germany. Data of a large statutory health insurance company were analysed and outpatients aged 0-24 years with a diagnosis of ASD during a 1-year-period (2009) were identified. For this cohort, the prescription of psychopharmacotherapy was evaluated. Aditionally, we analysed time trends in prescriptions from 2004 to 2009. One thousand one hundred twenty-four patients (75.4% male; mean age: 11.1 years) matched the inclusion criteria. The prevalence of ASD was 0.37% in males and 0.12% in females, respectively. Of all ASD patients, 33.0% were prescribed psychotropic drugs in 2009. 12.5% of ASD patients were treated with stimulants or atomoxetine, 11.7% with antipsychotics, 9.1% with antiepileptics, 6.8% with benzodiazepines, and 3.8% with antidepressants/SSRI. Regarding substances, methylphenidate (24.4% of all psychotropic prescriptions), risperidone (13.3%) and valproate (9.1%) were most frequently prescribed. Psychopharmacologic treatment prevalence was age-related and increased from 16.3% in individuals aged 0-4 years to 55.1% in 20-24 year olds. From 2004 to 2009, the proportion of ASD patients treated with psychotropic drugs rose from 25.9% to 33.0%. This naturalistic study furnishes evidence that the proportion of ASD patients treated with psychotropic drugs has grown considerably in Germany over the least years, with methylphenidate and risperidone being the most frequently prescribed substances. Compared with data from the USA, the proportion of ASD patients with psychopharmacological treatment is noticeably lower in Germany.

Transduction of the central nervous system after intracerebroventricular injection of adeno-associated viral vectors in neonatal and juvenile mice

Several neurodevelopmental and neurodegenerative disorders affecting the central nervous system are potentially treatable via viral vector-mediated gene transfer. Adeno-associated viral (AAV) vectors have been used in clinical trials because of their desirable properties including a high degree of safety, efficacy, and stability. Major factors affecting tropism, expression level, and cell type specificity of AAV-mediated transgenes include encapsidation of different AAV serotypes, promoter selection, and the timing of vector administration. In this study, we evaluated the ability of single-stranded AAV2 vectors pseudotyped with viral capsids from serotype 9 (AAV2/9) to transduce the brain and target gene expression to specific cell types after intracerebroventricular injection into mice. Titer-matched AAV2/9 vectors encoding the enhanced green fluorescent protein (eGFP) reporter, driven by the cytomegalovirus (CMV) promoter, or the neuron-specific synapsin-1 promoter, were injected bilaterally into the lateral ventricles of C57/BL6 mice on postnatal day 5 (neonatal) or 21 (juvenile). Brain sections were analyzed 25 days after injection, using immunocytochemistry and confocal microscopy. eGFP immunohistochemistry after neonatal and juvenile administration of viral vectors revealed transduction throughout the brain including the striatum, hippocampus, cerebral cortex, and cerebellum, but with different patterns of cell-specific gene expression. eGFP expression was seen in astrocytes after treatment on postnatal day 5 with vectors carrying the CMV promoter, expanding the usefulness of AAVs for modeling and treating diseases involving glial cell pathology. In contrast, injection of AAV2/9-CMV-eGFP on postnatal day 21 resulted in preferential transduction of neurons. Administration of AAV2/9-eGFP with the synapsin-1 promoter on either postnatal day 5 or 21 resulted in widespread neuronal transduction. These results outline efficient methods and tools for gene delivery to the nervous system by direct, early postnatal administration of AAV vectors. Our findings highlight the importance of promoter selection and age of administration on the intensity, distribution, and cell type specificity of AAV transduction in the brain.

The BOLD signal and neurovascular coupling in autism

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Neurovascular coupling and energy use may be changed in autism.

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The relationship between neural activity and the BOLD signal may be altered in autism.

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Simply comparing the BOLD signal of control and autistic people may not be meaningful.

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Combined techniques will aid the interpretation of group differences in the BOLD signal.

BOLD (blood oxygen level dependent) fMRI (functional magnetic resonance imaging) is commonly used to study differences in neuronal activity between human populations. As the BOLD response is an indirect measure of neuronal activity, meaningful interpretation of differences in BOLD responses between groups relies upon a stable relationship existing between neuronal activity and the BOLD response across these groups. However, this relationship can be altered by changes in neurovascular coupling or energy consumption, which would lead to problems in identifying differences in neuronal activity. In this review, we focus on fMRI studies of people with autism, and comparisons that are made of their BOLD responses with those of control groups. We examine neurophysiological differences in autism that may alter neurovascular coupling or energy use, discuss recent studies that have used fMRI to identify differences between participants with autism and control participants, and explore experimental approaches that could help attribute between-group differences in BOLD signals to either neuronal or neurovascular factors.

Therapeutic role of hematopoietic stem cells in autism spectrum disorder-related inflammation

Autism and autism spectrum disorders (ASDs) are heterogeneous, severe neuro-developmental disorders with core symptoms of dysfunctions in social interactions and communication skills, restricted interests, repetitive – stereotypic verbal and non-verbal behaviors. Biomolecular evidence points to complex gene-environmental interactions in ASDs. Several biochemical processes are associated with ASDs: oxidative stress (including endoplasmic reticulum stress), decreased methylation capacity, limited production of glutathione; mitochondrial dysfunction, intestinal dysbiosis, increased toxic metal burden, and various immune abnormalities. The known immunological disorders include: T-lymphocyte populations and function, gene expression changes in monocytes, several autoimmune-related findings, high levels of N-acetylgalactosaminidase (which precludes macrophage activation), and primary immune deficiencies. These immunological observations may result in minicolumn structural changes in the brain, as well as, abnormal immune mediation of synaptic functions. Equally, these immune dysregulations serve as the rationale for immune-directed interventions such as hematopoietic stem cells (HSCs), which are pivotal in controlling chronic inflammation and in the restoration of immunological balance. These properties make them intriguing potential agents for ASD treatments. This prospective review will focus on the current state-of-the-art knowledge and challenges intrinsic in the application of HSCs for ASD-related immunological disorders.

Delayed myelination in a mouse model of fragile X syndrome

Fragile X Syndrome is the most common inherited cause of autism. Fragile X mental retardation protein (FMRP), which is absent in fragile X, is an mRNA binding protein that regulates the translation of hundreds of different mRNA transcripts. In the adult brain, FMRP is expressed primarily in the neurons; however, it is also expressed in developing glial cells, where its function is not well understood. Here, we show that fragile X (Fmr1) knockout mice display abnormalities in the myelination of cerebellar axons as early as the first postnatal week, corresponding roughly to the equivalent time in human brain development when symptoms of the syndrome first become apparent (1-3 years of age). At postnatal day (PND) 7, diffusion tensor magnetic resonance imaging showed reduced volume of the Fmr1 cerebellum compared with wild-type mice, concomitant with an 80-85% reduction in the expression of myelin basic protein, fewer myelinated axons and reduced thickness of myelin sheaths, as measured by electron microscopy. Both the expression of the proteoglycan NG2 and the number of PDGFRα+/NG2+ oligodendrocyte precursor cells were reduced in the Fmr1 cerebellum at PND 7. Although myelin proteins were still depressed at PND 15, they regained wild-type levels by PND 30. These findings suggest that impaired maturation or function of oligodendrocyte precursor cells induces delayed myelination in the Fmr1 mouse brain. Our results bolster an emerging recognition that white matter abnormalities in early postnatal brain development represent an underlying neurological deficit in Fragile X syndrome.

Possible use of Trichuris suis ova in autism spectrum disorders therapy

Autism and autism spectrum disorders (ASDs) are heterogeneous, severe neurodevelopmental pathologies. The main core symptoms are: dysfunctions in social interactions and communication skills, restricted interests, repetitive and stereotypic verbal and non-verbal behaviors. Several biochemical processes are associated with ASDs: oxidative stress; endoplasmic reticulum stress; decreased methylation capacity; limited production of glutathione; mitochondrial dysfunction; intestinal dysbiosis; increased toxic metal burden; immune dysregulation. Current available treatments for ASDs can be divided into behavioral, nutritional and medical approaches, although no defined standard approach exists. Current drugs fail to benefit the ASD core symptoms and can have marked adverse effects, are mainly palliative and only sometimes efficacy in attenuating specific autistic behaviors. Helminthic therapy shows potential for application as anti-inflammatory agent. Several human diseases can be treated by helminths (i.e. inflammatory bowel disease, asthma, multiple sclerosis and autoimmune diabetes). Trichuris suis ova (TSO) show strong immunomodulatory properties. Authors hypothesize that TSO could be useful in addressing ASD immune dysregulations. TSO could be a novel therapeutic option for ASD management.

Focal brain inflammation and autism

Increasing evidence indicates that brain inflammation is involved in the pathogenesis of neuropsychiatric diseases. Autism spectrum disorders (ASD) are characterized by social and learning disabilities that affect as many as 1/80 children in the USA. There is still no definitive pathogenesis or reliable biomarkers for ASD, thus significantly curtailing the development of effective therapies. Many children with ASD regress at about age 3 years, often after a specific event such as reaction to vaccination, infection, stress or trauma implying some epigenetic triggers, and may constitute a distinct phenotype. ASD children respond disproportionally to stress and are also affected by food and skin allergies. Corticotropin-releasing hormone (CRH) is secreted under stress and together with neurotensin (NT) stimulates mast cells and microglia resulting in focal brain inflammation and neurotoxicity. NT is significantly increased in serum of ASD children along with mitochondrial DNA (mtDNA). NT stimulates mast cell secretion of mtDNA that is misconstrued as an innate pathogen triggering an auto-inflammatory response. The phosphatase and tensin homolog (PTEN) gene mutation, associated with the higher risk of ASD, which leads to hyper-active mammalian target of rapamycin (mTOR) signalling that is crucial for cellular homeostasis. CRH, NT and environmental triggers could hyperstimulate the already activated mTOR, as well as stimulate mast cell and microglia activation and proliferation. The natural flavonoid luteolin inhibits mTOR, mast cells and microglia and could have a significant benefit in ASD.

What's hAPPening at synapses? The role of amyloid β-protein precursor and β-amyloid in neurological disorders

Accumulating evidence suggests that dysregulated levels of amyloid β-protein precursor (APP) and its catabolites contribute to the impaired synaptic plasticity and seizure incidence observed in several neurological disorders, including Alzheimer's disease, fragile X syndrome, Down's syndrome, autism, epilepsy and Parkinson's disease as well as in brain injury. This review article summarizes what is known regarding the synaptic synthesis, processing and function of APP and amyloid-beta (Aβ), as well as discusses how these proteins could contribute to the altered synaptic plasticity and pathology of the aforementioned disorders. In addition, APP and its proteolytic fragments are emerging as biomarkers for neurological health, and pharmacological interventions that modulate their levels, such as secretase inhibitors, passive immunotherapy against Aβ and mGluR5 antagonists, are reviewed.

Brain functional networks in syndromic and non-syndromic autism: a graph theoretical study of EEG connectivity

BACKGROUND

Graph theory has been recently introduced to characterize complex brain networks, making it highly suitable to investigate altered connectivity in neurologic disorders. A current model proposes autism spectrum disorder (ASD) as a developmental disconnection syndrome, supported by converging evidence in both non-syndromic and syndromic ASD. However, the effects of abnormal connectivity on network properties have not been well studied, particularly in syndromic ASD. To close this gap, brain functional networks of electroencephalographic (EEG) connectivity were studied through graph measures in patients with Tuberous Sclerosis Complex (TSC), a disorder with a high prevalence of ASD, as well as in patients with non-syndromic ASD.

METHODS

EEG data were collected from TSC patients with ASD (n = 14) and without ASD (n = 29), from patients with non-syndromic ASD (n = 16), and from controls (n = 46). First, EEG connectivity was characterized by the mean coherence, the ratio of inter- over intra-hemispheric coherence and the ratio of long- over short-range coherence. Next, graph measures of the functional networks were computed and a resilience analysis was conducted. To distinguish effects related to ASD from those related to TSC, a two-way analysis of covariance (ANCOVA) was applied, using age as a covariate.

RESULTS

Analysis of network properties revealed differences specific to TSC and ASD, and these differences were very consistent across subgroups. In TSC, both with and without a concurrent diagnosis of ASD, mean coherence, global efficiency, and clustering coefficient were decreased and the average path length was increased. These findings indicate an altered network topology. In ASD, both with and without a concurrent diagnosis of TSC, decreased long- over short-range coherence and markedly increased network resilience were found.

CONCLUSIONS

The altered network topology in TSC represents a functional correlate of structural abnormalities and may play a role in the pathogenesis of neurological deficits. The increased resilience in ASD may reflect an excessively degenerate network with local overconnection and decreased functional specialization. This joint study of TSC and ASD networks provides a unique window to common neurobiological mechanisms in autism.

Novel treatments in autism spectrum disorders: from synaptic dysfunction to experimental therapeutics

Recent discoveries and advances in genetics and neuroscience have provided deeper understanding of the complex neurobiology of ASD. The development of novel treatments is strictly dependent on these findings in order to design new strategies in the pharmacotherapy of ASD. At this time, therapeutics are limited to treating associated core, symptoms. Studies of single gene disorders, such as Phelan-McDermid syndrome, Fragile X and Tuberous Sclerosis, might be of significant help since the neurobiology of these disorders is clearer and clinical trials are already underway for these conditions. The pathogenesis paradigm shift of ASD towards synaptic abnormalities has led to current research of the pathways to disease, which involves multiple dynamic systems. Interest in oxytocin is growing as it has been recognized to be implicated in social development and affiliative behaviours. In the future, progress is expected in possible new options for therapeutics in ASD. Children and adolescents with ASD and their families can provide vital information about their experiences with new treatments, which should be a priority for future research.

mGluR antagonists and GABA agonists as novel pharmacological agents for the treatment of autism spectrum disorders

INTRODUCTION

The CDC currently estimates the prevalence of autism spectrum disorders (ASD) at 1 in 88 children. Though the exact etiology of ASD is unknown, recent studies implicate synaptic maturation and plasticity in the pathogenesis of ASD leading to an imbalance of excitation and inhibition, and specifically a disproportionately high level of excitation. Pharmacological agents that modulate excitation and inhibition are currently in clinical trials for treatment of ASD and show promising preliminary results.

AREAS COVERED

This paper reviews the literature implicating the role of glutamate and GABA pathways in the pathophysiology of ASD. It also provides a review of the current results from both animal models and human clinical trials of drugs aimed at normalizing the imbalance of excitation and inhibition through the use of metabotropic glutamate receptor (mGluR) antagonists and GABA agonists.

EXPERT OPINION

Both mGluR antagonists and GABA agonists have promising preliminary data from animal model and small-scale Phase II human trials. They show significant efficacy in subpopulations and appear to have favorable side-effect profiles. Though preliminary data are extremely promising, results from ongoing larger, double-blind, placebo-controlled studies will give a more complete understanding of the efficacy and side-effect profile related to these drugs.