Synaptic Dysfunction in Neurodevelopmental Disorders Associated with Autism and Intellectual Disabilities

The discovery of the genetic causes of syndromic autism spectrum disorders and intellectual disabilities has greatly informed our understanding of the molecular pathways critical for normal synaptic function. The top-down approaches using human phenotypes and genetics helped identify causative genes and uncovered the broad spectrum of neuropsychiatric features that can result from various mutations in the same gene. Importantly, the human studies unveiled the exquisite sensitivity of cognitive function to precise levels of many diverse proteins. Bottom-up approaches applying molecular, biochemical, and neurophysiological studies to genetic models of these disorders revealed unsuspected pathogenic mechanisms and identified potential therapeutic targets. Moreover, studies in model organisms showed that symptoms of these devastating disorders can be reversed, which brings hope that affected individuals might benefit from interventions even after symptoms set in. Scientists predict that insights gained from studying these rare syndromic disorders will have an impact on the more common nonsyndromic autism and mild cognitive deficits.It is estimated that ∼1% of the human population has an autism spectrum disorder (ASD). ASD has widely varied behavioral manifestations, severity, and comorbid conditions (hence the term “spectrum”), but those diagnosed with autism are characterized by impaired communication and reciprocal social interactions, and restricted and repetitive patterns of activities and interests (Baird et al. 2006). Approximately 70% of those diagnosed with autism also have intellectual disability (ID), and 25% have a seizure disorder (Tuchman and Rapin 2002). There is a strong genetic basis for autism, but the risk architecture is highly heterogeneous, and a large number of genes have been implicated (Abrahams and Geschwind 2008). This daunting phenotypic and etiologic complexity, shared by other major psychiatric illnesses, has slowed progress toward developing new therapies.However, autism researchers are optimistic that the possibility of substantial progress may soon be realized (Krueger and Bear 2011). First, the genes have been discovered for numerous syndromic disorders that prominently feature ASD and ID. Second, these gene mutations have been reproduced in animal models that allow detailed examination of the underlying brain pathophysiology. Third, animal research has converged on altered synaptic function as a likely basis for impaired cognition and possibly ASD. Fourth, insights gained on how synapses function differently in the face of these mutations have suggested novel therapeutic interventions validated in preclinical models and that have shown promise in preliminary human clinical trials. Fifth, the fact that ASD and ID can be diagnosed in early childhood maximizes potential benefits of therapy because it can be started at a time when the brain is most plastic. Finally, animal studies using gene reactivation or pharmacological interventions suggest that substantial improvements can be seen even when treatments begin in adulthood (Ehninger et al. 2008b). Thus, a genetic diagnosis of a developmental brain disorder need not be a “life sentence” of permanent and inexorable mental disability.The path from gene discovery to novel treatment is outlined in Figure 1. This process often begins with astute clinical observations that some patients can be distinguished by a common set of phenotypic traits, thus defining a syndrome. Molecular genetic studies can then be undertaken to test the hypothesis that the syndrome has a genetic cause. In the event that disruption of a single gene or DNA segment causes the disease (i.e., a “highly penetrant” mutation), then it is possible to create an animal model (usually a mouse) that carries the same genetic disruption. Although the effects of the genetic lesion will likely manifest differently at the behavioral level in animals and humans because of differences in the complexity of the brains, it is reasonable to postulate that disruptions in elementary neuronal functions are likely to be shared. Understanding this neuronal pathophysiology is critical for identifying potential therapeutic targets. If these targets can be validated in the animal models, then chemistry ensues to generate molecules that can engage the target and satisfy the pharmacodynamic and pharmacokinetic drug requirements. If they are shown to be safe, drug candidates may then advance to human clinical trials. There are currently clinical trials ongoing in several single-gene syndromic disorders associated with ASD and ID. Most of these target alterations in synaptic signaling.Open in a separate windowFigure 1.The promise of molecular medicine in genetically defined disorders of brain development.The notion that some ASD and associated ID represent “synapsopathies” (or “synaptopathies”) is supported by the preponderance of penetrant mutations in genes associated with synaptic structure and function. The most common single-gene mutations in ASD with ID are associated with fragile X syndrome (FMR1), tuberous sclerosis (TSC1, TSC2), neurofibromatosis (NF1), Angelman syndrome (UBE3A), Rett syndrome (MECP2), the PTEN hamartoma tumor syndrome, and Phelan-McDermid syndrome (SHANK3) (for review, see Betancur 2011). Rare mutations in the neuroligin (NLGN3, NLGN2) and neurexin (NRXN1) genes also cause autism (Jamain et al. 2003). Although this is by no means an exhaustive list of genes implicated in autism (and many await discovery), it is notable nonetheless that these highly penetrant mutations occur in genes that are critical regulators of synaptic function, and further, illuminate biochemical pathways that might be pathogenic in ASD and ID (Fig. 2).Open in a separate windowFigure 2.(A) Schematic of a neuron and axonal-dendritic synapse that depict examples of cellular localization of the various types of defects in ASD/ID. (B) A signaling pathway at the excitatory synapses that couples activity as registered by the release of glutamate to local control of protein synthesis. Disruption of the gene products indicated in the colored boxes greatly increases the risk of ASD/ID. Syndromic disorders with increased prevalence of ASD include Phelan-McDermid Syndrome (SHANK3); Noonan syndrome (RAF1, MEK1); Neurofibromatosis type 1 (NF1); Costello syndrome (H-Ras, MEK1); Cowden syndrome (PTEN); Cardio-facio-cutaneous (CFC) syndrome (MEK1/2); Tuberous sclerosis complex (TSC1/2); Fragile X syndrome (FMRP); Angelman syndrome (AS UBE3a); Rett syndrome (RTT–MeCP2); and Rubinstein-Taybi syndrome (RTS–CREB binding protein, p300). Rare, nonsyndromic ASDs include NLGN3/4 and NRXN1; ID/ASD: SHANK2.In this article, we focus on a few syndromic disorders associated with ASD and ID that are characterized by penetrant mutations in genes that have been shown in animal models to disrupt synaptic function. Our goal is to highlight the similarities and differences in these syndromes and their underlying synaptic pathophysiology. Optimal synaptic function occurs within a narrow dynamic range along many dimensions, and it is not surprising that pathophysiology occurs at the edges of these spectra. What has come as a surprise, however, is that ASD and ID appear to be common consequences of disruptive mutations that cause synaptic pathophysiology at both ends of a spectrum. In other words, both “gain-of-function” and “loss-of-function” mutations can manifest in similar ways. Insights into the pathophysiology of ASD and ID have raised the possibility of therapeutic interventions to bring synapses into a normal operating range.     

Epigenomic-basis of Preemptive Medicine for Neurodevelopmental Disorders

Neurodevelopmental disorders (NDs) are currently thought to be caused by either genetic defects or various environmental factors. Recent studies have demonstrated that congenital NDs can result not only from changes in DNA sequence in neuronal genes but also from changes to the secondary epigenomic modifications of DNA and histone proteins. Thus, epigenomic assays, as well as genomic assays, are currently performed for diagnosis of the congenital NDs. It is recently known that the epigenomic modifications can be altered by various environmental factors, which potentially cause acquired NDs. Furthermore these alterations can potentially be restored taking advantage of use of reversibility in epigenomics. Therefore, epigenome-based early diagnosis and subsequent intervention, by using drugs that restore epigenomic alterations, will open up a new era of preemptive medicine for congenital and acquired NDs.     

Molecular Convergence of Neurodevelopmental Disorders

Neurodevelopmental disorders (NDDs) are caused by mutations in diverse genes involved in different cellular functions, although there can be crosstalk, or convergence, between molecular pathways affected by different NDDs. To assess molecular convergence, we generated human neural progenitor cell models of 9q34 deletion syndrome, caused by haploinsufficiency of EHMT1, and 18q21 deletion syndrome, caused by haploinsufficiency of TCF4. Using next-generation RNA sequencing, methylation sequencing, chromatin immunoprecipitation sequencing, and whole-genome miRNA analysis, we identified several levels of convergence. We found mRNA and miRNA expression patterns that were more characteristic of differentiating cells than of proliferating cells, and we identified CpG clusters that had similar methylation states in both models of reduced gene dosage. There was significant overlap of gene targets of TCF4 and EHMT1, whereby 8.3% of TCF4 gene targets and 4.2% of EHMT1 gene targets were identical. These data suggest that 18q21 and 9q34 deletion syndromes show significant molecular convergence but distinct expression and methylation profiles. Common intersection points might highlight the most salient features of disease and provide avenues for similar treatments for NDDs caused by different genetic mutations.     

Genetic and Environmental Factors in Complex Neurodevelopmental Disorders

Complex neurodevelopmental disorders, such as schizophrenia, autism, attention deficit (hyperactivity) disorder, (manic) depressive illness and addiction, are thought to result from an interaction between genetic and environmental factors. Association studies on candidate genes and genome-wide linkage analyses have identified many susceptibility chromosomal regions and genes, but considerable efforts to replicate association have been surprisingly often disappointing. Here, we summarize the current knowledge of the genetic contribution to complex neurodevelopmental disorders, focusing on the findings from association and linkage studies. Furthermore, the contribution of the interaction of the genetic with environmental and epigenetic factors to the aetiology of complex neurodevelopmental disorders as well as suggestions for future research are discussed.Key Words: Neurodevelopmental disorders, susceptibility genes, environmental factors, gene-environment interactions, association studies, linkage analysis.     

Is EEG-biofeedback an Effective Treatment in Autism Spectrum Disorders? A Randomized Controlled Trial

EEG-biofeedback has been reported to reduce symptoms of autism spectrum disorders (ASD) in several studies. However, these studies did not control for nonspecific effects of EEG-biofeedback and did not distinguish between participants who succeeded in influencing their own EEG activity and participants who did not. To overcome these methodological shortcomings, this study evaluated the effects of EEG-biofeedback in ASD in a randomized pretest–posttest control group design with blinded active comparator and six months follow-up. Thirty-eight participants were randomly allocated to the EEG-biofeedback, skin conductance (SC)-biofeedback or waiting list group. EEG- and SC-biofeedback sessions were similar and participants were blinded to the type of feedback they received. Assessments pre-treatment, post-treatment, and after 6 months included parent ratings of symptoms of ASD, executive function tasks, and 19-channel EEG recordings. Fifty-four percent of the participants significantly reduced delta and/or theta power during EEG-biofeedback sessions and were identified as EEG-regulators. In these EEG-regulators, no statistically significant reductions of symptoms of ASD were observed, but they showed significant improvement in cognitive flexibility as compared to participants who managed to regulate SC. EEG-biofeedback seems to be an applicable tool to regulate EEG activity and has specific effects on cognitive flexibility, but it did not result in significant reductions in symptoms of ASD. An important finding was that no nonspecific effects of EEG-biofeedback were demonstrated.     

HERVs Expression in Autism Spectrum Disorders

Background

Autistic Spectrum Disorder (ASD) is a heterogeneous neurodevelopmental disorder, resulting from complex interactions among genetic, genomic and environmental factors. Here we have studied the expression of Human Endogenous Retroviruses (HERVs), non-coding DNA elements with potential regulatory functions, and have tested their possible implication in autism.

Methods

The presence of retroviral mRNAs from four HERV families (E, H, K and W), widely implicated in complex diseases, was evaluated in peripheral blood mononuclear cells (PBMCs) from ASD patients and healthy controls (HCs) by qualitative RT-PCR. We also analyzed the expression of the env sequence from HERV-H, HERV-W and HERV-K families in PBMCs at the time of sampling and after stimulation in culture, in both ASD and HC groups, by quantitative Real-time PCR. Differences between groups were evaluated using statistical methods.

Results

The percentage of HERV-H and HERV-W positive samples was higher among ASD patients compared to HCs, while HERV-K was similarly represented and HERV-E virtually absent in both groups. The quantitative evaluation shows that HERV-H and HERV-W are differentially expressed in the two groups, with HERV-H being more abundantly expressed and, conversely, HERV-W, having lower abundance, in PBMCs from ASDs compared to healthy controls. PMBCs from ASDs also showed an increased potential to up-regulate HERV-H expression upon stimulation in culture, unlike HCs. Furthermore we report a negative correlation between expression levels of HERV-H and age among ASD patients and a statistically significant higher expression in ASD patients with Severe score in Communication and Motor Psychoeducational Profile-3.

Conclusions

Specific HERV families have a distinctive expression profile in ASD patients compared to HCs. We propose that HERV-H expression be explored in larger samples of individuals with autism spectrum in order to determine its utility as a novel biological trait of this complex disorder.     

The Cost of Autism Spectrum Disorders

Objective

A diagnosis of an autism spectrum disorders is usually associated with substantial lifetime costs to an individual, their family and the community. However, there remains an elusive factor in any cost-benefit analysis of ASD diagnosis, namely the cost of not obtaining a diagnosis. Given the infeasibility of estimating the costs of a population that, by its nature, is inaccessible, the current study compares expenses between families whose children received a formal ASD diagnosis immediately upon suspecting developmental atypicality and seeking advice, with families that experienced a delay between first suspicion and formal diagnosis.

Design

A register based questionnaire study covering all families with a child with ASD in Western Australia.

Participants

Families with one or more children diagnosed with an ASD, totalling 521 children diagnosed with an ASD; 317 records were able to be included in the final analysis.

Results

The median family cost of ASD was estimated to be AUD $34,900 per annum with almost 90% of the sum ($29,200) due to loss of income from employment. For each additional symptom reported, approximately $1,400 cost for the family per annum was added. While there was little direct influence on costs associated with a delay in the diagnosis, the delay was associated with a modest increase in the number of ASD symptoms, indirectly impacting the cost of ASD.

Conclusions

A delay in diagnosis was associated with an indirect increased financial burden to families. Early and appropriate access to early intervention is known to improve a child''s long-term outcomes and reduce lifetime costs to the individual, family and society. Consequently, a per symptom dollar value may assist in allocation of individualised funding amounts for interventions rather than a nominal amount allocated to all children below a certain age, regardless of symptom presentation, as is the case in Western Australia.     

神经元增殖与孤独症谱系障碍大脑过度生长

在患儿发育早期,某一亚类孤独症谱系障碍（autism spectrum disorders, ASDs）大脑呈过度生长趋势。研究发现,部分伴随有大脑过度增生的患者局部脑区神经元数目异常增多。进一步研究表明,神经元的增殖紊乱与局部脑区神经元数目异常增多密切相关。本综述从ASDs相关信号分子对神经元增殖的调控入手,归纳总结近年来基于神经元增殖调控异常的ASDs大脑过度增生的分子机制研究,为探究ASDs的发病机制提供一个重要的突破口。     

Animal-assisted Social Skills Training for Children with Autism Spectrum Disorders

Recent research indicates that youth with autism spectrum disorder (ASD) show increases in prosocial behaviors in the presence of animals, yet few studies have examined the effects of incorporating animals into treatments. The current study evaluated the effectiveness of an animal-assisted social skills training group for youth with ASD. It was hypothesized that incorporating dogs into social skills training (SST) would produce a greater effect on improving social skills, theory of mind, and feelings of inclusion than would be obtained from SST without an animal present. We compared social skills groups with therapy dogs to traditional social skills groups without an animal present. Students with ASD attending school at a therapeutic treatment facility (n = 31; ages 8–14) were assigned to either experimental or control groups, which were both provided with 12 weeks of weekly treatment. Following participation in SST, participants in the groups with dogs were rated as significantly less symptomatic than participants in the traditional social skills group on the Social Responsiveness Scale (SRS-2), a teacher-rated measure of autism-related symptoms. Based on self-report ratings using the Children’s Depression Inventory (CDI-2), participants in the groups with dogs experienced significantly greater reductions in symptoms measured by the Interpersonal Problems and Functional Problems subscales, and not on the other subscales of the CDI-2. Both groups showed improvement in theory of mind and decreased feelings of isolation and overall depressive symptoms; however, the effect of group on change over time was not significant. On the Social Language Development Test (SLDT), no significant differences were observed. The current findings indicate animal-assisted social skills training may be more beneficial for improving social skills and reducing related affective symptoms than traditional training models.     

Analysis of Hair Trace Elements in Children with Autism Spectrum Disorders and Communication Disorders

The primary objective of the present study is analysis of hair trace elements content in children with communication disorder (CD) and autism spectrum disorder (ASD). A total of 99 children from control, CD, and ASD groups (n = 33) were examined. All children were additionally divided into two subgroups according to age. Hair levels of trace elements were assessed using inductively coupled plasma mass spectrometry. The difference was considered significant at p < 0.01. The obtained data demonstrate that children with CD are characterized by significantly increased hair lithium (Li) (96 %; p = 0.008), selenium (Se) (66 %; p < 0.001), arsenic (As) (96 %; p = 0.005), beryllium (Be) (150 %; p < 0.001), and cadmium (Cd) (72 %; p = 0.007) content, being higher than the respective control values. In the ASD group, hair copper (Cu), iodine (I), and Be levels tended to be lower than the control values. In turn, the scalp hair content of Se significantly exceeded the control values (33 %; p = 0.004), whereas the level of iron (Fe) and aluminum (Al) tended to increase. After gradation for age, the most prominent differences in children with CD were detected in the elder group (5–8 years), whereas in the case of ASD—in the younger group (3–4 years old). Taking into account the role of hair as excretory mechanism for certain elements including the toxic ones, it can be proposed that children suffering from ASD are characterized by more profound alteration of metal handling and excretion in comparison to CD.     

Screening for Autism Spectrum Disorders with the Brief Infant-Toddler Social and Emotional Assessment

Objective

Using parent-completed questionnaires in (preventive) child health care can facilitate the early detection of psychosocial problems and psychopathology, including autism spectrum disorders (ASD). A promising questionnaire for this purpose is the Brief Infant-Toddler Social and Emotional Assessment (BITSEA). The screening accuracy with regard to ASD of the BITSEA Problem and Competence scales and a newly calculated Autism score were evaluated.

Method

Data, that was collected between April 2010 and April 2011, from a community sample of 2-year-olds (N = 3127), was combined with a sample of preschool children diagnosed with ASD (N = 159). For the total population and for subgroups by child''s gender, area under the Receiver Operating Characteristic (ROC) curve was examined, and across a range of BITSEA Problem, Competence and Autism scores, sensitivity, specificity, positive and negative likelihood ratio''s, diagnostic odds ratio and Youden''s index were reported.

Results

The area under the ROC curve (95% confidence interval, [95%CI]) of the Problem scale was 0.90(0.87–0.92), of the Competence scale 0.93(0.91–0.95), and of the Autism score 0.95(0.93–0.97). For the total population, the screening accuracy of the Autism score was significantly better, compared to the Problem scale. The screening accuracy of the Competence scale was significantly better for girls (AUC = 0.97; 95%CI = 0.95–0.98) than for boys (AUC = 0.91; 95%CI = 0.88–0.94).

Conclusion

The results indicate that the BITSEA scales and newly calculated Autism score have good discriminative power to differentiate children with and without ASD. Therefore, the BITSEA may be helpful in the early detection of ASD, which could have beneficial effects on the child''s development.