Genomic and epigenetic evidence for oxytocin receptor deficiency in autism

Intranasal oxytocin in the treatment of autism spectrum disorders: a review of literature and early safety and efficacy data in youth

BACKGROUND

There is a paucity of treatments targeting core symptom domains in Autism Spectrum Disorder (ASD). Several animal models and research in typically developing volunteers suggests that manipulation of the oxytocin system may have therapeutic potential for the treatment of social deficits. We review the literature for oxytocin and ASD and report on early dosing, safety and efficacy data of multi-dose oxytocin on aspects of social cognition/function, as well as repetitive behaviors and co-occurring anxiety within ASD.

METHODS

Fifteen children and adolescents with verbal IQs≥70 were diagnosed with ASD using the ADOS and the ADI-R. They participated in a modified maximum tolerated dose study of intranasal oxytocin (Syntocinon). Data were modeled using repeated measures regression analysis controlling for week, dose, age, and sex.

RESULTS

Among 4 doses tested, the highest dose evaluated, 0.4 IU/kg/dose, was found to be well tolerated. No serious or severe adverse events were reported and adverse events reported/observed were mild to moderate. Over 12 weeks of treatment, several measures of social cognition/function, repetitive behaviors and anxiety showed sensitivity to change with some measures suggesting maintenance of effect 3 months past discontinuation of intranasal oxytocin.

CONCLUSIONS

This pilot study suggests that daily administration of intranasal oxytocin at 0.4 IU/kg/dose in children and adolescents with ASD is safe and has therapeutic potential. Larger studies are warranted. This article is part of a Special Issue entitled Oxytocin and Social Behav.

Schizophrenia and alcohol dependence: diverse clinical effects of oxytocin and their evolutionary origins

Beginning in 1979 with the first report that central administration of oxytocin stimulates maternal behavior in virgin rats, decades of animal research and more recent human studies have demonstrated that oxytocin has many pro-social effects. These many findings suggest that oxytocin may be an effective treatment for social deficits that are hallmark features of disorders such as autism and schizophrenia. Effects in preclinical animal models also imply that oxytocin may be an efficacious pharmacotherapy in a wide range of psychiatric disorders including psychoses and addictions. To date, 3 small clinical trials found that daily intranasal oxytocin treatment for 2-8 weeks significantly reduced psychotic symptoms in schizophrenia. Two of these trials also found improvement in social cognition or neurocognition, areas in which patients have significant deficiencies that do not respond to conventional antipsychotic treatment and contribute to disability. In another small trial, intranasal oxytocin potently blocked alcohol withdrawal. After reviewing the rationale for these trials, they are described in more detail. Questions are then asked followed by discussions of the large gaps in our knowledge about brain oxytocin systems in humans. The hope is to highlight important directions for future investigations of the role of oxytocin in the pathophysiology of psychotic disorders and addictions and to extend clinical research in these areas. Heretofore unrecognized roles for which oxytocin may have been selected during the evolution of placental mammalian maternal-infant and other social attachments are considered as possible origins of oxytocin antipsychotic and antiaddiction effects.This article is part of a Special Issue entitled Oxytocin and Social Behav.

Glutamatergic candidate genes in autism spectrum disorder: an overview

Autism spectrum disorders (ASD) are neurodevelopmental disorders with early onset in childhood. Most of the risk for ASD can be explained by genetic variants that act in interaction with biological environmental risk factors. However, the architecture of the genetic components is still unclear. Genetic studies and subsequent systems biological approaches described converging functional effects of identified genes towards pathways relevant for neuronal signalling. Mouse models suggest an aberrant synaptic plasticity at the neuropathological level, which is believed to be conferred by dysregulation of long-term potentiation or depression of neuronal connections. A central pathway regulating these mechanisms is glutamatergic signalling. Here, we hypothesized that susceptibility genes for ASD are enriched for components of this pathway. To further understand the impact of ASD risk genes on the glutamatergic pathway, we performed a systematic review using the literature database "pubmed" and the "AutismKB" knowledgebase. We provide an overview of the glutamatergic system in typical brain function and development, and summarize findings from linkage, association, copy number variants, and sequencing studies in ASD to provide a comprehensive picture of the glutamatergic landscape of ASD genetics. Genetic variants associated with ASD were enriched in glutamatergic pathways, affecting receptor signalling, metabolism and transport. Furthermore, in genetically modified mouse models for ASD, pharmacological compounds acting on ionotropic or metabotropic receptor activity are able to rescue ASD reminscent phenotypes. We conclude that glutamatergic genetic risk factors for ASD show a complex pattern and further studies are needed to fully understand its mechanisms, before translation of findings into clinical applications and individualized treatment approaches will be possible.

Evidence for alterations in stimulatory G proteins and oxytocin levels in children with autism

The neurotransmitter oxytocin plays an important role in social affiliation. Low oxytocin levels and defects in the oxytocin receptor have been reported in childhood autism. However, little is known about oxytocin's post-receptor signaling pathways in autism. Oxytocin signals via stimulatory and inhibitory G proteins. c-fos mRNA expression has been used as a marker of OT signaling as well as of G protein signaling. Herein, we hypothesized that oxytocin and its signaling pathways would be altered in children with autism. We measured plasma oxytocin levels by ELISA, G-protein and c-fos mRNA by PCR, and G proteins by immunoblot in cultured peripheral blood mononuclear cells (PBMCs) in children with autism and in age-matched controls. Males with autism displayed elevated oxytocin levels compared to controls (p<0.05). Children with autism displayed significantly higher mRNA for stimulatory G proteins compared to controls (p<0.05). Oxytocin levels correlated strongly positively with c-fos mRNA levels, but only in control participants (p<0.01). Oxytocin, G-protein, and c-fos mRNA levels correlated inversely with measures of social and emotional behaviors, but only in control participants. These data suggest that children with autism may exhibit a dysregulation in oxytocin and/or its signaling pathways.

Novel region discovery method for Infinium 450K DNA methylation data reveals changes associated with aging in muscle and neuronal pathways

We describe a methodology for detecting differentially methylated regions (DMRs) and variably methylated regions (VMRs), in data from Infinium 450K arrays that are very widely used in epigenetic studies. Region detection is more specific than single CpG analysis as it increases the extent of common findings between studies, and is more powerful as it reduces the multiple testing problem inherent in epigenetic whole-genome association studies (EWAS). In addition, results driven by single erroneous probes are removed. We have used multiple publicly available Infinium 450K data sets to generate a consensus list of DMRs for age, supporting the hypothesis that aging is associated with specific epigenetic modifications. The consensus aging DMRs are significantly enriched for muscle biogenesis pathways. We find a massive increase in VMRs with age and in regions of the genome associated with open chromatin and neurotransmission. Old age VMRs are significantly enriched for neurotransmission pathways. EWAS studies should investigate the role of this interindividual variation in DNA methylation, in the age-associated diseases of sarcopenia and dementia.

Social Communication is an Emerging Target for Pharmacotherapy in Autism Spectrum Disorder - A Review of the Literature on Potential Agents

OBJECTIVE

To review the published literature and registered clinical trials on pharmacologic interventions targeting social communication impairment in Autism Spectrum Disorder (ASD).

METHODS

A comprehensive search of several databases (PubMed, MEDLINE, PsycINFO, Clinical trials.gov) was conducted to identify pharmacologic agents that have been, or will be, tested as treatments for social communication impairment in individuals with ASD. Evidence from basic science research supporting rational drug discovery is surveyed.

RESULTS

Data from animal models and early clinical trials suggest that novel and existing compounds, including N-methyl-D-aspartate (NMDA) modulators, γ-aminobutyric acid (GABA) agonists, metabotropic glutamate receptor (mGluR) antagonists and neuropeptides, may enhance social communication/function in ASD. Results from numerous Phase 2 and Phase 3 clinical trials are expected in the near future.

CONCLUSIONS

Recent evidence suggests that social communication may be an appropriate target for pharmacologic manipulation. It is hoped that, in combination with behavioural interventions, novel therapeutics may soon be clinically available to help improve social outcomes.

Association between the oxytocin receptor (OXTR) gene and mesolimbic responses to rewards

BACKGROUND

There has been significant progress in identifying genes that confer risk for autism spectrum disorders (ASDs). However, the heterogeneity of symptom presentation in ASDs impedes the detection of ASD risk genes. One approach to understanding genetic influences on ASD symptom expression is to evaluate relations between variants of ASD candidate genes and neural endophenotypes in unaffected samples. Allelic variations in the oxytocin receptor (OXTR) gene confer small but significant risk for ASDs for which the underlying mechanisms may involve associations between variability in oxytocin signaling pathways and neural response to rewards. The purpose of this preliminary study was to investigate the influence of allelic variability in the OXTR gene on neural responses to monetary rewards in healthy adults using functional magnetic resonance imaging (fMRI).

METHODS

The moderating effects of three single nucleotide polymorphisms (SNPs) (rs1042778, rs2268493 and rs237887) of the OXTR gene on mesolimbic responses to rewards were evaluated using a monetary incentive delay fMRI task.

RESULTS

T homozygotes of the rs2268493 SNP demonstrated relatively decreased activation in mesolimbic reward circuitry (including the nucleus accumbens, amygdala, insula, thalamus and prefrontal cortical regions) during the anticipation of rewards but not during the outcome phase of the task. Allelic variation of the rs1042778 and rs237887 SNPs did not moderate mesolimbic activation during either reward anticipation or outcomes.

CONCLUSIONS

This preliminary study suggests that the OXTR SNP rs2268493, which has been previously identified as an ASD risk gene, moderates mesolimbic responses during reward anticipation. Given previous findings of decreased mesolimbic activation during reward anticipation in ASD, the present results suggest that OXTR may confer ASD risk via influences on the neural systems that support reward anticipation.

Biomarkers in autism

Autism spectrum disorders (ASDs) are complex, heterogeneous disorders caused by an interaction between genetic vulnerability and environmental factors. In an effort to better target the underlying roots of ASD for diagnosis and treatment, efforts to identify reliable biomarkers in genetics, neuroimaging, gene expression, and measures of the body's metabolism are growing. For this article, we review the published studies of potential biomarkers in autism and conclude that while there is increasing promise of finding biomarkers that can help us target treatment, there are none with enough evidence to support routine clinical use unless medical illness is suspected. Promising biomarkers include those for mitochondrial function, oxidative stress, and immune function. Genetic clusters are also suggesting the potential for useful biomarkers.

Beyond labor: the role of natural and synthetic oxytocin in the transition to motherhood

Emerging research raises questions that synthetic oxytocin during childbirth may alter the endogenous oxytocin system and influence maternal stress, mood, and behavior. Endogenous oxytocin is a key component in the transition to motherhood, affecting molecular pathways that buffer stress reactivity, support positive mood, and regulate healthy mothering behaviors (including lactation). Synthetic oxytocin is widely used throughout labor and postpartum care in modern birth. Yet research on the implications beyond labor of maternal exposure to perinatal synthetic oxytocin is rare. In this article, we review oxytocin-related biologic pathways and behaviors associated with the transition to motherhood and evidence supporting the need for further research on potential effects of intrapartum oxytocin beyond labor. We include a primer on oxytocin at the molecular level.

Brain region-specific methylation in the promoter of the murine oxytocin receptor gene is involved in its expression regulation

Oxytocin is a nine amino acid neuropeptide that is known to play a critical role in fetal expulsion and breast-feeding, and has been recently implicated in mammalian social behavior. The actions of both central and peripheral oxytocin are mediated through the oxytocin receptor (Oxtr), which is encoded by a single gene. In contrast to the highly conserved expression of oxytocin in specific hypothalamic nuclei, the expression of its receptor in the brain is highly diverse among different mammalian species or even within individuals of the same species. The diversity in the pattern of brain Oxtr expression among mammals is thought to contribute to the broad range of social systems and organizations. Yet, the mechanisms underlying this diversity are poorly understood. DNA methylation is a major epigenetic mechanism that regulates gene transcription, and has been linked to reduced expression levels of the Oxtr in individuals with autism. Here we hypothesize that DNA methylation is involved in the expression regulation of Oxtr in the mouse brain. By combining bisulfite DNA conversion and Next-Generation Sequencing we found that specific CpG sites are differentially methylated between distinct brain regions expressing different levels of Oxtr mRNA. Some of these CpG sites are located within putative binding sites of transcription factors known to regulate Oxtr expression, including estrogen receptor α (ERα) and SP1. Specifically, methylation of the SP1 site was found to positively correlate with Oxtr expression. Furthermore, we revealed that the methylation levels of these sites in the various brain regions predict the relationship between ERα and Oxtr mRNA levels. Collectively, our results suggest that brain region-specific expression of the mouse Oxtr gene is epigenetically regulated by DNA methylation of its promoter.

The role of maternal care in shaping CNS function

Maternal care involves the consistent and coordinated expression of a variety of behaviours over an extended period of time, and adverse changes in maternal care can have profound impacts on the CNS and behaviour of offspring. This complex behavioural pattern depends on a number of integrated neuroendocrine mechanisms. This review will discuss the use of animal models in the study of the role of maternal care in shaping CNS function, the contributions of corticosteroid releasing hormone, vasopressin, oxytocin, and prolactin in this process, the molecular mechanisms involved, and the translational relevance of this research.

Epigenetic dysregulation of SHANK3 in brain tissues from individuals with autism spectrum disorders

The molecular basis for the majority of cases of autism spectrum disorders (ASD) remains unknown. We tested the hypothesis that ASD have an epigenetic cause by performing DNA methylation profiling of five CpG islands (CGI-1 to CGI-5) in the SHANK3 gene in postmortem brain tissues from 54 ASD patients and 43 controls. We found significantly increased overall DNA methylation (epimutation) in three intragenic CGIs (CGI-2, CGI-3 and CGI-4). The increased methylation was clustered in the CGI-2 and CGI-4 in ∼15% of ASD brain tissues. SHANK3 has an extensive array of mRNA splice variants resulting from combinations of five intragenic promoters and alternative splicing of coding exons. Altered expression and alternative splicing of SHANK3 isoforms were observed in brain tissues with increased methylation of SHANK3 CGIs in ASD brain tissues. A DNA methylation inhibitor modified the methylation of CGIs and altered the isoform-specific expression of SHANK3 in cultured cells. This study is the first to find altered methylation patterns in SHANK3 in ASD brain samples. Our finding provides evidence to support an alternative approach to investigating the molecular basis of ASD. The ability to alter the epigenetic modification and expression of SHANK3 by environmental factors suggests that SHANK3 may be a valuable biomarker for dissecting the role of gene and environment interaction in the etiology of ASD.

The contribution of epigenetics to understanding genetic factors in autism

Autism spectrum disorder is a grouping of neurodevelopmental disorders characterized by deficits in social communication and language, as well as by repetitive and stereotyped behaviors. While the environment is believed to play a role in the development of autism spectrum disorder, there is now strong evidence for a genetic link to autism. Despite such evidence, studies investigating a potential single-gene cause for autism, although insightful, have been highly inconclusive. A consideration of an epigenetic approach proves to be very promising in clarifying genetic factors involved in autism. The present article is intended to provide a review of key findings pertaining to epigenetics in autism in such a way that a broader audience of individuals who do not have a strong background in genetics may better understand this highly specific and scientific content. Epigenetics refers to non-permanent heritable changes that alter expression of genes without altering the DNA sequence itself and considers the role of environment in this modulation of gene expression. This review provides a brief description of epigenetic processes, highlights evidence in the literature of epigenetic dysregulation in autism, and makes use of noteworthy findings to illustrate how a consideration of epigenetic factors can deepen our understanding of the development of autism. Furthermore, this discussion will present a promising new way for moving forward in the investigation of genetic factors within autism.

Antiaggressive activity of central oxytocin in male rats

RATIONALE

A substantial body of research suggests that the neuropeptide oxytocin promotes social affiliative behaviors in a wide range of animals including humans. However, its antiaggressive action has not been unequivocally demonstrated in male laboratory rodents.

OBJECTIVE

Our primary goal was to examine the putative serenic effect of oxytocin in a feral strain (wild type Groningen, WTG) of rats that generally show a much broader variation and higher levels of intermale aggression than commonly used laboratory strains of rats.

METHODS

Resident animals were intracerebroventricularly (icv) administered with different doses of synthetic oxytocin and oxytocin receptor antagonist, alone and in combination, in order to manipulate brain oxytocin functioning and to assess their behavioral response to an intruder.

RESULTS

Our data clearly demonstrate that acute icv administered oxytocin produces dose-dependent and receptor-selective changes in social behavior, reducing aggression and potentiating social exploration. These antiaggressive effects are stronger in the more offensive rats. On the other hand, administration of an oxytocin receptor antagonist tends to increase (nonsignificantly) aggression only in low-medium aggressive animals.

CONCLUSIONS

These results suggest that transiently enhancing brain oxytocin function has potent antiaggressive effects, whereas its attenuation tends to enhance aggressiveness. In addition, a possible inverse relationship between trait aggression and endogenous oxytocinergic signaling is revealed. Overall, this study emphasizes the importance of brain oxytocinergic signaling for regulating intermale offensive aggression. This study supports the suggestion that oxytocin receptor agonists could clinically be useful for curbing heightened aggression seen in a range of neuropsychiatric disorders like antisocial personality disorder, autism, and addiction.

Mothers of autistic children: lower plasma levels of oxytocin and Arg-vasopressin and a higher level of testosterone

BACKGROUND

Autism is a pervasive neurodevelopmental disorder,thought to be caused by a combination of genetic heritability and environmental risk factors. Some autistic-like traits have been reported in mothers of autistic children. We hypothesized that dysregulation of oxytocin (OXT), Arg-vasopressin (AVP) and sex hormones, found in autistic children, may also exist in their mothers.

METHODS

We determined plasma levels of OXT (40 in autism vs. 26 in control group), AVP (40 vs. 17) and sex hormones (61 vs. 47) in mothers of autistic and normal children by enzyme immunoassay and radioimmunoassay, respectively and investigated their relationships with the children's autistic behavior scores (Childhood Autism Rating Scale (CARS) and Autism Behavior Checklist (ABC)).

RESULTS

Significantly lower plasma concentrations of OXT (p<0.001) and AVP (p<0.001), as well as a higher level of plasma testosterone (p<0.05), were found in mothers of autistic children vs. those of control. The children's autistic behavior scores were negatively associated with maternal plasma levels of OXT and AVP.

CONCLUSIONS

These results suggest that dysregulation of OXT, AVP and/or testosterone systems exist in mothers of autistic children, which may impact children's susceptibility to autism.

Polymorphisms in the oxytocin receptor gene are associated with the development of psychopathy

The co-occurrence of child conduct problems (CPs) and callous–unemotional (CU) traits confers risk for psychopathy. The oxytocin (OXT) system is a likely candidate for involvement in the development of psychopathy. We tested variations in the OXT receptor gene (OXTR) in CP children and adolescents with varying levels of CU traits. Two samples of Caucasian children, aged 4–16 years, who met DSM criteria for disruptive behavior problems and had no features of autism spectrum disorder, were stratified into low versus high CU traits. Measures were the frequencies of nine candidate OXTR polymorphisms (single nucleotide polymorphisms). In Sample 1, high CU traits were associated with single nucleotide polymorphism rs1042778 in the 3′ untranslated region of OXTR and the CGCT haplotype of rs2268490, rs2254298, rs237889, and rs13316193. The association of rs1042778 was replicated in the second rural sample and held across gender and child versus adolescent age groups. We conclude that polymorphic variation of the OXTR characterizes children with high levels of CU traits and CPs. The results are consistent with a hypothesized role of OXT in the developmental antecedents of psychopathy, particularly the differential amygdala activation model of psychopathic traits, and add genetic evidence that high CU traits specify a distinct subgroup within CP children.

Methylation of the oxytocin receptor gene and oxytocin blood levels in the development of psychopathy

Child conduct problems (CPs) are a robust predictor of adult mental health; the concurrence of callous–unemotional (CU) traits confers specific risk for psychopathy. Psychopathy may be related to disturbances in the oxytocin (OXT) system. Evidence suggests that epigenetic changes in the OXT receptor gene (OXTR) are associated with lower circulating OXT and social–cognitive difficulties. We tested methylation levels of OXTR in 4- to 16-year-old males who met DSM criteria for a diagnosis of oppositional–defiant or conduct disorder and were stratified by CU traits and age. Measures were DNA methylation levels of six CpG sites in the promoter region of the OXTR gene (where a CpG site is a cytosine nucleotide occurs next to a guanine nucleotide in the linear sequence of bases along its lenth, linked together by phosphate binding), and OXT blood levels. High CU traits were associated with greater methylation of the OXTR gene for two cytosine nucleotide and guanine nucleotide phosphate linked sites and lower circulating OXT in older males. Higher methylation correlated with lower OXT levels. We conclude that greater methylation of OXTR characterizes adolescent males with high levels of CU and CPs, and this methylation is associated with lower circulating OXT and functional impairment in interpersonal empathy. The results add genetic evidence that high CU traits specify a distinct subgroup within CP children, and they suggest models of psychopathy may be informed by further identification of these epigenetic processes and their functional significance.

Oxytocin pathways and the evolution of human behavior

This review examines the hypothesis that oxytocin pathways--which include the neuropeptide oxytocin, the related peptide vasopressin, and their receptors--are at the center of physiological and genetic systems that permitted the evolution of the human nervous system and allowed the expression of contemporary human sociality. Unique actions of oxytocin, including the facilitation of birth, lactation, maternal behavior, genetic regulation of the growth of the neocortex, and the maintenance of the blood supply to the cortex, may have been necessary for encephalization. Peptide-facilitated attachment also allows the extended periods of nurture necessary for the emergence of human intellectual development. In general, oxytocin acts to allow the high levels of social sensitivity and attunement necessary for human sociality and for rearing a human child. Under optimal conditions oxytocin may create an emotional sense of safety. Oxytocin dynamically moderates the autonomic nervous system, and effects of oxytocin on vagal pathways, as well as the antioxidant and anti-inflammatory effects of this peptide, help to explain the pervasive adaptive consequences of social behavior for emotional and physical health.

Performance comparison of bench-top next generation sequencers using microdroplet PCR-based enrichment for targeted sequencing in patients with autism spectrum disorder

Next-generation sequencing (NGS) combined with enrichment of target genes enables highly efficient and low-cost sequencing of multiple genes for genetic diseases. The aim of this study was to validate the accuracy and sensitivity of our method for comprehensive mutation detection in autism spectrum disorder (ASD). We assessed the performance of the bench-top Ion Torrent PGM and Illumina MiSeq platforms as optimized solutions for mutation detection, using microdroplet PCR-based enrichment of 62 ASD associated genes. Ten patients with known mutations were sequenced using NGS to validate the sensitivity of our method. The overall read quality was better with MiSeq, largely because of the increased indel-related error associated with PGM. The sensitivity of SNV detection was similar between the two platforms, suggesting they are both suitable for SNV detection in the human genome. Next, we used these methods to analyze 28 patients with ASD, and identified 22 novel variants in genes associated with ASD, with one mutation detected by MiSeq only. Thus, our results support the combination of target gene enrichment and NGS as a valuable molecular method for investigating rare variants in ASD.

Epigenetics and autism

This review identifies mechanisms for altering DNA-histone interactions of cell chromatin to upregulate or downregulate gene expression that could serve as epigenetic targets for therapeutic interventions in autism. DNA methyltransferases (DNMTs) can phosphorylate histone H3 at T6. Aided by protein kinase C β 1, the DNMT lysine-specific demethylase-1 prevents demethylation of H3 at K4. During androgen-receptor-(AR-) dependent gene activation, this sequence may produce AR-dependent gene overactivation which may partly explain the male predominance of autism. AR-dependent gene overactivation in conjunction with a DNMT mechanism for methylating oxytocin receptors could produce high arousal inputs to the amygdala resulting in aberrant socialization, a prime characteristic of autism. Dysregulation of histone methyltransferases and histone deacetylases (HDACs) associated with low activity of methyl CpG binding protein-2 at cytosine-guanine sites in genes may reduce the capacity for condensing chromatin and silencing genes in frontal cortex, a site characterized by decreased cortical interconnectivity in autistic subjects. HDAC1 inhibition can overactivate mRNA transcription, a putative mechanism for the increased number of cerebral cortical columns and local frontal cortex hyperactivity in autistic individuals. These epigenetic mechanisms underlying male predominance, aberrant social interaction, and low functioning frontal cortex may be novel targets for autism prevention and treatment strategies.

The role of oxytocin in psychiatric disorders: a review of biological and therapeutic research findings

LEARNING OBJECTIVES

After participating in this educational activity, the physician should be better able to 1. Identify the biological role of oxytocin in forming attachments. 2. Evaluate the relationship between various neuropsychiatric disorders and oxytocin. 3. Identify clinical implications of using oxytocin to treat various neuropsychiatric disorders. Oxytocin is a peptide hormone integral in parturition, milk letdown, and maternal behaviors that has been demonstrated in animal studies to be important in the formation of pair bonds and in social behaviors. This hormone is increasingly recognized as an important regulator of human social behaviors, including social decision making, evaluating and responding to social stimuli, mediating social interactions, and forming social memories. In addition, oxytocin is intricately involved in a broad array of neuropsychiatric functions and may be a common factor important in multiple psychiatric disorders such as autism, schizophrenia, and mood and anxiety disorders. This review article examines the extant literature on the evidence for oxytocin dysfunction in a variety of psychiatric disorders and highlights the need for further research to understand the complex role of the oxytocin system in psychiatric disease and thus pave the way for developing new therapeutic modalities. Articles were selected that involved human participants with various psychiatric disorders and that either compared oxytocin biology to healthy controls or examined the effects of exogenous oxytocin administration.

Cumulative risk on the oxytocin receptor gene (OXTR) underpins empathic communication difficulties at the first stages of romantic love

Empathic communication between couples plays an important role in relationship quality and individual well-being and research has pointed to the role of oxytocin in providing the neurobiological substrate for pair-bonding and empathy. Here, we examined links between genetic variability on the oxytocin receptor gene (OXTR) and empathic behaviour at the initiation of romantic love. Allelic variations on five OXTR single nucleotide polymorphisms (SNPs) previously associated with susceptibility to disorders of social functioning were genotyped in 120 new lovers: OXTRrs13316193, rs2254298, rs1042778, rs2268494 and rs2268490. Cumulative genetic risk was computed by summing risk alleles on each SNP. Couples were observed in support-giving interaction and behaviour was coded for empathic communication, including affective congruence, maintaining focus on partner, acknowledging partner's distress, reciprocal exchange and non-verbal empathy. Hierarchical linear modelling indicated that individuals with high OXTR risk exhibited difficulties in empathic communication. OXTR risk predicted empathic difficulties above and beyond the couple level, relationship duration, and anxiety and depressive symptoms. Findings underscore the involvement of oxytocin in empathic behaviour during the early stages of social affiliation, and suggest the utility of cumulative risk and plasticity indices on the OXTR as potential biomarkers for research on disorders of social dysfunction and the neurobiology of empathy.

Investigation of an F-18 oxytocin receptor selective ligand via PET imaging

The compound 1-(1-(2-(2-(2-fluoroethoxy)-4-(piperidin-4-yloxy)phenyl)acetyl)piperidin-4-yl)-3,4-dihydroquinolin-2(1H)-one (1) was synthesized and positively evaluated in vitro for high potency and selectivity with human oxytocin receptors. The positron emitting analogue, [F-18]1, was synthesized and investigated in vivo via PET imaging using rat and cynomolgus monkey models. PET imaging studies in female Sprague-Dawley rats suggested [F-18]1 reached the brain and accumulated in various regions of the brain, but washed out too rapidly for adequate quantification and localization. In vivo PET imaging studies in a male cynomolgus monkey suggested [F-18]1 had limited brain penetration while specific uptake of radioactivity significantly accumulated within the vasculature of the cerebral ventricles in areas representative of the choroid plexus.

Nonsocial functions of hypothalamic oxytocin

Oxytocin (OXT) is a hypothalamic neuropeptide composed of nine amino acids. The functions of OXT cover a variety of social and nonsocial activity/behaviors. Therapeutic effects of OXT on aberrant social behaviors are attracting more attention, such as social memory, attachment, sexual behavior, maternal behavior, aggression, pair bonding, and trust. The nonsocial behaviors/functions of brain OXT have also received renewed attention, which covers brain development, reproduction, sex, endocrine, immune regulation, learning and memory, pain perception, energy balance, and almost all the functions of peripheral organ systems. Coordinating with brain OXT, locally produced OXT also involves the central and peripheral actions of OXT. Disorders in OXT secretion and functions can cause a series of aberrant social behaviors, such as depression, autism, and schizophrenia as well as disturbance of nonsocial behaviors/functions, such as anorexia, obesity, lactation failure, osteoporosis, diabetes, and carcinogenesis. As more and more OXT functions are identified, it is essential to provide a general view of OXT functions in order to explore the therapeutic potentials of OXT. In this review, we will focus on roles of hypothalamic OXT on central and peripheral nonsocial functions.

Non-synonymous single-nucleotide variations of the human oxytocin receptor gene and autism spectrum disorders: a case-control study in a Japanese population and functional analysis

BACKGROUND

The human oxytocin receptor (hOXTR) is implicated in the etiology of autism spectrum disorders (ASDs) and is a potential target for therapeutic intervention. Several studies have reported single-nucleotide polymorphisms (SNPs) of the OXTR gene associated with ASDs. These SNPs, however, reside outside the protein-coding region. Not much is known about genetic variations that cause amino acid substitutions that alter receptor functions.

METHODS

Variations in the OXTR gene were analyzed in 132 ASD patients at Kanazawa University Hospital in Japan and 248 unrelated healthy Japanese volunteers by re-sequencing and real-time polymerase chain reaction-based genotyping. Functional changes in variant OXTRs were assessed by radioligand binding assay and measurements of intracellular free calcium concentrations ([Ca2+]i) and inositol 1,4,5-trisphosphate (IP3) levels.

RESULTS

Six subjects (4.5%) in the ASD group and two in the control group (0.8%) were identified as heterozygotes carrying the R376G variation (rs35062132; c.1126C>G); one individual from the ASD group (0.8%) and three members of the control group (1.2%) were found to be carrying R376C (c.1126C>T). The C/G genotype significantly correlated with an increased risk of ASDs (odds ratio (OR) = 5.83; 95% confidence interval (CI) = 1.16 to 29.33; P = 0.024, Fisher's exact test). Consistently, the G allele showed a correlation with an increased likelihood of ASDs (OR = 5.73; 95% CI = 1.15 to 28.61; P = 0.024, Fisher's exact test). The frequencies of the C/T genotype and the T allele in the ASD and control groups did not differ significantly. We also examined changes in agonist-induced cellular responses mediated by the variant receptors hOXTR-376G and hOXTR-376C. OXT-induced receptor internalization and recycling were faster in hOXTR-376G-expressing HEK-293 cells than in cells expressing hOXTR-376R or hOXTR-376C. In addition, the elevation in [Ca2+]i and IP3 formation decreased in the cells expressing hOXTR-376G and hOXTR-376C tagged with enhanced green fluorescent protein (EGFP), in comparison with the cells expressing the common-type hOXTR-376R tagged with EGFP.

CONCLUSIONS

These results suggest that the rare genetic variation rs35062132 might contribute to the pathogenesis of ASDs, and could provide a molecular basis of individual differences in OXTR-mediated modulation of social behavior.

Autism as early neurodevelopmental disorder: evidence for an sAPPα-mediated anabolic pathway

Autism is a neurodevelopmental disorder marked by social skills and communication deficits and interfering repetitive behavior. Intellectual disability often accompanies autism. In addition to behavioral deficits, autism is characterized by neuropathology and brain overgrowth. Increased intracranial volume often accompanies this brain growth. We have found that the Alzheimer's disease (AD) associated amyloid-β precursor protein (APP), especially its neuroprotective processing product, secreted APP α, is elevated in persons with autism. This has led to the "anabolic hypothesis" of autism etiology, in which neuronal overgrowth in the brain results in interneuronal misconnections that may underlie multiple autism symptoms. We review the contribution of research in brain volume and of APP to the anabolic hypothesis, and relate APP to other proteins and pathways that have already been directly associated with autism, such as fragile X mental retardation protein, Ras small GTPase/extracellular signal-regulated kinase, and phosphoinositide 3 kinase/protein kinase B/mammalian target of rapamycin. We also present additional evidence of magnetic resonance imaging intracranial measurements in favor of the anabolic hypothesis. Finally, since it appears that APP's involvement in autism is part of a multi-partner network, we extend this concept into the inherently interactive realm of epigenetics. We speculate that the underlying molecular abnormalities that influence APP's contribution to autism are epigenetic markers overlaid onto potentially vulnerable gene sequences due to environmental influence.

Research review: Social motivation and oxytocin in autism--implications for joint attention development and intervention

BACKGROUND AND SCOPE

The social motivation hypothesis (SMH) suggests that individuals with autism spectrum disorders (ASD) are less intrinsically rewarded by social stimuli than their neurotypical peers. This difference in social motivation has been posited as a factor contributing to social deficits in ASD. Social motivation is thought to involve the neuropeptide oxytocin. Here, we review the evidence for oxytocin effects in ASD, and discuss its potential role in one important social cognitive behavior.

METHODS

Systematic searches were conducted using the PsychINFO and MEDLINE databases and the search terms 'oxytocin' and 'autism'; the same databases were used for separate searches for 'joint attention', 'intervention', and 'autism', using the same inclusion criteria as an earlier 2011 review but updating it for the period 2010 to October 2012.

FINDINGS

Several studies suggest that giving oxytocin to both individuals with ASD and neurotypical individuals can enhance performance on social cognitive tasks. Studies that have attempted to intervene in joint attention in ASD suggest that social motivation may be a particular obstacle to lasting effects.

CONCLUSIONS

The review of the evidence for the SMH suggests a potential role for oxytocin in social motivation deficits in ASD. Because of its importance for later communicative and social development, the focus here is on implications of oxytocin and social motivation in the development of and interventions in joint attention. Joint attention is a central impairment in ASD, and as a result is the focus of several behavioral interventions. In describing this previous research on joint attention interventions in ASD, we pay particular attention to problems encountered in such studies, and propose ways that oxytocin may facilitate behavioral intervention in this area. For future research, integrating behavioral and pharmacological interventions (oxytocin administration) would be a worthwhile experimental direction to improve understanding of the role of oxytocin in ASD and help optimize outcomes for children with ASD.

Epigenetic regulation of the oxytocin receptor gene: implications for behavioral neuroscience

Genetic approaches have improved our understanding of the neurobiological basis of social behavior and cognition. For instance, common polymorphisms of genes involved in oxytocin signaling have been associated with sociobehavioral phenotypes in healthy samples as well as in subjects with mental disorders. More recently, attention has been drawn to epigenetic mechanisms, which regulate genetic function and expression without changes to the underlying DNA sequence. We provide an overview of the functional importance of oxytocin receptor gene (OXTR) promoter methylation and summarize studies that have investigated the role of OXTR methylation in behavioral phenotypes. There is first evidence that OXTR methylation is associated with autism, high callous-unemotional traits, and differential activation of brain regions involved in social perception. Furthermore, psychosocial stress exposure might dynamically regulate OXTR. Given evidence that epigenetic states of genes can be modified by experiences, especially those occurring in sensitive periods early in development, we conclude with a discussion on the effects of traumatic experience on the developing oxytocin system. Epigenetic modification of genes involved in oxytocin signaling might be involved in the mechanisms mediating the long-term influence of early adverse experiences on socio-behavioral outcomes.

Epigenomic strategies at the interface of genetic and environmental risk factors for autism

Autism spectrum disorders (ASD) have been increasing in prevalence over the last two decades, primarily because of increased awareness and diagnosis. However, autism is clearly a complex human genetic disorder that involves interactions between genes and environment. Epigenetic mechanisms, such as DNA methylation, act at the interface of genetic and environmental risk and protective factors. Advancements in genome-wide sequencing has broadened the view of the human methylome and revealed the organization of the human genome into large-scale methylation domains that footprint over neurologically important genes involved in embryonic development. Future integrative epigenomic analyses of genetic risk factors with environmental exposures and methylome analyses are expected to be important for understanding the complex etiology of ASD.

The EPIIC hypothesis: intrapartum effects on the neonatal epigenome and consequent health outcomes

There are many published studies about the epigenetic effects of the prenatal and infant periods on health outcomes. However, there is very little knowledge regarding the effects of the intrapartum period (labor and birth) on health and epigenetic remodeling. Although the intrapartum period is relatively short compared to the complete perinatal period, there is emerging evidence that this time frame may be a critical formative phase for the human genome. Given the debates from the National Institutes of Health and World Health Organization regarding routine childbirth procedures, it is essential to establish the state of the science concerning normal intrapartum epigenetic physiology. EPIIC (Epigenetic Impact of Childbirth) is an international, interdisciplinary research collaboration with expertise in the fields of genetics, physiology, developmental biology, epidemiology, medicine, midwifery, and nursing. We hypothesize that events during the intrapartum period - specifically the use of synthetic oxytocin, antibiotics, and cesarean section - affect the epigenetic remodeling processes and subsequent health of the mother and offspring. The rationale for this hypothesis is based on recent evidence and current best practice.

Age-dependent decrease and alternative splicing of methionine synthase mRNA in human cerebral cortex and an accelerated decrease in autism

The folate and vitamin B12-dependent enzyme methionine synthase (MS) is highly sensitive to cellular oxidative status, and lower MS activity increases production of the antioxidant glutathione, while simultaneously decreasing more than 200 methylation reactions, broadly affecting metabolic activity. MS mRNA levels in postmortem human cortex from subjects across the lifespan were measured and a dramatic progressive biphasic decrease of more than 400-fold from 28 weeks of gestation to 84 years was observed. Further analysis revealed alternative splicing of MS mRNA, including deletion of folate-binding domain exons and age-dependent deletion of exons from the cap domain, which protects vitamin B12 (cobalamin) from oxidation. Although three species of MS were evident at the protein level, corresponding to full-length and alternatively spliced mRNA transcripts, decreasing mRNA levels across the lifespan were not associated with significant changes in MS protein or methionine levels. MS mRNA levels were significantly lower in autistic subjects, especially at younger ages, and this decrease was replicated in cultured human neuronal cells by treatment with TNF-α, whose CSF levels are elevated in autism. These novel findings suggest that rather than serving as a housekeeping enzyme, MS has a broad and dynamic role in coordinating metabolism in the brain during development and aging. Factors adversely affecting MS activity, such as oxidative stress, can be a source of risk for neurological disorders across the lifespan via their impact on methylation reactions, including epigenetic regulation of gene expression.

Complex epigenetic regulation of engrailed-2 (EN-2) homeobox gene in the autism cerebellum

The elucidation of epigenetic alterations in the autism brain has potential to provide new insights into the molecular mechanisms underlying abnormal gene expression in this disorder. Given strong evidence that engrailed-2 (EN-2) is a developmentally expressed gene relevant to cerebellar abnormalities and autism, the epigenetic evaluation of this candidate gene was undertaken in 26 case and control post-mortem cerebellar samples. Assessments included global DNA methylation, EN-2 promoter methylation, EN-2 gene expression and EN-2 protein levels. Chromatin immunoprecipitation was used to evaluate trimethylation status of histone H3 lysine 27 (H3K27) associated with gene downregulation and histone H3 lysine 4 (H3K4) associated with gene activation. The results revealed an unusual pattern of global and EN-2 promoter region DNA hypermethylation accompanied by significant increases in EN-2 gene expression and protein levels. Consistent with EN-2 overexpression, histone H3K27 trimethylation mark in the EN-2 promoter was significantly decreased in the autism samples relative to matched controls. Supporting a link between reduced histone H3K27 trimethylation and increased EN-2 gene expression, the mean level of histone H3K4 trimethylation was elevated in the autism cerebellar samples. Together, these results suggest that the normal EN-2 downregulation that signals Purkinje cell maturation during late prenatal and early-postnatal development may not have occurred in some individuals with autism and that the postnatal persistence of EN-2 overexpression may contribute to autism cerebellar abnormalities.

Genome-wide analysis of DNA methylation in human amnion

The amnion is a specialized tissue in contact with the amniotic fluid, which is in a constantly changing state. To investigate the importance of epigenetic events in this tissue in the physiology and pathophysiology of pregnancy, we performed genome-wide DNA methylation profiling of human amnion from term (with and without labor) and preterm deliveries. Using the Illumina Infinium HumanMethylation27 BeadChip, we identified genes exhibiting differential methylation associated with normal labor and preterm birth. Functional analysis of the differentially methylated genes revealed biologically relevant enriched gene sets. Bisulfite sequencing analysis of the promoter region of the oxytocin receptor (OXTR) gene detected two CpG dinucleotides showing significant methylation differences among the three groups of samples. Hypermethylation of the CpG island of the solute carrier family 30 member 3 (SLC30A3) gene in preterm amnion was confirmed by methylation-specific PCR. This work provides preliminary evidence that DNA methylation changes in the amnion may be at least partially involved in the physiological process of labor and the etiology of preterm birth and suggests that DNA methylation profiles, in combination with other biological data, may provide valuable insight into the mechanisms underlying normal and pathological pregnancies.

DNA methylation of specific CpG sites in the promoter region regulates the transcription of the mouse oxytocin receptor

Oxytocin is a peptide hormone, well known for its role in labor and suckling, and most recently for its involvement in mammalian social behavior. All central and peripheral actions of oxytocin are mediated through the oxytocin receptor, which is the product of a single gene. Transcription of the oxytocin receptor is subject to regulation by gonadal steroid hormones, and is profoundly elevated in the uterus and mammary glands during parturition. DNA methylation is a major epigenetic mechanism that regulates gene transcription, and has been linked to reduced expression of the oxytocin receptor in individuals with autism. Here, we hypothesized that transcription of the mouse oxytocin receptor is regulated by DNA methylation of specific sites in its promoter, in a tissue-specific manner. Hypothalamus-derived GT1-7, and mammary-derived 4T1 murine cell lines displayed negative correlations between oxytocin receptor transcription and methylation of the gene promoter, and demethylation caused a significant enhancement of oxytocin receptor transcription in 4T1 cells. Using a reporter gene assay, we showed that methylation of specific sites in the gene promoter, including an estrogen response element, significantly inhibits transcription. Furthermore, methylation of the oxytocin receptor promoter was found to be differentially correlated with oxytocin receptor expression in mammary glands and the uterus of virgin and post-partum mice, suggesting that it plays a distinct role in oxytocin receptor transcription among tissues and under different physiological conditions. Together, these results support the hypothesis that the expression of the mouse oxytocin receptor gene is epigenetically regulated by DNA methylation of its promoter.

Mice heterozygous for the oxytocin receptor gene (Oxtr(+/-)) show impaired social behaviour but not increased aggression or cognitive inflexibility: evidence of a selective haploinsufficiency gene effect

We characterised the behavioural phenotype of mice heterozygous (Oxtr(+/-)) for the oxytocin receptor gene (Oxtr) and compared it with that of Oxtr null mice (Oxtr(-/-)), which display autistic-like behaviours, including impaired sociability and preference for social novelty, impaired cognitive flexibility, and increased aggression. Similar to Oxtr(-/-) mice, the Oxtr(+/-) showed impaired sociability and preference for social novelty but, unlike the null genotype, their cognitive flexibility and aggression were normal. By autoradiography, Oxtr(+/-) mice were found to have approximately 50% fewer oxytocin receptors (OXTRs) in all of the examined brain regions. Thus, because a partial reduction in Oxtr gene expression is sufficient to compromise social behaviour, the Oxtr acts as a haploinsufficient gene. Furthermore, the inactivation of the Oxtr gene affects specific behaviours in a dose-dependent manner: social behaviour is sensitive to even a partial reduction in Oxtr gene expression, whereas defects in aggression and cognitive flexibility require the complete inactivation of the Oxtr gene to emerge. We then investigated the rescue of the Oxtr(+/-) social deficits by oxytocin (OT) and Thr(4)Gly(7)OT (TGOT) administered i.c.v. at different doses. TGOT was more potent than OT in rescuing sociability and social novelty in both genotypes. Furthermore, the TGOT doses that reverted impaired sociability and preference for social novelty in Oxtr(+/-) were lower than those required in Oxtr(-/-), thus suggesting that the rescue effect is mediated by OXTR in Oxtr(+/-) and by other receptors (presumably vasopressin V1a receptors) in Oxtr(-/-). In line with this, a low dose of the selective oxytocin antagonist desGlyDTyrOVT blocks the rescue effect of TGOT only in the Oxtr(+/-) genotype, whereas the less selective antagonist SR49059 blocks rescue in both genotypes. In conclusion, the Oxtr(+/-) mouse is a unique animal model for investigating how partial loss of the Oxtr gene impair social interactions, and for designing pharmacological rescue strategies.

Integrative approaches utilizing oxytocin to enhance prosocial behavior: from animal and human social behavior to autistic social dysfunction

The prevalence of autism spectrum disorder (ASD) is as high as 1 in 100 individuals and is a heavy burden to society. Thus, identifying causes and treatments is imperative. Here, we briefly review the topics covered in our 2012 Society for Neuroscience Mini-Symposium entitled "Integrative Approaches Using Oxytocin to Enhance Prosocial Behavior: From Animal and Human Social Behavior to ASD's Social Dysfunction." This work is not meant to be a comprehensive review of oxytocin and prosocial behavior. Instead, we wish to share the newest findings on the effects of oxytocin on social behavior, the brain, and the social dysfunction of ASD at the molecular, genetic, systemic, and behavior levels, in varied subjects ranging from animal models to humans suffering from autism for the purpose of promoting further study for developing the clinical use of oxytocin in treating ASD.

The expanding genomic landscape of autism: discovering the 'forest' beyond the 'trees'

Autism spectrum disorders are neurodevelopmental disorders characterized by significant deficits in reciprocal social interactions, impaired communication and restricted, repetitive behaviors. As autism spectrum disorders are among the most heritable of neuropsychiatric disorders, much of autism research has focused on the search for genetic variants in protein-coding genes (i.e., the 'trees'). However, no single gene can account for more than 1% of the cases of autism spectrum disorders. Yet, genome-wide association studies have often identified statistically significant associations of genetic variations in regions of DNA that do not code for proteins (i.e., intergenic regions). There is increasing evidence that such noncoding regions are actively transcribed and may participate in the regulation of genes, including genes on different chromosomes. This article summarizes evidence that suggests that the research spotlight needs to be expanded to encompass far-reaching gene-regulatory mechanisms that include a variety of epigenetic modifications, as well as noncoding RNA (i.e., the 'forest'). Given that noncoding RNA represents over 90% of the transcripts in most cells, we may be observing just the 'tip of the iceberg' or the 'edge of the forest' in the genomic landscape of autism.

Association between oxytocin receptor gene polymorphisms and self-rated 'empathic concern' in schizophrenia

The nonapeptide oxytocin (OXT) and its receptor (OXTR) have been implicated in social cognition, empathy, emotion and stress regulation in humans. Previous studies reported associations between OXT and OXTR genetic polymorphisms and risk for disorders characterized by impaired socio-emotional functioning, such as schizophrenia and autism. Here we investigate the influence of two single nucleotide polymorphisms (SNPs) within the OXTR gene on a measure of socio-emotional functioning in schizophrenic patients. OXTR SNPs that were previously investigated in other studies were genotyped in 145 patients diagnosed with schizophrenia according to DSM-IV and 145 healthy controls matched for age and gender. The Interpersonal Reactivity Index (IRI) was used to assess cognitive ('perspective taking'), affective ('empathic concern') and self-related ('personal distress') dimensions of empathy. No group differences in genotype frequencies were observed. MANCOVA revealed a significant main (F [1,282] = 10.464; p<0.01) and interaction effect (genotype by diagnosis: F [1,282] = 4.329; p<0.05) of OXTR SNP rs2254298(A>GG) with 'empathic concern'. Within the schizophrenia group, linear regression analysis determined OXTR rs2254298 genotype, PANSS negative and general symptom score, and age of disease onset as being significantly associated with 'empathic concern'. OXTR rs2254298 significantly impacted PANSS general psychopathology scores. No associations were found for OXTR rs53576, IRI 'perspective taking' or 'personal distress' ratings. Our preliminary findings support hypotheses about an involvement of OXTR rs2254298 in emotional empathy in schizophrenic and healthy individuals, warranting independent replication.

An epigenetic framework for neurodevelopmental disorders: from pathogenesis to potential therapy

Neurodevelopmental disorders (NDDs) are characterized by aberrant and delayed early-life development of the brain, leading to deficits in language, cognition, motor behaviour and other functional domains, often accompanied by somatic symptoms. Environmental factors like perinatal infection, malnutrition and trauma can increase the risk of the heterogeneous, multifactorial and polygenic disorders, autism and schizophrenia. Conversely, discrete genetic anomalies are involved in Down, Rett and Fragile X syndromes, tuberous sclerosis and neurofibromatosis, the less familiar Phelan-McDermid, Sotos, Kleefstra, Coffin-Lowry and "ATRX" syndromes, and the disorders of imprinting, Angelman and Prader-Willi syndromes. NDDs have been termed "synaptopathies" in reference to structural and functional disturbance of synaptic plasticity, several involve abnormal Ras-Kinase signalling ("rasopathies"), and many are characterized by disrupted cerebral connectivity and an imbalance between excitatory and inhibitory transmission. However, at a different level of integration, NDDs are accompanied by aberrant "epigenetic" regulation of processes critical for normal and orderly development of the brain. Epigenetics refers to potentially-heritable (by mitosis and/or meiosis) mechanisms controlling gene expression without changes in DNA sequence. In certain NDDs, prototypical epigenetic processes of DNA methylation and covalent histone marking are impacted. Conversely, others involve anomalies in chromatin-modelling, mRNA splicing/editing, mRNA translation, ribosome biogenesis and/or the regulatory actions of small nucleolar RNAs and micro-RNAs. Since epigenetic mechanisms are modifiable, this raises the hope of novel therapy, though questions remain concerning efficacy and safety. The above issues are critically surveyed in this review, which advocates a broad-based epigenetic framework for understanding and ultimately treating a diverse assemblage of NDDs ("epigenopathies") lying at the interface of genetic, developmental and environmental processes. This article is part of the Special Issue entitled 'Neurodevelopmental Disorders'.

Intranasal oxytocin versus placebo in the treatment of adults with autism spectrum disorders: a randomized controlled trial

BACKGROUND

There are no effective medications for the treatment of social cognition/function deficits in autism spectrum disorder (ASD), and adult intervention literature in this area is sparse. Emerging data from animal models and genetic association studies as well as early, single-dose intervention studies suggest that the oxytocin system may be a potential therapeutic target for social cognition/function deficits in ASD. The primary aim of this study was to examine the safety/therapeutic effects of intranasal oxytocin versus placebo in adults with ASD, with respect to the two core symptom domains of social cognition/functioning and repetitive behaviors.

METHODS

This was a pilot, randomized, double-blind, placebo-controlled, parallel design trial of intranasal oxytocin versus placebo in 19 adults with ASD (16 males; 33.20 ± 13.29 years). Subjects were randomized to 24 IU intranasal oxytocin or placebo in the morning and afternoon for 6 weeks. Measures of social function/cognition (the Diagnostic Analysis of Nonverbal Accuracy) and repetitive behaviors (Repetitive Behavior Scale Revised) were administered. Secondary measures included the Social Responsiveness Scale, Reading-the-Mind-in-the-Eyes Test and the Yale Brown Obsessive Compulsive Scale - compulsion subscale and quality of life (World Health Organization Quality of Life Questionnaire - emotional/social subscales). Full-information maximum-likelihood parameter estimates were obtained and tested using mixed-effects regression analyses.

RESULTS

Although no significant changes were detected in the primary outcome measures after correcting for baseline differences, results suggested improvements after 6 weeks in measures of social cognition (Reading-the-Mind-in-the-Eyes Test, p = 0.002, d = 1.2), and quality of life (World Health Organization Quality of Life Questionnaire - emotion, p = 0.031, d = 0.84), both secondary measures. Oxytocin was well tolerated and no serious adverse effects were reported.

CONCLUSIONS

This pilot study suggests that there is therapeutic potential to daily administration of intranasal oxytocin in adults with ASD and that larger and longer studies are warranted.

TRIAL REGISTRATION

NCT00490802.

The effects of birth order and birth interval on the phenotypic expression of autism spectrum disorder

A rise in the prevalence of diagnosed cases of autism spectrum disorder (ASD) has been reported in several studies in recent years. While this rise in ASD prevalence is at least partially related to increased awareness and broadened diagnostic criteria, the role of environmental factors cannot be ruled out, especially considering that the cause of most cases of ASD remains unknown. The study of families with multiple affected children can provide clues about ASD etiology. While the majority of research on ASD multiplex families has focused on identifying genetic anomalies that may underlie the disorder, the study of symptom severity across ASD birth order may provide evidence for environmental factors in ASD. We compared social and cognitive measures of behavior between over 300 first and second affected siblings within multiplex autism families obtained from the Autism Genetic Resource Exchange dataset. Measures included nonverbal IQ assessed with the Ravens Colored Progressive Matrices, verbal IQ assessed with the Peabody Picture Vocabulary Test, and autism severity assessed with the Social Responsiveness Scale (SRS), an instrument established as a quantitative measure of autism. The results indicated that females were more severely impacted by ASD than males, especially first affected siblings. When first and second affected siblings were compared, significant declines in nonverbal and verbal IQ scores were observed. In addition, SRS results demonstrated a significant increase in autism severity between first and second affected siblings consistent with an overall decline in function as indicated by the IQ data. These results remained significant after controlling for the age and sex of the siblings. Surprisingly, the SRS scores were found to only be significant when the age difference between siblings was less than 2 years. These results suggest that some cases of ASD are influenced by a dosage effect involving unknown epigenetic, environmental, and/or immunological factors.

Carbon-11 N-methyl alkylation of L-368,899 and in vivo PET imaging investigations for neural oxytocin receptors

Compound L-368,899 was successfully alkylated with [(11)C]iodomethane to generate the oxytocin receptor selective (2R)-2-amino-N-((2S)-7,7-dimethyl-1-(((4-(o-tolyl)piperazin-1-yl)sulfonyl)methyl)bicyclo[2.2.1]heptan-2-yl)-N-[(11)C]methyl-3-(methylsulfonyl)propanamide ([(11)C]1) with very high radiochemical purity and high specific activity. PET imaging studies were performed with [(11)C]1 to investigate brain penetration and oxytocin receptor uptake using rat and cynomolgus monkey models. For rat baseline scans, brain penetration was observed with [(11)C]1, but no specific uptake could be distinguished in the brain region. By administering a peptide oxytocin receptor selective antagonist for peripheral blocking of oxytocin receptors, the uptake of [(11)C]1 was amplified in the rat brain temporarily to enable some visual uptake within the rat brain. A baseline scan of [(11)C]1 in a cynomolgus monkey model resulted in no detectable specific uptake in anticipated regions, but activity did accumulate in the choroid plexus.

DNA methylation of the oxytocin receptor gene predicts neural response to ambiguous social stimuli

Oxytocin and its receptor (OXTR) play an important role in a variety of social perceptual and affiliative processes. Individual variability in social information processing likely has a strong heritable component, and as such, many investigations have established an association between common genetic variants of OXTR and variability in the social phenotype. However, to date, these investigations have primarily focused only on changes in the sequence of DNA without considering the role of epigenetic factors. DNA methylation is an epigenetic mechanism by which cells control transcription through modification of chromatin structure. DNA methylation of OXTR decreases expression of the gene and high levels of methylation have been associated with autism spectrum disorders (ASD). This link between epigenetic variability and social phenotype allows for the possibility that social processes are under epigenetic control. We hypothesized that the level of DNA methylation of OXTR would predict individual variability in social perception. Using the brain's sensitivity to displays of animacy as a neural endophenotype of social perception, we found significant associations between the degree of OXTR methylation and brain activity evoked by the perception of animacy. Our results suggest that consideration of DNA methylation may substantially improve our ability to explain individual differences in imaging genetic association studies.