Genomic and epigenetic evidence for oxytocin receptor deficiency in autism

Rethinking schizophrenia

How will we view schizophrenia in 2030? Schizophrenia today is a chronic, frequently disabling mental disorder that affects about one per cent of the world's population. After a century of studying schizophrenia, the cause of the disorder remains unknown. Treatments, especially pharmacological treatments, have been in wide use for nearly half a century, yet there is little evidence that these treatments have substantially improved outcomes for most people with schizophrenia. These current unsatisfactory outcomes may change as we approach schizophrenia as a neurodevelopmental disorder with psychosis as a late, potentially preventable stage of the illness. This 'rethinking' of schizophrenia as a neurodevelopmental disorder, which is profoundly different from the way we have seen this illness for the past century, yields new hope for prevention and cure over the next two decades.

No association between oxytocin or prolactin gene variants and childhood-onset mood disorders

BACKGROUND

Oxytocin (OXT) and prolactin (PRL) are neuropeptide hormones that interact with the serotonin system and are involved in the stress response and social affiliation. In human studies, serum OXT and PRL levels have been associated with depression and related phenotypes. Our purpose was to determine if single nucleotide polymorphisms (SNPs) at the loci for OXT, PRL and their receptors, OXTR and PRLR, were associated with childhood-onset mood disorders (COMD).

METHODS

Using 678 families in a family-based association design, we genotyped 16 SNPs at OXT, PRL, OXTR and PRLR to test for association with COMD.

RESULTS

No significant associations were found for SNPs in the OXTR, PRL, or PRLR genes. Two of three SNPs 3' of the OXT gene were associated with COMD (p≤0.02), significant after spectral decomposition, but were not significant after additionally correcting for the number of genes tested. Supplementary analyses of parent-of-origin and proband sex effects for OXT SNPs by Fisher's Exact test were not significant after Bonferroni correction.

CONCLUSIONS

We have examined 16 OXT and PRL system gene variants, with no evidence of statistically significant association after correction for multiple tests.

Pentapeptide sharing between Corynebacterium diphtheria toxin and the human neural protein network

We describe the pentapeptides shared between the Corynebacterium diphtheria toxin and the human proteins associated with fundamental neural functions. We report that diphtheria toxin pentapeptides are spread among human antigens such as tuberous sclerosis proteins 1 and 2, reelin, contactin-4, neuroligins, semaphorin-5A, sodium channel protein type 1 subunit α, Williams-Beuren syndrome chromosomal region 1 protein, Williams-Beuren syndrome chromosomal region 20A protein. Williams-Beuren syndrome chromosomal region 8 protein, Bardet-Biedl syndrome 9 protein, Bardet-Biedl syndrome 10 protein, oligodendrocyte-myelin glycoprotein, neurofibromin-2, and periaxin. The data are discussed in relation to the bacterial immune escape phenomenon, and in the context of potential cross-reactions in diagnostic tests and immune therapies.

Autism spectrum disorders and epigenetics

OBJECTIVE

Current research suggests that the causes of autism spectrum disorders (ASD) are multifactorial and include both genetic and environmental factors. Several lines of evidence suggest that epigenetics also plays an important role in ASD etiology and that it might, in fact, integrate genetic and environmental influences to dysregulate neurodevelopmental processes. The objective of this review is to illustrate how epigenetic modifications that are known to alter gene expression without changing primary DNA sequence may play a role in the etiology of ASD.

METHOD

In this review, we summarize current knowledge about epigenetic modifications to genes and genomic regions possibly involved in the etiology of ASD.

RESULTS

Several genetic syndromes comorbid with ASD, which include Rett, Fragile X, Prader-Willi, Angelman, and CHARGE (Coloboma of the eye, Heart defects, Atresia of the nasal choanae, Retardation of growth and/or development, Genital and/or urinary abnormalities, and Ear abnormalities and deafness), all demonstrate dysregulation of epigenetic marks or epigenetic mechanisms. We report also on genes or genomic regions exhibiting abnormal epigenetic regulation in association with either syndromic (15q11-13 maternal duplication) or nonsyndromic forms of ASD. Finally, we discuss the state of current knowledge regarding the etiologic role of environmental factors linked to both the development of ASD and epigenetic dysregulation.

CONCLUSION

Data reviewed in this article highlight a variety of situations in which epigenetic dysregulation is associated with the development of ASD, thereby supporting a role for epigenetics in the multifactorial etiologies of ASD.

Autism and oxytocin: new developments in translational approaches to therapeutics

Autism is a neurodevelopmental disorder characterized by dysfunction in three core symptom domains: speech and communication deficits, repetitive or compulsive behaviors with restricted interests, and social impairment. The neuropeptide oxytocin, along with the structurally similar peptide arginine vasopressin, may play a role in the etiology of autism, and especially in the social impairment domain. Oxytocin is a nonapeptide (i.e., it has nine amino acids). It is synthesized in magnocellular neurons in the paraventricular nucleus and the supraoptic nucleus of the hypothalamus and is released into the bloodstream by way of axon terminals in the posterior pituitary. Oxytocin is released both peripherally, where it is involved in milk letdown and the facilitation of uterine contractions, and centrally, where it acts as a neuromodulator along with arginine vasopressin. Here, we discuss relevant translational research pertaining to the role of oxytocin in social and repetitive behaviors and consider clinical implications. We also discuss current research limitations, review recent preliminary findings from studies involving oxytocin in autism spectrum disorder patient populations, and point to possible directions for future research.

Two genetic variants of CD38 in subjects with autism spectrum disorder and controls

The neurobiological basis of autism spectrum disorder (ASD) remains poorly understood. Given the role of CD38 in social recognition through oxytocin (OT) release, we hypothesized that CD38 may play a role in the etiology of ASD. Here, we first examined the immunohistochemical expression of CD38 in the hypothalamus of post-mortem brains of non-ASD subjects and found that CD38 was colocalized with OT in secretory neurons. In studies of the association between CD38 and autism, we analyzed 10 single nucleotide polymorphisms (SNPs) and mutations of CD38 by re-sequencing DNAs mainly from a case-control study in Japan, and Caucasian cases mainly recruited to the Autism Genetic Resource Exchange (AGRE). The SNPs of CD38, rs6449197 (p<0.040) and rs3796863 (p<0.005) showed significant associations with a subset of ASD (IQ>70; designated as high-functioning autism (HFA)) in the U.S. 104 AGRE family trios, but not with Japanese 188 HFA subjects. A mutation that caused tryptophan to replace arginine at amino acid residue 140 (R140W; (rs1800561, 4693C>T)) was found in 0.6-4.6% of the Japanese population and was associated with ASD in the smaller case-control study. The SNP was clustered in pedigrees in which the fathers and brothers of T-allele-carrier probands had ASD or ASD traits. In this cohort OT plasma levels were lower in subjects with the T allele than in those without. One proband with the T allele who was taking nasal OT spray showed relief of symptoms. The two variant CD38 poloymorphysms tested may be of interest with regard of the pathophysiology of ASD.

Evidence that genetic variation in the oxytocin receptor (OXTR) gene influences social cognition in ADHD

Some children with ADHD also have social and communication difficulties similar to those seen in children with autistic spectrum disorders and this may be due to shared genetic liability. As the oxytocin receptor (OXTR) gene has been implicated in social cognition and autistic spectrum disorders, this study investigated whether OXTR polymorphisms previously implicated in autism were associated with ADHD and whether they influenced OXTR mRNA expression in 27 normal human amygdala brain samples. The family-based association sample consisted of 450 DSM-IV diagnosed ADHD probands and their parents. Although there was no association with the ADHD phenotype, an association with social cognitive impairments in a subset of the ADHD probands (N=112) was found for SNP rs53576 (F=5.24, p=0.007) with post-hoc tests demonstrating that the AA genotype was associated with better social ability compared to the AG genotype. Additionally, significant association was also found for rs13316193 (F=3.09, p=0.05) with post-hoc tests demonstrating that the CC genotype was significantly associated with poorer social ability than the TT genotype. No significant association between genotype and OXTR mRNA expression was found. This study supports previous evidence that the OXTR gene is implicated in social cognition.

Global methylation profiling of lymphoblastoid cell lines reveals epigenetic contributions to autism spectrum disorders and a novel autism candidate gene, RORA, whose protein product is reduced in autistic brain

Autism is currently considered a multigene disorder with epigenetic influences. To investigate the contribution of DNA methylation to autism spectrum disorders, we have recently completed large-scale methylation profiling by CpG island microarray analysis of lymphoblastoid cell lines derived from monozygotic twins discordant for diagnosis of autism and their nonautistic siblings. Methylation profiling revealed many candidate genes differentially methylated between discordant MZ twins as well as between both twins and nonautistic siblings. Bioinformatics analysis of the differentially methylated genes demonstrated enrichment for high-level functions including gene transcription, nervous system development, cell death/survival, and other biological processes implicated in autism. The methylation status of 2 of these candidate genes, BCL-2 and retinoic acid-related orphan receptor alpha (RORA), was further confirmed by bisulfite sequencing and methylation-specific PCR, respectively. Immunohistochemical analyses of tissue arrays containing slices of the cerebellum and frontal cortex of autistic and age- and sex-matched control subjects revealed decreased expression of RORA and BCL-2 proteins in the autistic brain. Our data thus confirm the role of epigenetic regulation of gene expression via differential DNA methylation in idiopathic autism, and furthermore link molecular changes in a peripheral cell model with brain pathobiology in autism.

The challenge of translation in social neuroscience: a review of oxytocin, vasopressin, and affiliative behavior

Social neuroscience is rapidly exploring the complex territory between perception and action where recognition, value, and meaning are instantiated. This review follows the trail of research on oxytocin and vasopressin as an exemplar of one path for exploring the "dark matter" of social neuroscience. Studies across vertebrate species suggest that these neuropeptides are important for social cognition, with gender- and steroid-dependent effects. Comparative research in voles yields a model based on interspecies and intraspecies variation of the geography of oxytocin receptors and vasopressin V1a receptors in the forebrain. Highly affiliative species have receptors in brain circuits related to reward or reinforcement. The neuroanatomical distribution of these receptors may be guided by variations in the regulatory regions of their respective genes. This review describes the promises and problems of extrapolating these findings to human social cognition, with specific reference to the social deficits of autism.

Early communication development in socially deprived children — similar to autism?

Social deprivation leads to various neuroanatomical, neuropsychological and behavioral disturbances in humans as well as in experimental animals. Shared characteristics of socially deprived subjects and subjects with autism have been documented. The aim of this study was to analyze early development of communication in institutionalized (INST) children (12–24 months) in comparison with age- and sexmatched group of typically developing (TD) children and a group of children with autism spectrum disorders (ASD). Our findings show that both socially deprived (INST) children and ASD children display delayed pattern of development in social, speech and symbolic domains. However, although INST children display significant developmental delay and share some features with ASD children, they have a qualitatively different developmental pattern of social communication in comparison to children with ASD. The results of this study indicate that growing up in an institution and lack of social and environmental stimuli influences development of skills that are fundamental for early speech and language development.

Defective oxytocin function: a clue to understanding the cause of autism?

The autism spectrum disorders are a group of conditions with neurobehavioral impairment affecting approximately 0.6% of children. The clinical presentation is complex and the etiology is largely unknown, although a major role of genetic factors is widely accepted. A number of genetic studies led to the identification of genes and/or copy number variants whose alterations are associated with autism, but no specific factor has been found so far to be responsible for a substantial proportion of cases. Epigenetic modifications may also play a role, as demonstrated by the occurrence of autism in genetic conditions caused by mutations in imprinted genes or regions.The article by Gregory et al. published this month in BMC Medicine, reports on genomic and epigenetic alterations of OXTR, the gene encoding the receptor for oxytocin. The involvement of this gene was suggested by its deletion in an autistic patient. The subsequent analysis of a group of unrelated autistic subjects did not show an OXTR deletion, but rather hypermethylation of the gene promoter, with a reduced mRNA expression.These findings address two major points of the current debate on the etiology and pathogenesis of autism: the role of oxytocin, known to be involved in modeling human behavior, and the possible involvement of epigenetic mechanisms. The nature of this epigenetic dysregulation is unknown but, if proved to be true, might explain the failure to identify sequence alterations in a host of candidate genes. Practical implications of these findings may be forthcoming, however not before extension and validation on a larger scale have confirmed their value.See the associated research paper by Gregory et al: http://www.biomedcentral.com/1741-7015/7/62.