Sex Differences In Autism Spectrum Disorder Research Articles

Gender effects on autism spectrum disorder: a multi-site resting-state functional magnetic resonance imaging study of transcriptome-neuroimaging.

The gender disparity in autism spectrum disorder (ASD) has been one of the salient features of condition. However, its relationship between the pathogenesis and genetic transcription in patients of different genders has yet to reach a reliable conclusion. To address this gap, this study aimed to establish a reliable potential neuro-marker in gender-specific patients, by employing multi-site functional magnetic resonance imaging (fMRI) data, and to further investigate the role of genetic transcription molecules in neurogenetic abnormalities and gender differences in autism at the neuro-transcriptional level. To this end, age was firstly used as a regression covariate, followed by the use of ComBat to remove the site effect from the fMRI data, and abnormal functional activity was subsequently identified. The resulting abnormal functional activity was then correlated by genetic transcription to explore underlying molecular functions and cellular molecular mechanisms. Abnormal brain functional activities were identified in autism patients of different genders, mainly located in the default model network (DMN) and precuneus-cingulate gyrus-frontal lobe. The correlation analysis of neuroimaging and genetic transcription further found that heterogeneous brain regions were highly correlated with genes involved in signal transmission between neurons' plasma membranes. Additionally, we further identified different weighted gene expression patterns and specific expression tissues of risk genes in ASD of different genders. Thus, this work not only identified the mechanism of abnormal brain functional activities caused by gender differences in ASD, but also explored the genetic and molecular characteristics caused by these related changes. Moreover, we further analyzed the genetic basis of sex differences in ASD from a neuro-transcriptional perspective.

Alterations of the Hippocampal Networks in Valproic Acid-Induced Rat Autism Model.

Autism Spectrum Disorder (ASD) is one of the most frequently diagnosed neurodevelopmental disorders, characterized among others by impairments in social interactions and repetitive behavior. According to one of the leading hypotheses about its origin, ASD is caused by the imbalance of excitatory and inhibitory circuit activity. ASD-related morphological and functional changes can be observed in several brain regions i.e., in the prefrontal cortex and the hippocampus. It is well-established that prenatal valproic-acid (VPA) exposure of rats on day 12.5 leads to neurodevelopmental alterations with autism-like clinical and behavioral symptoms. The aim of this study was to investigate potential changes in the excitability of neuronal networks and individual neurons of the hippocampus elicited by prenatal VPA treatment. As there are marked sex differences in ASD, offspring of both sexes were systematically tested, using two different age groups, to elucidate eventual differences in neurodevelopment after VPA treatment. Excitatory connections and long-term synaptic plasticity as well as intrinsic excitability of CA1 pyramidal cells were examined. Pregnant female Wistar rats received saline or 500 mg/kg VPA i. p. on gestation day 12.5. Brain slices of 6-week-old and 3-month-old offspring were investigated using extra- and intracellular electrophysiological techniques. Field potential- and whole-cell patch clamp recordings were carried out to measure network excitability and single cell activity in the CA1 region hippocampus. Enhanced excitability of hippocampal networks was detected in the 6-week-old VPA-treated male rats; however, this change could not be observed in 3-month-old males. Intrinsic excitability of single neurons, however, was increased in 3-month-old males. In 6-week-old treated females, the most prominent effect of VPA was an increase in voltage sag, to a similar degree to the neurons of the older age group. In 3-month-old females, a network excitability increase could be demonstrated, in a lesser degree than in younger males. It can be concluded, that VPA treatment had diverse effects on hippocampal excitability depending on the sex and the age of the animals. We found that certain alterations manifested in 6-week-old rats were compensated later, on the other hand, other changes persisted until the age of 3 months.

UNDERSTANDING SEX DIFFERENCES IN AUTISM SPECTRUM DISORDER

Autism spectrum disorder (ASD) is diagnosed more frequently in boys than in girls, at ratios of approximately 3-4:1. There is increasing appreciation that behavioral features, genetic risk factors, developmental paths, and treatment response differ across sexes, and girls with ASD remain an understudied group. Clare Harrop, PhD, examined sex-specific performance in visual attention. Christine Nordahl, PhD, employed fMRI to evaluate sex differences in amygdala structure and function. Dorothy Grice, MD, carried out deep phenotyping of DDX3X syndrome, a major cause of ASD in girls. Donna Werling, PhD, analyzed RNA-sequence data from prenatal and postnatal human prefrontal cortex in males and females. Dr. Harrop showed that visual interactive paradigms produced the largest differences in total attention between the ASD and typically developing (TD) groups; attention was greater when the sex of the subjects and gender of the objects were congruent. Dr. Nordahl demonstrated that global patterns of amygdala functional connectivity show robust sex differences in TD participants, but differences were attenuated in children with ASD; amygdala volume was positively correlated with internalizing behaviors in girls with ASD, but not in boys. Dr. Grice showed that 80% of individuals with DDX3X syndrome met the criteria for intellectual disability, 60% for ASD, and 53% for ADHD. Dr. Werling demonstrated that ASD risk genes were more likely to show female-skewed expression; however, the magnitude of the shifts was minimal. Male-biased expression was enriched for ASD-upregulated immune function–associated genes and for markers of endothelial cells and microglia. Studies of visual attention support the importance of reevaluating prior studies conducted with majority-male samples to consider biological sex and gender. Sex-specific patterns of amygdala development in ASD suggest differing etiologies and may be predictive of differential outcomes and treatment approaches. DDX3X syndrome provides an opportunity to examine genetic pathways to ASD and related phenotypes in girls. Transcriptome analyses indicate that sex effects act downstream from ASD risk genes via interacting pathways. Studies that delineate sex differences in ASD provide deeper understanding of risk pathways and trajectories and opportunities for more specific interventions. The discussants are Meng-Chuan Lai, MD, PhD, and Allison Jack, PhD, who will contextualize the talks to the larger field.

Sex differentiation of brain structures in autism: Findings from a gray matter asymmetry study.

Autism spectrum disorder (ASD) is diagnosed much more often in males than females. This male predominance has prompted a number of studies to examine how sex differences are related to the neural expression of ASD. Different theories, such as the "extreme male brain" theory, the "female protective effect" (FPE) theory, and the gender incoherence (GI) theory, provide different explanations for the mixed findings of sex-related neural expression of ASD. This study sought to clarify whether either theory applies to the brain structure in individuals with ASD by analyzing a selective high-quality data subset from an open data resource (Autism Brain Imaging Data Exchange I and II) including 35 males/35 females with ASD and 86 male/86 female typical-controls (TCs). We examined the sex-related changes in ASD in gray matter asymmetry measures (i.e., asymmetry index, AI) derived from voxel-based morphometry using a 2 (diagnosis: ASD vs. TC) × 2 (sex: female vs. male) factorial design. A diagnosis-by-sex interaction effect was identified in the planum temporale/Heschl's gyrus: (i) compared to females, males exhibited decreased AI (indicating more leftward brain asymmetry) in the TC group, whereas AI was greater (indicating less leftward brain asymmetry) for males than for females in the ASD group; and (ii) females with ASD showed reduced AI (indicating more leftward brain asymmetry) compared to female TCs, whereas there were no differences between ASDs and TCs in the male group. This interaction pattern supports the FPE theory in showing greater brain structure changes (masculinization) in females with ASD. LAY SUMMARY: To understand the neural mechanisms underlying male predominance in autism spectrum disorder (ASD), we investigated the sex differences in ASD-related alterations in brain asymmetry. We found greater changes in females with ASD compared with males with ASD, revealing a female protective effect. These findings provide novel insights into the neurobiology of sex differences in ASD.

Brain-based sex differences in autism spectrum disorder across the lifespan: A systematic review of structural MRI, fMRI, and DTI findings

Females with autism spectrum disorder (ASD) have been long overlooked in neuroscience research, but emerging evidence suggests they show distinct phenotypic trajectories and age-related brain differences. Sex-related biological factors (e.g., hormones, genes) may play a role in ASD etiology and have been shown to influence neurodevelopmental trajectories. Thus, a lifespan approach is warranted to understand brain-based sex differences in ASD. This systematic review on MRI-based sex differences in ASD was conducted to elucidate variations across the lifespan and inform biomarker discovery of ASD in females We identified articles through two database searches. Fifty studies met criteria and underwent integrative review. We found that regions expressing replicable sex-by-diagnosis differences across studies overlapped with regions showing sex differences in neurotypical cohorts. Furthermore, studies investigating age-related brain differences across a broad age-span suggest distinct neurodevelopmental patterns in females with ASD. Qualitative comparison across youth and adult studies also supported this hypothesis. However, many studies collapsed across age, which may mask differences. Furthermore, accumulating evidence supports the female protective effect in ASD, although only one study examined brain circuits implicated in “protection.” When synthesized with the broader literature, brain-based sex differences in ASD may come from various sources, including genetic and endocrine processes involved in brain “masculinization” and “feminization” across early development, puberty, and other lifespan windows of hormonal transition. Furthermore, sex-related biology may interact with peripheral processes, in particular the stress axis and brain arousal system, to produce distinct neurodevelopmental patterns in males and females with ASD. Future research on neuroimaging-based sex differences in ASD would benefit from a lifespan approach in well-controlled and multivariate studies. Possible relationships between behavior, sex hormones, and brain development in ASD remain largely unexamined.

An Exploration of Physical and Phenotypic Characteristics of Bangladeshi Children with Autism Spectrum Disorder.

This study explored the physical and clinical phenotype of Bangladeshi children with autism spectrum disorder (ASD). A totally of 283 children who were referred for screening and administered Module 1 of the Autism Diagnostic Observation Schedule (ADOS) were included. Overall, 209 met the ADOS algorithmic cutoff for ASD. A trend for greater weight and head circumference was observed in children with ASD versus non-ASD. Head circumference was significantly (p < 0.03) larger in ASD males compared with non-ASD males. A trend was also observed for symptom severity, higher in females than males (p = 0.068), with further analyses demonstrating that social reciprocity (p < 0.014) and functional play (p < 0.03) were significantly more impaired in ASD females than males. The findings help understand sex differences in ASD.

Sex Differences in Social Participation of High School Students with Autism Spectrum Disorder.

There is lack of consensus in the literature regarding sex differences in social outcomes for individuals on the autism spectrum. Furthermore, little research has focused on the social experiences of high school students with autism spectrum disorder (ASD) during the school day. Using a large racially/ethnically diverse sample of high school students with ASD receiving special education services (n = 547; 76 females, 471 males), we examined sex differences in social interactions of youth both during and after school. We also tested for sex differences in background and phenotypic characteristics including autism severity, IQ, adaptive behavior, and mental health. Results indicated few statistically significant differences between males and females in social interactions and phenotypic characteristics (including raw scores of autism symptom severity). However, analysis of standardized scores of autism symptoms suggested that symptom scores for females with ASD diverged more from same-sex peers in the normed sample than scores of males with ASD. Lack of sex difference in social participation for youth with ASD in this study stands in contrast to patterns of sex differences in the general population. Findings suggest that few differences between males and females with ASD, both in social participation and autism symptom severity, might result in females with ASD being more dissimilar to their same-sex peers than males with ASD. Implications of findings for understanding sex differences in ASD across the life course are discussed. LAY SUMMARY: The present study examined sex differences in social participation in a large, diverse sample of high school students with autism spectrum disorder (ASD). Males and females were very similar in their social interactions both at school and outside of school, based on reports by teachers and parents. Level of autism symptoms was also similar for males and females. However, standardized scores of autism symptoms, which take into account age and sex specific norms, suggested that females with ASD may have behaviors that are more divergent from their same-sex peers than males with ASD.

Differences in Developmental Functioning Profiles Between Male and Female Preschoolers Children With Autism Spectrum Disorder.

This study investigated differences in clinical symptoms and developmental functioning profiles as well as sex-specific correlations of clinical characteristics and communication abilities, motor skills, and maladaptive behaviors in male and female preschoolers with autism spectrum disorder (ASD). Fifty-two females (mean age 4.5 ± 2.16 years old) and 62 males (mean age 4.2 ± 1.17 years old) with ASD were enrolled and assessed by measures including the Autism Diagnostic Observation Schedule-Second Edition (ADOS-2) and Psychoeducational Profile-Third Edition (PEP-3). We found intellectual disability in 91.2% of the children. While preschoolers with ASD showed comparable severity of restricted and repetitive behaviors (P = 0.17), females with ASD were less severely affected than age and intelligence quotient-matched males with ASD in the ADOS-2 social affect domain (P value = 0.001) and calibrated severity scores (P = 0.002). Interestingly, sex-specific linear regressions revealed that fine motor skills were predictive of impaired social affect in males but not in females. Specifically, motor skills might be the core feature for sex differences in ASD. Although preliminary, this finding suggests the need for more sex-specific diagnostic and intervention strategies in order to improve early identification efforts and specific intervention targets. LAY SUMMARY: Little is known about differences in developmental and functional profiles in males and females with autism spectrum disorder (ASD). We found important similarities and differences in the core ASD symptoms between male and female preschoolers. In addition, fine motor skills seem to predict social affect impairment and ASD symptom severity in males with ASD. Autism Res 2020, 13: 1537-1547. © 2020 International Society for Autism Research, Wiley Periodicals, Inc.

Imaging-genetics of sex differences in ASD: distinct effects of OXTR variants on brain connectivity

Autism spectrum disorder (ASD) is more prevalent in males than in females, but the neurobiological mechanisms that give rise to this sex-bias are poorly understood. The female protective hypothesis suggests that the manifestation of ASD in females requires higher cumulative genetic and environmental risk relative to males. Here, we test this hypothesis by assessing the additive impact of several ASD-associated OXTR variants on reward network resting-state functional connectivity in males and females with and without ASD, and explore how genotype, sex, and diagnosis relate to heterogeneity in neuroendophenotypes. Females with ASD who carried a greater number of ASD-associated risk alleles in the OXTR gene showed greater functional connectivity between the nucleus accumbens (NAcc; hub of the reward network) and subcortical brain areas important for motor learning. Relative to males with ASD, females with ASD and higher OXTR risk-allele-dosage showed increased connectivity between the NAcc, subcortical regions, and prefrontal brain areas involved in mentalizing. This increased connectivity between NAcc and prefrontal cortex mirrored the relationship between genetic risk and brain connectivity observed in neurotypical males showing that, under increased OXTR genetic risk load, females with ASD and neurotypical males displayed increased connectivity between reward-related brain regions and prefrontal cortex. These results indicate that females with ASD differentially modulate the effects of increased genetic risk on brain connectivity relative to males with ASD, providing new insights into the neurobiological mechanisms through which the female protective effect may manifest.

3 RARE HEMIZYGOUS MUTATIONS WITHIN CHROMOSOME X NON-PSEUDOAUTOSOMAL REGIONS CONTRIBUTE MALE-SPECIFIC AUTISM RISK

Autism spectrum disorder (ASD) is consistently diagnosed 3 to 5 times more frequently in males than females, a dramatically sex-biased prevalence that suggests the involvement of sex-differential biological factors in modulating risk. The genomic scale of transcriptomic analyses of human brain tissue can provide an unbiased approach for identifying genes and associated functional processes at the intersection of sex-differential and ASD-impacted neurobiology. Several studies characterizing gene expression changes in the ASD brain have been published in recent years with increasing sample size and cellular resolution. These studies report several convergent patterns across data sets and genetically heterogeneous samples in the ASD brain, including elevated expression of gene sets associated with glial and immune function, and reduced expression of gene sets associated with neuronal and synaptic functions. Assessment of neurotypical cortex tissue has reported parallel patterns by sex, with male-elevated expression of overlapping sets of glial/immune-related genes and female-biased expression of neuron-associated genes, suggesting potential roles for these cell types in sex-differential ASD risk mechanisms. However, validating and further exploring these mechanisms is challenged by the available data, as existing studies of ASD brain include a limited number of female ASD donors and focus predominantly on cortex regions not known to show pronounced sex-differential morphology or function. With this review, we summarize convergent findings from several landmark studies of the transcriptome in ASD brain and their relationship to sex-differential gene expression, and we discuss limitations and remaining questions regarding transcriptomic analysis of sex differences in ASD.

Sex Differences in the Amygdala Resting-State Connectome of Children With Autism Spectrum Disorder

BackgroundMultifactorial liability models predict greater dissimilarity in the neural phenotype of autism spectrum disorder (ASD) in female individuals than in male individuals, while gender incoherence and extreme male brain models predict attenuated sex differences in ASD. The amygdala is an informative target to explore these models because it is implicated in both the neurobiology of ASD and sex differences in typical development. MethodsThis study investigated amygdala resting-state functional connectivity in a cohort of 116 children with ASD (36 female) and 58 typically developing children (27 female) 2 to 7 years of age during natural sleep. First, multivariate distance matrix regression assessed global sex and diagnostic differences across the amygdala connectome. Second, univariate general linear models identified regions with mean connectivity differences. ResultsMultivariate distance matrix regression revealed greater differences between typically developing children and those with ASD in females than in males, consistent with multifactorial liability models, and attenuated sex differences in the left amygdala connectome of children with ASD in a pattern consistent with the gender incoherence model. Univariate analysis identified similar sex differences in dorsomedial and ventral prefrontal cortices, lingual gyrus, and posterior cingulate cortex, but also noted that lower amygdala connectivity with superior temporal sulcus is observed across sexes. ConclusionsThis study provides evidence that compared with sex-matched control subjects, ASD manifests differently in the brain at the time of diagnosis and prior to the influence of compensatory mechanisms in male and female children, consistent with multifactorial liability models, and that ASD is associated with reduced sex differences in a pattern consistent with gender incoherence models.

Self-Reported Autism Spectrum Disorder Symptoms Among Adults Referred to a Gender Identity Clinic.

The purpose of this study was to (1) investigate autism spectrum disorder (ASD) symptoms in a sample of adults referred for gender dysphoria (GD) compared to typically developing (TD) populations, (2) see whether males assigned at birth with GD (MaBGDs) and females assigned at birth with GD (FaBGDs) differ in ASD symptom levels, (3) study the role of sexual orientation, and (4) investigate ASD symptoms' correlation with GD symptoms. The Autism-Spectrum Quotient (AQ) was used to measure ASD symptoms, and the Utrecht Gender Dysphoria Scale (UGDS) was used to measure the intensity of GD. Mean AQ scores of adults referred for GD (n = 326; 191 MaBGD and 135 FaBGD) were compared to three TD populations taken from the literature (n = 1316; 667 male and 644 female, 5 birth-assigned sex unknown). The mean AQ score in individuals referred for GD was similar to the TD samples. FaBGDs showed higher mean AQ scores than MaBGDs, and they had mean scores similar to TD individuals of the same experienced gender (TD males). After selecting individuals with an UGDS score indicative of GD, a positive association between ASD and GD symptoms was found. The co-occurrence of GD and ASD in adults may not be as prevalent as previously suggested. Attenuation of sex differences in ASD might explain FaBGDs' and MaBGDs' ASD symptoms' similarity to those of TD individuals of the same experienced gender. Intensity of ASD symptoms might be correlated with intensity of GD symptoms, warranting further studies to elaborate on their potential co-occurrence.

Sexually Dimorphic Epigenetic Regulation of Brain-Derived Neurotrophic Factor in Fetal Brain in the Valproic Acid Model of Autism Spectrum Disorder

Prenatal exposure to the antiepileptic, mood-stabilizing drug, valproic acid (VPA), increases the incidence of autism spectrum disorders (ASDs); in utero administration of VPA to pregnant rodents induces ASD-like behaviors such as repetitive, stereotyped activity, and decreased socialization. In both cases, males are more affected than females. We previously reported that VPA, administered to pregnant mice at gestational day 12.5, rapidly induces a transient, 6-fold increase in BDNF (brain-derived neurotrophic factor) protein and mRNA in the fetal brain. Here, we investigate sex differences in the induction of Bdnf expression by VPA as well as the underlying epigenetic mechanisms. We found no sex differences in the VPA stimulation of total brain Bdnf mRNA as indicated by probing for the BDNF protein coding sequence (exon 9); however, stimulation of individual transcripts containing two of the nine 5′-untranslated exons (5′UTEs) in Bdnf (exons 1 and 4) by VPA was greater in female fetal brains. These Bdnf transcripts have been associated with different cell types or subcellular compartments within neurons. Since VPA is a histone deacetylase inhibitor, covalent histone modifications at Bdnf 5′UTEs in the fetal brain were analyzed by chromatin immunoprecipitation. VPA increased the acetylation of multiple H3 and H4 lysine residues in the vicinity of exons 1, 2, 4, and 6; minimal differences between the sexes were observed. H3 lysine 4 trimethylation (H3K4me3) at those exons was also stimulated by VPA. Moreover, the VPA-induced increase in H3K4me3 at exons 1, 4, and 6 was significantly greater in females than in males, i.e., sexually dimorphic stimulation of H3K4me3 by VPA correlated with Bdnf transcripts containing exons 1 and 4, but not 6. Neither H3K27me3 nor cytosine methylation at any of the 117 CpGs in the vicinity of the transcription start sites of exons 1, 4, and 6 was affected by VPA. Thus, of the 6 epigenetic marks analyzed, only H3K4me3 can account for the sexually dimorphic expression of Bdnf transcripts induced by VPA in the fetal brain. Preferential expression of exon 1- and exon 4-Bdnf transcripts in females may contribute to sex differences in ASDs by protecting females from the adverse effects of genetic variants or environmental factors such as VPA on the developing brain.

Enhancing studies of the connectome in autism using the autism brain imaging data exchange II

The second iteration of the Autism Brain Imaging Data Exchange (ABIDE II) aims to enhance the scope of brain connectomics research in Autism Spectrum Disorder (ASD). Consistent with the initial ABIDE effort (ABIDE I), that released 1112 datasets in 2012, this new multisite open-data resource is an aggregate of resting state functional magnetic resonance imaging (MRI) and corresponding structural MRI and phenotypic datasets. ABIDE II includes datasets from an additional 487 individuals with ASD and 557 controls previously collected across 16 international institutions. The combination of ABIDE I and ABIDE II provides investigators with 2156 unique cross-sectional datasets allowing selection of samples for discovery and/or replication. This sample size can also facilitate the identification of neurobiological subgroups, as well as preliminary examinations of sex differences in ASD. Additionally, ABIDE II includes a range of psychiatric variables to inform our understanding of the neural correlates of co-occurring psychopathology; 284 diffusion imaging datasets are also included. It is anticipated that these enhancements will contribute to unraveling key sources of ASD heterogeneity.

Pleiotropic Mechanisms Indicated for Sex Differences in Autism.

Sexual dimorphism in common disease is pervasive, including a dramatic male preponderance in autism spectrum disorders (ASDs). Potential genetic explanations include a liability threshold model requiring increased polymorphism risk in females, sex-limited X-chromosome contribution, gene-environment interaction driven by differences in hormonal milieu, risk influenced by genes sex-differentially expressed in early brain development, or contribution from general mechanisms of sexual dimorphism shared with secondary sex characteristics. Utilizing a large single nucleotide polymorphism (SNP) dataset, we identify distinct sex-specific genome-wide significant loci. We investigate genetic hypotheses and find no evidence for increased genetic risk load in females, but evidence for sex heterogeneity on the X chromosome, and contribution of sex-heterogeneous SNPs for anthropometric traits to ASD risk. Thus, our results support pleiotropy between secondary sex characteristic determination and ASDs, providing a biological basis for sex differences in ASDs and implicating non brain-limited mechanisms.

Sex bias in autism spectrum disorder in neurofibromatosis type 1

BackgroundDespite extensive literature, little is known about the mechanisms underlying sex bias in autism spectrum disorder (ASD). This study investigates the sex differences in ASD associated with neurofibromatosis type 1, a single-gene model of syndromic autism.MethodsWe analysed data from n = 194 children aged 4–16 years with neurofibromatosis type 1. Sex differences were evaluated across the Autism Diagnostic Interview-Revised (ADI-R), Autism Diagnostic Observation Schedule (ADOS), verbal IQ, Social Responsiveness Scale (SRS) and Conners questionnaires.ResultsThere was 2.68:1 male:female ratio in children meeting ASD criteria on the deep phenotyping measures. On symptom profile, males with neurofibromatosis type 1 (NF1) + ASD were more impaired on reciprocal social interaction and communication domains of the ADI-R but we found no differences on the restricted, repetitive behaviours (RRBs) domain of the ADI-R and no differences on the social on the ADOS. NF1 ASD males and females were comparable on verbal IQ, and the inattention/hyperactivity domains of the Conners questionnaire.ConclusionsThere is a significant male bias in the prevalence of ASD in NF1. The phenotypic profile of NF1 + ASD cases includes greater social communication impairment in males. We discuss the implications of our findings and the rationale for using NF1 as a model for investigating sex bias in idiopathic ASD.

Sex differences in cortical volume and gyrification in autism.

BackgroundMale predominance is a prominent feature of autism spectrum disorders (ASD), with a reported male to female ratio of 4:1. Because of the overwhelming focus on males, little is known about the neuroanatomical basis of sex differences in ASD. Investigations of sex differences with adequate sample sizes are critical for improving our understanding of the biological mechanisms underlying ASD in females.MethodsWe leveraged the open-access autism brain imaging data exchange (ABIDE) dataset to obtain structural brain imaging data from 53 females with ASD, who were matched with equivalent samples of males with ASD, and their typically developing (TD) male and female peers. Brain images were processed with FreeSurfer to assess three key features of local cortical morphometry: volume, thickness, and gyrification. A whole-brain approach was used to identify significant effects of sex, diagnosis, and sex-by-diagnosis interaction, using a stringent threshold of p < 0.01 to control for false positives. Stability and power analyses were conducted to guide future research on sex differences in ASD.ResultsWe detected a main effect of sex in the bilateral superior temporal cortex, driven by greater cortical volume in females compared to males in both the ASD and TD groups. Sex-by-diagnosis interaction was detected in the gyrification of the ventromedial/orbitofrontal prefrontal cortex (vmPFC/OFC). Post-hoc analyses revealed that sex-by-diagnosis interaction was driven by reduced vmPFC/OFC gyrification in males with ASD, compared to females with ASD as well as TD males and females. Finally, stability analyses demonstrated a dramatic drop in the likelihood of observing significant clusters as the sample size decreased, suggesting that previous studies have been largely underpowered. For instance, with a sample of 30 females with ASD (total n = 120), a significant sex-by-diagnosis interaction was only detected in 50 % of the simulated subsamples.ConclusionsOur results demonstrate that some features of typical sex differences are preserved in the brain of individuals with ASD, while others are not. Sex differences in ASD are associated with cortical regions involved in language and social function, two domains of deficits in the disorder. Stability analyses provide novel quantitative insights into why smaller samples may have previously failed to detect sex differences.Electronic supplementary materialThe online version of this article (doi:10.1186/s13229-015-0035-y) contains supplementary material, which is available to authorized users.

Sex differences in autism spectrum disorders: does sex moderate the pathway from clinical symptoms to adaptive behavior?

We explored sex differences in diagnostic categories, clinical symptoms and adaptive behavior of persons with autism spectrum disorders, as well as sex-specific correlations of clinical and adaptive caracteristics. The study involved 108 patients (83 males, 6.73 ± 4.33 years old) diagnosed with autism spectrum disorders (ASD). Assessment included ADI-R and Vineland Adaptive Behavior Scale II. Males were more often diagnosed with typical autism. There were no sex differences in the autistic symptoms, while females showed better functioning in Daily living skills, without reaching statistically significant difference (p = 0.062). We have found different associations of autistic symptoms with different aspects of adaptive behavior in males and females. Social reciprocity in females correlated with social domain of adaptive behavior, in a positive direction. Our findings have shown that although there are no sex differences in autistic symptoms, females tend to be somewhat more functional, and are also less frequently diagnosed with typical autism. Our results have also shown that sex might moderate the way clinical symptoms are expressed in adaptive behavior. Social reciprocity might be the core feature regarding sex differences in ASD. Our findings might have diagnostic and therapeutical implications, pointing out to the need for individualized, sex-specific treatment in this group of disorders.

Sex differences in children with autism spectrum disorders compared with their unaffected siblings and typically developing children

This study examined the nature of cognitive and behavioral sex differences in children with autism spectrum disorders (ASDs) and two comparison groups: a group of typically developing (TD) children and a group of unaffected siblings of ASD children. Sex differences in core autistic symptoms, co-occurring behavioral symptoms, and cognitive styles were assessed in each group. Females with ASD were less severely affected than IQ- and age-matched males with ASD in the communication and repetitive stereotyped behavior domains, as measured by the ADI-R, but such sex differences were less significant than they were in the unaffected sibling group. Several behavioral/emotional symptom scores were significantly higher in male siblings than in female siblings. However, the ASD and TD groups did not show sex differences in any behavioral/emotional symptom scores. Males were superior in systemizing relative to empathizing, while the opposite was true for females in the unaffected sibling group and the TD children group; however, both males and females were superior in systemizing relative to empathizing in the ASD group. Our findings support the extreme male brain theory of autism, and further studies are needed to understand the mechanisms behind and developmental perspectives on the nature of sex differences in ASD.

Sex differences in cognitive domains and their clinical correlates in higher-functioning autism spectrum disorders

Despite the skewed sex ratio, few studies have addressed possible cognitive sex differences in autism spectrum disorders (ASDs). This study compared visual attention to detail (ATTD) and selected executive functions (EF) in 35 males and 21 females with higher-functioning ASD and unaffected sibling controls. Females with ASD outperformed males on EF as assessed by the Trail Making Test B-A. Males with ASD showed superior performance for ATTD as measured by the Block Design Test (BD) when compared with females. EF difficulties in males were correlated with more stereotypic behaviours and interests on the Autism Diagnostic Interview-Revised or the Autism Diagnostic Observation Schedule. The results indicated clinically meaningful cognitive sex differences in ASD, particularly an association between EF and stereotypic behaviours and interests. ATTD as a potential basis for specific cognitive strengths (e.g. scientific/savant skills) might be more pronounced in males with ASD.