Molecular Autism

Behavioral inflexibility and perseveration are core features of autism spectrum disorder and are frequently modeled in mice using reversal learning and repetitive behavior assays. Mutations in CACNA1D, which encodes the L-type calcium channel Cav1.3, have been linked to autism, yet their behavioral consequences remain incompletely characterized. We examined mice carrying the autism-associated Cacna1dG407R gain-of-function mutation across a battery of assays assessing learning, flexibility, and repetitive behavior. Mutant mice learned spatial discriminations and instrumental contingencies at rates comparable to wild-type controls but exhibited deficits during reversal learning following intermediate and extended overtraining, as well as under probabilistic reinforcement. Across ethological assays, mutant mice showed increased grooming, marble burying, and nestlet shredding, consistent with enhanced perseverative behavior. Anxiety-related measures and general locomotion were largely unaffected. These results identify Cav1.3 gain-of-function as a selective regulator of behavioral flexibility and support a role for calcium-dependent corticostriatal plasticity in autism-associated perseveration.

Mutations in the ATRX gene are a primary cause of ATR-X syndrome, which is characterized by intellectual disability, autism, and a range of brain structural abnormalities, including microcephaly. We previously showed that mice with conditional ATRX ablation in forebrain excitatory neurons display deficits in fear memory and autism-related behaviors, with some effects exhibiting sexual dimorphism. In this study, we used high-resolution magnetic resonance imaging (MRI) to systematically characterize brain structural changes associated with these behavioral abnormalities. Whole-brain analysis revealed male-specific microcephaly, while subregional analysis identified significant reductions in hippocampal structures and increased volume of the caudal cortex in mutant animals of both sexes. We also identified structural alterations in regions retaining ATRX expression, such as the thalamus, midbrain, cerebellum, and several fiber tracts. These findings suggest that ATRX loss disrupts the coordinated development of interconnected brain regions. Overall, our results implicate impaired cortico-thalamic-cerebellar connectivity as a potential neural substrate underlying the autistic-like behaviors observed in this mouse model, providing new insights into the neurobiological basis of ATR-X syndrome. LAY SUMMARYChanges in a gene called ATRX are known to affect brain development and are linked to intellectual disability and autism. In our previous work, we found that removing this gene early in brain development caused mice to show behaviors like those seen in people with autism. In this study, we used detailed brain scans to see if these behavioral changes were linked to differences in brain structure. We found that male mice without ATRX had smaller brains and bodies, while female mice did not show the same brain size reduction. However, both male and female mice had smaller areas of the brain important for memory and movement, and larger areas involved in thinking and sensing. We also saw changes in parts of the brain where ATRX was still present, suggesting that early changes in one area can affect how the whole brain develops. These findings help us understand how early disruptions in brain development might lead to autism-related behaviors.

A large subset of ASD associated genes, almost 50% of the highest confidence risk genes listed on the Simons Foundation Autism Research Institute database, are epigenetic modifiers. This suggests that the organization of sensory biology and its coupling to underlying genetic control are an important element underpinning this discord. Furthermore, sensory processing changes in individuals with autism spectrum disorder (ASD) has been a growing area of study in recent years. C. elegans have robust readouts for both developmental and sensory biology allowing these signatures of ASD to be systematically modelled. 52 epigenetic modifiers (65 strains) were selected for study in C. elegans based on gene function, presence of orthologues in C. elegans and the availability of viable putative null strains. This highlighted significant changes to reproduction, gross development and sensory processing across the range of epigenetic modifiers. Each strain was filtered against selective criteria for significant sensory and developmental phenotypes allowing for selective phenotypic profiles to emerge. These were three primary groups, those with sensory perturbations but unaffected gross development (6), developmentally affected genes with intact sensory function (10) and finally genes with impaired gross development and sensory function (11). Thus, this study provides a link between sensory and developmental outcomes in ASD associated mutant strains and suggests that more regular sensory testing should be performed in human cohorts to further refine sub-categorisation of ASD cohorts.

Autism Spectrum Disorder (ASD) is a large set of neurodevelopmental disorders of complex aetiology. A mix of genetic and environmental factors are likely to cause ASD. Genetic risk for autism comes from common genetic variation. Genomic imprinting refers to genes that have different expression patterns according to the parent of origin - being silenced when imprinted. Paternally active genes increase resource extraction from the mother and reduce resource burden on the father. Children with ASD show consistent overgrowth during their first 1-2 years of life. Recently, it has been shown that children with higher birth weight and length have an increased risk of developing ASD. This overgrowth and apparent larger birth weight and length are consistent with the notion that a paternally biased genome might underlie the risk for ASD. The study compared height, weight, head circumference and thoracic circumference for age-matched (ages 4-8 years old) male children with ASD (n=30) with neurotypical children (n=33). No clinically significant differences were found among the two groups. After weaning, relative paternal contribution to a childs somatic development would increase, thus one would expect paternally active genes to start changing the childs behaviour, so as to make the child less demanding of resources (overall, and thus also on the father), with a counterweight represented by maternally active genes. A relative overabundance of paternally active genes would explain the data presented here, that shows children with ASD being no different from controls. Given the fact presented by other studies, that children with ASD seem to get a head start in growth, the lack of differences found in this 4-8 years old group indicates that children with ASD might actually fall behind in somatic growth, or at least stagnate by middle childhood.

ObjectiveMaternal immune activation during pregnancy has been proposed as a mechanism linking prenatal inflammatory exposures to autism pathogenesis. While preclinical and epidemiological studies suggest a role for maternal inflammation and infection, findings in population-based cohorts are inconsistent. This study examined the associations between multiple prenatal inflammatory exposures and autistic traits, accounting for gene-environment interactions in the general pediatric population. MethodsWe leveraged data from 5,075 mother-child dyads participating in Generation R, a population-based pregnancy cohort in the Netherlands. Prenatal inflammatory exposures included 1) maternal serum cytokines; 2) high-sensitivity CRP; 3) self-reported fever during pregnancy; 4) a maternal polygenic score for CRP; and 5) a methylation profile score of CRP in cord blood. Child autistic traits were measured with the Social Responsiveness Scale at mean ages 6 and 13 years. Linear mixed models were applied to estimate associations adjusted for maternal, child and technical covariates. Interaction terms tested whether child polygenic score for autism moderated associations. ResultsNo significant associations were observed between prenatal inflammatory exposures and autistic traits, both as a continuous measure and above a clinical threshold. No evidence was found for interactions between prenatal inflammatory exposures and the child polygenic score for autism in influencing autistic traits. ConclusionOur findings suggest that typical fluctuations in maternal inflammation are unlikely to represent a major pathway linking prenatal environment to autism risk. We found no evidence that gene-environment interactions conferred additional risk for autistic traits.

Infants born preterm are at a significantly higher likelihood of having autism spectrum disorder (ASD). Preterm birth and ASD are both associated with neurological differences, notably autonomic nervous system (ANS) dysfunction, pointing to preterm ANS dysfunction as a potential pathway to ASD, particularly in VPT infants. In this study, a subset of very preterm (VPT) infants enrolled in a large, multisite clinical trial were enrolled in this study at birth (N=20). Continuous measures of minute-by-minute thermal gradients, defined by the difference between central and peripheral temperatures, and hour-by-hour abnormal heart rate characteristics (HRCs) were collected from birth-28 days (>40,000 samples/infant). Following NICU discharge, standardized measures of cognition, language, and motor skills were collected at adjusted ages 6, 9, and 12 months. At 12 months, assessments of social communication and early ASD symptoms were administered. Results suggest significant ASD concerns for half of the sample by 12 months of age. Neonatal abnormal HRCs were strongly associated with 12-month ASD symptoms (r=0.81, p<.01), as was birth gestational age (GA), birth weight (BW), and abnormal negative thermal gradients. ANS measures collected in the first month of neonatal life, more than a year prior to the ASD evaluation, were surprisingly strong predictors of ASD. This study highlights complementary ANS measures that describe how ANS dysfunction, likely resulting from an imbalance between the parasympathetic and sympathetic systems, may impact very early regulatory processes for neonates who later develop ASD. This finding offers a promising avenue for researching ANS-related etiological mechanisms and biomarkers of ASD.

BackgroundPreterm birth and other perinatal adversities lead to the loss of placental support including critical hormones, such as insulin-like growth factor 1 (IGF1), required for neurodevelopment. Decreased IGF1 and preterm birth are associated with neurodevelopmental disorder risk, including autism spectrum disorder. Whether placental Igf1 insufficiency drives neurodevelopmental risks is not understood. MethodsTo understand these mechanisms, placental-targeted CRISPR manipulation in mice was employed to create placental Igf1 insufficiency. Subsequently, embryonic forebrain development was assessed sex-specifically to identify structural and transcriptomic changes. Postnatal offspring were used to determine neurobehavioral trajectories relevant to neurodevelopmental disorders as assessed through learning, motor, and affective behavioral tasks and neurostereology. ResultsPlacental Igf1 insufficiency reduced embryonic forebrain growth, including decreased cell population across males and females. Embryonic forebrain transcriptomics revealed sex-specific alterations. Autism relevant developmental pathways were downregulated in male forebrain, driven by genes including Reln and Lama1. Altered genes in female forebrain were enriched for autism-risk genes including Grin2b and Dync1h1. Following these transcriptomic differences, postnatal neurobehavioral trajectories were sex specific. Male offspring uniquely showed reduced motor learning, increased stereotyped behaviors, altered reversal learning, and reduced forebrain neuronal number. Female offspring displayed opposite behavioral changes as males and few changes in forebrain structure. ConclusionsThe provision of Igf1 specifically from placenta is critical for offspring forebrain development. This temporary early deficit has persistent sex-specific neurobehavioral effects. These outcomes have relevance for autism risk and highlight mechanisms that could facilitate intervention development for adverse outcomes after early loss of placental hormone support in perinatal adversity.

Autism is a common neurodevelopmental disorder that despite its complex etiology, is marked by deficits in prediction that manifest in a variety of domains including social interactions, communication, and movement. The tendency of individuals with autism to focus on predictable schedules and interests that contain patterns and rules highlights the likely involvement of the cerebellum in this disorder. One candidate-autism gene is contact in associated protein 2 (CNTNAP2), and variants in this gene are associated with sensory deficits and anatomical differences. It is unknown, however, whether this gene directly impacts the brains ability to make and evaluate predictions about future events. The current study was designed to answer this question by training a genetic knockout rat on a rapid speech sound discrimination task. Rats with Cntnap2 knockout (KO) and their littermate wildtype controls (WT) were trained on a validated rapid speech sound discrimination task that contained unpredictable and predictable targets. We found that although both genotype groups learned the task in both unpredictable and predictable conditions, the KO rats responded more often to distractors during training as well as to the target sound during the predictable testing conditions compared to the WT group. There were only minor effects of sex on performance and only in the unpredictable condition. The current results provide preliminary evidence that removal of this candidate-autism gene may interfere with the learning of unpredictable scenarios and enhance reliance on predictability. Future research is needed to probe the neural anatomy and function that drives this effect.

The excitatory/inhibitory (E/I) imbalance theory suggests that excitatory and inhibitory alterations underlies autism characteristics. However, genetic underpinnings of this imbalance and its impact on brain function and behavior remains unclear. We explored causal links between glutamate and GABA gene-set polygenic scores (PGS) for autism and core autism characteristics, putting particular attention on the restricted-and repetitive behaviors domain by including functional activity (fMRI) during inhibitory control (in the anterior cingulate cortex (ACC) and striatum). Causal links between genes, brain and behavior was evaluated using Bayesian Constraint-based Causal Discovery (BCCD) algorithms, to build causal models of these relationships in a discovery sample (LEAP cohort: autistic = 343, neurotypical = 253) and two generalization cohorts with partially overlapping measures (TACTICS cohort: autistic = 60, neurotypical = 100, Simon Simplex Collection: autistic = 2756). In the discovery sample, we found a causal link between glutamate PGS and core clinical characteristics of autism, particularly the communication domain (Autism Diagnostic Interview-Revised) in autistic participants, with 95% reliability. We did not find links between functional activity during inhibitory control and other measures. For one generalization cohort, we further report on the impact of 1H-MRS measures of glutamate, identifying a causal link between GABA autism PGS on ACC glutamate concentrations. Not all links were identified in the generalization cohorts, which may be due to clinical and genetic differences between the cohorts. While our results reinforce the previously found association between glutamate genes and core clinical autism behaviors, task-based functional activity may not be causally related to RRBs.

Reproducible patterns of atypical functional connectivity of sensorimotor and higher-order networks have been previously identified in the autistic brain. However, the neurosignalling pathways underpinning these differences remain unclear. The {micro}-opioid system is involved in sensory processing as well as social and reward behaviours and has been implicated in autism, suggesting a potential role in shaping the autistic brain. Hence, we tested the hypothesis that there is atypical involvement of the {micro}-opioid system in these networks in autism. We used a placebo-controlled, double-blind, randomised, crossover study design to compare the effects of an acute dose of the {micro}-opioid receptor agonist tianeptine in autistic and non-autistic participants on functional connectivity (FC) of sensorimotor and frontoparietal networks. We found that tianeptine increased FC of a sensorimotor network previously characterised by atypically low FC in autism. The connectivity of the frontoparietal network was not significantly shifted. Our findings suggest that {micro}-opioid neurosignalling might contribute to functional brain differences in the sensorimotor network in autism. Given that sensorimotor system alterations are thought to be core to autism and contribute to other core autistic features, as well as adaptability and mental health, further research is warranted to explore the translational potential of {micro}-opioid modulation in autism.

Mimicry facilitates social bonding throughout the lifespan. Mimicry impairments in autism spectrum conditions (ASC) are widely reported, including differentiation of the brain networks associated with its social bonding and learning functions. This study examined associations between volumes of brain regions associated with social bonding versus procedural skill learning, and mimicry of gestures during a naturalistic interaction in ASC and neurotypical (NT) children. Consistent with predictions, results revealed reduced mimicry in ASC relative to the NT children. Mimicry frequency was negatively associated with autism symptom severity. Mimicry was predicted predominantly by the volume of procedural skill learning regions in ASC, and by bonding regions in NT. Further, bonding regions contributed significantly less to mimicry in ASC than in NT, while the contribution of learning regions was not different across groups. These findings suggest that associating mimicry with skill learning, rather than social bonding, may partially explain observed communication difficulties in ASC.

De novo mutations in the chromatin-remodeling factor CHD8 (Chromodomain-Helicase DNA-binding protein 8) have emerged as a key genetic risk factor for Autism Spectrum Disorder (ASD) and, more generally, neurodevelopmental disorders. Individuals with heterozygous mutations in CHD8 typically present hallmarks of ASD with comorbid cognitive disability and macrocephaly. Knockdown or haploinsufficiency of Chd8 in animal models has recapitulated phenotypes observed in patients, including increased head circumference and brain size. Here, we aimed to determine whether increased neuron numbers or soma size drives increased cortical volume. We performed design-based stereological analyses of cortical structure in adult male and female heterozygous Chd8 mice and wild-type littermate controls. Chd8 haploinsufficient male mice displayed a ~8-12% increase in cortical volume, no differences in cortical neuron number and comparable neuronal soma size. Our study reproduced previous reports of increased brain size associated with CHD8 mutation in humans and mice and are consistent with reported sex-specific impacts of Chd8 mutations in mice and increased burden of CHD8 mutations in human males with ASD. These findings suggest that the nature of the cortical enlargement due to Chd8 haploinsufficiency is complex and appears to be due to a factor other than an increased neuron number or soma size. Lay SummaryWe measured the size and neuron number in the neocortex in mice with heterozygous Chd8 mutation, a model relevant to Autism Spectrum Disorder. We found an increased cortical volume in male mutants, which was not accompanied by increased neuron number or soma size. Our results indicate that the enlarged brain in Chd8 mutant mice is complex, more evident here in males, and is due to factors other than increased neuron number.

IntroductionFragile X Syndrome (FXS), caused by Fmr1 mutations, is linked to cognitive and behavioral differences, including altered social interactions. Most mouse studies focus on adults, despite human research showing critical developmental changes in childhood and adolescence. We examined social behavior in juvenile male and female Fmr1 knockout (KO) mice as well as heterozygous (HET) females. We further assessed cortical activity in KO females to better understand early phenotypes. MethodsJuvenile mice of both sexes and genotypes were paired in same-sex, novel dyads for 10-minute interactions. Key social behaviors such as head, anogenital, and body sniffing, and physical touch, as well as distance travelled, were analyzed with a marker-less tracking software. Frontal-parietal EEG recordings were collected from wild-type (WT) and KO females in home cage and social contexts to analyze power spectra across frequency bands. ResultsHET and KO females engaged in more frequent but shorter interaction events compared to WT females, with HET females showing the highest counts. Males displayed similar trends when comparing KO and WT. Males engaged in overall higher interaction events than females. EEG analyses revealed altered oscillatory activity in KO females compared to WT females, especially within theta, alpha, and beta bands, most prominently during the early interaction phase. Locomotor activity correlated weakly with head/anogenital sniffing but more strongly with body sniffing and touch. DiscussionThese findings suggest that Fmr1-related differences in juvenile social behavior are sex-dependent and associated with cortical oscillatory changes. Characterizing these early phenotypes in both sexes allows us to further understand FXS development and informs potential routes for early intervention. Key PointsO_LIFragile X Syndrome (FXS), the leading inherited cause of autism, is associated with disruptions in social behavior. C_LIO_LIWhile social phenotypes are relatively well described in adult mouse models of FXS, juvenile manifestations remain poorly understood. C_LIO_LISocial behavior was assessed in juvenile male and female Fmr1 knockout (KO), heterozygous (HET, female only), and wildtype (WT) mice, and frontal-parietal EEG recordings were collected from WT and KO females. C_LIO_LIHET and KO females exhibited more frequent but shorter social interactions than WT females, with HET showing the greatest number of events. Males showed similar patterns when comparing KO and WT. Males engaged in higher overall interaction events than females. EEG recordings revealed altered oscillatory activity in KO compared to WT females, most pronounced during the early phase of social encounter. C_LIO_LIThese findings reveal sex- and genotype-dependent differences in juvenile social behavior and cortical activity, highlighting the importance of studying juvenile development in FXS. C_LI

BackgroundAlterations in the brains oxytocinergic system have been suggested to play an important role in the pathophysiology of autism spectrum disorder (ASD), but insights from pediatric populations are sparse. MethodsWe examined salivary oxytocin in school-aged children with (n=80) and without (n=40) ASD (boys/girls 4/1), as well as characterizations of DNA methylation (DNAm) of the oxytocin receptor gene (OXTR). Cortisol levels were also assessed to examine links between the oxytocinergic system and hypothalamic-pituitary-adrenal (HPA) axis signaling. ResultsChildren with ASD displayed altered (diminished) oxytocin levels in the morning, but not in the afternoon, after a mildly stress-inducing social interaction session. Notably, in the control group, higher oxytocin levels were predictive of lower stress-induced cortisol, likely reflective of a protective stress-regulatory mechanism for buffering HPA stress activity. In children with ASD, on the other hand, a more reactive stress regulatory mechanism was evident, involving a significant rise in oxytocin levels from the morning to the afternoon upon stress-induced cortisol release, i.e., to reactively cope with heightened HPA activity. Regarding epigenetic modifications, no overall pattern of OXTR hypo- or hypermethylation was evident in ASD. In control children, a notable association between OXTR methylation and levels of cortisol was evident, likely indicative of a compensatory downregulation of OXTR methylation (higher oxytocin receptor expression) in children with heightened HPA axis activity. ConclusionTogether, these observations bear important insights into altered oxytocinergic signaling in ASD, which may aid in establishing relevant biomarkers for diagnostic and/or treatment evaluation purposes targeting the oxytocinergic system in ASD.

Autism spectrum disorder (ASD) is characterised by social communication impairments and repetitive behaviours. Language deficits, including echolalia and restricted vocabulary, heighten caregiver stress and negatively affect the familys quality of life. Although animal models have advanced the understanding of individual ASD traits, their influence on kinship dynamics remains underexplored. To address this issue, we developed a clinically relevant ASD model in common marmosets by prenatal exposure to valproic acid (VPA) to produce ASD-like pups alongside their typically developing parents. We analysed 28,418 kinship calls from nine VPA-exposed and seven unexposed (UE) pups, along with their parents. Kinship vocalisations in VPA families exhibited significant alterations, including increased isolation calls, decreased affiliative calls, disruption of structured repetition patterns, and reduced developmental maturations. These deviations intensified after weaning, suggesting a link between social communicative stressors and altered family dynamics. Parental weight loss was correlated with kinship vocal deviations, potentially reflecting increased caregiver stress. This observation aligns with clinical reports of heightened stress in families raising children with ASD. VPA pups also displayed premature locomotion independence, indicating broader social and communication disruptions. These findings suggest that VPA marmosets are valuable models for investigating ASD-like traits in individuals and kinship-level dynamics. Kinship vocalisations provide critical insights into the interplay between communication impairments and caregiver stress, offering a promising avenue for developing non-invasive biomarkers for ASD-related challenges.

ObjectivesThe male preponderance in autism spectrum conditions (ASC) prevalence is among the most pronounced sex ratios across different neurodevelopmental conditions. Here, we aimed to elucidate the relationship between autism and typical sex-differential neuroanatomy, cognition, and related gene expression. MethodsUsing a novel deep learning framework trained to predict biological sex, we compared sex prediction model performance across neurotypical and autistic males and females. Multiple large-scale datasets were employed at different stages of the analysis pipeline: a) Pre-training: the UK Biobank sample (>10.000 individuals); b) Transfer learning and validation: the ABIDE datasets (1,412 individuals, 5-56 years of age); c) Test and discovery: the EU-AIMS/AIMS-2-TRIALS LEAP dataset (681 individuals, 6-30 years of age) and d) Specificity: the Neuroimage and ADHD200 datasets (887 individuals, 7-26 years of age). ResultsAcross both ABIDE and LEAP we showed that features positively predictive of neurotypical males were on average more predictive of autistic males (P=1.1e-23). Features positively predictive of neurotypical females were on average less predictive of autistic females (P=1.2e-22). These accuracy differences in autism were not observed in individuals with ADHD. In autistic females the male-shifted neurophenotype was further associated with poorer social sensitivity and emotional face processing while also with associated gene expression patterns of midgestational cell types. ConclusionsOur results demonstrate a shift in both autistic male and female individuals neuroanatomy towards male-characteristic patterns associated with typically sex-differential, social cognitive features and related gene expression patterns. Findings hold promise for future research aimed at refining the quest for biological mechanisms underpinning the etiology of autism.

Individuals on the autism spectrum often exhibit atypical responses to sensory stimuli and difficulties with behavioral regulation, reflecting altered functional patterns in core sensory-motor circuits. While impairments in higher cognitive functions are a hallmark of autism, they remain underexplored in rodent models compared to basic sensory-motor deficits. Furthermore, these sensory processing differences suggest the potential for using patterned auditory stimulation to modulate neural activity and mitigate symptoms. In this study, we investigated higher cognitive function in the valproic acid (VPA) rodent model of autism and evaluated whether auditory entrainment could ameliorate associated impairments. Pregnant dams received an intraperitoneal injection of VPA on embryonic day 12.5 (E12.5), and offspring were subsequently tested on a delayed non-match to place (DNMP) task to assess working memory. VPA-exposed animals showed significantly impaired performance and altered trial-by-trial learning dynamics, indicating deficits in working memory-based decision making. Notably, gamma-frequency auditory stimulation delivered during DNMP sessions led to increased gamma-frequency oscillations, and enhanced power in other bands (theta, beta) across brain regions, as assessed by LFP recordings in freely moving animals. More importantly, such stimulation eliminated the observed working memory impairments, enhancing performance both during and after entrainment. This provides strong evidence for the therapeutic potential of sensory entrainment in reversing autism-related cognitive deficits by modulating dysfunctional neural circuits.

Social motivation is critical to the development of healthy social functioning. Autism spectrum condition (ASC) is characterized in part by challenges with social communication and social interaction. The root of these challenges is hypothesized to be a deficit in social motivation, specifically in one or more subcomponents (e.g. social reward reward seeking or social orienting). Current social behavior assays lack the ability to quantitatively measure both social reward seeking and social orienting simultaneously. We have developed an automated socially-rewarded operant conditioning task coupled with video tracking, to quantify effort to achieve access to a social partner and concurrent social orienting behavior in mice. We established that adult wildtype mice will work for access to a social partner, that male mice exhibit greater social motivation compared to females, and there is high test-retest reliability in the task across multiple days. We then benchmarked the method with two test-case manipulations. We first tested a mouse model of Phelan-McDermid syndrome, a neurodevelopmental disorder associated with ASC. These Shank3B mutants failed to show social reward seeking and exhibited reduced social orienting. Next, we demonstrated that oxytocin receptor antagonism decreased social motivation in wildtype mice, consistent with its role in social reward circuitry. Intriguingly, only male mice were vulnerable to Shank3B mutation, while females were more vulnerable to oxytocin blockade, a double dissociation suggesting separate circuits for social motivation in male and female brain. Overall, we believe this method provides a valuable addition to the assessment of social phenotypes in rodent models of ASC and the mapping of potentially sex-specific social motivation circuits in the brain.

Along with the core characteristics of the condition, autistic individuals commonly experience motor coordination difficulties, potentially related to a reduced cortical connectivity. Being the largest human commissure, the corpus callosum (CC) plays an essential role in interhemispheric connectivity and has been often involved among autistic atypicalities. This study aimed to investigate the volumes of corpus callosum subregions in a group of drug-naive, autistic children and to explore its possible associations with both core features and motor coordination skills. Thirty-five autistic children (2.5-12 years) were compared with a group of 35 closely IQ-matched, non-autistic peers. CC was identified and segmented into five subregions using Freesurfer. Callosal volumes were compared between the two groups and correlated with parental ratings of core autistic features as assessed by the Social Responsiveness Scale and with motor features as assessed by the Developmental Coordination Disorder Questionnaire. Associations between CC volume and Autism Diagnostic Observation Schedule scores were also explored in autistic participants. Autistic children showed a reduced volume of the central segment of the CC, in the context of a comparable CC total volume. This reduction appeared to be correlated with symptoms of restricted and repetitive behaviours in autistic children, and to parental ratings of autistic mannerisms and motor skills across participants. These findings expand the current knowledge about the neural mechanisms underlying autism, suggesting that the reduced connectivity through the CC might have implications for both core and motor features of autistic individuals. Lay SummaryDifferences in brain development have been widely outlined in autism. Exploring brain scans of 35 autistic and non-autistic children aged 2.5-12 years and closely matched for cognitive functioning, we found that the central part of the corpus callosum was smaller for the autistic group. This reduction was associated with the level of restricted and repetitive behaviours in autistic children, and to parental ratings of autistic mannerisms and motor coordination skills across participants. This work offers new empirical evidence that interhemispheric connectivity is atypical in autism and that the corpus callosum can be involved in the manifestation of both core and motor characteristics of autistic children.

A biological understanding of the apparent sex bias in autism is lacking. We have identified Cntnap2 KO mice as a model system to help better understand this dimorphism. Using this model, we observed social deficits in juvenile male KO mice only. These male-specific social deficits correlated with reduced spine densities of Layer 2/3 and Layer 5 pyramidal neurons in the Anterior Cingulate Cortex, a forebrain region prominently associated with the control of social behaviour. Furthermore, in male KO mice, microglia showed an increased activated morphology and phagocytosis of synaptic structures compared to WT mice, whereas no differences were seen in female KO and WT mice. Our data suggest that sexually dimorphic microglial activity may be involved in the aetiology of ASD, disrupting the development of neural circuits that control social behaviour by overpruning synapses at a developmentally critical period.