Social Cognition in Autism and Other Neurodevelopmental Disorders: A Co-twin Control Study

The Social Shapes Test as a Self-Administered, Online Measure of Social Intelligence: Two Studies with Typically Developing Adults and Adults with Autism Spectrum Disorder

The Social Shapes Test (SST) is a measure of social intelligence which does not use human faces or rely on extensive verbal ability. The SST has shown promising validity among adults without autism spectrum disorder (ASD), but it is uncertain whether it is suitable for adults with ASD. We find measurement invariance between adults with (n = 229) or without ASD (n = 1,049) on the 23-item SST. We also find that adults without ASD score higher on the SST than adults with ASD (d = 0.21). We also provide two, 14-item versions which demonstrated good parallel test-retest reliability and are positively related to scores on the Frith-Happé task. The SST is suitable for remote, online research studies.

Association of verbal and non-verbal theory of mind abilities with non-coding variants of OXTR in youth with autism spectrum disorder and typically developing individuals: a case-control study

BACKGROUND

The ability to attribute mental states to others is called theory of mind (ToM) and is a substantial component of social cognition. This ability is abnormally developed in individuals with autism spectrum disorder (ASD). Several studies over the past decade have identified the oxytocin receptor gene (OXTR) and its variants as promising components for explaining the molecular mechanisms underlying Theory of Mind (ToM). The main aim of this study is to examine the association between rs2268498 and rs53576, two functional single nucleotide polymorphisms (SNPs), and verbal and non-verbal ToM in children and adolescents with ASD and a group of typically developing youth.

METHODS

The study involved 44 children and adolescents with high-functioning ASD aged 8 to 18 years old and 44 TD individuals who were matched on age and sex. In all participants, blood samples were collected and rs2268498 and rs53576 were genotyped. Happe's Strange Stories test and the moving shapes paradigm were used to measure verbal and non-verbal ToM in all participants.

RESULTS

The results of permutation tests and logistic regression suggested that in TD group, rs2268498 AA carriers showed significant higher scores in variables representing verbal ToM (ToM stories and appropriateness score) whereas, in ASD group, rs53576 AA carriers exhibited significant better performance in parameters related to non-verbal ToM (ToM general rule and intentionality score). The results of hierarchical clustering in both groups support the findings by distinguishing between language-related and language-independent aspects of ToM.

CONCLUSIONS

In the present study, we examined the association between rs2268498 and rs53576 and social functioning in individuals with ASD and TD group. We found preliminary evidence that rs2268498 and rs53576 are associated with ToM related abilities in healthy individuals as well as in autistic individuals. Accordingly, rs2268498 and rs53576 may play an important role in predicting ToM capabilities. It will be necessary to conduct further research to address the association of genetic variants with a deficit in ToM in individuals with ASD.

Computerized Cognitive Test Batteries for Children and Adolescents-A Scoping Review of Tools For Lab- and Web-Based Settings From 2000 to 2021

OBJECTIVE

Cognitive functioning is essential to well-being. Since cognitive difficulties are common in many disorders, their early identification is critical, notably during childhood and adolescence. This scoping review aims to provide a comprehensive literature overview of computerized cognitive test batteries (CCTB) that have been developed and used in children and adolescents over the past 22 years and to evaluate their psychometric properties.

METHOD

Among 3192 records identified from three databases (PubMed, PsycNET, and Web of Science) between 2000 and 2021, 564 peer-reviewed articles conducted in children and adolescents aged 3 to 18 years met inclusion criteria. Twenty main CCTBs were identified and further reviewed following PRISMA guidelines. Relevant study details (sample information, topic, location, setting, norms, and psychometrics) were extracted, as well as administration and instrument characteristics for the main CCTBs.

RESULTS

Findings suggest that CCTB use varies according to age, location, and topic, with eight tools accounting for 85% of studies, and the Cambridge Neuropsychological Test Automated Battery (CANTAB) being most frequently used. Few instruments were applied in web-based settings or include social cognition tasks. Only 13% of studies reported psychometric properties.

CONCLUSIONS

Over the past two decades, a high number of computerized cognitive batteries have been developed. Among these, more validation studies are needed, particularly across diverse cultural contexts. This review offers a comprehensive synthesis of CCTBs to aid both researchers and clinicians to conduct cognitive assessments in children in either a lab- or web-based setting.

White and gray matter correlates of theory of mind in autism: a voxel-based morphometry study

Autism spectrum disorder (ASD) is characterized by difficulties in theory of mind (ToM) and social communication. Studying structural and functional correlates of ToM in the brain and how autistic and nonautistic groups differ in terms of these correlates can help with diagnosis and understanding the biological mechanisms of ASD. In this study, we investigated white matter volume (WMV) and gray matter volume (GMV) differences between matching autistic and nonautistic samples, and how these structural features relate to age and ToM skills, indexed by the Reading the Mind in the Eyes (RMIE) measure. The results showed widespread GMV and WMV differences between the two groups in regions crucial for social processes. The autistic group did not express the typically observed negative GMV and positive WMV correlations with age at the same level as the nonautistic group, pointing to abnormalities in developmental structural changes. In addition, we found differences between the two groups in how GMV relates to ToM, particularly in the left frontal regions, and how WMV relates to ToM, mostly in the cingulate and corpus callosum. Finally, GMV in the left insula, a region that is part of the salience network, was found to be crucial in distinguishing ToM performance between the two groups.

Mentalizing in Adolescents and Young Adults with Attention Deficit Hyperactivity Disorder: Associations with Age and Attention Problems

INTRODUCTION

Growing, albeit heterogenous evidence questions whether attention deficit/hyperactivity disorder (ADHD) is associated with socio-cognitive impairments, especially beyond childhood. This study focuses on mentalizing - the socio-cognitive ability to attribute and reason in terms of mental states. We aimed to characterize mentalizing performance in terms of correct scores and types of errors in adolescents and young adults with ADHD.

METHODS

Forty-nine adolescents and adults with ADHD and 49 healthy controls matched for age and gender completed a computerized naturalistic mentalizing task, the Movie for Assessment of Social Cognition (MASC). Repeated measures analyses of variance examined the effects of age group and ADHD diagnosis on MASC performance. Additionally, associations between mentalizing scores, the severity of attention problems, and the presence of comorbidity were explored in the ADHD group.

RESULTS

Results showed an increased prevalence of hypomentalizing errors in adolescents with ADHD. Lower mentalizing scores in adolescents with ADHD were correlated with indices of inattentiveness, impulsivity, and vigilance problems. Hypomentalizing errors in adolescents showed to be particularly associated with inattentiveness, after controlling for age and comorbidity. In contrast, adults with ADHD performed similarly to controls and their scores on the mentalizing task were not correlated to attention problems.

CONCLUSION

These findings highlight potential developmental differences in mentalizing abilities in ADHD youths and their association with attentional impairments.

Hypermentalizing and Borderline Personality Disorder: A Meta-Analytic Review

OBJECTIVE

A hypermentalizing impairment, or tendency to overattribute mental states to others, has been identified among individuals with borderline personality disorder. However, associations between hypermentalizing and other disorders call into question the specificity of this impairment to borderline personality disorder. This study aimed to evaluate the relative strength of the association between hypermentalizing and borderline personality disorder compared with other disorders and to assess the impact of moderators on the relationship between hypermentalizing and psychopathology.

METHODS

The authors conducted a meta-analysis of 36 studies (N=4,188 people) to investigate the relative strength of the association between hypermentalizing and borderline personality disorder, compared with other disorders, and to assess the impact of moderators on this relationship. The Movie for the Assessment of Social Cognition, an ecologically valid experimental instrument, was used to measure hypermentalizing.

RESULTS

Results indicated support for an association between psychopathology and hypermentalizing (r=0.24, 95% confidence interval [CI]=0.17 to 0.31), but the association was not significantly stronger for borderline personality disorder (r=0.26, 95% CI=0.12 to 0.39) than for other disorders (r=0.24, 95% CI=0.14 to 0.33). Neither age nor gender significantly moderated the association between psychopathology and hypermentalizing.

CONCLUSIONS

Hypermentalizing may be related to psychopathology in general rather than borderline personality disorder in particular. The findings are discussed in view of the possibility that features of borderline personality disorder associated with other psychopathology may explain the overall association between psychopathology and hypermentalizing. Clinical implications for mentalization-based treatment and concerns that the measurement used for hypermentalization may be too narrow and not representative of variations in functioning across cultures and race-ethnicity also are discussed.

The Bidirectional Social-Cognitive Mechanisms of the Social-Attention Symptoms of Autism

Differences in social attention development begin to be apparent in the 6th to 12th month of development in children with Autism Spectrum Disorder (ASD) and theoretically reflect important elements of its neurodevelopmental endophenotype. This paper examines alternative conceptual views of these early social attention symptoms and hypotheses about the mechanisms involved in their development. One model emphasizes mechanism involved in the spontaneous allocation of attention to faces, or social orienting. Alternatively, another model emphasizes mechanisms involved in the coordination of attention with other people, or joint attention, and the socially bi-directional nature of its development. This model raises the possibility that atypical responses of children to the attention or the gaze of a social partner directed toward themselves may be as important in the development of social attention symptoms as differences in the development of social orienting. Another model holds that symptoms of social attention may be important to early development, but may not impact older individuals with ASD. The alterative model is that the social attention symptoms in infancy (social orienting and joint attention), and social cognitive symptoms in childhood and adulthood share common neurodevelopmental substrates. Therefore, differences in early social attention and later social cognition constitute a developmentally continuous axis of symptom presentation in ASD. However, symptoms in older individuals may be best measured with in vivo measures of efficiency of social attention and social cognition in social interactions rather than the accuracy of response on analog tests used in measures with younger children. Finally, a third model suggests that the social attention symptoms may not truly be a symptom of ASD. Rather, they may be best conceptualized as stemming from differences domain general attention and motivation mechanisms. The alternative argued for here that infant social attention symptoms meet all the criteria of a unique dimension of the phenotype of ASD and the bi-directional phenomena involved in social attention cannot be fully explained in terms of domain general aspects of attention development.

Assessment of theory of mind in Tunisian verbal children with autism spectrum disorder

The present study examined performance in Theory of Mind (ToM) in a group of 31 Arabic-speaking verbal children (7-12 years-old) with autism spectrum disorder (ASD), in comparison with neurotypical controls (NT) matched for age and for cognitive abilities. An innovative task in a digital format named "The Tunisian Social Situations Instrument" (TSSI) was used and allowed us to study four different subdomains of ToM: attribution of intention and epistemic ToM (cognitive ToM), affective ToM, and detection of faux pas (advanced ToM). Our study showed impairments in ToM in children with ASD, similar to those reported in the literature. Our findings additionally suggested that affective and advanced ToM, specifically the detection of faux pas, might be more challenging for ASD children than other components of ToM. Future studies with larger number of children may lead us to specify which subdomains are the most impaired in order to develop specific tools targeting these specific impairments.

Maternal high-fat diet modifies myelin organization, microglial interactions, and results in social memory and sensorimotor gating deficits in adolescent mouse offspring

Prenatal exposure to maternal high-fat diet (mHFD) acts as a risk factor for various neurodevelopmental alterations in the progeny. Recent studies in mice revealed that mHFD results in both neuroinflammation and hypomyelination in the exposed offspring. Microglia, the brain-resident macrophages, play crucial roles during brain development, notably by modulating oligodendrocyte populations and performing phagocytosis of myelin sheaths. Previously, we reported that mHFD modifies microglial phenotype (i.e., morphology, interactions with their microenvironment, transcripts) in the hippocampus of male and female offspring. In the current study, we further explored whether mHFD may induce myelination changes among the hippocampal-corpus callosum-prefrontal cortex pathway, and result in behavioral outcomes in adolescent offspring of the two sexes. To this end, female mice were fed with control chow or HFD for 4 weeks before mating, during gestation, and until weaning of their litter. Histological and ultrastructural analyses revealed an increased density of myelin associated with a reduced area of cytosolic myelin channels in the corpus callosum of mHFD-exposed male compared to female offspring. Transcripts of myelination-associated genes including Igf1 -a growth factor released by microglia- were also lower, specifically in the hippocampus (without changes in the prefrontal cortex) of adolescent male mouse offspring. These changes in myelin were not related to an altered density, distribution, or maturation of oligodendrocytes, instead we found that microglia within the corpus callosum of mHFD-exposed offspring showed reduced numbers of mature lysosomes and increased synaptic contacts, suggesting microglial implication in the modified myelination. At the behavioral level, both male and female mHFD-exposed adolescent offspring presented loss of social memory and sensorimotor gating deficits. These results together highlight the importance of studying oligodendrocyte-microglia crosstalk and its involvement in the long-term brain alterations that result from prenatal mHFD in offspring across sexes.

What's the Link Between Theory of Mind and Other Cognitive Abilities - A Co-twin Control Design of Neurodevelopmental Disorders

Theory of mind (ToM), or the ability to attribute mental states to oneself and others, is a core element of social cognition (SC). Even though its importance for social functioning in general, and neurodevelopmental disorders (NDDs), in particular, is well established, the links between ToM and other cognitive functions are not. Especially the familial underpinnings of such links remain unclear. Using a co-twin control design, we examined N = 311 twins (mean age M = 17.19 years, 47% females) diagnosed with autism spectrum disorder (ASD), attention-deficit/hyperactivity disorder (ADHD), other NDDs, or typically developing individuals. We used the Reading the Mind in the Eyes Test to operationalize ToM, the Fragmented Pictures Test for central coherence (CC), the Tower Test for executive functioning (EF), and the general ability index in the Wechsler Intelligence Scales for IQ. In the linear regressions, weak CC and a lower IQ were associated with a reduced ToM ability across pairs. Female sex and higher age were robustly associated with increased ToM ability, whereas EF was not associated with ToM. In the within-pair analyses, where unmeasured familial confounders are implicitly adjusted, the associations between ToM and other cognitive functions, were attenuated and the association with CC was non-significant. The result suggests that familial factors shared by the twins, such as genetic and shared environment, influence the association between CC, IQ, and ToM. Future studies need to include a larger sample of monozygotic twins, who are genetically identical, in order to draw more firm conclusions regarding the influence of familial factors, and to differentiate between shared environmental and genetic effects on the associations between cognitive functions.

Development and Feasibility of MindChip™: A Social Emotional Telehealth Intervention for Autistic Adults

The study aims to develop and pilot a telehealth social emotional program, MindChip™ delivered with a computer based interventions (CBI) (Mind Reading^©) for autistic adults. MindChip™ combined four theoretical perspectives and community feedback underpinning the essential mechanisms for targeting the social emotional understanding of autistic adults. A randomised pragmatic pilot trial (N = 25) was conducted to explore the feasibility of MindChip™ (n = 11) and to understand the preliminary efficacy of combining it with CBI compared to CBI only (n = 14). The use of MindChip™ and CBI combined demonstrated partial feasibility, with preliminary efficacy findings revealing increased emotion recognition generalisation outcomes compared to CBI only. Further research is required to improve the engagement and personalisation of the intervention for autistic adults.

The social brain in female autism: a structural imaging study of twins

A female advantage in social cognition (SoC) might contribute to women's underrepresentation in autism spectrum disorder (ASD). The latter could be underpinned by sex differences in social brain structure. This study investigated the relationship between structural social brain networks and SoC in females and males in relation to ASD and autistic traits in twins. We used a co-twin design in 77 twin pairs (39 female) aged 12.5 to 31.0 years. Twin pairs were discordant or concordant for ASD or autistic traits, discordant or concordant for other neurodevelopmental disorders or concordant for neurotypical development. They underwent structural magnetic resonance imaging and were assessed for SoC using the naturalistic Movie for the Assessment of Social Cognition. Autistic traits predicted reduced SoC capacities predominantly in male twins, despite a comparable extent of autistic traits in each sex, although the association between SoC and autistic traits did not differ significantly between the sexes. Consistently, within-pair associations between SoC and social brain structure revealed that lower SoC ability was associated with increased cortical thickness of several brain regions, particularly in males. Our findings confirm the notion that sex differences in SoC in association with ASD are underpinned by sex differences in brain structure.

Age-related parietal GABA alterations in children with autism spectrum disorder

GABA is the primary inhibitory neurotransmitter in the brain, and is essential to the balance of cortical excitation and inhibition. Reductions in GABA are proposed to result in an overly excitatory cortex that may cause, or contribute to, symptoms of autism spectrum disorder (ASD). This study employed a cross-sectional design to explore GABA+ differences in ASD and the impact of age, comparing 4-12 year olds with ASD (N = 24) to typically developing children (N = 35). GABA+ concentration was measured using edited magnetic resonance spectroscopy in the left parietal lobe. This study used a mixed model to investigate group differences between children with ASD and typically developing children. There was a significant difference in GABA+ levels between the groups, a significant effect of age and interaction between age and diagnostic group. The ASD group showed an association between GABA+ and age, with GABA+ levels gradually increasing with age (r = 0.59, p = 0.003). Typically developing children did not show age-related change in GABA+ concentration (r = 0.09, p = 0.60). By the age of 9, children with ASD showed GABA+ levels that were comparable to their typically developing peers. This study suggests that children with ASD have initially lower levels of GABA+ in the left parietal lobe compared to typically developing children, and that these initially lower levels of GABA+ increase with age in ASD within this region. It is suggested that this developmental shift of GABA+ levels within the left parietal lobe provides a possible explanation for the previously found reductions in childhood that does not persist in adults. LAY SUMMARY: This study measured levels of GABA in the left parietal lobe using magnetic resonance spectroscopy in children with ASD and typically developing children. GABA levels were initially lower in the ASD group, and increased with age, while GABA did not change with age in the typically developing group. This suggests that alterations in GABA signaling may be associated with ASD in childhood. Autism Res 2021, 14: 859-872. © 2021 International Society for Autism Research, Wiley Periodicals LLC.

Loss of P2Y12 Has Behavioral Effects in the Adult Mouse

While microglia have been established as critical mediators of synaptic plasticity, the molecular signals underlying this process are still being uncovered. Increasing evidence suggests that microglia utilize these signals in a temporally and regionally heterogeneous manner. Subsequently, it is necessary to understand the conditions under which different molecular signals are employed by microglia to mediate the physiological process of synaptic remodeling in development and adulthood. While the microglial purinergic receptor P2Y12 is required for ocular dominance plasticity, an adolescent form of experience-dependent plasticity, it remains unknown whether P2Y12 functions in other forms of plasticity at different developmental time points or in different brain regions. Using a combination of ex vivo characterization and behavioral testing, we examined how the loss of P2Y12 affects developmental processes and behavioral performance in adulthood in mice. We found P2Y12 was not required for an early form of plasticity in the developing visual thalamus and did not affect microglial migration into barrels in the developing somatosensory cortex. In adult mice, however, the loss of P2Y12 resulted in alterations in recognition and social memory, as well as anxiety-like behaviors, suggesting that while P2Y12 is not a universal regulator of synaptic plasticity, the loss of P2Y12 is sufficient to cause functional defects.

When Alterations in Social Cognition Meet Subjective Complaints in Autism Spectrum Disorder: Evaluation With the "ClaCoS" Battery

Background: Deficit in social communication is a core feature in Autism Spectrum Disorder but remains poorly assessed in classical clinical practice, especially in adult populations. This gap between needs and practice is partly due to a lack of standardized evaluation tools. The multicentric Research group in psychiatry GDR3557 (Institut de Psychiatrie) developed a new battery for social cognitive evaluation named "ClaCoS," which allows testing the main components of social cognition: Emotion Recognition, Theory of Mind, Attributional Style, and Social Perception and Knowledge. It further provides an assessment of subjective complaints in social cognition. Methods: We compared the social cognition abilities of 45 adults with Autism Spectrum Disorder without intellectual disability and 45 neurotypically developed volunteers using the "ClaCoS" battery, in order to determine its relevance in the evaluation of social cognition impairments in autism. A correlational approach allowed us to test the links between subjective complaints and objectively measured impairments for the different components of social cognition. Results: As expected, the Autism Spectrum Disorder group showed deficits in all four components of social cognition. Moreover, they reported greater subjective complaints than controls regarding their social abilities, correlated to the neuropsychological assessments. Conclusion: The "ClaCoS" battery is an interesting tool allowing to assess social impairments in autism and to specify the altered components, for a better adjustment of tailored social cognition training programs. Our results further suggest that people with Autism Spectrum Disorder have a good social cognitive insight, i.e., awareness into social cognitive functioning, and may thus benefit from social cognitive training tools.

Emotion perception and theory of mind in obesity: a systematic review on the impact of social cognitive deficits on dysfunctional eating behaviors

The aim of this paper was to summarize our current understanding of emotion perception and Theory of Mind (ToM) in obesity and how they relate to dysfunctional eating behaviors (DEB), frequently found in candidates for bariatric surgery. The literature was searched using the electronic databases PsychInfo, Medline, and Web of Science databases, and by additional hand searches through reference lists and specialist eating disorders journals. Relevant studies were included if they were written in English, included participants suffering from obesity and evaluation with tasks assessing social cognition, such as emotion recognition and perception, as well as ToM. Twelve studies analyzed for this systematic review suggest that deficits in such social cognitive domains may lie behind many emotional and social difficulties present in people with obesity, be they bariatric or not, which usually favor DEB. Our review suggests that people with obesity of all ages score significantly less than controls on instruments assessing emotion recognition and ToM, justifying a possible relationship between social cognitive impairments and dysfunctional eating behaviors, such as binges, emotional eating, and addition to food, frequently seen in people with obesity. These findings have important implications for our understanding of the social cognitive foundations of eating behavior in individuals with obesity. They can help not only the presurgical behavioral assessment, but also guide postoperative follow-up of this population.

Cognitive and Affective Aspects of Theory of Mind in Greek-Speaking Children with Autism Spectrum Disorders

Substantial research indicates that individuals with Autism Spectrum Disorder (ASD) have difficulties with Theory of Mind (ToM) abilities, but rarely have studies used a comprehensive battery to measure both the cognitive and affective aspects of ToM. The present study tested this ability in 24 Greek-speaking children with ASD (ages 7-14), and their performance was compared to 24 age-, gender- and language-matched typically developing controls. Results showed that ASD children's performance was selectively impaired in both ToM aspects, supporting the distinction between ToM components. This is the first study of ToM abilities among Greek-speaking children with ASD, and the findings confirm that children with ASD are experiencing difficulties with socio-emotional understanding across languages and cultures.

Genetic and Environmental Influences on Lobar Brain Structures in Twins With Autism

This investigation examined whether the variation of cerebral structure is associated with genetic or environmental factors in children with autism spectrum disorder (ASD) compared with typically developing (TD) controls. T1-weighted magnetic resonance imaging scans were obtained from twin pairs (aged 6-15 years) in which at least one twin was diagnosed with ASD or both were TD. Good quality data were available from 30 ASD, 18 discordant, and 34 TD pairs (n = 164). Structural measures (volume, cortical thickness, and surface area) were generated with FreeSurfer, and ACE modeling was completed. Lobar structures were primarily genetically mediated in TD twins (a2 = 0.60-0.89), except thickness of the temporal (a2 = 0.33 [0.04, 0.63]) and occipital lobes (c2 = 0.61 [0.45, 0.77]). Lobar structures were also predominantly genetically mediated in twins with ASD (a2 = 0.70-1.00); however, thickness of the frontal (c2 = 0.81 [0.71, 0.92]), temporal (c2 = 0.77 [0.60, 0.93]), and parietal lobes (c2 = 0.87 [0.77, 0.97]), and frontal gray matter (GM) volume (c2 = 0.79 [0.63, 0.95]), were associated with environmental factors. Conversely, occipital thickness (a2 = 0.93 [0.75, 1.11]) did not exhibit the environmental contributions that were found in controls. Differences in GM volume were associated with social communication impairments for the frontal (r = 0.52 [0.18, 0.75]), temporal (r = 0.61 [0.30, 0.80]), and parietal lobes (r = 0.53 [0.19, 0.76]). To our knowledge, this is the first investigation to suggest that environmental factors influence GM to a larger extent in children with ASD, especially in the frontal lobe.

ASD Phenotype-Genotype Associations in Concordant and Discordant Monozygotic and Dizygotic Twins Stratified by Severity of Autistic Traits

Autism spectrum disorder (ASD) is a highly heterogeneous neurodevelopmental disorder characterized by impaired social communication coupled with stereotyped behaviors and restricted interests. Despite the high concordance rate for diagnosis, there is little information on the magnitude of genetic contributions to specific ASD behaviors. Using behavioral/trait severity scores from the Autism Diagnostic Interview-Revised (ADI-R) diagnostic instrument, we compared the phenotypic profiles of mono- and dizygotic twins where both co-twins were diagnosed with ASD or only one twin had a diagnosis. The trait distribution profiles across the respective twin populations were first used for quantitative trait association analyses using publicly available genome-wide genotyping data. Trait-associated single nucleotide polymorphisms (SNPs) were then used for case-control association analyses, in which cases were defined as individuals in the lowest (Q1) and highest (Q4) quartiles of the severity distribution curves for each trait. While all of the ASD-diagnosed twins exhibited similar trait severity profiles, the non-autistic dizygotic twins exhibited significantly lower ADI-R item scores than the non-autistic monozygotic twins. Case-control association analyses of twins stratified by trait severity revealed statistically significant SNPs with odds ratios that clearly distinguished individuals in Q4 from those in Q1. While the level of shared genomic variation is a strong determinant of the severity of autistic traits in the discordant non-autistic twins, the similarity of trait profiles in the concordantly autistic dizygotic twins also suggests a role for environmental influences. Stratification of cases by trait severity resulted in the identification of statistically significant SNPs located near genes over-represented within autism gene datasets.