A multivariate twin study of autistic traits in 12-year-olds: testing the fractionable autism triad hypothesis

Profiles of autism characteristics in thirteen genetic syndromes: a machine learning approach

BACKGROUND

Phenotypic studies have identified distinct patterns of autistic characteristics in genetic syndromes associated with intellectual disability (ID), leading to diagnostic uncertainty and compromised access to autism-related support. Previous research has tended to include small samples and diverse measures, which limits the generalisability of findings. In this study, we generated detailed profiles of autistic characteristics in a large sample of > 1500 individuals with rare genetic syndromes.

METHODS

Profiles of autistic characteristics based on the Social Communication Questionnaire (SCQ) scores were generated for thirteen genetic syndrome groups (Angelman n = 154, Cri du Chat n = 75, Cornelia de Lange n = 199, fragile X n = 297, Prader-Willi n = 278, Lowe n = 89, Smith-Magenis n = 54, Down n = 135, Sotos n = 40, Rubinstein-Taybi n = 102, 1p36 deletion n = 41, tuberous sclerosis complex n = 83 and Phelan-McDermid n = 35 syndromes). It was hypothesised that each syndrome group would evidence a degree of specificity in autistic characteristics. To test this hypothesis, a classification algorithm via support vector machine (SVM) learning was applied to scores from over 1500 individuals diagnosed with one of the thirteen genetic syndromes and autistic individuals who did not have a known genetic syndrome (ASD; n = 254). Self-help skills were included as an additional predictor.

RESULTS

Genetic syndromes were associated with different but overlapping autism-related profiles, indicated by the substantial accuracy of the entire, multiclass SVM model (55% correctly classified individuals). Syndrome groups such as Angelman, fragile X, Prader-Willi, Rubinstein-Taybi and Cornelia de Lange showed greater phenotypic specificity than groups such as Cri du Chat, Lowe, Smith-Magenis, tuberous sclerosis complex, Sotos and Phelan-McDermid. The inclusion of the ASD reference group and self-help skills did not change the model accuracy.

LIMITATIONS

The key limitations of our study include a cross-sectional design, reliance on a screening tool which focuses primarily on social communication skills and imbalanced sample size across syndrome groups.

CONCLUSIONS

These findings replicate and extend previous work, demonstrating syndrome-specific profiles of autistic characteristics in people with genetic syndromes compared to autistic individuals without a genetic syndrome. This work calls for greater precision of assessment of autistic characteristics in individuals with genetic syndromes associated with ID.

Evaluating causal psychological models: A study of language theories of autism using a large sample

We used a large convenience sample (n = 22,223) from the Simons Powering Autism Research (SPARK) dataset to evaluate causal, explanatory theories of core autism symptoms. In particular, the data-items collected supported the testing of theories that posited altered language abilities as cause of social withdrawal, as well as alternative theories that competed with these language theories. Our results using this large dataset converge with the evolution of the field in the decades since these theories were first proposed, namely supporting primary social withdrawal (in some cases of autism) as a cause of altered language development, rather than vice versa. To accomplish the above empiric goals, we used a highly theory-constrained approach, one which differs from current data-driven modeling trends but is coherent with a very recent resurgence in theory-driven psychology. In addition to careful explication and formalization of theoretical accounts, we propose three principles for future work of this type: specification, quantification, and integration. Specification refers to constraining models with pre-existing data, from both outside and within autism research, with more elaborate models and more veridical measures, and with longitudinal data collection. Quantification refers to using continuous measures of both psychological causes and effects, as well as weighted graphs. This approach avoids "universality and uniqueness" tests that hold that a single cognitive difference could be responsible for a heterogeneous and complex behavioral phenotype. Integration of multiple explanatory paths within a single model helps the field examine for multiple contributors to a single behavioral feature or to multiple behavioral features. It also allows integration of explanatory theories across multiple current-day diagnoses and as well as typical development.

Variegation of autism related traits across seven neurogenetic disorders

Gene dosage disorders (GDDs) constitute a major class of genetic risks for psychopathology, but there is considerable debate regarding the extent to which different GDDs induce different psychopathology profiles. The current research speaks to this debate by compiling and analyzing dimensional measures of several autism-related traits (ARTs) across seven diverse GDDs. The sample included 350 individuals with one of 7 GDDs, as well as reference idiopathic autism spectrum disorder (ASD; n = 74) and typically developing control (TD; n = 171) groups. The GDDs were: Down, Williams-Beuren, and Smith-Magenis (DS, WS, SMS) syndromes, and varying sex chromosome aneuploidies ("plusX", "plusXX", "plusY", "plusXY"). The Social Responsiveness Scale (SRS-2) was used to measure ARTs at different levels of granularity-item, subscale, and total. General linear models were used to examine ART profiles in GDDs, and machine learning was used to predict genotype from SRS-2 subscales and items. These analyses were completed with and without covariation for cognitive impairment. Twelve of all possible 21 pairwise GDD group contrasts showed significantly different ART profiles (7/21 when co-varying for IQ, all Bonferroni-corrected). Prominent GDD-ART associations in post hoc analyses included relatively preserved social motivation in WS and relatively low levels of repetitive behaviors in plusX. Machine learning revealed that GDD group could be predicted with plausible accuracy (~60-80%) even after controlling for IQ. GDD effects on ARTs are influenced by GDD subtype and ART dimension. This observation has consequences for mechanistic, clinical, and translational aspects of psychiatric neurogenetics.

The hallmarks of autism

I suggest that the current study of autism is problematic, due to: (1) its failure to pursue a medical model of disease causation, with protocols for differential diagnoses of causes; (2) a notable incidence of unrecognized false positive diagnoses in children; (3) the conceptual equating of autism with sets of traits that have been shown to be genetically and phenotypically unrelated to one another; and (4) the expansion of use of the terms "autism" and "autism traits" to psychiatric conditions that have no substantive etiological or symptomatic overlap with autism. These problems can be alleviated by, like Kanner, considering autism as a syndrome, a constellation of traits, conceptualized as differences rather than deficits, some set of which is found in each affected individual to some degree. The original, prototypical form of autism can be delineated based on the "hallmarks" of autism: a set of core traits, originally explicated by Kanner, that defines a relatively-homogeneous group, and that connects with the larger set of autism symptoms. The hallmarks of autism provide a touchstone for research that is unambiguous, historically continuous to the present, and linked with major theories for explaining the causes and symptoms of autism. Use of the hallmarks of autism does not impact recognition and treatment of individuals with DSM diagnosed autism, or individuals with the many disorders that involve social deficits. This perspective is compatible with the research domain criteria approach to studying autism, via analyses of autism's constituent traits and the differential diagnosis of its individual-specific causes.

Comorbidity of Attention-Deficit Hyperactivity Disorder and Autism Spectrum Disorders: Current Status and Promising Directions

High rates of co-occurring Attention-Deficit Hyperactivity Disorder (ADHD) and Autism Spectrum Disorders (ASD) suggest common causal pathways, which await elucidation. What is well-established, however, is the negative impact of comorbid ADHD and ASD on outcomes for everyday living, particularly in social interaction and communication and on broader psychopathology. Neurocognitive approaches suggest correlates of comorbidity are rooted in functional connectivity networks associated with executive control. There is support for familial origins, with molecular-genetic studies suggesting a causal role of pleiotropic genes. Further investigation is needed to elucidate fully how genetic risk for ADHD and ASD affects neurodevelopment and to identify structural and functional neural correlates and their behavioral sequelae. Identification of intermediate phenotypes is necessary to advance understanding, which requires studies that include the full spectrum of ASD and ADHD symptom severity, use longitudinal designs and multivariate methods to probe broad constructs, such as executive and social function, and consider other sources of heterogeneity, such as age, sex, and other psychopathology. Randomized efficacy trials targeting comorbid symptomatology are needed to mitigate negative developmental outcomes.

Mapping the genetic and environmental aetiology of autistic traits in Sweden and the United Kingdom

Background

Autistic traits are influenced by both genetic and environmental factors, and are known to vary geographically in prevalence. But to what extent does their aetiology also vary from place to place?

Methods

We applied a novel spatial approach to data on autistic traits from two large twin studies, the Child and Adolescent Twin Study in Sweden (CATSS; N = 16,677, including 8307 twin pairs) and the Twins Early Development Study in the UK (TEDS; N = 11,594, including 5796 twin pairs), to explore how the influence of nature and nurture on autistic traits varies from place to place.

Results

We present maps of gene‐ and environment‐ by geography interactions in Sweden and the United Kingdom (UK), showing geographical variation in both genetic and environmental influences across the two countries. In Sweden genetic influences appear higher in the far south and in a band running across the centre of the country. Environmental influences appear greatest in the south and north, with reduced environmental influence across the central band. In the UK genetic influences appear greater in the south, particularly in more central southern areas and the southeast, the Midlands and the north of England. Environmental influences appear greatest in the south and east of the UK, with less influence in the north and the west.

Conclusions

We hope this systematic approach to identifying aetiological interactions will inspire research to examine a wider range of previously unknown environmental influences on the aetiology of autistic traits. By doing so, we will gain greater understanding of how these environments draw out or mask genetic predisposition and interact with other environmental influences in the development of autistic traits.

Pattern Unifies Autism

Autism is a highly heterogeneous condition, genetically and phenotypically. This diversity of causation and presentation has impeded its definition, recognition, assessment, and treatment. Current diagnostic criteria for autism involve two domains, restricted interests and repetitive behavior (RRBs) and social deficits, whose relationship remains unclear. I suggest that the large suite of traits associated with autism can be usefully conceptualized under the single rubric of "pattern," a term that connects autism with basic brain and cognitive functions and structures its phenotypes within a single theoretical framework. Autism thus involves increases and enhancements to pattern perception, pattern recognition, pattern maintenance, pattern generation, pattern processing, and pattern seeking. RRBs result from increased and imbalanced pattern-related perception and cognition, and social alterations result in part from the usual lack of clear pattern in social interactions, combined with the interference of RRBs with social development. This framework has strong implications for assessment of social and non-social autism-related traits, personalized therapy, and priorities for research.

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.

Maternal prenatal depressive symptoms and risk for early-life psychopathology in offspring: genetic analyses in the Norwegian Mother and Child Birth Cohort Study

BACKGROUND

Maternal prenatal depression is a known risk factor for early-life psychopathology among offspring; however, potential risk transmission mechanisms need to be distinguished. We aimed to test the relative importance of passive genetic transmission, direct exposure, and indirect exposure in the association between maternal prenatal depressive symptoms and early-life internalising and externalising psychopathology in offspring.

METHODS

We used structural equation modelling of phenotypic data and genetically informative relationships from the families of participants in the Norwegian Mother and Child Birth Cohort Study (MoBa). The analytic subsample of MoBa used in the current study comprises 22 195 mothers and 35 299 children. We used mothers' self-reported depressive symptoms during pregnancy, as captured by the Symptom Checklist, and their reports of symptoms of psychopathology in their offspring during the first few years of life (measured at 18, 36, and 60 months using the Child Behavior Checklist).

FINDINGS

Maternal prenatal depressive symptoms were found to be associated with early-life psychopathology primarily via intergenerationally shared genetic factors, which explained 41% (95% CI 36-46) of variance in children's internalising problems and 37% (30-44) of variance in children's externalising problems. For internalising problems, phenotypic transmission also contributed significantly, accounting for 14% (95% CI 5-19) of the association, but this contribution was found to be explained by exposure to concurrent maternal depressive symptoms, rather than by direct exposure in utero.

INTERPRETATION

Associations between maternal prenatal depressive symptoms and offspring behavioural outcomes in early childhood are likely to be at least partially explained by shared genes. This genetic confounding should be considered when attempting to quantify risks posed by in-utero exposure to maternal depressive symptoms.

FUNDING

UK Economic and Social Research Council, Norwegian Research Council, Norwegian Ministries of Health and Care Services, and Education & Research, Wellcome Trust, Royal Society, and National Institute for Health Research.

Genes and Pathways Regulated by Androgens in Human Neural Cells, Potential Candidates for the Male Excess in Autism Spectrum Disorder

BACKGROUND

Prenatal exposure to androgens during brain development in male individuals may participate to increase their susceptibility to develop neurodevelopmental disorders such as autism spectrum disorder (ASD) and intellectual disability. However, little is known about the action of androgens in human neural cells.

METHODS

We used human neural stem cells differentiated from embryonic stem cells to investigate targets of androgens.

RESULTS

RNA sequencing revealed that treatment with dihydrotestosterone (DHT) leads to subtle but significant changes in the expression of about 200 genes, encoding proteins of extracellular matrix or involved in signal transduction of growth factors (e.g., insulin/insulin growth factor 1). We showed that the most differentially expressed genes (DEGs), RGCC, RNF144B, NRCAM, TRIM22, FAM107A, IGFBP5, and LAMA2, are reproducibly regulated by different androgens in different genetic backgrounds. We showed, by overexpressing the androgen receptor in neuroblastoma cells SH-SY5Y or knocking it down in human neural stem cells, that this regulation involves the androgen receptor. A chromatin immunoprecipitation combined with direct sequencing analysis identified androgen receptor-bound sequences in nearly half of the DHT-DEGs and in numerous other genes. DHT-DEGs appear enriched in genes involved in ASD (ASXL3, NLGN4X, etc.), associated with ASD (NRCAM), or differentially expressed in patients with ASD (FAM107A, IGFBP5). Androgens increase human neural stem cell proliferation and survival in nutrient-deprived culture conditions, with no detectable effect on regulation of neurite outgrowth.

CONCLUSIONS

We characterized androgen action in neural progenitor cells, identifying DHT-DEGs that appear to be enriched in genes related to ASD. We also showed that androgens increase proliferation of neuronal precursors and protect them from death during their differentiation in nutrient-deprived conditions.

A Low Rank Model for Phenotype Imputation in Autism Spectrum Disorder

Autism Spectrum Disorder is a highly heterogeneous condition currently diagnosed using behavioral symptoms. A better understanding of the phenotypic subtypes of autism is a necessary component of the larger goal of mapping autism genotype to phenotype. However, as with most clinical records describing human disease, the phenotypic data available for autism contains varying levels of noise and incompleteness that complicate analysis. Here we analyze behavioral data from 16,291 subjects using 250 items from three gold standard diagnostic instruments. We apply a low-rank model to impute missing entries and entire missing instruments with high fidelity, showing that we can complete clinical records for all subjects. Finally, we analyze the low-rank representation of our subjects to identify plausible subtypes of autism, setting the stage for genome-to-phenome prediction experiments. These procedures can be adapted and used with other similarly structured clinical records to enable a more complete mapping between genome and phenome.

Examining the Association Between Autistic Traits and Atypical Sensory Reactivity: A Twin Study

OBJECTIVE

Atypical responses to sensory stimuli are common features of autism spectrum disorders (ASD). Consequently, atypical sensory reactivity (SR) is now a diagnostic feature of ASD. Quantitative genetic research on ASD has overlooked these symptoms, however. We therefore investigated the association between autistic traits and SR using twin methods.

METHOD

Autistic traits and SR were assessed by 2 separate scales in 12,419 Swedish twin pairs (n = 3,586 monozygotic [MZ], n = 8,833 dizygotic [DZ]) when the twins were 9 or 12 years of age. The classic twin design estimated the degree to which etiological factors associated with autistic traits were also associated with SR, and the degree to which such shared factors explained the covariance between these phenotypes. DeFries-Fulker analysis estimated the genetic correlation between screening diagnoses of ASD, defined broadly and strictly, and SR.

RESULTS

Autistic traits and SR were both highly heritable (62%-75% and 66%-71%, respectively). There was a moderate phenotypic correlation between autistic traits and SR (r = 0.47). Genetic influences on these phenotypes correlated moderately (genetic correlation = 0.60). These overlapping genetic factors explained most of the correlation between autistic traits and SR. Genetic correlations with SR increased for broad ASD (genetic correlation = 0.72) and strict ASD (genetic correlation = 0.80).

CONCLUSION

The genetic overlap observed between autistic traits and SR lends quantitative genetic support to the notion that ASD and SR are strongly linked. Such symptoms may thus comprise part of the ASD genotype, as well as phenotype. Associations persisted across all definitions of ASD, indicating a genetic link between the broader ASD phenotype and SR.

Developmental neurogenetics and multimodal neuroimaging of sex differences in autism

Examining sex differences in the brain has been historically contentious but is nonetheless important for advancing mental health for both girls and boys. Unfortunately, females in biomedical research remain underrepresented in most mental health conditions including autism spectrum disorders (ASD), even though equal inclusion of females would improve treatment for girls and yield benefits to boys. This review examines sex differences in the relationship between neuroanatomy and neurogenetics of ASD. Recent findings reveal that girls diagnosed with ASD exhibit more intellectual and behavioral problems compared to their male counterparts, suggesting that girls may be less likely diagnosed in the absence of such problems or that they require a higher mutational load to meet the diagnostic criteria. Thus far, the female biased effect of chromosome 4, 5p15.33, 8p, 9p24.1, 11p12-13, 15q, and Xp22.3 and the male biased effect of 1p31.3, 5q12.3, 7q, 9q33.3, 11q13.4, 13q33.3, 16p11.2, 17q11-21, Xp22.33/Yp11.31, DRD1, NLGN3, MAOA, and SHANK1 deletion have been discovered in ASD. The SNPs of genes such as RYR2, UPP2, and the androgen receptor gene have been shown to have sex-biasing factors in both girls and boys diagnosed with ASD. These sex-related genetic factors may drive sex differences in the neuroanatomy of these girls and boys, including abnormal enlargement in temporal gray and white matter volumes, and atypical reduction in cerebellar gray matter volumes and corpus callosum fibers projecting to the anterior frontal cortex in ASD girls relative to boys. Such factors may also be responsible for the attenuation of brain sexual differentiation in adult men and women with ASD; however, much remains to be uncovered or replicated. Future research should leverage further the association between neuroanatomy and genetics in girls for an integrated and interdisciplinary understanding of ASD.

Association of Sex With Recurrence of Autism Spectrum Disorder Among Siblings

IMPORTANCE

Autism spectrum disorder (ASD) is known to be more prevalent among males than females in the general population. Although overall risk of recurrence of ASD among siblings has been estimated to be between 6.1% and 24.7%, information on sex-specific recurrence patterns is lacking.

OBJECTIVE

To estimate high-confidence sex-specific recurrence rates of ASD among siblings.

DESIGN, SETTING, AND PARTICIPANTS

This observational study used an administrative database to measure the incidence of ASD among children in 1 583 271 families (37 507 with at least 1 diagnosis of ASD) enrolled in commercial health care insurance plans at a large US managed health care company from January 1, 2008, through February 29, 2016. Families in the study had 2 children who were observed for at least 12 months between 4 and 18 years of age.

MAIN OUTCOMES AND MEASURES

The primary measure of ASD recurrence was defined as the diagnosis of ASD in a younger sibling of an older sibling with an ASD diagnosis.

RESULTS

Among the 3 166 542 children (1 547 266 females and 1 619 174 males; mean [SD] age, 11.2 [4.7] years) in the study, the prevalence of ASD was 1.96% (95% CI, 1.94%-1.98%) among males and 0.50% (95% CI, 0.49%-0.51%) among females. When a male was associated with risk in the family, ASD was diagnosed in 4.2% (95% CI, 3.8%-4.7%) of female siblings and 12.9% (95% CI, 12.2%-13.6%) of male siblings. When a female was associated with risk in the family, ASD was diagnosed in 7.6% (95% CI, 6.5%-8.9%) of female siblings and 16.7% (95% CI, 15.2%-18.4%) of male siblings.

CONCLUSIONS AND RELEVANCE

These findings are in agreement with the higher rates of ASD observed among males than among females in the general population. Our study provides more specific guidance for the screening and counseling of families and may help inform future investigations into the environmental and genetic factors that confer risk of ASD.

Sensory perception in autism

Autism is a complex neurodevelopmental condition, and little is known about its neurobiology. Much of autism research has focused on the social, communication and cognitive difficulties associated with the condition. However, the recent revision of the diagnostic criteria for autism has brought another key domain of autistic experience into focus: sensory processing. Here, we review the properties of sensory processing in autism and discuss recent computational and neurobiological insights arising from attention to these behaviours. We argue that sensory traits have important implications for the development of animal and computational models of the condition. Finally, we consider how difficulties in sensory processing may relate to the other domains of behaviour that characterize autism.

Serum Oxytocin Levels and an Oxytocin Receptor Gene Polymorphism (rs2254298) Indicate Social Deficits in Children and Adolescents with Autism Spectrum Disorders

The neuropeptide oxytocin (OT) and its receptor (OXTR) have been predicted to be involved in the regulation of social functioning in autism spectrum disorders (ASD). Objective of the study was to investigate serum OT levels and the OXTR rs2254298 polymorphism in Chinese Han children and adolescents with ASD as well as to identify their social deficits relevant to the oxytocinergic system. We tested serum OT levels using ELISA in 55 ASD subjects and 110 typically developing (TD) controls as well as genotyped the OXTR rs2254298 polymorphism using PCR-RFLP in 100 ASD subjects and 232 TD controls. Autistic symptoms were assessed by the Autism Behavior Checklist (ABC) and the Childhood Autism Rating Scale (CARS). There were no significant associations between OXTR rs2254298 polymorphism and ASD, serum OT levels and age, as well as serum OT levels and intelligent quotient (IQ) in both ASD and TD groups. However, ASD subjects exhibited elevated serum OT levels compared to TD controls and positive correlations between serum OT levels and “adaptation to change score” in the CARS and CARS total scores. Moreover, in the ASD group, significant relationships were revealed between the single-nucleotide polymorphism (SNP) rs2254298 and serum OT levels, the category “stereotypes and object use” in the ABC and the category “adaptation to change” in the CARS. These findings indicated that individuals with ASD may exhibit a dysregulation in OT on the basis of changes in OXTR gene expression as well as environmentally induced alterations of the oxytocinergic system to determine their social deficits.

The Genetic Overlap of Attention-Deficit/Hyperactivity Disorder and Autistic-like Traits: an Investigation of Individual Symptom Scales and Cognitive markers

Attention-deficit/hyperactivity disorder (ADHD) and autism spectrum disorders (ASDs) frequently co-occur. However, due to previous exclusionary diagnostic criteria, little is known about the underlying causes of this covariation. Twin studies assessing ADHD symptoms and autistic-like traits (ALTs) suggest substantial genetic overlap, but have largely failed to take into account the genetic heterogeneity of symptom subscales. This study aimed to clarify the phenotypic and genetic relations between ADHD and ASD by distinguishing between symptom subscales that characterise the two disorders. Moreover, we aimed to investigate whether ADHD-related cognitive impairments show a relationship with ALT symptom subscales; and whether potential shared cognitive impairments underlie the genetic risk shared between the ADHD and ALT symptoms. Multivariate structural equation modelling was conducted on a population-based sample of 1312 twins aged 7–10. Social-communication ALTs correlated moderately with both ADHD symptom domains (phenotypic correlations around 0.30) and showed substantial genetic overlap with both inattention and hyperactivity-impulsivity (genetic correlation = 0.52 and 0.44, respectively). In addition to previously reported associations with ADHD traits, reaction time variability (RTV) showed significant phenotypic (0.18) and genetic (0.32) association with social-communication ALTs. RTV captured a significant proportion (24 %) of the genetic influences shared between inattention and social-communication ALTs. Our findings suggest that social-communication ALTs underlie the previously observed phenotypic and genetic covariation between ALTs and ADHD symptoms. RTV is not specific to ADHD symptoms, but is also associated with social-communication ALTs and can, in part, contribute to an explanation of the co-occurrence of ASD and ADHD.

Close genetic relationships between a spousal pair with autism-affected children and high minor allele content in cases in autism-associated SNPs

Parents of children affected with autism spectrum disorders (ASD) often have mild forms of autistic-like characteristics. Past studies have focused on searching for individual genetic risk loci of ASD. Here we studied the overall properties of the genomes of ASD trios by using previously published genome-wide data for common SNPs. The pairwise genetic distance (PGD) between a spousal pair with ASD-affected children was found smaller than that of a random pair selected among the spouses in the ASD trios, and spousal relatedness correlated with severe forms of ASD. Furthermore, for a set of 970 ASD associated SNPs, cases showed higher homozygous minor allele content than parents. These results indicate new genetic elements in the broad phenotypes of parents with ASD-affected offspring and in ASD pathogenesis.

Rare Inherited and De Novo CNVs Reveal Complex Contributions to ASD Risk in Multiplex Families

Rare mutations, including copy-number variants (CNVs), contribute significantly to autism spectrum disorder (ASD) risk. Although their importance has been established in families with only one affected child (simplex families), the contribution of both de novo and inherited CNVs to ASD in families with multiple affected individuals (multiplex families) is less well understood. We analyzed 1,532 families from the Autism Genetic Resource Exchange (AGRE) to assess the impact of de novo and rare CNVs on ASD risk in multiplex families. We observed a higher burden of large, rare CNVs, including inherited events, in individuals with ASD than in their unaffected siblings (odds ratio [OR] = 1.7), but the rate of de novo events was significantly lower than in simplex families. In previously characterized ASD risk loci, we identified 49 CNVs, comprising 24 inherited events, 19 de novo events, and 6 events of unknown inheritance, a significant enrichment in affected versus control individuals (OR = 3.3). In 21 of the 30 families (71%) in whom at least one affected sibling harbored an established ASD major risk CNV, including five families harboring inherited CNVs, the CNV was not shared by all affected siblings, indicating that other risk factors are contributing. We also identified a rare risk locus for ASD and language delay at chromosomal region 2q24 (implicating NR4A2) and another lower-penetrance locus involving inherited deletions and duplications of WWOX. The genetic architecture in multiplex families differs from that in simplex families and is complex, warranting more complete genetic characterization of larger multiplex ASD cohorts.

Autism spectrum disorder and attention-deficit/hyperactivity disorder in early childhood: A review of unique and shared characteristics and developmental antecedents

Autism spectrum disorder (ASD) and attention-deficit/hyperactivity disorder (ADHD) have overlapping characteristics and etiological factors, but to which extent this applies to infant- and preschool age is less well understood. Comparing the pathways to ASD and ADHD from the earliest possible stages is crucial for understanding how phenotypic overlap emerges and develops. Ultimately, these insights may guide preventative and therapeutic interventions. Here, we review the literature on the core symptoms, temperament and executive function in ASD and ADHD from infancy through preschool age, and draw several conclusions: (1) the co-occurrence of ASD and ADHD increases with age, severity of symptoms and lower IQ, (2) attention problems form a linking pin between early ASD and ADHD, but the behavioral, cognitive and sensory correlates of these attention problems partly diverge between the two conditions, (3) ASD and ADHD share high levels of negative affect, although the underlying motivational and behavioral tendencies seem to differ, and (4) ASD and ADHD share difficulties with control and shifting, but partly opposite behaviors seem to be involved.

A Comprehensive Review of the (1)H-MRS Metabolite Spectrum in Autism Spectrum Disorder

Neuroimaging studies of neuropsychiatric behavior biomarkers across spectrum disorders are typically based on diagnosis, thus failing to account for the heterogeneity of multi-dimensional spectrum disorders such as autism (ASD). Control group trait phenotypes are also seldom reported. Proton magnetic resonance spectroscopy (¹H-MRS) measures the abundance of neurochemicals such as neurotransmitters and metabolites and hence can probe disorder phenotypes at clinical and sub-clinical levels. This detailed review summarizes and critiques the current ¹H-MRS research in ASD. The literature reports reduced N-acetylaspartate (NAA), glutamate and glutamine (Glx), γ-aminobutyric acid (GABA), creatine and choline, and increased glutamate for children with ASD. Adult studies are few and results are inconclusive. Overall, the literature has several limitations arising from differences in ¹H-MRS methodology and sample demographics. We argue that more consistent methods and greater emphasis on phenotype studies will advance understanding of underlying cortical metabolite disturbance in ASD, and the detection, diagnosis, and treatment of ASD and other multi-dimensional psychiatric disorders.

The Relationship Among Genetic Heritability, Environmental Effects, and Autism Spectrum Disorders: 37 Pairs of Ascertained Twin Study

Autism spectrum disorders (ASD) comprise a heterogeneous group of neurodevelopmental disorders that have strong heritability. To better understand the heritable factors in twins with clinically diagnosed ASD and to discuss the relationship between social impairments and genetic and environmental factors. In last 13 years, over 12,000 cases of ASD were diagnosed in the children's development and behavior center, the authors review 37 pairs of these twins, in each pair, and at least 1 twin had been diagnosed with an ASD, and found that the concordance rate was 80% [95% confidence interval (CI) 51.9-95.7%] for monozygotic twins and 13.6% (95% CI: 2.9-34.9%) for dizygotic twins. The heritability of social impairments for ASD was 60.9% (95% CI: 47.3-74.5%). In addition, the rate of nonshared environmental factors was 39.1% (95% CI: 25.5-52.7%), and there were no shared environmental effects. Genetics and special environmental effect play an important role on ASD social impairments.

Examining the Genetic and Environmental Associations between Autistic Social and Communication Deficits and Psychopathic Callous-Unemotional Traits

Background

Difficulties in appropriate social interaction are characteristic of both children with autism spectrum disorders and children with callous-unemotional traits (who are at risk of developing psychopathy). Extant experimental studies suggest that the nature of atypical social cognition that characterises these two profiles is not identical. However, ‘empathizing’ difficulties have been hypothesised for both groups, raising questions about the degree of aetiological separation between social impairments that characterize each disorder. This study explored the relative contribution of independent vs. shared aetiological influences to social and communication impairments associated with autistic traits and callous-unemotional traits, indexed by parent-report in a population-based cohort of twins.

Methods

Participants were over 5,000 twin pairs from a UK cohort (the Twins Early Development Study; TEDS), assessed for callous-unemotional traits at 7 years and autistic social and communication impairments at 8 years. Multivariate model-fitting was used to explore the relative contribution of independent vs. overlapping genetic/environmental influences on these traits.

Results

Both social and communication impairments and callous-unemotional traits were highly heritable, although the genetic and environmental influences accounting for individual differences on each domain were predominantly independent.

Conclusions

Extant evidence from experimental and neuro-imaging studies has suggested that, despite some superficially overlapping behaviours, the social difficulties seen in children with autism spectrum disorders and callous-unemotional traits are largely distinct. The current study is the first to demonstrate considerable aetiological independence of the social interaction difficulties seen in children with autism spectrum disorders and those with callous-unemotional traits.

Face processing among twins with and without autism: social correlates and twin concordance

Autism spectrum disorder (ASD) has a strong heritable basis, as evidenced by twin concordance rates. Within ASD, symptom domains may arise via independent genetic contributions, with varying heritabilities and genetic mechanisms. In this article, we explore social functioning in the form of (i) electrophysiological and behavioral measures of face processing (P1 and N170) and (ii) social behavior among child and adolescent twins with (N = 52) and without ASD (N = 66). Twins without ASD had better holistic face processing and face memory, faster P1 responses and greater sensitivity to the effects of facial inversion on P1. In contrast, N170 responses to faces were similar across diagnosis, with more negative amplitudes for faces vs non-face images. Across the sample, stronger social skills and fewer social difficulties were associated with faster P1 and N170 responses to upright faces, and better face memory. Twins were highly correlated within pairs across most measures, but correlations were significantly stronger for monozygotic vs dizygotic pairs on N170 latency and social problems. We suggest common developmental influences across twins for face processing and social behavior, but highlight (i) neural speed of face processing and (ii) social difficulties as important avenues in the search for genetic underpinnings in ASD.

Are we under-estimating the association between autism symptoms?: The importance of considering simultaneous selection when using samples of individuals who meet diagnostic criteria for an autism spectrum disorder

The magnitude of symptom inter-correlations in diagnosed individuals has contributed to the evidence that autism spectrum disorders (ASD) is a fractionable disorder. Such correlations may substantially under-estimate the population correlations among symptoms due to simultaneous selection on the areas of deficit required for diagnosis. Using statistical simulations of this selection mechanism, we provide estimates of the extent of this bias, given different levels of population correlation between symptoms. We then use real data to compare domain inter-correlations in the Autism Spectrum Quotient, in those with ASD versus a combined ASD and non-ASD sample. Results from both studies indicate that samples restricted to individuals with a diagnosis of ASD potentially substantially under-estimate the magnitude of association between features of ASD.

DRD3 gene and striatum in autism spectrum disorder

A single-nucleotide polymorphism (SNP) of the DRD3 gene (rs167771) was recently associated with autism spectrum disorders (ASD). Different polymorphisms of rs167771 corresponded to varying degrees of stereotyped behaviour. As DRD3 receptors are relatively overexpressed in the striatum, we investigated whether striatal volume was related to these polymorphisms in autism. We assessed volumes of caudate nucleus and putamen in 86 participants with ASD (mean age 15.3 years). MANCOVA showed an association between alleles of the rs167771 SNP and the volume of striatal structures. Furthermore, greater caudate nucleus volume correlated with stereotyped behaviour. These findings support a relationship between DRD3 gene SNPs, striatum and stereotyped behaviour in ASD.

Common and distinct impacts of autistic traits and alexithymia on social reward

According to the social motivation hypothesis of autism, individuals with high levels of autistic traits experience reduced levels of reward from social interactions. However, empirical evidence to date has been mixed, with some studies reporting lower levels of social reward in individuals with Autism Spectrum Disorder (ASD), and others finding no difference when compared to typically developing controls. Alexithymia, a subclinical condition associated with the reduced ability to identify and describe one’s own emotions, has been found to account for other affective difficulties observed inconsistently in individuals with ASD. The current study used a nonclinical sample (N = 472) to explore the associations between autistic traits and the value of six types of social reward, as measured by the Social Reward Questionnaire. In addition, we measured alexithymia to assess if this accounted for associations between autistic traits and social reward. There were three main findings. Firstly, higher levels of autistic traits were associated with significantly less enjoyment of admiration and sociability, and adding alexithymia to these models did not account for any additional variance. Secondly, both autistic traits and alexithymia were uniquely associated with reduced levels of enjoyment of prosocial interactions and sexual relationships. Thirdly, autistic traits were associated with higher levels of enjoyment of passivity and negative social potency, but these associations were no longer significant once alexithymia was taken into account, suggesting that co-occurring alexithymia accounted for these apparent associations. Overall, the current findings provide a novel and more nuanced picture of the relationship between autistic traits and social reward.

Increased female autosomal burden of rare copy number variants in human populations and in autism families

Autosomal genetic variation is presumed equivalent in males and females and makes a major contribution to disease risk. We set out to identify whether maternal copy number variants (CNVs) contribute to autism spectrum disorders (ASDs). Surprisingly, we observed a higher autosomal burden of large, rare CNVs in females in the population, reflected in, but not unique to, ASD families. Meta-analysis across control data sets confirms female excess in CNV number (P=2.1 × 10(-5)) and gene content (P=4.1 × 10(-3)). We additionally observed CNV enrichment in ASD mothers compared with control mothers (P=0.03). We speculate that tolerance for CNV burden contributes to decreased female fetal loss in the population and that ASD-specific maternal CNV burden may contribute to high sibling recurrence. These data emphasize the need for study of familial CNV risk factors in ASDs and the requirement of sex-matched comparisons.

Where are the strongest associations between autistic traits and traits of ADHD? evidence from a community-based twin study

Autism spectrum conditions (ASC) and attention-deficit/hyperactivity disorder (ADHD) regularly co-occur. Twin studies increasingly indicate that these conditions may have overlapping genetic causes. Less is known about the degree to which specific autistic traits relate to specific behaviours characteristic of ADHD. We hence tested, using the classical twin design, whether specific dimensional autistic traits, including social difficulties, communication atypicalities and repetitive behaviours, would display differential degrees of aetiological overlap with specific traits of ADHD, including hyperactivity/impulsivity and inattention. Parents of approximately 4,000 pairs of 12-year-old twins completed the Childhood Autism Spectrum Test and Conners' Parent Rating Scale. These measures were divided into subscales corresponding to different types of autistic and ADHD behaviours. Twin model fitting suggested that the degree of genetic overlap was particularly strong between communication difficulties and traits of ADHD (genetic correlations = .47-.51), while repetitive behaviours and social difficulties showed moderate (genetic correlations = .12-.33) and modest (.05-.11) genetic overlap respectively. Environmental overlap was low across all subscales (correlations = .01-.23). These patterns were also apparent at the extremes of the general population, with communication difficulties showing the highest genetic overlap with traits of ADHD. These findings indicate that molecular genetic studies seeking to uncover the shared genetic basis of ASC and ADHD would benefit from taking a symptom-specific approach. Furthermore, they could also help to explain why studies of the communication abilities of individuals with ASC and ADHD have produced overlapping findings.

A twin study of heritable and shared environmental contributions to autism

The present study examined genetic and shared environment contributions to quantitatively-measured autism symptoms and categorically-defined autism spectrum disorders (ASD). Participants included 568 twins from the Interactive Autism Network. Autism symptoms were obtained using the Social Communication Questionnaire and Social Responsiveness Scale. Categorically-defined ASD was based on clinical diagnoses. DeFries-Fulker and liability threshold models examined etiologic influences. Very high heritability was observed for extreme autism symptom levels ([Formula: see text]). Extreme levels of social and repetitive behavior symptoms were strongly influenced by common genetic factors. Heritability of categorically-defined ASD diagnosis was comparatively low (.21, 95 % CI 0.15-0.28). High heritability of extreme autism symptom levels confirms previous observations of strong genetic influences on autism. Future studies will require large, carefully ascertained family pedigrees and quantitative symptom measurements.

Motor function and perception in children with neuropsychiatric and conduct problems: results from a population based twin study

Background

Children with early symptomatic psychiatric disorders such as Attention-Deficit/Hyperactivity Disorder (ADHD) and Autism Spectrum Disorder (ASD) have been found to have high rates of motor and/or perception difficulties. However, there have been few large-scale studies reporting on the association between Conduct Disorder (CD) and motor/perception functions. The aim of the present study was to investigate how motor function and perception relate to measures of ADHD, ASD, and CD.

Methods

Parents of 16,994 Swedish twins (ages nine and twelve years) were interviewed using the Autism-Tics, ADHD and other Comorbidities inventory (A-TAC), which has been validated as a screening instrument for early onset child psychiatric disorders and symptoms. Associations between categorical variables of scoring above previously validated cut-off values for diagnosing ADHD, ASD, and CD on the one hand and motor and/or perception problems on the other hand were analysed using cross-tabulations, and the Fisher exact test. Associations between the continuous scores for ADHD, ASD, CD, and the subdomains Concentration/Attention, Impulsiveness/Activity, Flexibility, Social Interaction and Language, and the categorical factors age and gender, on the one hand, and the dependent dichotomic variables Motor control and Perception problems, on the other hand, were analysed using binary logistic regression in general estimated equation models.

Results

Male gender was associated with increased risk of Motor control and/or Perception problems. Children scoring above the cut-off for ADHD, ASD, and/or CD, but not those who were ‘CD positive’ but ‘ADHD/ASD negative’, had more Motor control and/or Perception problems, compared with children who were screen-negative for all three diagnoses. In the multivariable model, CD and Impulsiveness/Activity had no positive associations with Motor control and/or Perception problems.

Conclusions

CD symptoms or problems with Impulsiveness/Activity were associated with Motor control or Perception problems only in the presence of ASD symptoms and/or symptoms of inattention. Our results indicate that children with CD but without ASD or inattention do not show a deviant development of motor and perceptual functions. Therefore, all children with CD should be examined concerning motor control and perception. If problems are present, a suspicion of ADHD and/or ASD should be raised.

Assessing behavioural and cognitive domains of autism spectrum disorders in rodents: current status and future perspectives

The establishment of robust and replicable behavioural testing paradigms with translational value for psychiatric diseases is a major step forward in developing and testing etiology-directed treatment for these complex disorders. Based on the existing literature, we have generated an inventory of applied rodent behavioural testing paradigms relevant to autism spectrum disorders (ASD). This inventory focused on previously used paradigms that assess behavioural domains that are affected in ASD, such as social interaction, social communication, repetitive behaviours and behavioural inflexibility, cognition as well as anxiety behaviour. A wide range of behavioural testing paradigms for rodents were identified. However, the level of face and construct validity is highly variable. The predictive validity of these paradigms is unknown, as etiology-directed treatments for ASD are currently not on the market. To optimise these studies, future efforts should address aspects of reproducibility and take into account data about the neurodevelopmental underpinnings and trajectory of ASD. In addition, with the increasing knowledge of processes underlying ASD, such as sensory information processes and synaptic plasticity, phenotyping efforts should include multi-level automated analysis of, for example, representative task-related behavioural and electrophysiological read-outs.

Strong genetic influences on the stability of autistic traits in childhood

OBJECTIVE

Disorders on the autism spectrum, as well as autistic traits in the general population, have been found to be both highly stable across age and highly heritable at individual ages. However, little is known about the overlap in genetic and environmental influences on autistic traits across age and the contribution of such influences to trait stability itself. The present study investigated these questions in a general population sample of twins.

METHOD

More than 6,000 twin pairs were rated on an established scale of autistic traits by their parents at 8, 9, and 12 years of age and by their teachers at 9 and 12 years of age. Data were analyzed using structural equation modeling.

RESULTS

The results indicated that, consistently across raters, not only were autistic traits stable, and moderately to highly heritable at individual ages, but there was also a high degree of overlap in genetic influences across age. Furthermore, autistic trait stability could largely be accounted for by genetic factors, with the environment unique to each twin playing a minor role. The environment shared by twins had virtually no effect on the longitudinal stability in autistic traits.

CONCLUSIONS

Autistic traits are highly stable across middle childhood. and this stability is caused primarily by genetic factors.

Association study in siblings and case-controls of serotonin- and oxytocin-related genes with high functioning autism

Background

Autism spectrum disorder (ASD) is heritable and neurodevelopmental with unknown causes. The serotonergic and oxytocinergic systems are of interest in autism for several reasons: (i) Both systems are implicated in social behavior, and abnormal levels of serotonin and oxytocin have been found in people with ASD; (ii) treatment with selective serotonin reuptake inhibitors and oxytocin can yield improvements; and (iii) previous association studies have linked the serotonin transporter (SERT; SLC6A4), serotonin receptor 2A (HTR2A), and oxytocin receptor (OXTR) genes with ASD. We examined their association with high functioning autism (HFA) including siblings and their interaction.

Methods

In this association study with HFA children (IQ > 80), siblings, and controls, participants were genotyped for four single nucleotide polymorphisms (SNPs) in OXTR (rs2301261, rs53576, rs2254298, rs2268494) and one in HTR2A (rs6311) as well as the triallelic HTTLPR (SERT polymorphism).

Results

We identified a nominal significant association with HFA for the HTTLPR s allele (consisting of S and L_G alleles) (p = .040; odds ratio (OR) = 1.697, 95% CI 1.191–2.204)). Four polymorphisms (HTTLPR, HTR2A rs6311, OXTR rs2254298 and rs53576) in combination conferred nominal significant risk for HFA with a genetic score of ≥4 (OR = 2.09, 95% CI 1.05–4.18, p = .037). The resulting area under the receiver operating characteristic curve was 0.595 (p = .033).

Conclusions

Our findings, combined with those of previous reports, indicate that ASD, in particular HFA, is polygenetic rather than monogenetic and involves the serotonergic and oxytocin pathways, probably in combination with other factors.

Electronic supplementary material

The online version of this article (doi:10.1186/2049-9256-2-1) contains supplementary material, which is available to authorized users.

Narrowly versus broadly defined autism spectrum disorders: differences in pre- and perinatal risk factors

This study examined the differential contribution of pre- and perinatal risks in narrowly versus broadly defined autism spectrum disorder (ASD) and across core symptom domains, IQ and co-morbid problems. Children with a DSM-IV diagnosis of autistic disorder (AD) (n = 121) or pervasive developmental disorder not otherwise specified (PDD-NOS) (n = 75) were compared to a typical control sample (n = 311). Diagnoses were based on extensive assessments between 12 and 49 months of age (M = 33.3, SD = 6.4) and re-evaluated at 43-98 months (M = 68.1, SD = 10.7) in 70% of the cases. Compared with controls, cases with ASD were more likely to be firstborn and show a suboptimal condition after birth. Case mothers reported more infections and more stress during pregnancy. Although the ASD subgroups showed mostly overlapping risks, cases with PDD-NOS differed from those with AD by higher exposure to smoking during pregnancy (SDP) and by a negative association of smoking with IQ, regardless of confounders. SDP appears to contribute more to broadly defined (PDD-NOS) than to narrowly defined ASD (AD). Findings suggest differences in etiological contributors between ASD phenotypes.

Exploring the ‘fractionation’ of autism at the cognitive level

Autism spectrum disorders are defined by difficulties across a range of areas: social and communication difficulties and restricted and repetitive behaviours and interests. It has been suggested that this triad of symptoms cannot be explained by a single cause at the genetic, neural or cognitive level. This article reviews the evidence for a ‘fractionable’ autism triad at the cognitive level, highlighting questions for future research.

Chromosomal abnormalities in patients with autism spectrum disorders from Taiwan

Autism spectrum disorders (ASD) are childhood-onset neurodevelopmental disorders characterized by verbal communication impairments, social reciprocity deficits, and the presence of restricted interests and stereotyped behaviors. Genetic factors contribute to the incidence of ASD evidently. However, the genetic spectrum of ASD is highly heterogeneous. Chromosomal abnormalities contribute significantly to the genetic deficits of syndromic and non-syndromic ASD. In this study, we conducted karyotyping analysis in a sample of 500 patients (447 males, 53 females) with ASD from Taiwan, the largest cohort in Asia, to the best of our knowledge. We found three patients having sex chromosome aneuploidy, including two cases of 47, XXY and one case of 47, XYY. In addition, we detected a novel reciprocal chromosomal translocation between long arms of chromosomes 4 and 14, designated t(4;14)(q31.3;q24.1), in a patient with Asperger's disorder. This translocation was inherited from his unaffected father, suggesting it might not be pathogenic or it needs further hits to become pathogenic. In line with other studies, our study revealed that subjects with sex chromosomal aneuploidy are liable to neurodevelopmental disorders, including ASD, and conventional karyotyping analysis is still a useful tool in detecting chromosomal translocation in patients with ASD, given that array-based comparative genomic hybridization technology can provide better resolution in detecting copy number variations of genomic DNA.

What have we learned from recent twin studies about the etiology of neurodevelopmental disorders?

PURPOSE OF REVIEW

The relative influence of genes and environment on the liability to neurodevelopmental disorders (NDDs) can be investigated using a twin design. This review highlights the results of the most recent twin studies of NDDs.

RECENT FINDINGS

Recent twin studies have confirmed that NDDs show moderate-to-high heritability, and that from an etiological viewpoint both autism spectrum disorder (ASD) and attention deficit hyperactivity disorder (ADHD) are best regarded as the extremes on a continuous liability distribution. Both ASD and ADHD show high heritability in childhood and a substantial drop in heritability in adulthood, which is likely explained by the use of different assessment strategies in childhood versus adulthood, or by a complex mechanism of gene-by-environment interaction. NDDs show substantial comorbidity among each other, and with other mental health problems, which is partly because of a shared genetic etiology between different disorders.

SUMMARY

The findings of twin studies implicate substantial heritability of NDDs, and warrant large-scale molecular genetic studies for such traits.

Quantitative Nature of Social Vulnerability and Autism: An Important Paradigm Shift in the DSM-5 for Autism Spectrum Disorder

In the Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSM-IV), autistic characteristics in social interaction and communication are described as qualitative impairments. However, the difference between autistics and nonautistics in the draft of the 5th edition (DSM-5 draft) is quantitative rather than qualitative. The word “qualitative” is deleted in the draft text, and it is specified that the relation between social demands and individual limited capacities is critical for symptom manifestation (criterion C). Because the proposed levels of support requirement in the draft are mere observable outcomes of social vulnerability, the boundary between level 1 and nonautistic condition is determined by the relation between social demands and individual capacities. In addition to the introduction of the single category (autism spectrum disorder (ASD)) to cover the entire case spectrum, the DSM-5 draft is clearly based on a conviction that ASD is indistinguishable from the normal behavioral range. This concise review provides an explanation for this implicit paradigm shift from qualitative to quantitative. Importantly, the conditional role of social demands for symptom manifestation in the draft can be plausibly interpreted using a unique liability-probability model.

The disruption of Celf6, a gene identified by translational profiling of serotonergic neurons, results in autism-related behaviors

The immense molecular diversity of neurons challenges our ability to understand the genetic and cellular etiology of neuropsychiatric disorders. Leveraging knowledge from neurobiology may help parse the genetic complexity: identifying genes important for a circuit that mediates a particular symptom of a disease may help identify polymorphisms that contribute to risk for the disease as a whole. The serotonergic system has long been suspected in disorders that have symptoms of repetitive behaviors and resistance to change, including autism. We generated a bacTRAP mouse line to permit translational profiling of serotonergic neurons. From this, we identified several thousand serotonergic-cell expressed transcripts, of which 174 were highly enriched, including all known markers of these cells. Analysis of common variants near the corresponding genes in the AGRE collection implicated the RNA binding protein CELF6 in autism risk. Screening for rare variants in CELF6 identified an inherited premature stop codon in one of the probands. Subsequent disruption of Celf6 in mice resulted in animals exhibiting resistance to change and decreased ultrasonic vocalization as well as abnormal levels of serotonin in the brain. This work provides a reproducible and accurate method to profile serotonergic neurons under a variety of conditions and suggests a novel paradigm for gaining information on the etiology of psychiatric disorders.

Examining and interpreting the female protective effect against autistic behavior

Male preponderance in autistic behavioral impairment has been explained in terms of a hypothetical protective effect of female sex, yet little research has tested this hypothesis empirically. If females are protected, they should require greater etiologic load to manifest the same degree of impairment as males. The objective of this analysis was to examine whether greater familial etiologic load was associated with quantitative autistic impairments in females compared with males. Subjects included 3,842 dizygotic twin pairs from the Twins Early Development Study (TEDS) and 6,040 dizygotic twin pairs from the Child and Adolescent Twin Study of Sweden (CATSS). In both samples, we compared sibling autistic traits between female and male probands, who were identified as children scoring in the top 90th and 95th percentiles of the population autistic trait distributions. In both TEDS and CATSS, siblings of female probands above the 90th percentile had significantly more autistic impairments than the siblings of male probands above the 90th percentile. The siblings of female probands above the 90th percentile also had greater categorical recurrence risk in both TEDS and CATSS. Results were similar in probands above the 95th percentile. This finding, replicated across two nationally-representative samples, suggests that female sex protects girls from autistic impairments and that girls may require greater familial etiologic load to manifest the phenotype. It provides empirical support for the hypothesis of a female protective effect against autistic behavior and can be used to inform and interpret future gene finding efforts in autism spectrum disorders.

Coherence and other autistic spectrum traits and eating disorders: building from mechanism to treatment. The Birgit Olsson lecture

AIM

To revisit Gillberg's hypothesis proposed in 1992, which was that anorexia nervosa should be considered within the spectrum of autistic disorders.

METHOD

A search was made of the literature relating to the behavioural traits, and cognitive, emotional and neuroanatomical intermediate phenotypes that are shared between autistic spectrum disorders (ASD) and anorexia nervosa.

RESULTS

People with eating disorders in the acute phase (less so after recovery) share some behavioural traits (social impairment and restricted and repetitive behaviours) and intermediate phenotypes (weak central coherence, and impaired set shifting and theory of mind) with people in the autistic spectrum.

CONCLUSION

Behavioural and intermediate neuropsychological traits are shared between eating disorders and ASD. In part, these are familial but also they are accentuated by the illness state and may be secondary to starvation. These traits have implications for prognosis and treatment.

Gene × gene interaction in shared etiology of autism and specific language impairment

BACKGROUND

To examine the relationship between autism spectrum disorders (ASD) and specific language impairment (SLI), family studies typically take a comparative approach where families with one disease are examined for traits of the other disease. In contrast, the present report is the first study with both disorders required to be present in each family to provide a more direct test of the hypothesis of shared genetic etiology.

METHODS

We behaviorally assessed 51 families including at least one person with ASD and at least one person with SLI (without ASD). Pedigree members were tested with 22 standardized measures of language and intelligence. Because these extended families include a nonshared environmental contrast, we calculated heritability, not just familiality, for each measure twice: 1) baseline heritability analysis, compared with; 2) heritability estimates after statistically removing ASD subjects from pedigrees.

RESULTS

Significant increases in heritability on four supra-linguistic measures (including Pragmatic Judgment) and a composite language score but not on any other measures were observed when removing ASD subjects from the analysis, indicating differential genetic effects that are unique to ASD. Nongenetic explanations such as effects of ASD severity or measurement error or low score variability in ASD subjects were systematically ruled out, leaving the hypothesis of nonadditive genetics effects as the potential source of the heritability change caused by ASD.

CONCLUSIONS

Although the data suggest genetic risk factors common to both SLI and ASD, there are effects that seem unique to ASD, possibly caused by nonadditive gene-gene interactions of shared risk loci.