Russell Schachar

Russell Schachar
SickKids · Department of Psychiatry

About

432
Publications
89,934
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31,464
Citations
Citations since 2017
144 Research Items
13397 Citations
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Introduction
Skills and Expertise

Publications

Publications (432)
Article
Neurodevelopmental disorders (NDDs) including autism spectrum disorder (ASD), attention‐deficit hyperactivity disorder (ADHD) and obsessive–compulsive disorder (OCD) are thought to arise in part from the disruption in the excitatory/inhibitory balance of gamma‐aminobutyric acid (GABA) and glutamate in the brain. Recent evidence has shown the involv...
Preprint
Full-text available
While 1-2% of individuals meet the criteria for a clinical diagnosis of obsessive-compulsive disorder (OCD), many more (~15-40%) experience subclinical obsessive-compulsive symptoms (OCS) during their life. To characterize the genetic underpinnings of OCS and its genetic relationship to OCD, we conducted the largest genome-wide association study (G...
Article
Full-text available
Despite significant disruption to school during the COVID-19 pandemic, research on the impact on children is sparse. This study examines in-person and virtual learning contexts and the impact of school format on mental health (MH). Children and adolescents were recruited from community and clinical settings. Parents and children completed prospecti...
Article
Full-text available
Sensory processing abilities are highly variable within and across people diagnosed with autism and attention-deficit/hyperactivity disorder (ADHD). This study examined the transdiagnostic nature of sensory processing abilities, and their association with features of autism and ADHD, in a large sample of autistic people (n = 495) and people with AD...
Poster
Full-text available
Objectives The Autism Spectrum Quotient (AQ) is a widely used autism trait measure for screening and research. To optimize rapid recruitment of children and youth from the general population we adopted the validated AQ-28 version to include adolescents via self-report and children via parent-report. Here we explore discriminant and ecological valid...
Preprint
Full-text available
Deficits in effective executive function, including inhibitory control are associated with risk for a number of psychiatric disorders and significantly impact everyday functioning. These complex traits have been proposed to serve as endophenotypes, however their genetic architecture is not yet well understood. To identify the common genetic variati...
Poster
Attention-deficit hyperactivity disorder (ADHD) and autism spectrum disorder (ASD) are common and impairing childhood neurodevelopmental disorders which exhibit impairment in executive functions. Executive functions are higher-level mental processes essential for daily functioning and goal attainment. There is growing evidence for genetic and neura...
Preprint
Full-text available
We assessed the relationship of gene copy number variation (CNV) in mental health/neurodevelopmental traits and diagnoses, physical health, and cognitive biomarkers in a community sample of 7,100 unrelated European, and East Asian children and youth (Spit for Science). Diagnoses of mental health disorders were found in 17.5% of participants and 27....
Article
Full-text available
Attention-deficit/hyperactivity (ADHD) and autism spectrum (ASD) disorders are commonly co-occurring conditions characterized by neurocognitive impairments. Few studies have directly compared neurocognitive profiles in ADHD and ASD and fewer still have controlled for comorbidity of ADHD and ASD. All direct comparisons have been in clinic samples, l...
Article
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Objective To determine the association between pubertal stage, sex and behavioural profile across and within neurodevelopmental disorders (NDDs) compared with typically developing (TD) youth. Methods This was a cross-sectional study from the Province of Ontario Neurodevelopmental Disorders network, including children/youth with various NDDs and TD...
Article
Full-text available
Objectives Sensory processing is the ability to discern and understand information from one’s sensory organs. Understanding sensory processing patterns in different clinical groups could elicit evidence that sensory processing patterns are a transdiagnostic mechanism in neurodevelopmental disorders. Furthermore, there is little evidence of how sens...
Article
Full-text available
Alterations in the structural maturation of the amygdala subnuclei volumes are associated with anxiety behaviors in adults and children with neurodevelopmental and associated disorders. This study investigated the relationship between amygdala subnuclei volumes and anxiety in 233 children and adolescents (mean age = 11.02 years; standard deviation...
Preprint
Objectives: Sensory processing is the ability to discern and understand information from one’s sensory organs. Understanding sensory processing patterns in different clinical groups could elicit evidence that sensory processing patterns are a transdiagnostic mechanism that is important to understand in neurodevelopmental disorders. Furthermore, the...
Article
Full-text available
Background Externalizing and internalizing behaviors contribute to clinical impairment in children with neurodevelopmental disorders (NDDs). Although associations between externalizing or internalizing behaviors and cortico-amygdalar connectivity have been found in clinical and non-clinical pediatric samples, no previous study has examined whether...
Data
The Asymmetric Laplace Gaussian (ALG) Distribution as the Brain Inhibition Model-Cover Page: Brain Sciences 2022, 12(6)
Preprint
Full-text available
Hoarding Disorder (HD) is a mental disorder characterized by persistent difficulties discarding or parting with possessions, often resulting in cluttered living spaces, distress, and impairment. Its etiology is largely unknown, but twin studies suggest that it is moderately heritable. In this study, we pooled phenotypic and genomic data from seven...
Article
Full-text available
Measurements of response inhibition components of reactive inhibition and proactive inhibition within the stop-signal paradigm have been of particular interest to researchers since the 1980s. While frequentist nonparametric and Bayesian parametric methods have been proposed to precisely estimate the entire distribution of reactive inhibition, quant...
Article
Full-text available
Objectives Canadian province-wide lockdowns have challenged children’s mental health (MH) during the COVID-19 pandemic, with autistic children being at particular risk. The purpose of our study was to identify sub-groups of autistic children with distinct mental health change profiles, to understand the child-, parent-, and system-specific factors...
Article
Full-text available
Over the past few decades, neuroimaging has become a ubiquitous tool in basic research and clinical studies of the human brain. However, no reference standards currently exist to quantify individual differences in neuroimaging metrics over time, in contrast to growth charts for anthropometric traits such as height and weight ¹ . Here we assemble an...
Article
Full-text available
This large cross-sectional study examined the impact of COVID-19 emergency measures on child/adolescent mental health for children/adolescents with and without pre-existing psychiatric diagnoses. Using adapted measures from the CRISIS questionnaire, parents of children aged 6–18 (N = 1013; 56% male; 62% pre-existing psychiatric diagnosis) and self-...
Article
Full-text available
Background Atypical processing of unfamiliar, but less so familiar, stimuli has been described in Autism Spectrum Disorder (ASD), in particular in relation to face processing. We examined the construct of familiarity in ASD using familiar and unfamiliar songs, to investigate the link between familiarity and autism symptoms, such as repetitive behav...
Article
Full-text available
Impairments in emotional face processing are demonstrated by individuals with neurodevelopmental disorders (NDDs), including autism spectrum disorder (ASD) and attention-deficit/hyperactivity disorder (ADHD), which is associated with altered emotion processing networks. Despite accumulating evidence of high rates of diagnostic overlap and shared sy...
Article
Background: Autism Spectrum Disorder (ASD) and Attention Deficit Hyperactivity Disorder (ADHD) have considerable overlap, supporting the need for a dimensional framework that examines neurodevelopmental domains which cross traditional diagnostic boundaries. In the following study, we use factor analysis to deconstruct the ASD-ADHD phenotype into i...
Preprint
Full-text available
Objective We designed The Irritability and Dysregulation of Emotion Scale (TIDES-13) to test whether irritability consisted of several sub-dimensions that would correlate differentially with internalizing/externalizing psychopathology, age, and gender. Method Parent-report (n = 3935, mean age = 8.9) and youth self-report (n = 579, mean age = 15.1)...
Article
Objective: The investigators examined the factors predictive of novel oppositional defiant disorder in the 6-12 months following traumatic brain injury (TBI). Methods: Children ages 5-14 years old who experienced a TBI were recruited from consecutive admissions to five hospitals. Participants were evaluated soon after injury (baseline) for prein...
Article
This systematic review and meta-analysis updates evidence pertaining to response inhibition in obsessive-compulsive disorder (OCD) as measured by the stop-signal task (SST). We conducted a meta-analysis of the literature to compare response inhibition in patients with OCD and healthy controls, metaregressions to determine relative influences of age...
Article
Full-text available
Background: Many phenotypic studies have estimated the degree of comorbidity between Autism Spectrum Disorder (ASD) and Attention Deficit Hyperactivity Disorder (ADHD), but few have examined the latent, or unobserved, structure of combined ASD and ADHD symptoms. This is an important perquisite toward better understanding the overlap between ASD and...
Article
Full-text available
There is a need to develop a multipurpose obsessive–compulsive disorder (OCD) measure that is useful for cross disorder research and as a reliable clinical rating scale. The current study examined the psychometric properties and established clinical cutoffs for the parent‐report version of the Toronto Obsessive–Compulsive Scale (TOCS), a 21‐item ra...
Preprint
Sensory processing abilities are highly variable within and across people diagnosed with autism spectrum disorder (ASD) and attention-deficit/hyperactivity disorder (ADHD). This study examined the transdiagnostic nature of sensory processing abilities, and their association with features of ASD and ADHD, in a large sample of autistic people (n = 49...
Article
Objective: The investigators aimed to assess predictive factors of novel oppositional defiant disorder (ODD) among children and adolescents in the first 6 months following traumatic brain injury (TBI). Methods: Children ages 5-14 years who experienced a TBI were recruited from consecutive admissions to five hospitals. Testing of a biopsychosocia...
Article
Full-text available
Objective: To summarize existing knowledge about the characteristics of attention problems secondary to traumatic brain injuries (TBI) of all severities in children. Methods: Computerized databases PubMed and PsychINFO and gray literature sources were used to identify relevant studies. Search terms were selected to identify original research examin...
Article
Full-text available
Restricted interests and repetitive behaviors (RRBs) are core symptoms of autism spectrum disorder (ASD), and commonly occur in attention-deficit/hyperactivity disorder (ADHD). Little is known about how RRBs manifest in ADHD. We quantified and compared factor structures of RRBs in children with ASD (n = 634) or ADHD (n = 448), and related factors t...
Article
Background: Neurocognitive impairments are common in OCD, although not well studied in children and youth with the disorder. Method: Using the stop-signal task (SST), we measured response inhibition (stop-signal reaction time-SSRT), sustained attention (reaction time variability-RTV), reaction time (RT), and performance monitoring (post-error sl...
Article
Full-text available
Shared etiological pathways are suggested in ASD and ADHD given high rates of comorbidity, phenotypic overlap and shared genetic susceptibility. Given the peak of cortical gyrification expansion and emergence of ASD and ADHD symptomology in early development, we investigated gyrification morphology in 539 children and adolescents (6–17 years of age...
Article
Full-text available
The distribution of single Stop Signal Reaction Times (SSRT) in the stop signal task (SST) has been modelled with two general methods: a nonparametric method by Hans Colonius (1990) and a Bayesian parametric method by Dora Matzke, Gordon Logan and colleagues (2013). These methods assume an equal impact of the preceding trial type (go/stop) in the S...
Preprint
Full-text available
This systematic review and meta-analysis updates evidence pertaining to deficient response inhibition in obsessive-compulsive disorder (OCD) as measured by the stop-signal task (SST). We conducted a meta-analysis of the literature to compare response inhibition in patients with OCD and healthy controls, meta-regressions to determine relative influe...
Preprint
Full-text available
Over the past 25 years, neuroimaging has become a ubiquitous tool in basic research and clinical studies of the human brain. However, there are no reference standards against which to anchor measures of individual differences in brain morphology, in contrast to growth charts for traits such as height and weight. Here, we built an interactive online...
Article
Full-text available
Social communication differences are seen in autism spectrum disorder (ASD), attention-deficit/hyperactivity disorder (ADHD), and obsessive-compulsive disorder (OCD), but the brain mechanisms contributing to these differences remain largely unknown. To address this gap, we used a data-driven and diagnosis-agnostic approach to discover brain correla...
Article
Full-text available
We examined the correlation between interviewer-administered Vineland Adaptive Behavior Scale II (VABS-II) and the parent-rated Adaptive Behavior Assessment System II (ABAS-II) questionnaire in 352 participants (ages 1.5–20.8 years) with autism spectrum disorder (ASD) to determine if ABAS could be used as a screen to reduce the number of VABS inter...
Article
Full-text available
Background: Autism spectrum disorder (ASD) is a complex neurodevelopmental disorder that often involves impaired cognition, communication difficulties and restrictive, repetitive behaviors. ASD is extremely heterogeneous both clinically and etiologically, which represents one of the greatest challenges in studying the molecular underpinnings of ASD...
Article
Background In recent years, a number of studies have begun to explore the nature of Attention-Deficit/Hyperactivity Disorder (ADHD) in children with Autism Spectrum Disorder (ASD). In this study, we examined the relationship between both symptoms of ADHD and symptoms of ASD on cognitive task performance in a sample of higher-functioning children an...
Article
The identification of children with traumatic brain injury (TBI) who are at risk of death or poor global neurological functional outcome remains a challenge. Magnetic resonance imaging (MRI) can detect several brain pathologies that are a result of TBI, however, the types and locations of pathology that are the most predictive remain to be determin...
Article
Full-text available
Previous work from our lab has shown that basal cortisol levels are different between healthy young adults who spontaneously use caudate nucleus-dependent response strategies compared to young adults who use hippocampus-dependent spatial navigation strategies. Young adults who use caudate nucleus dependent strategies display lower basal cortisol le...
Article
Objective To evaluate the impact of a Harry Potter-based mental health literacy curriculum, imparting cognitive behavioral therapy (CBT) skills, on suicidality and well-being in middle-schoolers. Methods Students (aged 11-14; grades 7-8) who received a 3-month teacher-delivered intervention embedded in the language arts curriculum (N=200) were com...
Article
Full-text available
Background A recent genome-wide association study (GWAS) identified 12 independent loci significantly associated with attention-deficit/hyperactivity disorder (ADHD). Polygenic risk scores (PRS), derived from the GWAS, can be used to assess genetic overlap between ADHD and other traits. Using ADHD samples from several international sites, we derive...
Article
Full-text available
Using a novel trait-based measure, we examined genetic variants associated with obsessive-compulsive (OC) traits and tested whether OC traits and obsessive-compulsive disorder (OCD) shared genetic risk. We conducted a genome-wide association analysis (GWAS) of OC traits using the Toronto Obsessive-Compulsive Scale (TOCS) in 5018 unrelated Caucasian...
Preprint
Full-text available
Background: Externalizing and internalizing behaviors are common and contribute to impairment in children with neurodevelopmental disorders (NDDs). Associations between externalizing or internalizing behaviors and cortico-amygdalar connectivity have been found in children with and without clinically significant internalizing/externalizing behaviors...
Preprint
Measurements of response inhibition components of reactive inhibition and proac-tive inhibition within the stop signal paradigm have been of special interest for researchers since the 1980s. While frequentist nonparametric and Bayesian para-metric methods have been proposed to precisely estimate the entire distribution of reactive inhibition, quant...
Preprint
The distribution of single Stop Signal Reaction Times (SSRT) in the stop signaltask (SST) has been modeled with two general methods: a nonparametric method by Hans Colonius (1990); and a Bayesian parametric method by Dora Matzke, Gordon Logan and colleagues (2013). These methods assume an equal impact of thepreceding trial type (go/stop) in the SST...
Article
Full-text available
Introduction : There is significant overlap in the type of structural language impairments exhibited by children with autism spectrum disorder (ASD) and children with attention deficit hyperactivity disorder (ADHD). This similarity suggests that the cognitive impairment(s) contributing to the structural language deficits in ASD and ADHD may be shar...
Article
Full-text available
Autism spectrum disorder (ASD), obsessive-compulsive disorder (OCD) and attention-deficit/hyperactivity disorder (ADHD) are clinically and biologically heterogeneous neurodevelopmental disorders (NDDs). The objective of the present study was to integrate brain imaging and behavioral measures to identify new brain-behavior subgroups cutting across t...
Article
Full-text available
Autism spectrum disorder (ASD) is classically associated with poor face processing skills, yet evidence suggests that those with obsessive-compulsive disorder (OCD) and attention deficit hyperactivity disorder (ADHD) also have difficulties understanding emotions. We determined the neural underpinnings of dynamic emotional face processing across the...
Article
With high survival rates for pediatric acute lymphoblastic leukemia (ALL), long-term quality of life is a prominent consideration in treatment. We concurrently evaluated cognition, behavior, and quality of life in child and adolescent ALL survivors and determined associations between them. The sample included 83 controls (mean age: 12.5 years) and...
Article
Full-text available
Background: A decreased ability to inhibit a speeded motor response is a well-studied deficit in Attention Deficit Hyperactivity Disorder (ADHD), and has been proposed as an endophenotype. Inhibitory control has been assessed reliably with the Stop Signal Task (SST) and is associated with prior documented differences in regional brain function usi...
Article
Full-text available
Introduction: Cure rates for pediatric acute lymphoblastic leukemia (ALL) have reached an all-time high (>90%); however, neurocognitive difficulties continue to affect quality of life in at least a subset of survivors. There are relatively few quantitative neuroimaging studies in child and adolescent ALL survivors treated with chemotherapy only. U...
Article
Full-text available
The Stop Signal Reaction Time (SSRT) is a latency measurement for the unobservable human brain stopping process, and was formulated by Logan (1994) without consideration of the nature (go/stop) of trials that precede the stop trials. Two asymptotically equivalent and larger indices of mixture SSRT and weighted SSRT were proposed in 2017 to address...
Article
Full-text available
Background: A growing body of research has demonstrated associations between specific neurodevelopmental disorders and variation in DNA methylation (DNAm), implicating this molecular mark as a possible contributor to the molecular etiology of these disorders and/or as a novel disease biomarker. Furthermore, genetic risk variants of neurodevelopmen...
Article
Full-text available
Background: Hoarding, originally only considered a symptom of obsessive-compulsive disorder (OCD), is now categorized as a separate disorder in the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5). We studied candidate serotonergic genes and the distinctness of hoarding in children and adolescents and hypothesized...
Article
Objective: To examine the effectiveness of four doses of psychostimulant medication, combining extended-release methylphenidate (ER-MPH) in the morning with immediate-release MPH (IR-MPH) in the afternoon, on cognitive task performance. Method: The sample comprised 24 children (19 boys and 5 girls) who met the Diagnostic and Statistical Manual of...
Preprint
Background: Autism spectrum disorder (ASD) and attention-deficit/hyperactivity disorder (ADHD) show high rates of comorbidity. Restricted interests and repetitive behaviors (RRBs) are a core symptom of ASD and commonly occur in ADHD. However, little is known about how RRBs manifest in ADHD, nor how they relate to cognitive abilities and sex across...