Russell Schachar

SickKids · Department of Psychiatry

Attention-deficit/hyperactivity disorder (ADHD) symptoms can be categorized by hyperactivity/impulsivity and inattention dimensions. Irritability and deficits in facial emotion recognition (FER) are common in ADHD. Previous studies show a stronger correlation between irritability and hyperactivity/impulsivity symptoms but not inattention. Poor FER...

Autism spectrum disorder (ASD) and attention-deficit/hyperactivity disorder (ADHD) are neurodevelopmental conditions that share genetic etiology and frequently co-occur. Given this comorbidity and the well-established clinical heterogeneity within both conditions, identifying individuals with similar brain signatures may be valuable for predicting...

Objectives Attention‐deficit/hyperactivity disorder (ADHD) is the most common neurodevelopmental condition and is characterized by inattention, hyperactivity, and impulsivity. Research suggests that some populations, such as females and individuals with high intelligence quotients may be a risk for late ADHD diagnosis and subsequent treatment. Our...

The cerebellum, through its connectivity with the cerebral cortex, plays an integral role in regulating cognitive and affective processes, and its dysregulation can result in neurodevelopmental disorder (NDD)-related behavioural deficits. Identifying cerebellar-cerebral functional connectivity (FC) profiles in children with NDDs can provide insight...

Executive functions are neurocognitive processes involved in regulating thought and action. It is unknown whether youth diagnosed with attention-deficit/hyperactivity disorder (ADHD) and autism spectrum disorder (ASD) have similar executive functioning. This review aimed to synthesize the literature directly comparing executive functioning in youth...

Neurodevelopmental conditions can be associated with decreased health-related quality of life; however, the predictors of these outcomes remain largely unknown. We characterized the predictors of health-related quality of life (HRQoL) in a sample of neurodiverse children and youth. We used a cross-sectional subsample from the Province of Ontario Ne...

Objective Racial/ethnic disparities in the prevalence of psychiatric disorders have been reported, but have not accounted for the prevalence of the traits that underlie these disorders. Examining rates of diagnoses in relation to traits may yield a clearer understanding of the degree to which racial/ethnic minority youth in Canada differ in their a...

Background Anxiety disorders are the most common psychiatric problems among Canadian youth and typically have an onset in childhood or adolescence. They are characterized by high rates of relapse and chronicity, often resulting in substantial impairment across the lifespan. Genetic factors play an important role in the vulnerability toward anxiety...

Objective To examine the theoretical and empirical contribution of Joe Biederman and his colleagues to the understanding of executive function (EF) and ADHD. Method We searched PubMed for references to EF in Biederman’s publications and conducted a narrative review of this literature. Results In 50 or more papers using neuropsychological tests, r...

Background: Irritability is a trans-diagnostic trait associated with a wide range of psychopathology (e.g., ADHD, major depression [MDD], bipolar disorder [BPD], etc.) and significant concurrent and future impairment in children and youth. Irritability involves both externalizing (e.g., temper outbursts) and internalizing (e.g., internalized negati...

ADHD is a neurodevelopmental disorder with genetic and environmental risk factors. Twin studies estimate the heritability to be 70-80% but the largest GWAS to date estimated the SNP heritability to be 14%. This difference in heritability may be due to non-polygenic effects. However, there may be additional polygenic effects that were not detected i...

Objective: To evaluate if children and adolescents with a diagnosis of ASD or ADHD have distinct executive function (EF) profiles. Methods: Peer-reviewed articles comparing ASD, ADHD, and typically developing individuals under 19 years of age were identified. The domains evaluated were: working memory, response inhibition, planning, cognitive fl...

Background Parent and child mental health has suffered during the pandemic and transition phase. Structured and shared parenting may be intervention targets beneficial to families who are struggling with parent or child mental health challenges. AimsFirst, we investigated associations between structured and shared parenting and parent depression sy...

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 variat...

We assessed the relationship of gene copy number variation (CNV) in mental health/neurodevelopmental traits and diagnoses, physical health, and cognition in a community sample of 7100 unrelated children and youth of European or East Asian ancestry (Spit for Science). Clinically significant or susceptibility CNVs were present in 3.9% of participants...

Introduction: Poor quality T1-weighted brain scans systematically affect the calculation of brain measures. Removing the influence of such scans requires identifying and excluding scans with noise and artefacts through a quality control (QC) procedure. While QC is critical for brain imaging analyses, it is not yet clear whether different QC approa...

Background: Racial/ethnic disparities in the prevalence of mental health diagnoses have been reported but have not accounted for the prevalence of the traits that underlies these disorders. Examining rates of diagnoses in relation to traits may yield a clearer understanding of how racial/ethnic youth differ in their access to assessment and care. W...

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...

Background: Intrathecal injections provide important access to the central nervous system for delivery of anesthetic, analgesic or chemotherapeutic drugs that do not otherwise cross the blood-brain barrier. The administration of drugs via this route in animal models is challenging due to an inability to visualize the small target space during inje...

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...

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...

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...

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...

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...

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...

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...

Abstract Background Existing literature on ethnic and racial disparities in youth mental health is largely based in the US and focuses on the prevalence of mental health diagnoses rather than the underlying prevalence of mental health traits. It is critical to examine rates of mental health diagnoses in relation to the prevalence of mental health t...

The comorbidity of autism spectrum disorder (ASD) and attention-deficit/hyperactivity disorder (ADHD) diagnoses is well established. An ASD diagnosis is associated with elevated ADHD traits and symptoms, as well as strengths in attention. In the ASD literature, attentional strengths have been described as maladaptive (e.g., hyperfocus), in contrast...

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....

Résumé Objectifs Les confinements dans les provinces canadiennes ont malmené la santé mentale des enfants pendant la pandémie de COVID-19, et les enfants autistes y ont été particulièrement vulnérables. La présente étude visait à recenser les sous-groupes d’enfants autistes ayant des profils distincts de modification à leur santé mentale, afin de...

The ability to recognize emotions evident in people’s faces contributes to social functioning and might be affected by ADHD and irritability. Given their high co-occurrence, we examined the relative contribution of ADHD and irritability to facial emotion recognition (FER). We hypothesized that irritability but not ADHD traits would predict increase...

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...

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...

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...

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...

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...

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...

The Asymmetric Laplace Gaussian (ALG) Distribution as the Brain Inhibition Model-Cover Page: Brain Sciences 2022, 12(6)

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...

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...

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...

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...

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...

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-...

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 its...

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...

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)...

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...

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...

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...

Background: 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),...

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...

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...

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...

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 slowin...

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...

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...

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...