Symptoms of attention deficit hyperactivity disorder (ADHD) are common in individuals with autism spectrum disorders (ASD), but it is not clear how these issues manifest in young children or how they correlate with other features of autism.
To compare inattention and hyperactivity symptoms as measured by the Abberant Behavior Checklist (ABC) in young children with ASD, developmental delay (DD) without ASD, and typical development (TD), and to characterize attention deficits in ASD. In particular, we explored whether these behaviors were related to child cognitive and behavior scores, demographic factors, and selected environmental risk factors previously associated with ASD.
Participants were children 3-5 years of age, who were enrolled in the CHildhood Autism Risks from Genetics and the Environment (CHARGE) population-based case-control study. TD and DD control groups were defined according to scores on the Social Communication Questionnaire (SCQ), Mullen Scales of Early Learning (MSEL), and the Vineland Adaptive Behavior Scales (VABS), while ASD diagnosis was confirmed by ADOS and ADI-R. Mean scores on the hyperactivity subscale of the ABC were compared by diagnostic group. We also separated the hyperactivity subscale into 2 subdomains: hyperactivity/impulsivity (10 of 13 subscale items), and inattention (3 of 13 subscale items), and compared these subdomain scores by diagnostic group. We calculated Pearson correlation coefficients for the subscale and subdomain scores vs. SCQ, MSEL, and VABS scores. Associations between scores and demographic (income, parental age, education, and race) or environmental factors (distance from major road as a measure of air pollution, prenatal vitamin use, maternal pre-pregnancy obesity) were assessed by t-tests. Linear regression was used to examine these associations adjusted for potentially confounding factors.
560 ASD cases, 391 TD controls, and 168 DD controls were included in these analyses. Mean hyperactivity subscale scores increased from TD to DD, and from DD to ASD, with significantly higher scores in the ASD group compared to each of the other groups. 35% of ASD cases scored in the top quintile of hyperactivity/impulsivity subdomain scores, compared to 24% of DD and 2% of TD. 40% of the ASD group were in the top quintile of inattention scores, compared to 20% of the DD group and 1% of the TD group. Hyperactivity and inattention subdomain scores were highly correlated with ABC irritability, lethargy, and stereotypy subscales across diagnostic groups (r~.5-.7). Overall, scores were not correlated with VABS or MSEL scores, though hyperactivity subscale scores were moderately correlated with reduced MSEL expressive language scores in cases only (r=.31). In adjusted analyses, low maternal education (high school or less) was significantly associated with higher hyperactivity subscale and hyperactivity/impulsivity subdomain scores in case children (corresponding to ~4 point score increase), while maternal obesity was associated with lower hyperactivity scores (~3 point decrease). No other factors demonstrated associations with these scores.
Our results demonstrate a high prevalence of hyperactivity/impulsivity and inattention problems in children with ASD, and suggest the need for further study of these issues in association with subphenotypes and risk factors in autism.
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