IMPORTANCE Symptom severity and adaptive functioning are fundamental domains of the autism spectrum disorder (ASD) phenotype. To date, the longitudinal association between these 2 domains has not been examined. OBJECTIVE To describe the developmental trajectories of autistic symptom severity and adaptive functioning in a large inception cohort of preschool children with ASD. DESIGN, SETTING, AND PARTICIPANTS The sample consisted of 421 newly diagnosed preschool children with ASD 2 to 4 years old (355 boys; mean age at study enrollment, 39.87 months) participating in a large Canadian multisite longitudinal study (Pathways in ASD Study). Prospective data collected at 4 points from time of diagnosis to age 6 years were used to track the developmental trajectories of children. MAIN OUTCOMES AND MEASURES Autistic symptom severity was indexed using the Autism Diagnostic Observation Schedule. Adaptive functioning was indexed using the Vineland Adaptive Behavior Scales, Second Edition. RESULTS Two distinct trajectory groups provided the best fit to the autistic symptom severity data. Group 1 (11.4% of the sample) had less severe symptoms and an improving trajectory (P < .05), whereas group 2 (88.6% of the sample) had more severe symptoms and a stable trajectory. Three distinct trajectory groups provided the best fit to the adaptive functioning data. Group 1 (29.2% of the sample) showed lower functioning and a worsening trajectory, group 2 (49.9% of the sample) had moderate functioning and a stable trajectory, and group 3 (20.9% of the sample) had higher functioning and an improving trajectory (P < .05). Cross-trajectory overlap between the autistic symptom severity and adaptive functioning groups was low (φ = 0.13, P < .05). Sex was a significant predictor of autistic symptom severity group membership and age at diagnosis, and language and cognitive scores at baseline predicted membership in adaptive functioning trajectories. Trajectories of both symptom severity and adaptive functioning predicted several different outcomes at age 6 years. CONCLUSIONS AND RELEVANCE Findings confirm the heterogeneous nature of developmental trajectories in ASD. Change in adaptive functioning suggests that improvement is possible in roughly 20% of the sample. Autistic symptom severity appears to be more stable, with roughly 11% of the sample showing a marked decrease in symptom severity. During the preschool years, there appears to be only a small amount of "yoking" of developmental trajectories in autistic symptom severity and adaptive functioning. It is imperative that a flexible suite of interventions that target both autistic symptom severity and adaptive functioning should be implemented and tailored to each child's strengths and difficulties.

This study examined the factor structure of the Repetitive Behavior Scale-Revised (RBS-R) in a sample of 287 preschool-aged children with autism spectrum disorder (ASD). A confirmatory factor analysis was used to examine six competing structural models. Spearman's rank order correlations were calculated to examine the associations between factor scores and variables of interest. The 3- and 5-factor models were selected as preferable on the basis of fit statistics and parsimony. For both models, the strongest correlations were with problem behavior scores on the Child Behavior Checklist and repetitive behavior scores on the ADI-R. Developmental index standard scores were not correlated with factors in either model. The results confirm the utility of the RBS-R as a measure of repetitive behaviors in young children with ASD.

Study findings suggest that the two symptom dimensions of SCD and FIRB proposed for the DSM 5 can be used in FMM to stratify children with ASD empirically into three relatively homogeneous subgroups.

Mental health problems are the leading health problems that Canadian children currently face after infancy. At any given time, 14% of children aged 4 to 17 years (over 800 000 in Canada) experience mental disorders that cause significant distress and impairment at home, at school, and in the community. Fewer than 25% of these children receive specialized treatment services. Without effective prevention or treatment, childhood problems often lead to distress and impairment throughout adulthood, with significant costs for society. Children's mental health has not received the public policy attention that is warranted by recent epidemiologic data. To address the neglect of children's mental health, a new national strategy is urgently needed. Here, we review the research evidence and suggest the following 4 public policy goals: promote healthy development for all children, prevent mental disorders to reduce the number of children affected, treat mental disorders more effectively to reduce distress and impairment, and monitor outcomes to ensure the effective and efficient use of public resources. Taken together, these goals constitute a public health strategy to improve the mental health of Canadian children.