Patterns of objectively measured motor activity among infants developing ASD and concerns for ADHD.

BACKGROUND: Heightened motor activity is a hallmark of attention-deficit/hyperactivity disorder (ADHD), yet high activity levels are also often reported in young children with autism spectrum disorder (ASD). It is currently unclear whether increased motor activity represents a distinct versus shared early predictor of ASD and ADHD; no prior studies have directly examined this prospectively. We investigated differences in longitudinal patterns of objectively measured motor activity during early development. METHODS: Participants included 113 infants at high and low risk for ASD or ADHD. Continuous motion-based activity was recorded using tri-axial accelerometers at 12, 18, 24, and 36 months of age. At 36 months, participants were categorized into one of three outcome groups: ASD (n = 19), ADHD Concerns (n = 17), and Typically Developing (TD; n = 77). Group differences in trajectories of motor activity were examined in structured and semistructured contexts. Associations with behaviors relevant to ASD, ADHD, and general development were also examined. RESULTS: In both structured and semistructured contexts, both the ASD and ADHD Concerns groups exhibited heightened activity relative to the TD group by 18 months; the ASD group exhibited higher activity than the ADHD Concerns group at 24-36 months in the structured context only. Attention/behavior regulation, nonverbal, and verbal development-but not social engagement-were differentially associated with objectively measured activity by outcome group across contexts. CONCLUSIONS: Overactivity may be a shared, rather than distinct, precursor of atypical development in infants/toddlers developing ASD and concerns for ADHD, emerging as early as 18 months. Group differences in overactivity may be context-specific and associated with different underlying mechanisms.

Longitudinal Differences in Response to Name Among Infants Developing ASD and Risk for ADHD.

Diminished response to name, a potential early marker of autism spectrum disorder (ASD), may also indicate risk for other disorders characterized by attention problems, including attention-deficit/hyperactivity disorder (ADHD). Using a familial risk design, we examined whether response to name ability at 6, 12, 18, 24, and 36 months of age differed between three 36-month outcome groups: ASD, ADHD Concerns, or a Comparison group. Persistent differences between the ASD and Comparison groups were evident beginning at 12 months; differences between the ADHD Concerns and Comparison groups were evident between 12 and 18 months only. Results suggest that response to name may be a general marker for ASD and ADHD risk in infancy but a specific indicator of ASD by 24-months.

Shared and distinct developmental pathways to ASD and ADHD phenotypes among infants at familial risk.

Autism spectrum disorder (ASD) and attention-deficit/hyperactivity disorder (ADHD) are believed to share partially overlapping causal mechanisms suggesting that early risk markers may also overlap. Using latent profile analysis (LPA) in a sample of infants enriched for ASD and ADHD, we first examined the number of distinct groups of 3-year-old children, based on ADHD and ASD symptomatology. To investigate early predictors of ASD and ADHD symptom profiles, we next examined differences in trajectories of infant behaviors among the LPA classes spanning general development, negative affect, attention, activity level, impulsivity, and social behavior. Participants included 166 infants at familial risk for ASD (n = 89), ADHD (n = 38), or low-risk for both (n = 39) evaluated at 12, 18, 24, and 36 months of age. A three-class solution was selected reflecting a Typically Developing (TD) class (low symptoms; n = 108), an ADHD class (high ADHD/low ASD symptoms; n = 39), and an ASD class (high ASD/ADHD symptoms; n = 19). Trajectories of infant behaviors were generally suggestive of a gradient pattern of differences, with the greatest impairment within the ASD class followed by the ADHD class. These findings indicate a mixture of overlapping and distinct early markers of preschool ASD- and ADHD-like profiles that can be difficult to disentangle early in life.