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The current study investigated longitudinal associations between parent-rated temperament, observed exuberance and accelerometer activity level at 18-months and symptoms of ASD and ADHD at 36-months in a sample of 54 children at elevated likelihood for ASD. For the specific parent-rated temperament scales, most observed significant associations appeared to be specific for either ASD or ADHD symptoms. Indeed, by controlling for overlapping symptoms a different pattern of associations emerged. These results illustrate how temperamental measures may signal risk for later ASD versus ADHD symptomatology in infants at elevated likelihood for ASD. In addition, they indicate the potential of adopting a broader view on neurodevelopmental disorders by investigating not only ASD traits, but also co-occurring disorders such as ADHD in samples of elevated likelihood for ASD.

The purpose of the current study was to use the infant sibling design to explore whether proband traits of autism and ADHD could provide information about their infant sibling’s temperament. This could help us to gain information about the extent to which infant temperament traits are differentially associated with autism and ADHD traits. We used parent-ratings of autistic traits and ADHD traits (CRS-3) in older siblings diagnosed with autism (age range 4 to 19 years), and their infant siblings’ temperament traits (IBQ) at 9 months of age in 216 sibling pairs from two sites (BASIS, UK, and EASE, Sweden) to examine associations across siblings. We found specific, but modest, associations across siblings after controlling for sex, age, developmental level and site. Proband autistic traits were specifically related to low levels of approach in the infant siblings, with infant developmental level explaining part of the variance in infant approach. Proband ADHD traits were specifically related to high levels of infant activity even after controlling for covariates. Our findings suggest that proband traits of autism and ADHD carry information for infant sibling’s temperament, indicating that inherited liability may influence early emerging behaviours in infant siblings. The impact of sex, age, developmental level and site are discussed.

Background: Children with ASD and/or ADHD often struggle with tasks that demand executive functioning (EF) and deferred gratification. However, whether children with a family history of ASD and/or ADHD differ on these types of tasks in comparison to peers with a family history of typical likelihood is not known. In addition, little is known about the specificity of these domains in relation to autistic traits, ADHD traits and adaptive behaviors early in life and whether deferred gratification and strong EF skills may function as protective factors in the trait-adaptive behaviour association.

Methods:  A total of 77 infant siblings at 3 years of age participated in the study and we examined the effect of type of family history -FH-ASD, FH-ASD/ADHD and family history of typical likelihood FH-TL- on EF performance, deferred gratification skills and adaptive behaviors, as well as specific and shared associations, including moderation effects. Measures included behavioral lab-tasks (common EF and deferred gratification), parent-rated adaptive behavior using VABS, and clinician ratings using ADOS-2 (autistic symptoms) and ADHD DSM-5 Rating Scale (ADHD RS). 

Results: Lower levels of deferred gratification was specifically related to adaptive behavior, while lower level performance on common EF was specific for ADHD traits and adaptive behavior. Finally, deferred gratification moderated the association between autistic symptoms and adaptive behavior, in that stronger ability to defer gratification attenuated the association between autistic traits and adaptive functions. 

Conclusions: In terms of specificity, we found unique associations between deferred gratification and autistic traits, and between common EF and ADHD traits. Finally, the results are in line with the idea that strong EF may act as a protective factor for children with an elevated likelihood of ASD and/or ADHD. However, our findings point at more affective than cognitive aspects of EF as particularly important for attenuating the association between autistic traits and adaptive behaviors.