Early Self-Regulation in Infant Siblings : Specific and Shared Associations to Emerging Autism and Co-ocurring ADHD

Abstract: The overall aim of this thesis was to examine aspects of self-regulation and the emergence of co-occurring autism and ADHD traits early in life, to enhance our understanding of specific and shared mechanisms underlying these conditions. Previous studies have shown that vulnerabilities in temperament and executive functions (EF) are closely related to both conditions, with overlapping as well as specific features associated to each phenotype. However, most previous studies focus on older children, and it is unclear if specific and shared markers are evident already before symptoms of autism and ADHD emerge. By using an infant-sibling design we were able to follow infants with a family history of autism and/or ADHD, before clinical symptoms emerge.  Study I and II focused on infant temperament as either predictors of later autistic and/or ADHD traits or as being predicted by familial quantitative traits, to understand specific and shared associations to autistic and ADHD traits. In Study I, we examined if temperament traits in 1.5-year olds predict autism and ADHD traits at 3 years. Parent-rated temperament showed specific associations to autistic or ADHD traits, respectively. We found some overlap in regulation difficulties across both trait domains. In Study II, we explored the possibility to use probands’ autistic and ADHD traits to predict temperament traits in their 10-month old infant siblings (a between-individual design). We found that higher levels of probands’ autistic symptoms were specifically associated to lower levels of infant sibling’s approach, whereas higher levels of proband’s ADHD symptoms were specifically associated to increased activity levels in the infant siblings. Proband autism and ADHD traits thus provide unique information about the infant siblings’ temperament. Study III focused on specific and shared links between executive functions and deferred gratification and concurrent associations to autistic traits, ADHD traits, and adaptive behaviors in 3-year-olds. We found that deferred gratification may function as a protective factor, moderating autistic traits and adaptive behaviors and thus act as a buffer for adaptive behaviors Together, these studies contribute to our understanding of specific and shared early aspects of self-regulation and their associations to autistic and/or ADHD traits.