Mental health in toddlers at high-risk for Autism Spectrum Disorders: a longitudinal investigation

Submission note: A thesis submitted in total fulfilment of the requirements for the degree of Doctor of Clinical Psychology to the School of Psychological Science, Faculty of Science, Technology, and Engineering, La Trobe University, Bundoora.

The objective in this program of research was to investigate mental health during toddlerhood in children at familial high-risk for Autism Spectrum Disorders (ASD) by virtue of having an older sibling with the diagnosis. Research has shown that siblings of children with ASD are almost 20 times more likely to have ASD than general population samples. However, there have been mixed results on whether these high-risk siblings are also at increased risk for mental health difficulties. Arguably, this increased risk for mental health problems may be due to both genetic and environmental risk factors. Firstly, ASD confers increased risk for mental health problems. Secondly, high-risk siblings may be at increased risk for temperamental difficulties, which are a known risk factor for mental health problems in typically developing samples. Thirdly, environmental risk factors including the presence of mental health difficulties in parents and probands with ASD may place younger siblings at increased risk of also developing mental health problems. The results showed that at both 2- and 3-years, younger siblings of children with ASD showed elevated mental health problems compared to children growing up in family environments unaffected by ASD (i.e., low-risk siblings). Although there were key differences in temperament between high- and low-risk siblings, this was only found to be an important predictor of concurrent and prospective internalising problems. Lastly, parent stress and proband mental health difficulties were found to be important predictors of toddler mental health difficulties concurrently at age 2-years, but had less prospective impact to age 3-years. Siblings of children with ASD therefore appear to be at increased risk for mental health problems even in toddlerhood and it is important to consider both genetic and environmental risk factors when developing mental health prevention and intervention strategies.