Autism spectrum disorder (ASD) is recognized as a significant public health concern, with 1 to 2 in 100 children receiving an ASD diagnosis. There is a need for longitudinal research to better understand the long-term outcomes for children and adolescents diagnosed with ASD. Difficulties with executive functions (EF) are recognized as a core challenge in ASD, making it a focal point of investigation to better understand ASD.
This thesis explored the relationship between EF, co-occurring psychopathology symptoms, and adaptive functioning among individuals with ASD. The thesis is part of the Lillehammer Neurodevelopmental Follow-up Study (LINEUP). LINEUP is a 10-year longitudinal study of children and adolescents with neurodevelopmental disorders, recruited from Child and Adolescence Mental Health Outpatient Clinics at Innlandet Hospital Trust in Norway. The assessments took place across three waves: baseline (T1), 2-year follow-up (T2), and 10-year follow-up (T3). The study included 173 participants with a mean age of 11.7 years at baseline: 38 diagnosed with ASD, 85 with ADHD, and 50 typically developing (TD) participants. TD participants were recruited from local schools.
The first aim was to investigate the longitudinal development of EF in individuals with ASD compared to the ADHD and the TD groups (Paper I). EF were assessed with neuropsychological tests targeting EF core components of working memory, inhibition, and cognitive flexibility. By analyzing test results across T1, T2 and T3, we found that the ASD and ADHD groups mainly had parallel maturation in EF performance, consistently lagging behind the TD group.
The second aim was to explore EF as a concurrent and longitudinal predictor for co-occurring psychopathology symptoms at baseline, 2- and 10-year follow-up (Paper II). In this study, which included 38 individuals with ASD and 50 TD individuals, we found that the baseline level of EF difficulties was a significant predictor of internalizing and externalizing problems 10 years later, independent of the severity of autism symptoms.
The third aim was to investigate adaptive functioning in emerging adults with ASD, and to investigate longitudinal predictors of adaptive functioning (Paper III). In this study, EF difficulties emerged as a significant predictor of later adaptive functioning for individuals with ASD and TD individuals, while ASD diagnosis and co-occurring psychopathology symptoms were found to be insignificant predictors. Despite reporting lower adaptive functioning than the TD group, a considerable proportion of emerging adults with ASD fared well in terms of independent living (46%), having at least one close friend (75%) and being in education or employed (71%).
This thesis points to the importance of EF difficulties in understanding development and outcomes for children and adolescents with ASD. The findings suggest that EF difficulties may serve as a persistent cognitive vulnerability for some individuals with ASD, and that greater EF difficulties predict future elevated levels of co-occurring psychopathology symptoms and lower adaptive functioning. One relevant implication is that individuals with ASD and EF difficulties might benefit from support and facilitation in educational settings, workplaces and social environments. By mapping individual cognitive strengths and difficulties alongside daily functioning, healthcare professionals, school staff, and parents can collaborate on providing targeted support based on individual needs. This could be a key step to ensure that children and adolescents with ASD and EF difficulties receive the necessary support to manage daily life effectively, and potentially improve their future outcomes.