Timing of diagnosis, depression and self-harm in adolescents with autism spectrum disorder

This exploratory study aimed to explore the association between depression and self-harming behaviour in adolescence and the timing of diagnosis for autism spectrum disorder. We analysed data on 11,320 14 year olds, including 396 children with autism spectrum disorder, from the UK Millennium Cohort Study. Exposures were the timing of diagnosis for autism spectrum disorder confirmed by parental report at ages 5, 7, 11 and 14. Outcomes were depression measured by the Short Mood and Feelings Questionnaire (scores ⩾12) and self-report of self-harming behaviour, both assessed at age 14. Data were analysed using multivariable regression analysis. 91% of the autism spectrum disorder group had within-typical-range cognitive ability. After adjusting for child and family confounders, there was a positive linear trend between diagnostic age and depression, with children diagnosed between ages 7 and 11 and children diagnosed after age 11 showing increased symptoms (odds ratio = 2.21 and 3.58, respectively). A similar trend was observed for self-harming behaviour, with children diagnosed after age 11 showing the strongest association (odds ratio = 3.16). These results suggest the importance of earlier diagnosis in preventing secondary mental health problems in this population, particularly among those without cognitive delays. Further studies replicating across a wider intellectual spectrum and clarifying the underlying mechanism are warranted. Lay Abstract Children with autism spectrum disorder are at increased risk of depression and self-harming behaviours. The question of whether timing of diagnosis of autism spectrum disorder is associated with these consequences in adolescence has not yet been studied. This exploratory study aimed to explore the association between depression and self-harming behaviour in adolescence and the parent-reported timing of diagnosis for autism spectrum disorder using a large population-based cohort in the United Kingdom. Most of the children with autism spectrum disorder in our study had within-typical-range cognitive ability. We found a linear association between timing of autism spectrum disorder diagnosis and depression and self-harming behaviour in adolescence; later diagnosis of autism spectrum disorder, particularly diagnosis in adolescence, was associated with the increased risk of self-reported depressive symptoms and self-harming behaviour in adolescence among children with autism spectrum disorder. Our findings, albeit observational, suggest that interventions targeting the earlier diagnosis of autism spectrum disorder and approaches to improve person–environment fit may help prevent secondary mental health problems in this population, particularly among those without cognitive delays and those diagnosed late. Further studies replicating across a wider intellectual spectrum and clarifying the underlying mechanism are warranted.