Autism and Depression in Young Adulthood: Cohort Studies in Sweden and England

Background:  Depression is considered one of the most common comorbidities in autism, but longitudinal studies following children through early adulthood are scarce. Genetic links between autism and depression have been suggested, but environmental factors such as bullying may be important modifiable intermediaries, but have not been adequately investigated.

Objectives:  1) To use two large population based cohorts with complementary strengths to assess the association between childhood autism spectrum disorders and autistic traits and adult depression. 2) To assess the risk of depression in non autistic siblings. 3) To assess whether bullying in adolescence mediates the relationship between autistic traits and adult depression.

Methods:  In the Stockholm Youth Cohort, we assessed the risk of a depression diagnosis in young adulthood (age 18 to 27 years) in children with autism as compared to the general population, and their non autistic siblings. In the Avon Longitudinal Study of Parents and Children (ALSPAC), we studied the trajectory of depressive symptoms (measured by the Moods and Feelings Questionnaire), and relative risks for depression at age 18 years (measured by the Clinical Interview Schedule- Revised) in relation to four dichotomised autistic trait measures known to optimally predict an autism diagnosis in ALSPAC: the Children's Communication Checklist (coherence subscale), the Social and Communication Disorders Checklist, a repetitive behaviour measure, and the Emotionality, Activity and Sociability scale (sociability subscale). We used structural equation models to estimate the mediating effect of bullying in adolescence in the association between autistic traits and depression at age 18 years.

Results:  A diagnosis of autism was strongly associated with a diagnosis of depression in young adulthood [adjusted RR 3.7 (95% CI 3.5-3.9)] in the Stockholm Youth Cohort. Individuals with autism were over two fold more likely to have a diagnosis of depression in young adulthood when directly compared to their non autistic siblings [adjusted OR 2.6 (1.9-3.5)], who were themselves at a higher risk of depression than the general population. In ALSPAC, children with all trait measures of autism had higher rates of depressive symptoms at age 10, but the social communication trait had the strongest association with a depression diagnosis at age 18 (adjusted RR 1.56 (1.02 to 2.40), p=0.041]. Bullying in adolescence accounted for 42% of the total estimated association between low social cognition and depression at age18 years in ALSPAC.

Conclusions:  Taken together, the findings suggest that children with autism are at a higher risk of depression in young adulthood than the general population, and that social communication impairments may be the key autistic feature in relation to adult depression. Despite the potential role of a genetic predisposition to depression, the substantial role of bullying as a potentially mediating mechanism suggests that this may be a target for intervention and preventative action against depression in young people with autism.