Childhood trauma as a mediator between autistic traits and depression: Evidence from the ALSPAC birth cohort

Background
Autistic traits have been associated with greater risk of childhood trauma and adulthood psychopathology. However, the role that childhood trauma plays in the association among autism, autistic traits, and depression in adulthood is poorly understood.

Methods
We used a UK-based birth cohort with genotype and phenotype data on autism, autistic traits, childhood trauma, and depression in up to 9,659 individuals prospectively followed up until age 28 years. Using mixed-effects growth-curve models, we assessed trajectories of depression symptoms over time according to autism diagnosis, autism polygenic score and trait measures, and explored whether these differed by trauma exposure. We further investigated the association between autism/autistic traits and depression in adulthood using confounder-adjusted logistic regression models and undertook mediation analyses to investigate the relationship with childhood trauma.

Results
All autism variables demonstrated increased depressive symptom trajectories between ages 10 and 28 years. Social communication difficulties (SCDs) were most strongly associated with a depression diagnosis in adulthood (age 24 OR = 1.86; 95% CIs: 1.15–3.01). Trauma and autistic traits combined to further increase depression symptom scores. Mediation analyses provided evidence for direct pathways between autistic traits and increased risk of depression alongside indirect pathways through increased risk of trauma.

Conclusions
Autism/autistic traits increase the odds of experiencing childhood trauma and of being diagnosed with depression at ages 18 and 24. Depressive symptom trajectories emergent in childhood persist into adulthood. The combined effect of SCDs and childhood trauma is greater than the individual exposures, suggesting worse depression symptomatology following trauma in individuals with SCDs.