Depression in Autistic Adults: Rumination and Insistence on Sameness

Background: Autistic people are four times more likely to experience depression than typically developing people. Rumination defined as repetitive thinking about sadness, has been shown to be a key risk factor for depression in the general population. Autistic people may be at elevated risk of rumination due to the repetitive, restricted behaviours, interests or activities (RRBIs) characteristic of Autism. RRBIs may contribute to the elevated levels of depression by increasing the risk of repetitive thinking patterns. RRBIs have been classified into two sub-types, insistence on sameness (IS) and repetitive sensory motor (RSM) behaviours. Of these two sub-types, the phenomena making up IS, particularly an adherence to restricted routines and ritualised verbal and non-verbal behaviours are most likely to be related to depression. Research has found links between autistic traits, rumination and depression in the general population, and in a small sample of autistic adolescents and adults.

Objectives: Firstly, we investigated whether levels of rumination are higher in autistic adults compared to typically developing adults using a non-clinical sample. Secondly, we investigated the contribution of IS to depression in a mixed community and clinical autistic population and the potential for rumination as a mediator of this relationship.

Methods: We recruited a community sample of autistic participants (n=34) and typically developing participants (n=35). Autistic participants all had a validated diagnosis from a health professional. We also recruited a sample of autistic participants with validated clinical diagnoses of autism and depression (n=66) from NHS clinics who were participating in a clinical trial of a depression treatment (ADEPT). For the current study participants completed self-report measures of repetitive behaviour (IS subscale of RBQ-2A), Rumination (subscale of RRQ) and Depression (PHQ-9).

Results: As predicted, Rumination scores were significantly higher in the community autism sample (M=3.94, SD=0.70) compared to the typically developing sample (M=3.1, SD=0.89), t(67)=4.51, p<.001. Further, the community autism sample also had higher significantly higher scores on the depression measure (M=11.7, SD=6.1) compared to the typically developing sample (M=3.9, SD=2.5), t(66)=6.9, p<.001). A mediation analysis using ordinary least squares path analysis which included all autistic participants (n=100) found that IS scores affected depression scores via an effect on rumination levels. There was a significant positive effect of IS on rumination (a=0.52, p<.001) and rumination had a significant effect on depression scores (b=2.37 p=.01). A bootstrap confidence interval was generated for the indirect effect and was above zero (0.22 – 2.48). IS scores did still affect depression scores when controlling for rumination (c’= 2.12, p<.05), but to a lesser extent than when rumination was not included in the model (c=3.35, p<.001) demonstrating partial mediation.

Conclusions: Depression and rumination scores are higher in autistic people compared to non-autistic people. Moreover, insistence on sameness, a core feature of the Repetitive Behaviours domain in Autism, contributes to depression by increasing levels of rumination. Thus, a tendency towards behavioural repetition contributes to repetitive thinking patterns with negative content which contributes in turn to elevated depression symptoms.