Functional benefits of co-occurring autistic symptoms in schizophrenia is delimited by symptom severity

Background: Impairments in daily functioning characterize both autism spectrum disorder and schizophrenia. Research has shown that a subsample of schizophrenia patients presents autistic symptoms, leading to the hypothesis that their co-occurrence would be associated with a ‘double dose’ of deficit. A growing body of research examined this hypothesis by looking at the joint effect of autistic and positive psychotic symptoms, and yielded contrasting results, ranging from benefits to adverse effects. We hypothesized that the interactive effect of autistic and positive symptoms on functioning in schizophrenia might depend on the patients' symptom severity. Method: In 170 schizophrenia patients, a two-step cluster analysis identified two groups of patients with different levels of autistic and positive symptom severity. Using general linear models, we examined the interactions of groups, autistic and positive symptoms on functioning. Results: Autistic and positive symptoms were interactively associated with better functioning, but only in the symptomatically less severe patients. In contrast, autistic and positive symptoms were independently associated with worse functioning in the symptomatically more severe patients. These associations were observed above and beyond the effects of I.Q. and illness duration. Conclusions: The findings highlight the complex role played by co-occurring autistic symptoms in schizophrenia, whose beneficial effects on functioning appear to depend on patients’ psychopathological severity. Our findings may help to reconcile the seemingly contrasting results from previous studies, and to understand the heterogeneity of behavior and functional outcomes in schizophrenia. This study underscores the potential utility of routinely assessing autism in schizophrenia, in order to better formulate individualized rehabilitative programs.