Understanding the Overlap Between Autism and Schizophrenia Spectrum Disorders: A systematic review of latent variable studies in clinical settings

BackgroundAutism and schizophrenia spectrum disorders (SSDs) are distinct diagnostic categories which frequently cooccur and can have similar symptomatic presentations. Differential diagnosis is challenging due to overlapping characteristics and a lack of differential assessments. Latent variable approaches (LVAs) explore underlying dimensions rather than symptom-based diagnostic criteria. This study is a systematic review and narrative synthesis of all LVAs of autism and SSDs in clinical settings to identify shared and differential features to guide clinical differentiation and inform the development of sensitive assessments and clinical guidelines.Methods The review was designed and conducted in accordance with PRISMA guidelines. Quality was appraised using the Joanna Briggs Institute Checklist. Findings were synthesised using a narrative synthesis approach.ResultsTwenty-one studies (n = 10,502 participants) were included in the review. A narrative synthesis of findings resulted in three broad study categories: (i) symptom analyses; (ii) cognitive analyses; (iii) symptom-cognitive interaction analyses. Autistic traits and SSD symptoms frequently cooccurred in patient subgroups. Cooccurrence was often linked with earlier onset, elevated SSD symptoms, and poorer functioning. Three overlapping dimensions were identified including: negative symptoms, difficulties in executive functioning and processing speed, and social cognition. Differential developmental trajectories distinguished autism and SSDs, namely early developmental difficulties and later cognitive stability was indicative of autism, while early cognitive stability and later decline was indicative of SSDs. ConclusionsAssessing autistic traits in SSDs and SSD symptoms in autism alongside comprehensive developmental histories may support more accurate differential diagnosis. Longitudinal, transdiagnostic research integrating symptoms, cognitive, and developmental profiles is needed to further clarify the differentiation and overlap and inform individualised interventions.