OBJECTIVE

Autism spectrum disorder (ASD) and obsessive-compulsive disorder (OCD), albeit distinct diagnoses, overlap in presentation and frequently co-occur. However, the relationship between them remains poorly understood. We reviewed comparative studies of ASD and OCD to identify patterns of convergence and divergence across these diagnoses at cognitive, neurobiological, and genetic levels.

METHOD

We searched MEDLINE, Web of Science, and PsycInfo databases. The systematic review was registered on PROSPERO (ID: CRD42023395895). Studies that compared individuals with ASD and OCD regarding cognition, neurobiology, or genetics were included. Articles were screened in 2 phases: (1) for relevancy, and (2) based on exclusion and inclusion criteria. We conducted a qualitative synthesis of the results.

RESULTS

The search yielded 2,009 articles. After excluding irrelevant articles (n = 1,623), including studies examining compulsivity without an OCD scale (n = 71), nonempirical reports (n = 97), nonhuman studies (n = 42), studies that were out of scope (n = 6), duplicates (n = 7), and studies with fewer than 20 participants in any comparator group (n = 111), 50 articles remained and were included in the qualitative synthesis.

CONCLUSION

At a genetic level, ASD and OCD share heritability, but studies of polygenic risk are limited. At a neuroimaging level, both diagnoses are associated with reduced cortical thickness in the temporal lobe, but ASD is specifically associated with increased frontal cortical thickness. At a cognitive level, inflexibility may be characteristic of both conditions, but performance in facial emotion processing and sustained attention may differ. The literature is limited by heterogeneity and reduced focus on quantitative traits. Future studies are needed to clarify these relationships.