OCD symptom severity and comorbid psychiatric diagnoses in a Swedish genetic epidemiological obsessive-compulsive disorder cohort

Background We have established an epidemiological obsessive-compulsive disorder (OCD) cohort in Sweden. Individuals contributed DNA for genotyping and sequencing and also completed a Swedish translation of the Obsessive-Compulsive Inventory-Revised (OCI-R), a self-report questionnaire for assessing the severity and type of symptoms of OCD. This study made use of the OCI-R data to examine the severity and symptom dimensions of OCD as well as comorbidity with other psychiatric disorders. Methods OCI-R data for 1,134 individuals were available for this study, 1,010 diagnosed with OCD, and 124 diagnosed with chronic tic disorders without OCD used as a comparison group. We first evaluated the psychometric properties of the Swedish translation of the OCI-R. Then, we linked data from the Swedish national registries to access and analyze psychiatric comorbidities of OCD. Results The Swedish translation of OCI-R demonstrated internal consistency (Cronbach’s α = 0.9) and clear agreement with the OCI-R six-factor model. The mean total OCI-R score for females was significantly higher than for males. The most comorbid psychiatric condition to OCD were anxiety disorders (13.6%) and major depression (12%). We observed that individuals with OCD frequently had additional comorbid psychiatric disorders and that the severity of OCD was significantly higher in individuals with at least one additional psychiatric comorbidity compared to individuals with no psychiatric comorbidity. Conclusion We showed that the Swedish translation of the OCI-R has appropriate psychometric properties. Using an epidemiological framework, we were able to assess the severity and symptom dimensions of OCD and comorbidity with other psychiatric disorders.