Prevalence of self-reported subthreshold phenotypes of major mental disorders and their association with functional impairment, treatment and full-threshold syndromes in a community-residing cohort of young adults

Aim: Subthreshold syndromes (STS) frequently precede the onset of full-threshold syndromes (FTS) of the corresponding mental disorder (homotypic continuity). This study examines whether subthreshold conditions are comorbid and whether there is heterotypic continuity also between STS and FTS. Methods: Data were extracted from the Brisbane “19Up” cohort study of twins and siblings (N = 1838; 56% female) on individuals who (i) completed self-report ratings of depression-like (DLE), hypomanic-like (HMLE) and psychotic-like experiences (PLE) and (ii) were assessed for mood and psychotic FTS using the Composite International Diagnostic Interview (CIDI). Associations between STS and FTS were estimated using adjusted prevalence ratios (APR) and 95% confidence intervals (CI). Results: STS are prevalent, with 22% reporting DLE, 14% HMLE and 5% PLE; 7% reported >1 STS, with PLE most likely to demonstrate comorbidity. Individuals with DLE were likely to meet CIDI criteria for depression (APR: 3.71, 95% CI: 2.83, 4.89), hypo/mania (APR: 3.62, 95% CI: 2.21, 5.94) and psychotic disorders (APR: 1.74, 95% CI 1.08, 2.83). Individuals with HMLE were likely to meet CIDI criteria for depression (APR: 2.29, 95% CI: 1.58, 3.31) and hypo/mania (APR: 2.51, 95% CI: 1.29, 4.91); those with PLE were likely to meet criteria for hypo/mania (APR: 5.8, 95% CI: 1.90, 17.70) and psychotic disorders (APR: 17.27, 95% CI: 7.54, 39.65). Conclusions: The findings suggest that STS are common among young adults and show heterotypic as well as homotypic continuity with FTS and support the need for more trans-diagnostic research on the evolution of major mental disorders