Evidence suggests a familial coaggregation of major psychiatric disorders, including schizophrenia, bipolar disorder, major depression (MDD), autism spectrum disorder (ASD) and attention-deficit hyperactivity disorder (ADHD). Those disorders are further related to suicide and accidental death. However, whether death by suicide may coaggregate with accidental death and major psychiatric disorders within families remains unclear.

To clarify the familial coaggregation of deaths by suicide with accidental death and five major psychiatric disorders.

Using a database linked to the entire Taiwanese population, 68 214 first-degree relatives of individuals who died by suicide between 2003 and 2017 and 272 856 age- and gender-matched controls were assessed for the risks of death by suicide, accidental death and major psychiatric disorders.

A Poisson regression model showed that the first-degree relatives of individuals who died by suicide were more likely to die by suicide (relative risk RR = 4.61, 95% CI 4.02–5.29) or accident (RR = 1.62, 95% CI 1.43–1.84) or to be diagnosed with schizophrenia (RR = 1.53, 95% CI 1.40–1.66), bipolar disorder (RR = 1.99, 95% CI 1.83–2.16), MDD (RR = 1.98, 95% CI 1.89–2.08) or ADHD (RR = 1.34, 95% CI 1.24–1.44).

Our findings identified a familial coaggregation of death by suicide with accidental death, schizophrenia, major affective disorders and ADHD. Further studies would be required to elucidate the pathological mechanisms underlying this coaggregation.

Family coaggregation of attention-deficit/hyperactivity disorder (ADHD), autism spectrum disorder (ASD), bipolar disorder (BD), major depressive disorder (MDD) and schizophrenia have been presented in previous studies. The shared genetic and environmental factors among psychiatric disorders remain elusive.

This nationwide population-based study examined familial coaggregation of major psychiatric disorders in first-degree relatives (FDRs) of individuals with ASD. Taiwan's National Health Insurance Research Database was used to identify 26 667 individuals with ASD and 67 998 FDRs of individuals with ASD. The cohort was matched in 1:4 ratio to 271 992 controls. The relative risks (RRs) and 95% confidence intervals (CI) of ADHD, ASD, BD, MDD and schizophrenia were assessed among FDRs of individuals with ASD and ASD with intellectual disability (ASD-ID).

FDRs of individuals with ASD have higher RRs of major psychiatric disorders compared with controls: ASD 17.46 (CI 15.50–19.67), ADHD 3.94 (CI 3.72–4.17), schizophrenia 3.05 (CI 2.74–3.40), BD 2.22 (CI 1.98–2.48) and MDD 1.88 (CI 1.76–2.00). Higher RRs of schizophrenia (4.47, CI 3.95–5.06) and ASD (18.54, CI 16.18–21.23) were observed in FDRs of individuals with both ASD-ID, compared with ASD only.

The risk for major psychiatric disorders was consistently elevated across all types of FDRs of individuals with ASD. FDRs of individuals with ASD-ID are at further higher risk for ASD and schizophrenia. Our results provide leads for future investigation of shared etiologic pathways of ASD, ID and major psychiatric disorders and highlight the importance of mental health care delivered to at-risk families for early diagnoses and interventions.

Whether the first-degree relatives (FDRs) of patients with obsessive-compulsive disorder (OCD) have an increased risk of the major psychiatric disorders, namely schizophrenia, bipolar disorder, OCD, major depressive disorder (MDD), autism spectrum disorder (ASD), and attention deficit hyperactivity disorder (ADHD), remains unclear.

Using the Taiwan National Health Insurance Research Database with the whole population sample size (n = 23 258 175), 89 500 FDRs, including parents, offspring, siblings, and twins, of patients with OCD were identified in our study. The relative risks (RRs) of major psychiatric disorders were assessed among FDRs of patients with OCD.

FDRs of patients with OCD had higher RRs of major psychiatric disorders, namely OCD (RR 8.11, 95% confidence interval (CI) 7.68–8.57), bipolar disorder (RR 2.85, 95% CI 2.68–3.04), MDD (RR 2.67, 95% CI 2.58–2.76), ASD (RR 2.38, 95% CI 2.10–2.71), ADHD (RR 2.19, 95% CI 2.07–2.32), and schizophrenia (RR 1.97, 95% CI 1.86–2.09), compared with the total population. Different familial kinships of FDRs, such as parents, offspring, siblings, and twins consistently had increased risks for these disorders. In addition, a dose-dependent relationship was found between the numbers of OCD probands and the risk of each major psychiatric disorder.

The FDRs, including parents, offspring, siblings, and twins, of patients with OCD have a higher risk of OCD, schizophrenia, bipolar disorder, MDD, ADHD, and ASD. The familial co-aggregation of OCD with OCD and other major psychiatric disorders was existent in a dose-dependent manner. Given the increased risks of psychiatric disorders, medical practitioners should closely monitor the mental health of the FDRs of patients with OCD.