Coaggregation of Major Psychiatric Disorders in First-Degree Relatives of Individuals With Attention-Deficit/Hyperactivity Disorder: A Nationwide Population-Based Study

BACKGROUND: Attention-deficit/hyperactivity disorder (ADHD) is a highly heritable mental illness that is easily passed from one generation to the next. Studies have shown that first-degree relatives (FDRs; ie, parents, offspring, and siblings) of individuals with ADHD had a higher risk of also having ADHD. However, the familial coaggregation of ADHD with other major psychiatric disorders, specifically schizophrenia (ICD-9-CM code 295), bipolar disorder (ICD-9-CM cods 296 except codes 296.2, 296.3, 296.9, and 296.82), major depressive disorder (ICD-9-CM codes 296.2 and 296.3), and autism spectrum disorder (ASD; ICD-9-CM code 299), remains unclear. METHODS: Among the entire Taiwanese population in 2010, there were 220,966 parents of children with ADHD (ICD-9-CM code 314), 174,460 siblings of children with ADHD, and 5,875 children of parents with ADHD. Matched control individuals who did not have FDRs with ADHD (1:4) were selected based on age, sex, and their relation to family members. RESULTS: FDRs (parents, offspring, siblings, and twins) of ADHD-diagnosed individuals had higher relative risks (95% CI) of major psychiatric disorders than the controls: 1.69 (1.60-1.79) for schizophrenia, 2.21 (2.10-2.32) for bipolar disorder, 2.08 (2.02-2.13) for major depressive disorder, 4.14 (3.90-4.39) for ASD, and 6.87 (6.73-7.01) for ADHD. DISCUSSION: These results show that ADHD coaggregated with other major psychiatric disorders, specifically schizophrenia, bipolar disorder, major depressive disorder, and ASD, within families. The results suggest that public health officials and psychiatrists should closely monitor and follow the mental health of FDRs of ADHD-diagnosed individuals, such as parents and siblings of children with ADHD.