Youth with subthreshold bipolar I disorder (BP-I) had similarly elevated risk for BP-I and major depressive disorder in first-degree relatives as youth with full BP-I, a recent study found. BP-I probands were youth aged 6 to 17 years meeting criteria for BP-I, full (n=239) or subthreshold (n=43), and also included were their first-degree relatives (n=687 and n=120, respectively). Comparators were youth with ADHD (n=162), controls without ADHD or bipolar disorder (n=136), and their first-degree relatives (n=511 and n=411, respectively). Researchers randomly selected 162 non-bipolar ADHD probands and 136 non-bipolar, non-ADHD control probands of similar age and sex distribution to the BP-I probands from case−control ADHD family studies. They found:

• Rates of full BP-I significantly differed between the 4 groups (χ²₃=32.72): Relatives of full BP-I probands and relatives of subthreshold BP-I probands had significantly higher rates of full BP-I than relatives of ADHD probands and relatives of control probands.
• Relatives of full BP-I, subthreshold BP-I, and ADHD probands also had significantly higher rates of major depressive disorder compared to relatives of control probands.