Table 2

Approximate lifetime rates of mood disorder in various classes of relative of bipolar probands

Degree of relationship to bipolar probandRisk of bipolar disorder (%)(Additional) risk of unipolar depression (%)
Monozygotic co-twin40–7015–25
First degree relative5–1010–20
General population (ie, unrelated)0.5–1.55–10
  • The lifetime risk of major mood disorder in a relative is obtained by adding the risk of bipolar disorder and the risk of unipolar depression. General population lifetime risk of unipolar depression is notoriously difficult to quantify but the figures in the table are based on a definition of clinically significant depression comparable to that used in the genetic studies.