Bipolar Disorder Runs in Families

It's double trouble: There's a strong genetic influence in those with the disorder.

By Hara Estroff Marano, published on October 1, 2003 - last reviewed on November 20, 2015

Bipolar disorder is often considered a condition that reflects
genetic influence. One twin study reveals just how genetic the disorder

If one identical twin develops bipolar disorder, the likelihood of
the other twin developing the condition is 85 to 89 percent. The high
probability of double trouble comes not from the environment the twins
inhabited together while they were developing but from the genes they
share, reports a team of British and Canadian investigators. Only 15 percent of
instances of bipolar disorder can be attributed to factors specific to
individuals or to their unique life experiences outside the family of

What's more, the genetic loading for bipolar disorder is restricted
to liability to mania.

Interestingly, the study also demonstrates that unipolar depression
is not simply a less severe form of bipolar disorder. Only 10 percent of twins
with unipolar major depression had a co-twin with bipolar

Nevertheless, there is some genetic overlap; susceptibility to
bipolar disorder seems to make sufferers susceptible to unipolar
depression as well. Fifty percent of the co-twins with bipolar disorder
also had unipolar disorder.