Genetic factors in Bipolar Disorder
Bipolar disorder tends to be familiar, meaning that it “runs in
families.” About half the people with bipolar disorder have a
family member with a mood disorder, such as depression. A
person who has one parent with bipolar disorder has a 15 to
25 percent chance of having the condition. A person who has
a non-identical twin with the illness has a 25 percent chance
of illness, the same risk as if both parents have bipolar
disorder. A person who has an identical twin (having exactly
the same genetic material) with bipolar disorder has an even
greater risk of developing the illness about an eightfold
greater risk than a nonidentical twin. A study of adopted
twins (where a child whose biological parent had the illness
is raised in an adoptive family untouched by the illness) has
helped researchers. Researchers conclude that the lifetime
chance of an identical twin (of a bipolar twin) to also develop
bipolar disorder is about 40% to 70%.In more studies at
Johns Hopkins University, researchers interviewed all firstdegree
relatives of patients with bipolar I and bipolar II
disorder and concluded that bipolar II disorder was the most
common affective disorder in both family sets. The
researchers found that 40% of the 47 first-degree relatives of
the bipolar II patients also had bipolar II disorder; 22% of the
219 first-degree relatives of the bipolar I patients had bipolar
II disorder Studies at Stanford University that explored the
genetic connection of bipolar disorder found that children
with one biological parent with bipolar I or bipolar II disorder
have an increased likelihood of getting bipolar disorder. In
this study, researchers reported that 51% of the bipolar
offspring had a psychiatrhiatric disorder, most commonly
major depression, dysthymia (mild depression), bipolar
disorder, or attention deficit hyperactivity disorder (ADHD).
Interestingly, the bipolar parents in the study who had a
childhood history of ADHD were more likely to have
children with bipolar disorder but not ADHD.
Bipolar disorder is frequently inherited, with genetic factors
accounting for approximately 80% of the cause of the
condition. If one parent has bipolar disorder, there is a 10%
chance that his or her child will develop the illness. If both
parents have bipolar disorder the likelihood of their child
developing the illness rises to 40%. However, just because
one family member has the illness, it is not necessarily the
case that other family members will also develop the illness.
The following factors might also be involved in the onset of
bipolar disorder.