If a parent has been diagnosed with depression, what are the risks of the children inheriting it?
Many different
studies have been conducted to examine the influence of genetics on the
development of depression. First-degree relatives of persons with major
depression are two to three times more likely to have major depression
than are the first-degree relatives of non-depressed persons. In adoption
studies, the biological children of affected (depressed) parents remain
at an increased risk for a mood disorder even when adopted by
non-affected (non-depressed) parents. Identical twins (who share 100% of
genetic material) have concordance rates for depression of approximately
50%, and non-identical twins have concordance rates of 10% to 25%. In a
strictly genetic illness, identical twins would both be affected because
they share 100% of the genes. Twin studies have shown that a twin of a
depressed person has only a 50% likelihood of also having depression.
This number, however, is significantly greater than the rate in
non-identical twins, thereby demonstrating that there is at least some
genetic contribution to development of this disorder. The fact that there
is not 100% concordance between identical twins demonstrates that
environmental influences also have a role in precipitating a depressive
episode.
Genetic and environment factors
Life
circumstances are often expected to precipitate a depressive episode in
affected individuals. Trauma, financial distress, death of a loved one,
and relationship problems are some types of stressors that may be
associated with development of depression. No matter how extreme,
however, no specific environmental situation will cause a depressive
episode in all persons. Therefore, environmental conditions alone are not
usually sufficient to explain a depression. The specific event more
typically will precipitate a depression in one who is vulnerable to its
development at that time.
Family
history of depression
Putting
together genetic and environmental factors as contributors to the onset
of depression means that with a family history of depression, an
individual has a higher relative risk than the general population for
developing depression. In fact, the greater number of mood disorders that
are present in a person's family, the higher the risk becomes for
development of depression. Stressful life events, specific environmental
circumstances, or certain psychological processes may serve as a trigger
of a depressive episode in someone with a genetic predisposition for the
disorder.
