Genes and Inheritance
Mood disorders run in families, and genes play a role in their development. There is no single gene for depression or bipolar disorder, but rather a set of around a dozen genes which can increase the risk of these conditions. The role that genes play is different for each person and depends on how many mood-genes they inherited.
Life experience also influences this genetic risk. Some genes may never express themselves if a child is raised in a supportive environment. Likewise, stress and trauma can activate genes for mood disorders. Our experience of life shapes our brain physically.
Other pages on this site describe the two main types of mood disorders: unipolar depression and bipolar disorder. Among these, genes play a stronger role in bipolar disorder, while environment is a stronger force in unipolar depression.
For parents, it is important to understand that while mood disorders have a genetic basis, this does not mean they will always be passed on to children. Even if your child inherits the genes, the genes may not get activated; indeed a supportive, empathic environment can sometimes keep them from activating. Below are the average risks of inheriting a mood disorder:
> If you have unipolar depression, your child will have a 16% chance of developing any mood disorder. Most of this risk is of depression (14%), with a small chance of bipolar disorder (2%).
> If you have bipolar disorder, your child will have a 20% chance of developing any mood disorder. Still, most of this risk is of depression (13%) and the rest is of bipolar disorder (7%).
You may have noticed that, even if you have bipolar disorder, your child has a greater risk of developing unipolar depression than bipolar. Research is evolving in people with this genetic pattern, described more in the section on Bipolar Spectrum.
 from Ghaemi, N. Mood Disorders. Lipincott, Williams & Wilkins, 2007.
To continue on to the next section, click Rating Scales.
—Updated 3/5/13 by Chris Aiken, MD