Episode 20: Family, by host, Laura Milkins. Our guest, Scott Shoemaker, tells the story of his struggles with depression. How writing about his anxiety and depression helped him cope and find a way to help others: Sunday, April 10, 2016
Exerpt From Stanford School of Medicine: Genetics of Brain Function
How common is major depression? At least 10% of people in the U.S. will experience major depressive disorder at some point in their lives. Two times as many women as men experience major depression.
How do we know that genes play a role in causing depression? Scientists look at patterns of illness in families to estimate their “heritability,” or roughly what percentage of their cause is due to genes. To do this we find people with the disease who have a twin, and then find out whether the twin is also ill. Identical (monozygotic) twins share 100% of their genes, while non-identical (“fraternal” or dizygotic) twins share 50% of their genes. If genes are part of the cause, we expect a patient’s identical twin to have a much higher risk of disease than a patient’s non-identical twin. That is the case for major depression. Heritability is probably 40-50%, and might be higher for severe depression.
This could mean that in most cases of depression, around 50% of the cause is genetic, and around 50% is unrelated to genes (psychological or physical factors). Or it could mean that in some cases, the tendency to become depressed is almost completely genetic, and in other cases it is not really genetic at all. We don’t know the answer yet.
We can also look at adoption studies, to see whether an adopted person’s risk of depression is greater if a biological parent had depression. This also seems to be the case.
Here’s a link to read the whole story: http://depressiongenetics.stanford.edu/mddandgenes.html