Why Does Depression run in families?

Professor Andrew McIntosh, University of Edinburgh

Our work looks at where depression seems to run in some families. 
The commonest explanation for this is that people have genetic factors which run within families and explain why some people develop it more often than others.

Now while that's clearly part of the explanation, we think that family members might resemble each other for other reasons, for example, two people might be brought up by the same parents and that environment shared by siblings might may explain some of the risk of depression. We also think that the environment shared by people living in the same household as adults (perhaps spouses or partners) might also have might also be the one reason why people resemble each other with regard to their mood.

So we've looked at this issue in Generation Scotland, which is a large family-based study of more than 20,000 individuals – on whom there's detailed information both on genetics and on the environments which they share.

Now as expected we found that genetic factors are one reason that people develop depression; that explain the variation risk within families, and why depression seems to be passed down from one generation to the other, but in fact, that's not the whole story; the other part of the story seems to be that individuals may be more or less likely to develop depression depending on the environments they share with their spouse or partner. We found that individuals with depression were more likely to be affected if their spouse is also affected.  Now, this was true of depression but it was also true of other negative states such as chronic pain.  So an individual who had depression was more likely to have a partner with chronic pain and vice versa.  Now we think that these findings underline the importance of genetics in depression research, but they also suggest that we need to search within environments of the individuals who are affected, to identify the risk factors that cause depression in families.


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