One of the problems with depression as a disorder is that the symptoms never seem to manifest the same. To give you an idea of what I’m talking about, here are some of the DSM IV recognized symptoms of depression:
1) Insomnia or hypersomnia (not sleeping OR sleeping too much)
2) Having no appetite OR eating too much
3) Slowed motor movements OR motor agitation
…you get where I’m coming from here. Some of the symptoms are universal, depressed mood most of the day, lack of pleasure in previously enjoyed activities, feelings of worthlessness or guilt. But it seems that every patient shows a different constellation of symptoms. And of course this makes diagnosis and treatment complicated. What scientists want to find is an underlying mechanism, an underlying problem that occurs in EVERYONE with depression (or at least in most people).
In order to find this, a lot of studies have looked at genes in people who had major depressive disorder (MDD) at time of death (often this involves comparing suicides to accidental deaths. It’s a really depressing kind of study to do, but we gotta look somewhere). Most of them have looked at very specific molecular targets, and a lot of them have ended up nowhere, though some have gotten somewhere.
But this study went all they way. They went ahead and did a whole genome expression analysis of depressed subjects and controls (post-mortem).
And they found something!