The biologization of psychiatry

A friend of mine once pointed out to me the reconceptualization of mental disorders once we discovered biological tools for probing the mind. Years ago, people started doing brain imaging of schizophrenics to see how their brains were different from normal brains. It turned out there were a some pretty drastic differences. Once people could see the biological correlates of the behavioral symptoms and saw them as causes, the definition of schizophrenia began to shift from a set of behaviors to a set of biological pathologies. Now theoretically you could look at someone who acts like a schizophrenic but doesn't have the typical brain damage and say, "oh, you're not really schizophrenic, it must be something else" - an impossible diagnosis few years ago, not just practically but also theoretically.

The trend continues:

A blood test that measures the activity of genes can accurately detect mental illnesses such as schizophrenia, a small trial suggests.

RNA molecules are produced whenever a gene is active and, by measuring levels of these molecules in the blood, a team led by Ming Tsuang, at the University of California in San Diego has distinguished healthy individuals from patients with either schizophrenia or bipolar disorder (manic depression).

These conditions are currently diagnosed by assessing patients' behaviour. "A laboratory test would enable earlier diagnosis and more timely treatment," Tsuang says.

Tsuang's team ... measured the levels of eight specific RNA molecules, all from genes linked to schizophrenia or bipolar disorder. The researchers could then tell the groups apart with an accuracy of 95 to 97 per cent

If this pans out (e.g., the unique gene expression profile is not caused by the drugs that the patients were taking), we have an even further shift in the biologization of psychiatry.

(Also, the part about lab tests providing quicker diagnoses was kind of weird - behavior only takes an hour or so to diagnose - I don't see that a lab test would be any faster. Realistically, the lab test would probably just supplement the psychiatric evaluation, the way a tumor biopsy (and more recently gene expression analysis) supplements a cancer diagnosis.)

I'm also slightly uncomfortable at the idea that this could "redefine" mental disorders - that one day, you could present with all the classic signs of major depression but then get your blood test and be told that you're not "really" depressed. And any time there is something that resembles a Kuhnian paradigm shift, I get a little uncomfortable because it makes me wonder if we're really getting any closer to "the truth" in scientific research.

Then again, this isn't a huge shift. We already believed that all behaviors are caused ultimately by biological mechanisms in the brain. And even before being able to see what's going on the brain, psychologists were always debating whether some commonly accepted disorder might "really" be, at some deeper level, an amalgamation of two different disorders, or a disguised manifestation of something else. For example, obsessive-compulsive disorder has different subtypes with different causes - one which runs in families, is linked to Tourettes' syndrome, and tends to start in childhood, and one which starts in early adulthood and is linked to depression and generalized anxiety disorder.

So I suspect that most people already knew that behavioral diagnoses were an operational definition pending further investigations of the causes, and that recent advances in brain imaging and DNA microarray technology have taken advantage of a longstanding desire to see what's "really" happening.