The Gene-Environment Connection: Can We Change It?

"Jane" asks: "Is bipolar genetic or can it be brought on by traumatic experiences?"

She goes on to say: "I have had several traumatic things happen to me and just wondered if this has caused me to be the way I am. I have two siblings without bipolar, so it just makes me think that one or all my experiences set this off."

Great question, Jane. How great? A few weeks ago I would have answered your query quite a bit differently than I'm answering now. Not that I would have been wrong a few weeks ago, but attending two psychiatric conferences very recently has added a new layer of insights.

Let's start off with the proposition that we're talking about the interaction between genes and environment. It's not either-or. It's both-and. A simple way of putting it is our genes are all about how we react to whatever life throws our way. But it's not quite that simple, as we shall see.

Bipolar is highly heritable, as established by numerous family studies. But finding bipolar genes has been a rather daunting and frustrating task. The experts are in agreement that we are looking for many genes, each with a small effect. Your particular collection of "bipolar" genes is likely to vary somewhat (or even quite a bit) from my collection of bipolar genes.

It gets more complicated, because our brains are not organized according to the DSM (the diagnostic bible), so in all likelihood we need to be looking for more than "bipolar" genes. These would include more common gene variations that effect the general population as well, such as messed up sleep, or overreaction to stressful events.

Genes that affect how we react to the environment

Let me give you an example, involving a landmark study published in Science in 2003:

Scientists had been tracking a certain New Zealand population from birth. One year, they surveyed this population about recent stressful events in their lives, such as death in the family, losing a job, or breakup with a partner.

Lo and behold, among those meeting the criteria for four recent stressful events, 43 percent of those with a certain gene variation (what they call the short allele to the serotonin transporter gene) experienced depression vs just 17 percent with the long allele.

It's important to note that this gene variation is not a "depression" gene. Rather, think of the variation as making one susceptible to stress and its downstream effects (which may include depression). Call it a "stress" gene. One variation renders us vulnerable to stress, the other sets us up to be more resilient.

This particular gene is one of many that affects the function of the brain's amygdala. The amygdala mediates fear and arousal, and kicks off our limbic "fight or flight" response. You are probably alive today because your fight or flight system responded just as it should when you encountered a dangerous situation. But suppose, say, you get a panic attack in a supermarket for no good reason? Then, your amygdala is far too sensitive for your own good.

This study is a classic example of genes and environment interacting. A host of other related findings corroborate the principle, and a number of studies have implicated that same stress gene (as well as others) in numerous other mental illnesses and conditions.