Genetic Testing

Genetic testing is used in a variety of ways in healthcare. In psychiatry, genetic testing is primarily used to gain insight into the body’s ability to metabolize (break down and use) medicines. Most medicines are processed in the liver through a series of complicated biochemical reactions involving different enzyme systems. Pharmacists spend years learning about these enzyme systems, which are labeled with names like ‘cytochrome P450 2D6’ (aka CYP2D6). Have I mentioned that you’ll receive college credit for reading this page???

Let’s keep it simple. Imagine your liver as a massive interstate system, with multiple lanes of traffic headed in the same direction. Next, hang a sign over each lane of traffic with its ‘name’- one of the major enzyme systems that works in the liver. Don’t forget CYPD26! Now, add traffic. Each car or truck represents a medicine. A medicine will always travel in the same ‘lane’ because it will require that biochemical process to break it down. Therefore, the car representing fluoxetine (Prozac) will always be found in the lane labeled CYP2D6. To complete our imaginary interstate system we need speed limit signs. Let’s start with a uniform 65 MPH for each lane. Traffic should be moving along nicely.

This is where genetics enter the picture. Based on the genes you inherited the speed limit signs over some lanes of traffic will change. A couple of them may increase to 80 MPH. The cars in those lanes are now moving much faster, which means those medicines are being broken down and eliminated more quickly. You may need a higher dose to achieve the response you need. Other lanes of traffic may drop to 55 or even 45 MPH. See how traffic is backing up? Slower metabolism means that you may have higher blood concentrations of a medicine than other people taking the same dose. In some cases, this can explain side effects or other poor responses. Does it mean you shouldn’t take that medication? Perhaps. There might be another medicine that suits you better. Or it may just mean that you need a lower dose than usual.

To complicate matters, some medicines travel in as many as 5 lanes of traffic at once. This is where our analogy breaks down a little, but you get the idea. Liver metabolism is complicated, but genetic testing can help by giving us information about your posted speed limits. Instead of learning based on trial and error, we can make more informed decisions. This is especially helpful if you have a history of poor responses to medication in the form of adverse reactions (side effects). Or, maybe you’ve tried several medicines and none of them has worked.