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Proving the usefulness of pharmacogenetics

In Pharmacogenetics on March 7, 2008 at 10:37 am

Pharmacogenetics is the analysis of genetic markers that informs you of how efficiently you metabolize a given drug. Three genes are commonly analyzed: Cyp2C9, Cyp2C19 and Cyp2D6. These genes are important for the metabolism of drugs used for treating psychiatric disorders ranging from mild depression to severe psychosis. Of course, there are other things that influence how you respond to a drug, like compliance, diet and smoking, but the genetic differences have profound stand-alone effects. For a patient experiencing adverse events or no response at all when taking his medicine, pharmacogenetics can be a tremendous help in choosing more fitting medications (other brands or another (sub)class of drugs). Pharmacogenetics is thus, a vital part of personalized medicine.

There are a couple of arguments against pharmacogenetics analysis we in the diagnostic lab often meet:

1: It’s too expensive

2: The frequency of mutant alleles in the normal population does not differ from that in a given patient population. Thus, physicians seems to be unable to pick the right patients, and pharmacogenetics ends up as an inefficient (as well as over hyped and expensive) general screening method.

The first objection is easy to respond to: A patient that has to try many different drugs to achieve the desired effect without adverse reactions, costs much more than this once in a life-time test allowing a targeted approach straight towards the medication most likely to be suitable.

The second objection can be countered by saying that the overall frequency in a population is irrelevant to the patient, as finding his individual response to the drug is what matters. This argument however is just an argument favoring screening in any given field of medicine. One can still argue that the overall cost-effectiveness is insufficient. Thus, it seems that one either has to prove that physicians are able to pick the right patients (resulting in targeted diagnostics rather than general screening), or prove that general screening with pharmacogenetics is cost-effective.

Now, it seems that doctors using our lab are able to pick the right patients. This is based on results from a small study we have performed (more details below). The argument saying pharmacogenetics is just expensive general screening, thus, falls.

The study of whether general screening is also justified, we need to leave to others, but indications are that doctors are rapidly learning how to use pharmacogenetics.

Consequently, pharmacogenetics seems to be justified in terms of cost-effectiveness and it is undoubtedly in the best interest of the patient.

Our small study (595 patients) can be summarized like this:

Allele Our frequency (%) Frequency (%) in a normalpopulation with similar ethnicity
2C9*2 11,5 10
2C9*3 6,9 7,4
2C19*2 16,7 9,1
2D6*3 1,3 1,1
2D6*4 20,0 15,6
2D6*6 1,0 1,2
2D6 gene duplication 2,1 2,2
2D6 gene deletion 3,4 2,4

The frequency in all but three (2C9*3, 2D6*6 and 2D6 duplication which had similar frequencies), were higher in our selected population than the normal population. Consequently, it seems that physicians are able to pick the right patients. There seems to be no general screening of patients receiving psychoactive drugs, among physicians using our service.