Molecular Diagnostics offers a test that can determine which
type of genes a person has for enzymes that metabolize antidepressant
medication. The test costs $ 300 to $400, and can be ordered
by healthcare professionals, or by consumers.
The idea is that it might be possible to predict which medications
might be better for a particular patient. That has appeal,
because many people have to try more than one medication in the quest
to find one that is both tolerable and effective.
If a person metabolizes a drug much more rapidly than most
people, then that person might need a higher than expected dose, or
might need to take the medication more frequently than the usual
recommendation. If a person metabolizes the drug much more
slowly than most people do, then that person might be more susceptible
to adverse effects; this might call for a lower dose than what most
persons would take.
test was approved by the FDA. But the approval was
based only upon the fact that the test accurately can detect the genes
it is claimed to detect. That does not say anything about
whether the test has any clinical usefulness.
In fact, there are many things that sound good in theory, but which
turn out to have no clinical utility.
The US Centers for Disease Control and Prevention (CDC) set out to
determine whether the test has any clinical utility. On 19
December, 2007, they issued a href="http://www.cdc.gov/od/oc/media/pressrel/2007/s071219.htm">press
release on the subject. It was written by href="http://www.cdc.gov/genomics/about/mkhoury.htm">Muin J.
Khoury, M.D., Ph.D., Director of the href="http://www.cdc.gov/genomics/default.htm">National
Office of Public Health Genomics (NOPHG).
The resulting study was published in the December issue of Genetics
in Medicine (Genet Med. 2007:9(12):819-825) and is openly
from the EGAPP Working Group: testing for cytochrome P450 polymorphisms
in adults with nonpsychotic depression treated with selective serotonin
Summary of Recommendation: The EGAPP Working Group found insufficient
evidence to support a recommendation for or against use of CYP450
testing in adults beginning SSRI treatment for non-psychotic
depression. In the absence of supporting evidence, and with
consideration of other contextual issues, EGAPP discourages use of
CYP450 testing for patients beginning SSRI treatment until further
clinical trials are completed.
Notice that they did not say the test is useless. Rather,
they said that there is no evidence that it is useful. We
simply do not know. Notice also that they did not say that
the evidence is too weak to support a conclusion. There is no
evidence at all, at least that they could find.
There is a much longer and more detailed analysis published by the
href="http://www.ahrq.gov/">Agency for Healthcare Research
and Quality, in href="http://www.ahrq.gov/downloads/pub/evidence/pdf/cyp450/cyp450.pdf">this
157-page PDF file. The conclusion is the same.
Although we all have high hopes for personalized medicine and
rel="tag">pharmacogenomics, this particular test,
at this particular time, has no objectively validated utility.