A few companies (Harmonyx and GeneSight) have been marketing genetic tests for ADHD,
claiming that they will allow you to predict the medications that will work the
best for a given patient. This sounds
great, because normally a patient has to find the best medication for ADHD
symptoms through a sometimes lengthy and painful process of trial and error. But do these genetic tests really work?
Well, they do for certain types of patients, but the information
could be unhelpful or misleading for others.
How the tests work
Pharmacogenetic testing is based on the idea that genes
regulate how medications are used and metabolized in the body and that
different people carry different variations of those genes.
The tests offered by Harmonyx and GeneSight are actually a
bundle of several tests which look for variations in the genes CYP2B6 (Harmonyx
only), CYP2D6 (both enzymes in the liver that change the drug you ingest into
something else) and ADRA2A and COMT (both related to how stimulants work in the
brain). The company sends you a report of which drugs
are green (most likely to be effective), yellow (use with caution) , or red
(avoid), and the specifics of your genetic variations.
How effective is testing in predicting
which medication will work the best?
The short answer
is, generally not very effective, with the exception of atomoxetine
(Strattera). For atomoxetine, studies
have shown that people who break down atomoxetine slowly due to a genetic
variation in CYP2D6 experience a higher incidence of side effects at lower
doses.
The main problem
is that for all other drugs besides atomoxetine, there have been either no studies,
or conflicting studies of poor quality (unrandomized, open label, small, etc.)
of whether genetic variants exhibit different responses to medication in
ways that are important to patients.
Almost all studies in the pharmacogenetics of ADHD have been done with
methylphenidate, which means that testing cannot distinguish between the
different stimulants.
For a more
technical breakdown of each individual test and references for the above conclusion, please see Pharmacogenetic
Testing For ADHD: Why It is Not Ready
for Prime Time
Disadvantages of
Testing
Cost
The price tag on the Harmonyx test is relatively low for a
battery of 4 laboratory tests. The
company states that it hopes to keep the cost at less than $100.
The cost of Genesight testing is not disclosed on their
website, though there is a patient assistance program available.
Unhelpful test results
The Harmonyx and Genesight tests do not provide enough
information to definitely identify which drug will be the most effective. The genetic testing provided cannot allow a
doctor to choose among stimulants or formulations of the same medication(liquid,
capsule, extended/immediate/intermediate/combined release), for example. Unfortunately, clincial experience has shown that these
details can be important in finding a drug and dose that works and does not
have intolerable side effects.
Misleading test
results
Particularly when it comes to ADRA2a and COMT, it is
difficult to know whether genetic status really makes a difference in predicting
response to stimulants, guanfacine or clonidine. If a patient has a genetic profile associated
with nonresponse in one study, it does not mean they will not respond, only
that their chances are less.
Genetic discrimination
If ADRA2a or COMT are proven to be causes of ADHD or other
psychiatric illnesses, insurance companies or employers may be able to use
genetic information to discriminate against you if that information is out
there.
When testing might be
helpful
For most patients, pharmacogenetic testing may be an
unnecessary expense and possibly misleading.
However in the following situations, testing could become useful.
When the patient is
taking or considering several medications
Several commonly used antidepressants or
antipsychotics--medications not necesssarily considered ADHD medications, but
often used for symptoms indirectly related to ADHD, such as aggression,
anxiety, or depression, are known to be subject to variations in drug
metabolism in the liver.
Patients considering
atomoxetine.
Testing can reveal the liver's inability to process
atomoxetine normally, allowing a patient to avoid a drug that would either be
unlikely to reach therapeutic levels or likely build up to toxic levels.
Bottom line: Is pharmacogenetic testing worth it?
Because it takes a certain amount of sophisticated medical
knowledge to decide if these tests will be useful and to interpret the results,
and because this field is rapidly evolving, I don't think it is a great idea
for a person to just walk into a pharmacy and order one of these tests for
themselves on a whim. Test results could
be disappointing, unnecessarily anxiety provoking, and at worst, misleading or
wrong.
However, if you fit one of the above criteria, it may be an
excellent idea to discuss testing with your physician (I would recommend a
psychiatrist) to help you weigh the pros and cons and get a perspective on the
latest research. The Harmonyx test is
particularly inexpensive and it may be hard to find an alternative (there are
alternative genetic tests for the same genes available to your physician) that
is cheaper.
References:
"ADHD Medication Testing." Harmonyx. YX
Genomics, 2015. Web. 02 Oct. 2015.
"Find the Right Medication for ADHD with
GeneSight." Find the Right Medication for ADHD with GeneSight.
AssureRxHealth, Inc., 2015. Web. 02 Oct. 2015.
Wellbutrin
[package insert]. GlaxoSmithKline, Research Triangle Park , NC
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