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Genetic Testing in Clinical Practice: What Psychiatrists Need to Know

Over the past few years, a number of companies have begun to offer genetic testing services marketed primarily to psychiatrists. These tests can be used to evaluate a patient’s genetic code to look for the presence of subtle differences in certain genes that can influence the way the patient metabolize medications, as well as differences that may be related to an individual patient’s likelihood of responding to certain classes of medications and of developing certain disease states.

Humans have about three billion base pairs of the four nucleotide base molecules making up their DNA. Only 1.2% of this DNA serves as a “blueprint” for making proteins that play important roles in the function of our bodies, while another 8.8% of this DNA serves regulatory functions (instructions for what to do with the “blueprints”). This leaves about 90% of our DNA that does not serve either of these purposes and may be so-called “junk DNA” (as far as we currently know).

All human beings share 99.99% of their genetic code with all other human beings (and if that were not enough to stamp out any remaining feelings that you are special or unique, recognize that we share about 98% of our genetic code with chimpanzees, about 60% of our genetic code with bananas, and about 33% with yeast).

Various companies offer testing for an array of genes including the Cytochrome P450 (abbreviated CYP) family of genes, which code for a corresponding family of enzymes involved in drug metabolism (more commonly involving degradation and elimination of medications, but sometimes involving the activation of a medication by metabolizing a pro-drug into the active form of the drug).

Members of this family of genes include CYP2D6, CYP1A2, CYP2C9, CYP2C19, CYP3A4, and others. Variants of these genes can produce enzymes that may work much more or less efficiently than is normal and can lead to a patient experiencing blood levels of medications that are much higher or lower than would be expected based on an average dose of the administered medication.

There is also a test for the gene for the serotonin transporter, SLC6A4, which has two main variants, short and long. The short form of the gene is associated with lower rates of response/remission to serotonin reuptake inhibitors.

Gene

Role

Effects caused by variants

CYP2D6, CYP1A2, CYP2C9, CYP2C19, CYP3A4 and others

Metabolism of medications (elimination or in some cases activation)

Blood levels that may be significantly higher or lower than predicted based on dose

SLC6A4

Serotonin Transporter Gene (target for serotonin reuptake  inhibitors)

Short form of the allele produces fewer receptors and is associated with lower remission rates

HTR2A

Serotonin 2A receptor

Variant can increase risk of drug reaction with serotonin reuptake inhibitors

COMT

Enzyme involved in metabolism of dopamine

Differing response rates to some stimulant medications

ADRA2A

Adrenoreceptor 2A

Differing response rates to some stimulant medications

MTHFR

Methylenetetrahydrofolate reductase

Converts folic acid into the active form, L-Methylfolate

OPRM1

Mu opioid receptor

Differing efficacy of opiate pain medications

Knowing about a patient’s genetic profile can increase our ability to select a medication that is more likely to be effective and less likely to cause side effects.  As this technology becomes more common, more available, and more affordable, it may become a standard of care. Use of this type of testing can provide valuable clinical information not only for psychotropic medications, but also for all medications that a patient may take now or in the future.

Do you use genetic testing in your daily practice?

Chris Bojrab, MD, is the president of Indiana Health Group, the largest multidisciplinary behavioral health private practice in Indiana, established in 1987. He is a board certified psychiatrist and a Distinguished Fellow of the American Psychiatric Association who treats child, adolescent, adult, and geriatric patients. His areas of interest include psychopharmacology, sleep disorders, and gambling addiction. For more information and disclosures, visit  www.chrisbojrabmd.com

The views expressed on this blog are solely those of the blog post author and do not necessarily reflect the views of Psych Congress Network or other Psych Congress Network authors.

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