Understanding Pharmacogenetics: What Everyone Should Know and Consider

What is Pharmacogenetics testing Pharmacogenetics refers to using inherited genetic differences to help healthcare providers decide what medications to give patients and at what dosage. The goal is a “personalized” approach that gives patients the greatest benefit with the fewest side effects.

We know that the “one-size-fits-all” approach to prescribing medication doesn’t work well. Adverse drug responses are responsible for about 5 percent of hospitalizations in the U.S. every year, and are estimated to be the 6th leading cause of death for hospitalized patients. Much of this is due to differences in how our bodies metabolize or break down and use these drugs. 

New genetic tests are now trying to categorize an individual as being a poor, “typical”, or fast-metabolizer. By knowing this information prior to starting treatment, the doctor or other healthcare provider would be able to make decisions about dosage or possibly an alternative drug.

As a genetic counselor who regularly sees patients in a general practice setting, I’m increasingly seeing patients with genetic testing results that include some of this information. Below I outline what people need to know about these types of tests, and what they can, and can’t tell us.  If you’re considering genetic testing, discussing the pros and cons with a genetic counselor or healthcare provider can be helpful.  

The Benefits of Pharmacogenetics

Overall, most genes we inherit are very similar to everyone else’s.  That said, there are significant variations that give us our differences in characteristics like hair color, eye color and height, and also in how we metabolize foods and medications.

The FDA has guidelines for genetic testing prior to prescribing certain medications.  There are a number of drugs that require testing and many for which testing is recommended. You can speak to a genetic counselor or your healthcare provider if you have questions or concerns about genetic testing as it relates to the medications you’re prescribed. 

A commonly used drug called Warfarin provides a good example of this. Warfarin is used to help reduce the risk for a blood clot. Studies have shown that there are differences in how individuals metabolize and use this drug based on one enzyme that breaks the drug down and another that uses it in our bodies. If we can gather information through genetic testing about these enzymes and how they work in each individual, the hope is we can adjust dosage accordingly, reducing risk and maximizing benefits.

Limitations

Unfortunately, what makes us respond differently to medications is often not as simple as a single gene.  Differences in our response can be influenced by age, ethnicity, gender, weight, drug to drug interactions, and by many genes interacting with one another.  

Finding associations between a drug and the genes involved in its metabolism is difficult. Because of our differences, it’s hard to determine how much a single gene is influencing us versus influences from environmental factors such as our diets or our habits.  For example, it would be very helpful to know how a person will respond to a psychiatric medication prior to prescribing.  To date, evidence is lacking for how genetic testing can help with the prescribing and dosage of most medication.  Without successful quality measures it’s difficult for insurance companies to pay for genetic testing versus the current treatment approaches. 

Concerns

Pharmacogenetics has great potential and we are well on our way to understanding how our genetics play a role in how we metabolize medications. It’s important for everyone considering genetic testing to speak with a well-informed healthcare provider about the pros and cons of testing prior to moving forward.Genetic testing has entered the mainstream. At-home genetic testing has become available to the general population looking for ancestry clues or potential risk factors for our health. For pharmacogenetics, some testing companies are directly marketing to consumers but unfortunately, are making promises not supported by evidence.  

For example, many of these companies heavily market a test for MTHFR, a gene involved with blood clotting. The American College of Medical Genetics currently does not support widespread testing for this gene because there is little practical information for your doctor in the test results, and currently there are no reliable recommendations for how your doctor should use the results.

In addition, some companies make promises about gene-drug interactions in children that are not known. Many companies also advertise a “maximum out of pocket” cost that you will pay for these tests, but the true cost of the tests is not disclosed to the patient or the doctors. By failing to disclose cost information, insurance companies are reluctant to cover these tests, making the availability and coverage of testing even more difficult for patients who could benefit from a known gene-drug test.  

Conclusion

Pharmacogenetics has great potential and we are well on our way to understanding how our genetics play a role in how we metabolize medications. It’s important for everyone considering genetic testing to speak with a well-informed healthcare provider about the pros and cons of testing prior to moving forward.  Patients also need to understand that a single gene may influence many different drugs. Therefore, these tests could impact not only the medication currently being considered but potentially future prescriptions. If you’re considering at-home genetic testing read 5 Questions to Ask Before Ordering an At-Home DNA Test

A genetic counselor can help you consider all of this, review what’s known about gene variations in an understandable way, and discuss the implications for you and your family, now and in the future.  

Meeting with a pharmacist can also be beneficial. Since there are many factors to consider in choosing a medication or dosage, including drug-drug interactions, a pharmacist may be able to work with you and your healthcare team to help ensure the safest and healthiest results possible.

Jay Flanagan, MS, CGC, is a preconception and prenatal expert for the National Society of Genetic Counselors and is a genetic counselor at Sanford Health in Sioux Falls, South Dakota. 

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