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Pharmacogenomics: Enabling Your Doctor to Predict Your Response to a Given Drug.

Updated on March 20, 2013
A segment of DNA showing the pairing of nucleotide bases, Adenine (A) to Thymine (T), and Guanine (G) to Cytosine (C).
A segment of DNA showing the pairing of nucleotide bases, Adenine (A) to Thymine (T), and Guanine (G) to Cytosine (C). | Source

What Is A Gene?

A gene is a segment of DNA that codes for the synthesis of a protein or RNA chain that the organism needs to survive. So, in order to understand what a gene is, you have to understand the structure of DNA. A DNA molecule consists of two strands. Each strand consists of a sugar-phosphate backbone to which four different bases are covalently bonded. The strands are held together by hydrogen bonds between the bases. The bases are small nitrogen-containing cyclic organic molecules called adenine (A), guanine (G), cytosine (C) and thymine (T). All along the strands, adenine pairs with thymine and guanine pairs with cytosine (see diagram at right). The term "DNA sequence" refers to the order in which the base pairs appear in the strands. The DNA sequence is what accounts for genetic differences between individuals. That is to say that people differ from one another because their DNA molecules have different sequences of base pairs. Now, we can return to the definition of a gene as a segment of DNA. The "segment of DNA" is a specific sequence of base pairs that sends a message to the cell regarding a protein that the individual needs for survival. The human genome contains about 20,000 to 25,000 genes.

Pharmacogenomics and How It May One Day Help You Get the Right Drug

Doctors and medical researchers have often wondered why it is that a particular drug works well for one person, but fails to do anything good for another. The answer may lie in a person's genes. The still-emerging field of pharmacogenomics seeks to match specific variations in genes with responses to a given medication. It is part of the field of personalized medicine which seeks to use your genetic profile to assess your risk of getting a particular disease. Pharmacogenomics tries to correlate certain DNA sequences with specific responses to a given medication.

Cancer chemotherapy drugs are good examples to use to explain how pharmacogenomics will work when it is incorporated into the practice of medicine. If you are diagnosed with colon cancer, your doctor may assign you to one of the established chemotherapy multi-drug regimens. He or she will base the assignment on things like your age, sex, weight and medical history. Even so, your doctor has no idea how you will actually react to the drug regimen. It may work well or it may do nothing but produce unpleasant side effects. Now, if the choice of chemotherapy regimen can be guided by the specific DNA sequences that you have, a more informed choice of drug regimen can be made. Your doctor may be able to see, for example, that one of your DNA sequences correlates with an adverse reaction to the drug regimen he or she was contemplating. In this case, a regimen more likely to give good results could be used instead.

According to the Mayo Clinic, it may be quite some time before pharmacogenomics is incorporated into the practice of medicine. The reason is that the number of DNA sequences that govern an individual's response to medications may be very large, maybe in the millions. Characterization of all of them would take years. In addition, it may be that response to medication is determined not just by one DNA sequence but by many interacting sequences.

Pharmacogenomics and Ovarian Cancer


This hub has been written for the sole purpose of providing information to the reader. It is not intended to be a source of any kind of medical advice or instruction, and it should not be used in the diagnosis of any illness, disease or condition. You should consult your doctor if you have questions about a specific medical problem.


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    • healthwriterbob profile image

      healthwriterbob 6 years ago from United States

      Hi Kris,

      Thanks for your comments. I agree that using a person's genetic profile to predict response to a particular drug may be more complicated than it appears right now. You point to the variability in environmental factors and there is also the idea that response to a drug may depend on an interaction between genes. Take care and thanks again for your insight.

    • Kris Heeter profile image

      Kris Heeter 6 years ago from Indiana

      It will be interesting to see how this all plays out. I personally suspect it's not going to be as straight forward as many hope - there are still a lot of hurdles. The presence of a particular gene variant in a person's genome doesn't always mean that it will expressed (or not expressed). Many environmental factors come into play that affect gene expression and that will still vary from person to person. But this is definitely an interesting topic to track and who knows, maybe some good advances will come!

    • healthwriterbob profile image

      healthwriterbob 6 years ago from United States

      Hi kschimmel,

      Thanks for your feedback. For cancer patients in particular, the wrong decision about chemotherapy can lead to a bad experience with side effects and no progress toward getting better. Take care.

    • kschimmel profile image

      Kimberly Schimmel 6 years ago from North Carolina, USA

      This is very interesting. It would certainly be great to be able to predict who might react badly to a drug before it is prescribed or used.