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Pharmacogenetics refers to genetic differences that can affect individual responses to drugs, both in terms of therapeutic effect as well as adverse effects. Put more simply, we want to find the most effective and safe medications for our individual patients using their specific DNA fingerprint. We want to create the best “personalized” treatment plans that we can by analyzing our individual patient’s genes. We are already using pharmacogenetics to analyze whether or not certain medications will be safe in the individual patient. In oncology, we someday hope to use individual cancer genetic analysis to understand which chemotherapy agents will be the most effective. What about in asthma?
Asthma is a chronic disease that can affect children and adults. For many individuals with persistent asthma we recommend using daily controller medications to help prevent ongoing symptoms and exacerbations. The first line of controller therapy for most persistent asthmatics is the use of daily inhaled steroids. There are many individuals who do well with this, but there are others than need further treatment. For the latter group, we usually recommend adding either a long acting beta agonist (a.k.a. LABA, they are long acting versions of the common rescue medication albuterol) or a leukotriene modifying agent (like Singulair). There are some really well done studies that show that the use of LABA’s have a greater chance of helping more people than using medications like Singulair. But on an individual basis, most clinicians know that there are some people where the Singulair actually works better than the LABA. At this point we don’t have any reliable baseline tests to distinguish which treatment will work better for our individual patients.
Investigators from the University of Dundee in England have previously shown that young asthmatics with a specific genetic background (Arg16 genotype of ADRB2) were at higher risk for having exacerbations when they were taking daily beta agonists (like the LABA we talked about earlier). They estimate that about 15% of Caucasian asthmatics have this specific genetic profile. This study was retrospective, meaning they analyzed the genetic makeup of this group of children and looked back in time for any associations or correlations.
These same investigators have now taken the next step. They have published a study where they took 62 young persistent asthmatics that only had this specific genetic fingerprint and randomized them to either take a LABA or Singulair in addition to their daily inhaled steroid for one year. School absences (the primary outcome) were reduced in the Singulair group. Rescue inhaler use was also reduced with this group compared to the LABA group. Greater improvements occurred in both symptom and quality of life scores with Singulair vs the LABA. They showed that patients with this specific genetic code may fare better by using Singulair vs a LABA as add-on therapy to the daily inhaled steroids. This in turn provides evidence for geneticly directed personalized medicine.
One caution on over-interpreting these results, this study was very small (only 62 patients involved). Much larger studies are required to provide definitive conclusions regarding the true utility of this approach. Regardless, this is incredibly exciting and hopefully shows us a glimpse to our future where more “personalized” medicine is not science fiction.
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Dr. Ananth Thyagarajan (Dr. T.)
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