Studying specific genes that influence a person’s response to medication has become one of medicine’s hottest area of research. The field – aptly named pharmacogenetics after the two areas of research it intersects – seeks to provide a tailor-made drug regimen, where genetically compatible medications can be personalized to the individual. Pharmacogenetic research has evolved on the coattails of genome sequencing, a once out-of-reach technique that has become inexpensive and efficient in recent years. Finding out your specific variations of drug-responsive genes has become a swift procedure, with many companies offering at-home testing kits that require little more effort than swabbing the inside of your cheek.
Further research into drug-gene responses is of dire need. Adverse responses to medication puts over 200,000 Canadians in hospital per year, costing the lives of nearly 10,000 patients annually, and tallying a healthcare expenditure cost of an estimated $13 billion. Predicting drug efficacy and safety by reading the genetic code offers an alluring improvement to these statistics; experts believe that a national implementation of pharmacogenetic testing could reduce adverse drug-related deaths by one-third.
Although pharmacogenetic tests are used in a wide range of clinical settings, the purpose of the assay is two-tiered: to test for metabolic enzymes and other genes that broadly shape drug metabolism in the body, and to test diseased tissue to assess whether a patient will respond well to a specific medication. The CYP family of genes that code for the distinct liver enzymes involved in the metabolism of most drugs forms the basis of most pharmacogenetic tests. Variations in the CYP genes can modulate the function of these metabolic enzymes, influencing the rate of drug metabolism, its anticipated toxicity, and the required dose. For instance, a person with fast-acting metabolic enzymes will likely require a higher dose of medication than another whose metabolism is slower. Ancestry contributes somewhat to the patterns of CYP gene inheritance – as Dr. James Kennedy, head of the Tanenbaum Centre of Pharmacogenetics at the Centre for Addiction and Mental Health (CAMH) in Toronto explains: “Our liver enzymes evolved to protect us from poisonous plants that grew around [our ancestral populations] and what they ate to survive, and this has led to differences in how we metabolize drugs.” Supporters of the movement towards pharmacogenetic testing believe that knowing your drug metabolism status should be as commonplace as being aware of your blood type.
Despite the surge in both DNA sequencing speed and ability, pharmaceutical companies have been hesitant to adopt the genetic testing practices that would identify the best-responding patients to their drugs. The same tests designed to improve drug efficacy for some patients will lure others away from using the same medication. Some pharmaceutical executives even argue that personalized drug consumption may halt drug development. Both Health Canada and its US-equivalent, the Food and Drug Administration, recommend, but don’t mandate, that drug companies divulge information as to which known gene variants can render a particular medication ineffective. What’s more, pharmacogenetic testing kits are largely unregulated in Canada – Health Canada has issued 20 licenses for kits devised for “medical purposes”, but others intended for “research purposes” are unlicensed and therefore widely available. This, as Iris Cohn, pharmacogenetics advisor at SickKids Hospital points out, can lead to a second-rate quality of results.
As it stands, research into pharmacogenetics is largely outpacing its implementation in the Canadian healthcare system. While some doctors may be interested in pharmacogenetic testing for their patients, others are hesitant to do so because they were not taught how to interpret these results during their medical training. Additionally, some physicians believe that pharmacists have an equal responsibility in understanding and effectuating pharmacogenetic testing for their patients as a standard-of-care measure. No matter to whom the interpreting onus falls, the market is awash with demand for these tests; companies like OneOme and RxOme have helped hundreds of Canadians resolve their drug metabolism status. And insurance companies are taking note: Sun Life, Great-West Life and Manulife have each aligned themselves with different pharmacogenetics research initiatives within the last year. Sun Life, for instance, has partnered with CAMH in their ongoing IMPACT study that profiles participant’s saliva as a means to determine how they will respond to various psychotropic medications. This enhanced collaboration between different health services to drive research as well as improve drug safety and efficacy may be the boost the government needs to follow suit and join in the efforts.