Personalized medicine, also referred to as precision medicine, holds great promise to improve healthcare. According to the National Cancer Institute, personalized medicine integrates “information about a person’s genes, proteins, and environment to prevent, diagnose, and treat disease.” As the cost of genetic analysis decreases and research advances, it is becoming increasingly possible to include a person’s genetic make-up in the repertoire of tools that inform his or her healthcare. Realizing this vision presents a number of challenges, and much research is needed. Still, there are already a number of success stories that illustrate the potential for improving people’s health. For example, personal genome sequencing has been used to diagnose children with rare conditions when other approaches have failed and has been applied in efforts to predict a person’s susceptibility to a medical condition. In addition, a growing number of medications are prescribed based on a person’s genetic make-up, and new drugs are being developed to target subsets of certain diseases that are defined by the presence of specific genetic variants.
The stories of Nic Volker and the Beery twins have drawn much attention to the potential for personal genome sequencing to advance healthcare. Nic Volker is the first child to receive a diagnosis and successful treatment as a result of genome sequencing. Nic, now thriving, had been terribly sick with a rare, undiagnosed medical condition and endured over one hundred surgeries by age 4. A portion of Nic’s genome was sequenced to look for a genetic mutation that caused his illness, which led to a diagnosis and pointed doctors towards a treatment. The Beery twins, Noah and Alexis, were misdiagnosed with cerebral palsy as babies. Years of medical treatments, mysterious symptoms and a search for answers ensued. After having their genomes sequenced as teenagers, they were accurately diagnosed and successfully treated.
How might personalized medicine change how drugs are prescribed?
Another way that genetics can contribute to disease treatment is for identifying medications that will be most effective with minimal side effects. Traditionally, when prescribing a medication, a doctor may take into account a patient’s age, weight, and kidney and liver function, and then wait to see how the patient responds. Some will respond positively, some will not respond at all, and some will have a negative reaction and suffer side effects. It is estimated that nearly 70% of Americans take at least one prescription medicine, and there are many questions about the risks of medications that are overprescribed, underused or given to people for whom the drug is not working as hoped.
The field of pharmacogenomics is exploring how people’s genes impact their response to medications. According to the National Institutes of Health’s Genetics Home Reference, “this relatively new field combines pharmacology (the science of drugs) and genomics (the study of genes and their functions) to develop effective, safe medications and doses that will be tailored to a person’s genetic makeup.” With genetic testing before treatment, people may avoid medications that will cause harm or be ineffective, and hopefully find the drug that will most effectively treat their illness.
Pharmacogenomics tries to address the fact that a person’s genetic make-up can influence how quickly they break down or metabolize certain drugs, which may make the same dosage of a medication work for one person, but ineffective or toxic for another. Warfarin, commonly known as Coumadin, is an anticoagulant used to prevent blood clots and is an example of a widely prescribed and successful drug for which the dosage can be adjusted based on genetic markers that influence a person’s metabolism. The medical community is not uniformly aligned on the benefits of genetic testing for warfarin dosing, and research is continuing to examine whether genetic testing is helpful in finding the most safe and effective dose for patients and reducing the frequency of adverse reactions and hospitalizations.
Tailoring treatment to an individual’s genetics
A major goal of personalized medicine is to develop or identify treatments for diseases based on a person’s genetic make-up. Towards this, some of the greatest strides have been made in the field of cancer treatment. Scientists have been able to develop drugs that are particularly effective for specific subsets of certain types of cancer, each of which harbors particular genetic mutations (for example, the drug Herceptin is used to treat breast cancer patients whose tumors have an overabundance of a protein called HER2). Researchers are also exploring the possibility of finding treatments for multiple cancer types that are classified not by the organs from which the disease originated (e.g., lung, breast, pancreas), but by the genomic characteristics that they share. A national-wide clinical trial is now under way to test this approach, which will collect and perform DNA sequencing on cancer biopsies from thousands of patients.
Drugs that are targeted to specific genetic make-up are also being developed for diseases other than cancer. For example, Kalydeco is a cystic fibrosis drug that was approved in the United States in 2012 to treat the 4% of cystic fibrosis patients who carry a specific mutation in the CFTR gene.
Going forward, a number of challenges will need to be addressed in order for personalized or precision medicine to be become widely applicable. While researchers are finding more DNA variants that differ between individuals with and without particular diseases, a lot more work is needed to verify these potential genetic links, and to work out how these genetic differences might contribute to disease. Developing genetically-targeted treatments is also difficult and expensive, and some of these treatments cost tens of thousands of dollars. How to make sure that all patients, regardless of socioeconomic status, will be able to benefit from these medical advances, especially if they contributed to the research and development of these new treatments, will be an important and difficult question to be tackled.
Dina Fine Maron, “A Very Personal Problem” (Scientific American, May 2016)
Jeneed Interlandi, “The Paradox of Precision Medicine” (Scientific American, April 2016)
Ed Yong, “How One Woman Deciphered Her Own Genetic Mutation” (The Atlantic, August 2014)
Julie Steenhuysen, “As Sequencing Moves into Clinical Use, Insurers Balk” (Reuters, June 2014)
Susan Young Rojahn, “Gene Test Helps Patients Avoid Thyroid Surgery” (MIT Technology Review, February 2014)
Gina Kolata, “In Treatment for Leukemia, Glimpses of the Future” (New York Times, July 2012)