The sequencing of the human genome was declared complete in 2003. With the completion of that project came the promise that this information would usher in an era of personalized medicine and transform the treatment of human health and disease.
Just “knowing” the sequence, however, is not equivalent to “understanding” the sequence. There are many layers of understanding that must go into deciphering the human genetic code for medical use. Not all DNA sequence encodes for genes. Consider that:
- Of the DNA that does encode for genes, there is plenty of variability in the sequence of genes amongst individual people.
- Of this variability, some of it is harmless and some of it is harmful.
- Furthermore, once harmful versus harmless sequence is determined, proposed harmful DNA changes must be proven to be causative of medical issues.
The scientific exercise of proving causality typically includes rigorous study, publication, and very often repetition to be deemed “clinically actionable.” Only when a proposed harmful DNA sequence has gone through this level of scrutiny and survived can it be considered for real-life applications in the doctor’s office. And, to most folks, almost more importantly at that point is who will pay to test for this information.
The information contained in the human genome is referred to as genomic information for which there are many medical applications including:
- Inherited diseases outside of cancer; and
Most of us are quite familiar with the first two topics, but are less familiar with Pharmacogenomics.
So, what is Pharmacogenomics? Simply put, it is the role of genetics in drug response. Drugs must be absorbed, metabolized, used at the intended site of action in the body, and then eliminated. Each one of these steps is influenced by enzymes and proteins in our body that, you guessed it, are programmed by our DNA! Therefore, each one of us has genetic variation that determines our own personal response to medications. Some people are prone to bad outcomes with medications. Two simple examples are 1) that a dose is not enough to treat a dangerous condition, or, 2) that a patient can’t break down the active drug fast enough such that a normal dose for most people ends up being a toxic dose in the patient. Another scenario worth mentioning for patients on more than one medication is that one drug can change the activity of a second drug landing a patient into one of the two aforementioned dangerous situations.
There is increasingly more evidence making its way into the medical literature that supports the use of pharmacogenomics testing in the real world and the costs of performing this testing are rapidly decreasing. It is very exciting that Medicare has recently made a decision to pay for a pharmacogenomics test for tailoring depression medication. Clinical implementation of pharmacogenomics information is a facet of personalized medicine that not only requires doctors having the evidence that this information can improve patient outcomes, but it also requires that healthcare payers cover the cost of the testing.
Nikoletta Sidiropoulos, MD, is Director of Molecular Pathology in the Department of Pathology and Laboratory Medicine at The University of Vermont Medical Center.