Ask the Doctors: Genetic testing
Q. I read about genetic testing in all fields of medicine. But I don’t fully understand the concept. I was hoping you could explain how genetic testing relates to heart disease.
A. You are correct that genetic testing has become more widely used in recent years, but it still represents only a small portion of the diagnostic methodology utilized by physicians on a daily basis. Human beings have 23 pairs of chromosomes, which contain more than 20,000 genes. Genes are sequences of DNA which encode proteins, which function as part of the molecular machinery of living cells. Given their sheer number, you can see how critical and complex the roles of genes are in our body’s functioning. One might imagine that knowing someone’s entire DNA sequence would give us great insights into their health, but this is frequently not the case. Common disorders such as coronary artery disease (CAD) and hypertension are believed to result from the effects of multiple genes, and in each gene, there can be many different subtle variations. We must also take into account that environmental factors (such as diet, exercise, and smoking) interact with our genetic background to result in disease or not. Currently, genetic testing is not widely used as a screening tool to help determine their risk of developing certain heart diseases.
Certain kinds of cardiovascular problems do have clear connections to single genes, and these include cardiomyopathies (heart failure stemming from dysfunction of the heart muscle), arrhythmias, abnormalities of cholesterol metabolism, vascular disorders, and inborn malformations of the heart and other organ systems. If a family member is found to have a specific disorder, the first step is to make a detailed family tree of relationships and diseases, known as a pedigree. With the assistance of a certified genetic counselor, the pedigree can be analyzed, and it can be determined if genetic testing is indicated for the proband and other members of the family. It can include complete or partial sequencing of the genome, or examination for particular genetic markers (mutations or variations in the DNA) that tend to associate with diseases. Such testing is expensive, and the interpretation of its results can be very involved. Fortunately, the Genetic Information Nondiscrimination Act (GINA) of 2008 protects people against health insurance and employment discrimination as a result of genetic testing, but life insurance and long-term disability are not currently protected. Obtaining a genetic risk assessment on your own from a third-party organization is discouraged, since interpreting the results can be complex and confusing. Perhaps in the future, the role of genetic testing for the average patient can be more clearly delineated, but for now it is a specialized field with applications to a subset of cardiovascular ailments.
Ask the Doctors: Calcium channel blocker
Q. I’ve been taking a long-acting calcium channel blocker for a few years to help control my high blood pressure. I recently found out there are short-acting calcium channel blockers. What exactly is the difference?
A. Calcium channel blockers (CCBs) work by reducing the influx of calcium into smooth muscle cells, limiting their strength of contraction. When treating hypertension, CCBs are useful be-cause they help relax blood vessels and lower blood pressure (BP). At one time, short-acting CCBs were utilized for their BP-lowering capabilities. Given their rapid onset of action, they could be used to drop BP quickly during a hypertensive urgency, if needed. Studies during the 1990s showed, however, that individuals taking short-acting CCBs—particularly short-acting nifedipine—were at higher risk for heart attack than people not taking those drugs. As a result, caregivers are discouraged from using short-acting CCBs to treat hypertension, angina, or myocardial infarction. Only long-acting CCBs are in frequent use, because their efficacy and safety have been well established.
—Leslie Cho, M.D., Editor-in-Chief, and Adam W. Grasso, M.D., PhD, Director, Cleveland Clinic Cardiology Consultation Service