Have you heard the one about how having children runs in families? It’s true . . . if your parents didn’t have kids, most likely you won’t either. OK, bad joke—but it introduces us to the topic of genetics and how it impacts your cardiac health. How close do you have to be to someone genetically for it to affect your likelihood of having a heart attack? If your dad had a heart attack when he was 60, does that have the same implications for you as your mom having a heart attack at the same age? What about a cousin having a cardiac event at 60?
Disease and illness are caused broadly by two factors: nature and nurture. In this context, “nature” refers to what we are endowed with naturally—our genetic inheritance, coded in our cells by DNA, the molecules that make up our chromosomes. “Nurture” refers most obviously to the support you get from your parents, but more broadly includes the entire environment in your life. Do you smoke? What type of foods do you eat? Do you live downstream from a factory that releases toxic chemicals into the drinking water?
Human illnesses are caused by varying combinations of nature and nurture, some being more the first, some more the second. For instance, emphysema and lung cancer are almost entirely “environmental” illnesses caused by smoking. But even these diseases have a genetic component, in terms of which individuals are more susceptible to the damage caused by tobacco. At the other extreme, sickle cell anemia is almost entirely genetic, caused by a particular mutation (a change in the usual code of a gene) in the blood cell protein hemoglobin. Even here, though, environmental factors can be triggers to an attack.
Most diseases have a more balanced combination between nature and nurture. Focusing on the heart, the major problems of coronary heart disease, congestive heart failure and atrial fibrillation are examples of this mixed causation. Coronary heart disease, for instance, is affected by genetics—what doctors refer to as having a “positive family history”—but is also affected by smoking, having hypertension, high cholesterol and diabetes. Interestingly, each of those last three things has their own genetic component, so the genetic tendency to coronary heart disease is seen not only in having a family member who has had a heart attack, but a family tendency toward hypertension, high cholesterol and diabetes.
We are learning more and more about the specific genes that cause coronary heart disease (which is the heart problem about which we have the largest genetic database) and we will eventually be able to do quick blood tests to find these genetic tendencies. For now, though, our practical means of assessing for that genetic tendency is to ask about a family history of heart disease. And because each of us shares the most genetic material (DNA) with our closest relatives, we focus the question on first degree relatives: parents and siblings. With your mom and dad, brother or sister, you share 50% of your DNA (on average). You only share 25% with your grandparents and only 12.5% with your cousins—explaining these numbers, though, is a bit beyond the scope of this blog!
The other thing to keep in mind is that coronary heart disease is very common in the United States, partly due to the environment we all grow up in (simply put—we eat too much of the wrong things!). Developing blockages in arteries is almost inevitable if you live long enough. So, when we consider how strong the genetic factor is, we look at how young a person is when they develop heart disease. A person who has a heart attack at the age of 45 is much more likely to have a strong genetic tendency to heart disease than a person who has a heart attack at the age of 85.
We use the ages of 55 in men and 65 in women as reasonable “cutoff” points for what we consider to be “premature” coronary heart disease. Based on all this, when cardiologists ask patients about their family history, we ask: “Did your father or a brother have a heart attack (or bypass surgery or angioplasty) before the age of 55, or did your mother or a sister have those heart issues before the age of 65?” If the answer is “Yes,” you are considered to have a positive family history of (coronary) heart disease.
In the next blog, I’ll address why we use a different age cutoff for men and women. In the meantime, it’s important for you to research your genetic tendencies by knowing what major illnesses your parents and siblings have had and at what ages they developed them.
Greg Koshkarian, MD, FACC