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 impact on your likelihood of having a heart attack? If your mom had a heart attack when she was 80, does that have the same implications for you if it occurred when she was only 50?
Disease and illness are caused broadly by two factors: nature and nurture. Nature refers here to what we are endowed with naturally—our genetic inheritance, coded in our cells by DNA, the molecules that make up our chromosomes. Nurture of course includes the support you get from your parents, but more broadly refers to the the entire environment in a person’s 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 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 clearly examples of this balanced causation. Coronary heart disease, for instance, is affected by genetics—known currently by 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 that we have some of the largest data on genetics) and 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 and 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 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 35 is much more likely to have some strong genetic tendency 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 learn about what your genetic tendencies are by knowing what major illnesses your parents and siblings have/had and what ages they developed them.
Greg Koshkarian, MD, FACC