Genetics

Genetics can influence the risk for heart disease in many ways. Genes control every aspect of the cardiovascular system, from the strength of the blood vessels to the way cells in the heart communicate. For many common conditions, such as coronary artery disease, stroke, atrial fibrillation, and diabetes, there are many risk factors—genetic, lifestyle, and environmental—that increase a person’s risk of developing the disease.

Genetic tests do not currently exist to measure individual risk for most cardiovascular diseases because the specific genetic factors are not yet fully understood. This makes family history, along with information about patient lifestyle and environment, one of the most important tools doctors have for assessing individual risk. When a family member is diagnosed with cardiovascular disease, other family members may be encouraged to undergo screening to detect early stages of disease.

Aspects of family history that indicate a higher risk for heart disease include:

• Early onset of cardiovascular disease, for instance coronary artery disease in men younger than 55 and women younger than 65
• Cardiovascular disease in two or three relatives on the same side of the family
• Late onset of cardiovascular disease on both sides of the family
• The loss of a family member to sudden cardiac death

With the appropriate medical treatment, people at increased risk for heart disease can delay the onset and lessen the severity of the disease.

While coronary artery disease, stroke, and diabetes are common diseases with many contributing factors, other less common cardiac conditions have a stronger genetic component. Genetic testing can be used to diagnose conditions such as hypertrophic cardiomyopathy, long QT syndrome, and similar arrhythmia conditions that can run in families. A genetic variation (mutation) in a single gene can be detected in some patients and identify the underlying genetic cause of the disease.

Inherited conditions that lead to arrhythmias and sudden cardiac death are particularly well understood. These conditions fall into two categories. One group of conditions results from problems with the flow of certain molecules between the cells in the heart. An imbalance of these molecules can impair the electrical impulses that control the heartbeat. Examples of these conditions include:

• Brugada Syndrome: a genetic disorder of the heart rhythm that can cause ventricular fibrillation and sudden cardiac arrest
• CPVT (catecholaminergic polymorphic ventricular tachycardia): a disorder of the calcium channels in the heart muscle, resulting in problems with electrical signalling and irregular heartbeats, especially during exercise, and even sudden cardiac death
• Long QT Syndrome: a prolonged electrical recovery phase (QT interval) of the heartbeat that can result in rapid, chaotic beats and sudden cardiac death

The second group of conditions results from changes in the structure of the heart. These conditions can also cause abnormal heart rhythms, but typically they are diagnosed due to changes in the size of the heart chambers or thickness of the heart muscle. Hypertrophic cardiomyopathy and arrhythmogenic right ventricular cardiomyopathy can both cause deadly arrhythmias.

Genetic testing is available for inherited arrhythmias. Patients with these conditions should be referred to a specialized clinic for expert evaluation and genetic counselling.

Action Tips

• Make sure your family doctor knows
• Discuss risk and lifestyle with your children and siblings
• As some diseases are more common in some families, your own risk may be higher than average. The higher risk may be caused by genes you have inherited. Or it may be because people in the same family tend to be alike in the choices they make about diet and healthy living. Having a family history means that you should try to make lifestyle changes to reduce your risk.