Hypertrophic cardiomyopathy is an inherited condition caused by genetic mutation. It can lead to exercise intolerance, heart failure, arrhythmias, and sudden death. Hypertrophic cardiomyopathy (HCM) is an inherited condition in which the heart muscle is thickened, usually in an asymmetric fashion, leading to an increased risk of heart problems such as heart failure, arrhythmias, and sudden cardiac death
Hypertrophic cardiomyopathy (HCM) is an inherited condition in which the heart muscle is thickened, usually in an asymmetric fashion, leading to an increased risk of heart problems such as heart failure, arrhythmias, and sudden cardiac death (SCD).
Hypertrophied (thickened) heart muscle can cause problems with the outflow of blood from the heart's main pumping chamber to the aorta, which can lead to fainting and exercise intolerance. HCM can also cause leakage of the mitral valve, known as mitral regurgitation.
HCM is a genetic condition that can be caused by several different mutations in various proteins in the heart. This article discusses HCM and its causes, including genetics and risk factors for complications.
While mutations that cause HCM are usually passed down from a family member, they can also be sporadic in some cases, meaning the mutation occurs randomly, without a parent being affected.
Adding to the complexity, however, is the fact that several different types of mutations exist. And even people who have inherited a mutation that causes HCM may not develop it or its complications, a phenomenon known as variable penetrance.
Furthermore, someone with HCM may have more or less severe symptoms than a family member, which is known as variable expression.
The most common type of mutations that cause HCM are mutations in sarcomeric proteins in the heart.
Sarcomeres are proteins found in muscle cells. Mutations in sarcomeres that cause HCM result in thickening of the heart muscle, disorganized muscle fibers, and scarring.
The following is a list of mutations in sarcomeric proteins known to cause HCM:
In people who have a sarcomere mutation, mutations in beta myosin heavy chain and myosin binding protein C3 are the most common causes. They are found in about 70% of cases. The other sarcomere mutations each account for only 1%–5% of HCM mutations.
Genetic testing is performed in people whose imaging tests reveal signs of HCM. It is particularly useful after a diagnosis of HCM to test family members for the gene mutation.
Many different genetic mutations can cause HCM, and people with a mutation have variable severity—such as not having HCM or developing symptoms later in life. Mutations in sarcomeres, which make up heart muscle fibers, are responsible for most HCM cases.
Not everyone with HCM has an identified mutation that has been shown to cause HCM. Some people may have variants in the related genes, but it remains unclear if they are the cause of HCM. These are known as "variants of uncertain significance."
As our understanding of genetics in HCM evolves, these variants may be further clarified.
Heart muscle thickening, disorganization, and scarring in HCM can lead to arrhythmias and sudden cardiac death. In fact, HCM is the most commonly identified cause of sudden death in athletes younger than 30 years old.
Healthcare providers use risk factors to determine the risk of sudden death and make recommendations about exercise restrictions and implantable cardioverter defibrillators (ICDs). These devices monitor the heart rhythm and provide a shock of electricity to stop dangerous arrhythmias.
The following are factors found to be associated with increased risk of SCD.
The risk of sudden death is increased if a family member has experienced SCD. This is particularly true when the family member is a close relative (first or second degree relative) and was less than 50 years of age at the time of death.
The left ventricle is the main muscular chamber of the heart that pumps blood to the body. Noninvasive imaging tests, such as echocardiogram and cardiac magnetic resonance imaging (MRI), give information about the left ventricle that can predict who is at higher risk of SCD.
Findings that may indicate HCM include:
Those with HCM who have had recent unexplained fainting spells are also at risk of SCD. "Unexplained" syncope, or fainting, means that there was no obvious cause of loss of consciousness, such as a vasovagal event (for example, passing out when getting blood drawn).
People with HCM undergo heart rhythm monitoring to evaluate for arrhythmias. Those whose rhythm monitoring show an arrhythmia called nonsustained ventricular tachycardia (NSVT) that are frequent, long, or very fast, are at higher risk of SCD.
Hypertrophic cardiomyopathy is an inherited disease that can be caused by several different genetic mutations. Having a genetic mutation increases risk, but does not mean that your heart will necessarily be severely affected. Genetic testing is particularly useful for evaluating family members.
If hypertrophic cardiomyopathy runs in your family, you should have an evaluation by a cardiologist, who will evaluate your symptoms, family history, and order any necessary testing.
Finding out that you have a genetic mutation for hypertrophic cardiomyopathy can provoke anxiety, especially if other family members have experienced problems from thickened heart muscle. Know that not everyone with the mutation goes on to have detectable heart problems, and there are many promising treatments for people with HCM. Cardiac testing will help you and your healthcare provider determine a treatment and follow-up plan.Causes of Hypertrophic Cardiomyopathy View Story