Asymmetric septal hypertrophy also called Familial hypertrophic cardiomyopathy is an inherited heart condition by thickening (hypertrophy) of the heart (cardiac) muscle. Thickening usually occurs in the interventricular septum, which is the muscular wall that separates the lower left chamber of the heart (the left ventricle) from the lower right chamber (the right ventricle). In some people, thickening of the interventricular septum impedes the flow of oxygen-rich blood from the heart, which may lead to an abnormal heart sound during a heartbeat (heart murmur) and other signs and symptoms of the condition. Other affected individuals do not have physical obstruction of blood flow, but the pumping of blood is less efficient, which can also lead to symptoms of the condition. Cardiac hypertrophy often begins in adolescence or young adulthood, although it can develop at any time throughout life.
The symptoms of familial hypertrophic cardiomyopathy are variable, even within the same family. Many affected individuals have no symptoms. Other people with familial hypertrophic cardiomyopathy may experience chest pain; shortness of breath, especially with physical exertion; a sensation of fluttering or pounding in the chest (palpitations); lightheadedness; dizziness; and fainting.
While most people with familial hypertrophic cardiomyopathy are symptom-free or have only mild symptoms, this condition can have serious consequences. It can cause abnormal heart rhythms (arrhythmias) that may be life threatening. People with familial hypertrophic cardiomyopathy have an increased risk of sudden death, even if they have no other symptoms of the condition. A small number of affected individuals develop potentially fatal heart failure, which may require heart transplantation.
Familial hypertrophic cardiomyopathy (HCM) is caused by mutations in any of several genes. The genes most commonly responsible are the MYH7, MYBPC3, TNNT2, and TNNI3 genes. Other genes that have not yet been identified may also be responsible for familial HCM.
The genes known to be responsible for familial HCM give the body instructions to make proteins that play important roles in contraction of the heart muscle. The proteins form structures in muscle cells called sarcomeres, which are needed for muscle contractions. Sarcomeres are made of protein fibers that attach to each other and release, allowing muscles to contract. The contractions of heart muscle are needed to pump blood to the rest of the body.
While it is unclear exactly how mutations in these genes cause familial HCM, they are thought to lead to abnormal structure or function of sarcomeres, or reduce the amount of proteins made. When the function of sarcomeres is impaired, normal heart muscle contractions are disrupted.
Familial hypertrophic cardiomyopathy (HCM) is inherited in an autosomal dominant manner. This means that having only one changed (mutated) copy of the responsible gene in each cell is enough to cause features of the condition. When a person with an autosomal dominant condition has children, each child has a 50% (1 in 2) chance to inherit the mutated copy of the gene.
In rare cases, a person with familial HCM has a mutation in both copies of the responsible gene, which leads to more severe signs and symptoms.
Familial hypertrophic cardiomyopathy (HCM) is caused by mutations in any of several known genes, and possibly other genes that have not yet been identified. Genetic testing for HCM is most informative as a "family test" rather than a test of one person. Results are most accurately interpreted after merging both genetic and medical test results from multiple family members. Ideally, the family member first having genetic testing should have a definitive diagnosis of HCM and be the most severely affected person in the family. Genetic testing of at-risk, asymptomatic relatives is possible when the responsible mutation has been identified in an affected family member. Testing should be performed in the context of formal genetic counseling.
An algorithm showing a general approach to finding the specific genetic cause in people with HCM can be viewed here.
The Genetic Testing Registry (GTR) provides information about the genetic tests for familial HCM. The intended audience for the GTR is health care providers and researchers. Patients and consumers with specific questions about a genetic test should contact a health care provider or a genetics professional.
As is often the case with genetic testing in general, there are benefits and limitations of genetic testing for familial HCM. Testing may confirm the diagnosis in a person with symptoms, and may help to identify family members at risk. However, results are sometimes unclear; testing cannot detect all mutations; and results cannot be used to predict whether a person will develop symptoms, age of onset, or long-term outlook (prognosis).
Treatment may depend on severity of symptoms and may include medications, surgical procedures, and/or an implantable cardioverter-defibrillator (ICD)