Hypertrophic cardiomyopathy (HCM) is a heart condition that people typically inherit from their biological parents through their genes. Genetic testing can help identify people at risk of developing HCM and guide care.

HCM is the most common inherited heart condition. Any biological child of an adult with HCM has a 50% chance of inheriting the condition. It causes stiffness in the heart muscle wall, reducing blood flow to and from the heart.

Genetic testing can be a useful tool in identifying certain gene changes that can lead to HCM. This can help people with HCM start treatment early and inform clinical advice on monitoring the condition in their biological siblings, children, or parents.

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HCM is the most common inherited heart condition. It may be the leading cause of death due to cardiac arrest in athletes and young people in the United States. However, sudden cardiac arrest due to HCM is rare.

Genetic testing is an important tool in identifying genetic variations that can lead to HCM. The test is a simple, noninvasive procedure in which a healthcare professional collects a blood or saliva sample and sends it to a lab.

Lab technicians will then check the sample for 30–50 genes that may have links to HCM. The technicians look for changes in the genes, also known as mutations, by comparing the genes in a person’s sample with a database of samples from people with and without HCM.

A person usually receives results up to 3 months after providing the sample.

Genetic testing for HCM is important, as the condition often has no symptoms.

People with a known family history of HCM should undergo genetic testing for the condition. However, this is not always clear. The first sign of HCM in a family may be a sudden death due to a cardiac event.

After the sudden death of a family member

Post-mortem genetic testing is available following a sudden death. This testing can support family care by allowing healthcare professionals to do the following:

  • diagnose HCM as the cause of death
  • identify which gene alterations may be responsible for HCM
  • notify immediate family members about the benefits of screening and genetic testing

Before becoming pregnant

People looking to conceive may also benefit from HCM testing.

HCM only requires a single copy of the gene variation to develop. This is known as an autosomal dominant pattern of inheritance. It means the gene can pass to children even if just one biological parent carries a genetic variation related to HCM.

Some people may choose to have prenatal testing for HCM, although this is rare. It is impossible to predict the onset of symptoms, and the prenatal test carries a high risk of complications. For these reasons, doctors do not often recommend this type of testing.

However, doctors can carry out genetic testing before implanting an embryo during in vitro fertilization (IVF). This allows them to implant only the embryos that do not carry the alteration.

A genetic marker is a DNA sequence with a known place on a chromosome — the home of all genes. These markers help doctors identify and compare genes.

Laboratories test up to 50 genetic markers for HCM-linked variations. However, the most common markers for HCM include:

  • MYH7
  • MYBPC3
  • TNNT2
  • TNNI3

These genes produce proteins that have specific roles in helping heart muscle develop and function. They form cells called sarcomeres that drive muscle contractions, controlling the pumping of the heart.

By identifying which HCM-linked genes have an alteration, doctors can more easily identify and manage the underlying cause of HCM. Rarely, tests will find markers that have unclear links to HCM. Doctors call these variants of uncertain significance (VUS).

A doctor will not use these markers to make an HCM diagnosis, as more research is necessary to link them to the condition in a clinically helpful way. Instead, the test will come back with an inconclusive result.

HCM genetic test results will either come back phenotype-positive, meaning the test found a variation on an HCM-linked gene, or phenotype-negative, meaning the person does not have an alteration.

The results of HCM genetic testing only indicate the risk of developing HCM. Testing cannot predict the outcome of HCM or how it may progress. However, variations of some genes, such as TNNT2, have links to a high rate of sudden death or specific symptoms.

Having the gene does not mean a person will definitely develop HCM.

Recommendations a doctor may make

Based on test results, a doctor may make recommendations related to physical activity levels.

If a person’s sample is phenotype-positive, it is best for their immediate biological family members, such as parents, siblings, and children, to also undergo testing. The follow-up tests are much quicker after a test identifies the gene alteration in an initial family member.

A doctor may also recommend regular imaging tests, such as echocardiogram scans, to monitor heart health and check for anomalies over time.

The genes that cause HCM have a 50% risk of passing from biological parents to offspring. However, having a genetic variation does not automatically mean a person will develop the related condition. The gene also needs to become active, which does not always happen.

There is no evidence that HCM skips a generation. If it seems to, it may be because the condition in one individual’s case has no symptoms or there is no expression – or “switching on” – of the gene variation in that generation.

A person with HCM may not feel any symptoms. Others may only notice symptoms during exercise or physical effort.

Some people experience:

A person may experience no symptoms at first but become more aware of them over time.

Genetic testing through a simple blood or saliva test can provide insight into disease risk for people with hypertrophic cardiomyopathy (HCM) or a family history of the condition.

After a sudden cardiac death due to HCM, post-mortem genetic testing can identify the gene responsible for a person’s HCM so that family members can determine their level of risk. A genetic test can also guide decisions for family planning in people with an HCM-linked variation. During IVF, doctors can ensure only embryos without the gene undergo implantation.

Genetic testing is not compulsory but can guide management for people with HCM, as different genes point to different causes. Regular echocardiogram scans can help people with certain gene variations monitor their heart health moving forward.