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URL of this page: https://medlineplus.gov/genetics/condition/nonsyndromic-hypertrophic-cardiomyopathy/

Nonsyndromic hypertrophic cardiomyopathy

Description

Hypertrophic cardiomyopathy is a heart condition that is characterized by the thickening (hypertrophy) of the heart (cardiac) muscle. This condition is called nonsyndromic hypertrophic cardiomyopathy when it is not associated with signs and symptoms affecting other parts of the body and when it cannot be explained by other causes, such as chronic high blood pressure.

The symptoms of nonsyndromic hypertrophic cardiomyopathy often appear in adolescence or young adulthood, although they can begin at any time throughout life. In most affected individuals, hypertrophy 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). This thickening of the interventricular septum can obstruct the flow of oxygen-rich blood from the heart, which may cause an abnormal heart sound during a heartbeat (heart murmur).

The features of nonsyndromic hypertrophic cardiomyopathy can vary, even among members of the same family. While some affected individuals have no associated symptoms, others may experience chest pain; shortness of breath, especially during physical activity; or a sensation of fluttering or pounding in the chest (palpitations). Affected individuals may also have episodes of dizziness or fainting (syncope).

Most people with nonsyndromic hypertrophic cardiomyopathy have a normal life expectancy. However, some affected individuals develop an abnormal heart rhythm (arrhythmia) that may be life-threatening. A small number of affected individuals develop heart failure. Although uncommon, people with nonsyndromic hypertrophic cardiomyopathy have an increased risk of sudden death, even if they have no other symptoms of the condition.

Frequency

Hypertrophic cardiomyopathy affects approximately 1 in 500 people worldwide. Nonsyndromic hypertrophic cardiomyopathy likely accounts for more than half of all cases.

Causes

Genetic changes that cause disease are called pathogenic variants. Pathogenic variants in one of several genes can cause nonsyndromic hypertrophic cardiomyopathy, but variants in the MYH7 and MYBPC3 genes are the most common genetic cause of this condition.

Many of the genes that are associated with nonsyndromic hypertrophic cardiomyopathy provide instructions for producing proteins that play an important role in the function of cardiac muscle. Many of these proteins are associated with structures called sarcomeres. Sarcomeres, which are the basic units of muscle contraction, are made up of overlapping thick and thin protein filaments. These thick and thin filaments shift so that the thin filaments move past the thick filaments. This movement shortens the sarcomere and contracts the muscle. Regular contractions of cardiac muscle pump blood to the rest of the body.

The protein produced from the MYH7 gene is the major component of the thick filament in sarcomeres. The protein produced from the MYBPC3 gene provides structural support to the thick filament and helps regulate muscle contractions.

Pathogenic variants in the genes that are associated with nonsyndromic hypertrophic cardiomyopathy cause cells to produce proteins that do not function properly. Many of these altered proteins impair the function of the sarcomeres and disrupt cardiac muscle contraction. Researchers do not understand exactly how changes in the genes that are associated with cardiac muscle and sarcomere function lead to the characteristic features of nonsyndromic hypertrophic cardiomyopathy.

Approximately 70 percent of people with nonsyndromic hypertrophic cardiomyopathy do not have a pathogenic variant in one of the genes that is associated with this condition. In these cases, the cause of the condition is unknown. People who have pathogenic variants in the genes that are associated with sarcomere function tend to show signs and symptoms of nonsyndromic hypertrophic cardiomyopathy earlier in life than people in whom no pathogenic variants are detected.

Hypertrophic cardiomyopathy may occur as part of a syndrome that affects other organs and tissues in the body. These forms of the condition are described as "syndromic" and are caused by variants in other genes.

Learn more about the genes associated with Nonsyndromic hypertrophic cardiomyopathy

Additional Information from NCBI Gene:

Inheritance

Nonsyndromic hypertrophic cardiomyopathy has different inheritance patterns depending on the specific gene involved. When nonsyndromic hypertrophic cardiomyopathy occurs in multiple family members, it may be called familial hypertrophic cardiomyopathy.

Nonsyndromic hypertrophic cardiomyopathy is typically inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder.  However, some people who have the altered gene never develop features of the condition. This is known as incomplete penetrance.

Although many individuals with nonsyndromic hypertrophic cardiomyopathy have a parent with the condition, some people have the condition as a result of a new (de novo) variant in a gene that occurs during the formation of reproductive cells (eggs or sperm) in an individual's parent or during early embryonic development. 

Some cases of nonsyndromic hypertrophic cardiomyopathy are inherited in an autosomal recessive pattern, which means both copies of the gene in each cell must have a pathogenic variant to cause the disorder. The parents of an individual with an autosomal recessive condition each carry one copy of the altered gene, but they typically do not show signs and symptoms of the condition.

In rare cases, affected individuals have a pathogenic variant in two or more genes that are associated with the condition. This can lead to more severe signs and symptoms.

When hypertrophic cardiomyopathy is part of a syndrome, it follows the inheritance pattern of that syndrome.

Other Names for This Condition

  • CMH
  • Familial hypertrophic cardiomyopathy
  • FHM
  • HCM
  • Hereditary ventricular hypertrophy
  • Idiopathic hypertrophic subaortic stenosis

Additional Information & Resources

Genetic Testing Information

Patient Support and Advocacy Resources

Clinical Trials

Catalog of Genes and Diseases from OMIM

Scientific Articles on PubMed

References

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