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Heart Disease
  What Is Hypertrophic Cardiomyopathy?

By Stephanie Trelogan, MS

Reviewed by Andy Avins, MD and Christopher Friedrich, MD, PhD





In hypertrophic cardiomyopathy, the heart muscle cells become enlarged. In fact, the word "hypertrophy" literally means enlargement. This enlargement results in a thickening of the walls of the heart, which then prevents the heart from functioning properly.

 
 
 

Who Gets Hypertrophic Cardiomyopathy?

Hypertrophic cardiomyopathy occurs in no more than 2 out of 500 people.
Hypertrophic cardiomyopathy is relatively rare, occurring in no more than 0.2 percent of the US population, or 2 in 500 people. It can affect men and women of all ages. Most cases of hypertrophic cardiomyopathy are inherited. However, some cases occur when there is no family history of disease.

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Signs and Symptoms

People with hypertrophic cardiomyopathy often have no signs of the disease.
Hypertrophic cardiomyopathy varies widely in its initial symptoms and in how the disease progresses. Many people remain stable after diagnosis and others improve. However some people have worsening symptoms and lead severely restricted lives. In many cases, the disease results in congestive heart failure.

People with hypertrophic cardiomyopathy are also at risk of cardiac sudden death, in which a person's heart gives out suddenly. Cardiac sudden death is different than a heart attack because a heart attack is specifically caused by arteries leading to the heart becoming clogged. In cardiac sudden death, the heart simply stops beating. Because people with hypertrophic cardiomyopathy often have no symptoms, sudden death can sometimes be the first and only sign of disease. Of those adults who are actually diagnosed, only 50 percent have symptoms. The others are diagnosed during regular screening in people with a family history of the disease or when an abnormality is detected during a test for something else.

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What Causes Hypertrophic Cardiomyopathy?

The heart muscles are highly adaptive and can enlarge when they are being strained either by heart valves that don't function properly or by high blood pressure. These enlarged muscles make the heart walls thicker and able to beat stronger. However, the thickening can also obstruct blood flow. Normally, the heart will return to its normal size if the strain subsides, for example if you get your blood pressure under control.

The heart muscles' ability to regulate its thickness is controlled by specific genes. Genetic mutations in these genes cause hypertrophy even when the heart is not being strained. This inappropriate thickening of the heart muscles is what happens in genetic cases of hypertrophic cardiomyopathy.

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Genetics of Hypertrophic Cardiomyopathy

Sixty to seventy percent of hypertrophic cardiomyopathy is inherited.
People can develop hypertrophic cardiomyopathy in two ways. In some cases, they can develop what is called a sporadic case of hypertrophic cardiomyopathy, which is not inherited from either parent. However, 60 to 70 percent of people develop hypertrophic cardiomyopathy by inheriting a gene that predisposes them to the disease. These mutations are inherited in an autosomal dominant fashion. This means that a person only has to inherit a mutated version of the gene from one parent in order to be at risk.

Researchers have identified several genes that can cause hypertrophic cardiomyopathy. Of these genes, four are well characterized and a fifth gene has not yet been identified, but researchers know that it is located on chromosome 7. All of the genes identified so far are part of the mechanism that allows the heart muscle to contract. They are:

  • Beta-myosin heavy chain (MYH7)
  • Alpha-tropomyosin (TMSA)
  • Cardiac troponin-T (TNNT2)
  • Myosin binding protein C (MYBPC).
  • Unidentified gene on chromosome 7 (CMH5)
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Genetic Testing

Commercial genetic testing is not yet available for mutations that predispose a person to hypertrophic cardiomyopathy. Instead, if you have a strong family history of hypertrophic cardiomyopathy, your doctor will probably recommend that you follow the same advice as people in the general populations. That is, don't smoke, watch your weight, and exercise regularly. Your doctor may also recommend a more frequent screening schedule than for people in the general population.

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More on Screening for Heart Disease (Coming Soon)

Treatment

In most cases, doctors can't treat cardiomyopathy once it develops. Instead, they treat symptoms of congestive heart failure, which may include drugs, hospitalization, or heart transplant.

If the cardiomyopathy blocks blood from passing through the heart, surgery that removes the blockage can ease symptoms in about 70 percent of people, but results in death in about 1 to 3 percent. Also, about five percent of those who have surgery develop a slow heartbeat, which can be corrected with a pacemaker.

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References

Carrier, L., et al. (1993) Mapping of a novel gene for familial hypertrophic cardiomyopathy to chromosome 11. Nature Genetics, 4, 311–313.

Coonar, A. S. and McKenna, W. J. (1997) Hypertrophic Cardiomyopathy. In P. A. Poole-Wilson, et al. (Eds.), Heart Failure. (pp. 379–399). New York, NY: Churchill Livingstone, Inc.

MacRae, C.A., et al. (1995) Familial hypertrophic cardiomyopathy with Wolff-Parkinson-White syndrome maps to a locus on chromosome 7q3. Journal of Clinical Investigation, 96, 1216–1220.

Thierfelder, L., et al. (1994) Alpha-tropomyosin and cardiac troponin T mutations cause familial hypertrophic cardiomyopathy: a disease of the sarcomere. Cell, 77, 701–712.

Watkins, H., et al. (1995) Mutations in genes for cardiac troponin T and alpha-tropomyosin in hypertrophic cardiomyopathy. New England Journal of Medicine, 332, 1058–1064.

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