One Disease, Many Causes

In some, dilated cardiomyopathy may occur sporadically in only one family member who develops the disease, but the cause of the disease is genetic in nature. In other families, dilated cardiomyopathy is due to causes, such as:

• Disease of the arteries of the heart, due to high cholesterol, smoking, inactivity, genetics, and other factors;
• Disease of the valves of the heart, due to age, infection, structural changes present since birth, or other factors;
• Diabetes
• High blood pressure (hypertension)
• Infections of the heart muscle (myocarditis)
• Drugs or medications toxic to the heart (cocaine, amphetamine, certain cancer drugs)

In young patients, dilated cardiomyopathy is often due to an underlying genetic change.  This has important implications for a patient's siblings, children, and parents. Additionally, in some cases, other organ systems may be affected due to the same genetic change.

In as many as 40% of all patients with dilated cardiomyopathy, a family member who also has cardiomyopathy is identified. These families are often found to have a genetic cause of disease.

Familial dilated cardiomyopathy changes in the heart

Familial dilated cardiomyopathy is most often due to underlying genetic abnormalities in the muscle cells of the heart (cardiomyocytes).

These heart muscle cells, which are the fundamental units of the heart, contract (shorten) every time your heart beats – over 3 billion times over the average American human lifetime. Even small changes in how these cells function, over time, can lead to weakness of the heart and heart failure. These changes also lead to abnormalities in the structure of the heart, as the heart muscle cells are replaced by fibrous tissue or fatty tissue. Hearts that have a lot of fibrous or fatty tissue do not contract as well as hearts with mostly muscle cells.

Over time, these hearts weaken and dilate. These dilated hearts are also more prone to bad heart rhythms (arrhythmias) that can lead to symptoms or early sudden death.

Genetics of familial dilated cardiomyopathy

Familial dilated cardiomyopathy is caused by a mutation in one of many genes. Genes, which are present in every cell of your body, encode for RNA and protein, which are the fundamental building blocks of the cell. A single mutation in one gene leads to changes in the code that makes a protein. This in turn may affect the function of the cells in which that protein is found. There are many genes, which when mutated, may cause dilated cardiomyopathy. 

Most of these gene mutations are inherited in a dominant fashion, meaning that family members sharing just one copy of the mutated gene are at risk for developing overt signs of disease. For other genes, inherited in a recessive fashion, two mutations are required to develop disease. Other forms of inheritance are also seen in families presenting with dilated cardiomyopathy. 

Learn more about genetic testing.