There are multiple causes for cardiomyopathy, but it is not always easy to identify the exact cause in children. According to the Pediatric Cardiomyopathy Registry, up to two-thirds of diagnosed children do not have a known cause. When the cause of the heart muscle damage is unknown, it is called idiopathic.
Cardiomyopathy can be inherited or acquired. In most cases, cardiomyopathy is congenital and caused be genetic mutations that are inherited from one or both parents. The disease can also be caused by mutations that occur sporadically, where there is no family history of the disease. When cardiomyopathy is acquired after birth, it develops from another disease, condition, or an external factor.
Cardiomyopathy in children is usually classified by a genetic cause: 1) myocarditis and other viral infections, 2) familial or inherited, 3) associated neuromuscular disorders, 4) associated metabolic disorders, and 5) associated malformation syndromes. Children can be screened for cardiomyopathy and associated cardiomyopathy disorders with genetic testing. A geneticist can recommend the appropriate panel tests and genetic testing company to use.
There are close to 100 genetic mutations that can cause cardiomyopathy in children. Deoxyribonucleic acid (DNA) is the hereditary material that carries a persons genetic information and is located in a cell. Genes are segments of DNA that provide instructions to the body on how to function. When there are genetic mutations associated with cardiomyopathy, the DNA is altered and specific proteins that control the function of the heart are affected. This change in instruction affects how the heart pumps blood through the body.
Genetic mutations may result in either primary cardiomyopathies affecting only the heart muscle or secondary cardiomyopathies that affect different areas of the body along with the heart. Secondary cardiomyopathies are usually linked to genetic disorders, such as Noonan syndrome, Barth syndrome, Duchenne muscular dystrophy, and certain fatty acid oxidation disorders. These disorders often require specialized evaluation and testing by other specialists.
Cardiomyopathy can be inherited in three ways:
- Autosomal Dominant: A parent carrying a genetic mutation has a 50 percent chance of passing the mutation on to a child of either gender. The parent may either be diagnosed with cardiomyopathy or may be a carrier without the disease manifesting.
- Autosomal Recessive: Both parents carry a genetic mutation that when combined can cause secondary cardiomyopathy in their child. A child of either gender has a 25 percent chance of inheriting both mutations and developing the disease.
- X-linked: A parent has a 50 percent chance of passing on a genetic mutation on the X chromosome to a child of either gender. More commonly, sons will present with the disease and daughters will be carriers without the disease manifesting.
An Overview of Inheritance for Cardiomyopathies is a resource that was jointly developed by the Childrens Cardiomyopathy Foundation and the American Heart Association. It provides detailed information on inheritance patterns.
Cardiomyopathy may be caused by external factors or other non-genetic diseases. The most common cause of acquired cardiomyopathy is myocarditis, a viral infection that weakens the heart muscle. In such cases, a virus such as Coxsackie B causes the body's immune system to malfunction leading to inflammation of the heart muscle.
In other cases, children with cancer who undergo chemotherapy may develop cardiomyopathy. Drugs (doxorubicin and daunorubicin) used to treat cancer can be toxic to the heart and cause heart muscle damage and problems with the hearts pumping ability.
Other causes of acquired cardiomyopathy include:
- Cardiovascular conditions (congenital heart defect, Kawasaki)
- Inflammatory or infectious diseases
- Immunological diseases
- Toxin reactions (drug, alcohol, metal, radiation exposure)
- Obesity or nutritional deficiencies
- Connective tissue and autoimmune disease (Ehlers Danlos, scleroderma)
- Endocrine diseases
It is not known whether genetic factors may increase the risk of myocarditis or anthracycline-induced cardiotoxicity in children.