Genetic Classification of Cardiomyopathies

According to the Pediatric Cardiomyopathy Registry, cardiomyopathies with a genetic origin can be classified in four main categories. These include both primary (affecting only the heart) and secondary (resulting from another disease) forms of cardiomyopathy.

Familial or Inherited

This category includes primary cardiomyopathies that are isolated to the heart and caused by a genetic mutation that is passed down from generation to generation. Familial or inherited cardiomyopathies account for 24 percent of pediatric cardiomyopathy cases with a known cause. Familial forms exist for:

  • Dilated cardiomyopathy
  • Hypertrophic cardiomyopathy
  • Restrictive cardiomyopathy
  • Arrhythmogenic right ventricular cardiomyopathy

The same genetic mutation may be present in all affected members of a family, but severity and progression of the disease can vary considerably from person to person. One family member may be barely affected, while another may have severe complications. In some families it may appear that the genetic mutation skips a generation, when in fact a family member does have the mutation but it has not expressed itself. That person will not have any symptoms and the echocardiogram will appear normal.

Neuromuscular Disorders

Neuromuscular diseases include those affecting the nerve or skeletal muscles. Common symptoms are decreased muscle tone, weakness during infancy, loss of motor control, decreased muscle relaxation and decreased muscle bulk. These include:

  • Muscular dystrophies (Duchenne and Becker)
  • Congenital myopathies
  • Metabolic myopathies
  • Ataxias (Friedreich Ataxia)

Such diseases account for 22 percent of pediatric cardiomyopathy cases with a known cause.

Metabolic Disorders

Inborn errors of metabolism account for 16 percent of pediatric cardiomyopathy cases with a known cause. This category includes:

  • Mitochondrial abnormalities (MELAS, MERRF, respiratory chain diseases, mitochondrial myopathies)
  • Fatty acid oxidation disorders (carnitine deficiency, VCHAD, LCHAD, LCAD, MCAD)
  • Gaucher’s disease
  • Pompe disease
  • Barth syndrome

With all these diseases, there is a problem with the body’s energy production and the body cannot process enough energy to meet its needs. This puts excess strain on the heart leading to heart failure. Usually patients appear to be physically normal in early childhood, but as the body’s energy metabolism continues to be impaired, toxic substances may accumulate throughout the body leading to multiple organ failure. Common symptoms include muscle weakness, decreased muscle tone, growth retardation, developmental delays, failure to thrive, constant vomiting and lethargy. In advanced stages, the child may have low blood sugar, exhibit stroke like symptoms and experience seizures.

In contrast, patients with lysosomal storage diseases such as Pompe, Cori, and Andersen cannot break down glycogen, the storage form of sugar. These syndromes are characterized by problems with growth, brain dysfunction, decreased muscle tone, muscle weakness, and symptoms of heart failure.

Malformation Syndrome

Malformation syndromes are characterized by minor and major physical abnormalities with distinctive facial features. Noonan syndrome is the most common form associated with HCM. Common symptoms include short stature, webbed neck, wide-set eyes, low-set ears and extra skin folds. Malformation syndromes account for 10 percent of pediatric cardiomyopathy cases with known causes.

Associated Genetic Disorders

 

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