Hypertrophic cardiomyopathy is characterized by an abnormal growth of muscle fibers on the heart muscle. This abnormal growth may result in the thickening and stiffening of the septum – a muscular structure separating the right and left ventricles. Because of the rigidity of the muscle, the ventricle cannot relax properly and the mitral valve may be compromised. The ejection fraction may be higher than normal (60 to 90 percent). Although most patients with hypertrophic cardiomyopathy never experience symptoms, the condition may result in heart failure, sudden cardiac death, stroke, arrhythmias and other cardiac events.

Hypertrophic cardiomyopathy is generally considered a genetic disease. It is an autosomal dominant condition. “Autosomal” means that it can occur in either males or females. “Dominant” basically means that there is a 50 percent chance that a child will inherit a condition (at conception) if one parent has the condition, or a 75 percent chance if both parents have the condition.

Although it runs in families, the nature of the disease may vary widely among family members having the condition. For example, a parent may have only minor hypertrophy and few – if any – symptoms, while a sibling or older child may have pronounced thickening and more obvious symptoms. Symptoms are rare in young children and, if they are going to develop, they tend to appear in the teen years.

Currently, about 150 different genetic mutations have been identified for hypertrophic cardiomyopathy. A mutation is an alteration of a region of DNA on a gene. The mutations in hypertrophic cardiomyopathy affect proteins involved in normal contraction of heart muscle. Genetic mutations can be either inherited or occur spontaneously during fetal development.

While genetic factors are known to play a role in the development of hypertrophic cardiomyopathy, researchers are still working to identify the complex interaction between genes that results in the condition. For example, researchers have linked hypertrophic cardiomyopathy with irregularities in the connective tissue of the heart, which are arranged in a disorganized and abnormal pattern. Ultimately, genetic testing might enable physicians to better understand why the disease is so variable, even among family members, and better design treatments.