Familial hypertrophic cardiomyopathy: A genetic disorder of the heart characterized by increased growth (hypertrophy) in thickness of the wall of the left ventricle, the largest of the four chambers of the heart.

Familial hypertrophic cardiomyopathy (FHCM) can surface any time in life. It may, in a worst-case scenario, lead to death. One in about 500 people have FHCM. Five to 10%of people with FHCM suffer fatal cardiac arrest. It is the leading cause of sudden death in athletes and young people.

Former US Defense Secretary Les Aspin died in 1995 at 56 from a stroke linked to the disorder. John Stewart, a 7-foot University of Kentucky basketball recruit, collapsed and died of the disease during a high school tournament game in 1999.

A measurement of the thickness of the left ventricle wall can predict who is most at risk for FHMC. The test is done by echocardiography, a routine ultrasound test of the heart. Persons with a maximum wall thickness less than three-quarters of an inch (19 mm) are virtually free of risk for fatal cardiac arrest over 20 years whereas those with a wall thickness more than 1.2 inches (30 mm) have a 40% chance of fatal cardiac arrest during that time period. Patients in danger can be fitted with implantable defibrillators, which can shock a spasmodic heart back to life.

The disease exhibits an autosomal dominant pattern of inheritance. Men and women with FHCM stand a 50-50 chance of transmitting the FHCM gene to each of their children. There are various kinds of FHCM (symmetrical, asymmetrical forms, etc.). Genes for the disorder have been mapped to chromosomes 14q12 and 15q14.

FHCM is also known by other names including hypertrophic cardiomyopathy (HCM), hereditary ventricular hypertrophy, asymmetrical septal hypertrophy (ASH), and hypertrophic subaortic stenosis.