Sometimes inherited heart disease strikes very early in life. Jim D. died at 4 days of age, two days after suffering cardiac arrest. Two years later, his parents had another son. Like Jim, Kerry seemed normal at birth, but at 36 hours of age his heart rate plummeted, he had a seizure, and he stopped breathing. He was resuscitated. A blood test revealed excess long-chain fatty acids, indicating a metabolic disorder, an inability to utilize fatty acids. Lack of food triggered the symptoms because the boys could not use fatty acids for energy, as healthy people do. Kerry was able to survive for three years by following a diet low in fatty acids and eating frequently. Once he became comatose because he missed a meal. Eventually, he died of respiratory failure.

Kerry and Jim had inherited a deficiency of a mitochondrial enzyme that processes long-chain fatty acids. Because this is a primary energy source for cardiac muscle, their tiny hearts ultimately failed. There are several other types of inborn errors of cardiac energy metabolism.

The human genome project--an ongoing worldwide effort to describe all human genes--is revealing the genetic underpinnings of many illnesses that affect the cardiovascular system. Medical geneticists begin by gathering members of families with a specific illness, then identifying a particular DNA sequence that ill relatives have in common but healthy individuals lack. Finding this gene then leads to finding the protein it encodes. The protein abnormality or absence may explain the illness--at the molecular, cellular, tissue, organ, and organismal levels.

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