SIDS is the sudden death of an infant under one year of age which remains unexplained after a thorough case investigation, including a complete autopsy, examination of the death scene, and review of the medical history.

According to the American Sudden Infant Death Syndrome Institute, SIDS is the leading cause of death among infants 1 to 12 months old. It kills about 2,500 infants each year in the United States.

SIDS remains unpredictable despite years of research. Since 1983, the rate of SIDS has fallen by over 50 percent. However, there are still about 2,500 deaths per year in the United States and thousands more throughout the world.

Over the years, researchers have ruled out a number of possible causes of sudden infant death syndrome, including suffocation, vomiting or choking, birth defects and infection.

Exactly why SIDS occurs remains a mystery, but many experts believe multiple factors are involved.

It is likely that an infant must have some sort of biological vulnerability, such as a heart or brain defect, combined with an environmental stressor, such as stomach sleeping, and be in a critical developmental period before SIDS can occur. The mother's health and behavior during pregnancy may also play a role.

When a sudden death occurs in someone over 12 months of age, it is referred to as Sudden Unexplained Death Syndrome (SUDS).

Now scientists at the Montefiore-Einstein Center for Cardiogenetics in New York, N.Y., have identified genetic mutations that contribute to Long QT Syndrome (LQTS) could cause the heart to malfunction electrically, and result in unexplained deaths like SIDS or SUDS. LQTS is an inherited disease that leads to palpitations, seizures, fainting or sudden death because the heart cannot pump blood efficiently.

The Montefiore-Einstein Center for Cardiogenetics offers a genetic test for LQTS to those who have lost a loved one due to SIDS or SUDS.