Nearly 10 percent of sudden infant death syndrome (SIDS) victims have mutations or variations in genes associated with potentially lethal heart rhythms (arrhythmias), according to two newly published studies involving Vanderbilt researchers.

Arrhythmia-susceptibility genes represent important genetic contributors to SIDS, said Alfred L. George Jr., M.D., senior author on one of the studies.

According to the Centers for Disease Control and Prevention, approximately 2,200 deaths each year in the United States are attributed to SIDS, making it the third leading cause of death among all infants, but the leading cause of mortality in infants age 1 month to 1 year. Several behavioral and environmental factors – such as prone (stomach) sleeping position and exposure to cigarette smoke – are known risk factors.

 

Campaigns to educate parents about these potential dangers may explain the decrease in SIDS since the early 1990s.

However, SIDS continues to be a leading cause of infant mortality in developed countries, and the underlying basis of the condition remains unclear. A popular theory proposes that SIDS occurs because of a combination of risks including abnormal physiological state, environmental factors and developmental vulnerabilities. Genetic factors have also been proposed to be important.

“SIDS is not one disease,” said George, the Grant W. Liddle Professor of Medicine and director of the Division of Genetic Medicine. “Multiple conditions can increase the risk of sudden death in an infant. Some have been identified, but many have not.”

Some SIDS victims carry mutations in genes associated with conditions such as the long QT syndrome (LQTS) that predispose individuals to life-threatening arrhythmias and sudden death. New results showed that 9.5 percent of SIDS victims harbored mutations in genes associated with inherited forms of cardiac arrhythmia, such as LQTS.

The findings also suggest that there may be strategies to identify whether infants are a carrier of one of these mutations before the tragic event of their death, George said.

Inherited arrhythmias are manageable conditions that can be treated with medications or implantable devices, George said.

“There’s potentially an infant death every other day in the U.S. due to this problem (arrhythmias),” he said. “This is critical because knowing how often mutations are transmitted from parents rather than occur spontaneously, will help establish the risk to siblings of SIDS victims,” he said.

George hopes that eventually, all of the causes of SIDS – environmental, developmental and genetic factors – will be identified. 

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