Heart gone haywire blamed in some sudden infant deaths

November 19, 2002

CHICAGO, Nov. 19 - The world's first comprehensive population-based genetic autopsy suggests that an electrical problem in the heart may cause one out of 20 cases (5 percent) of sudden infant death syndrome (SIDS), researchers reported today at the American Heart Association's Scientific Sessions 2002.

The problem is similar to a heart condition called long Q-T syndrome that contributes to sudden death in young people and adults. In long Q-T syndrome, the heart electrically recharges itself too slowly or in a disorganized fashion in preparation for the next heartbeat, says lead author Michael J. Ackerman, M.D., Ph.D., an assistant professor at the Mayo Clinic in Rochester, Minn. When combined with a trigger, such as intense emotion or physical exertion, a long Q-T heart can go out of control and cause cardiac arrest and sudden death.

"This often explains cases in which children die suddenly while playing in the sandbox, teen-agers die of unexplained drowning, or previously healthy young adults die suddenly while jogging or shoveling snow," he explains.

Cardiac arrest can be fatal within minutes unless the heart's electrical pattern is restored spontaneously or with the aid of a defibrillator, he says.

Current estimates suggest long Q-T syndrome may affect as many as one in 5,000, says Ackerman.

According to U.S. Vital Statistics, about 3,000 infants die each year of SIDS, defined as the sudden and unexplained death of an infant less than one year old. Several possible causes or triggers have been suggested for SIDS, including babies sleeping on their stomachs, nervous system problems related to breathing, abnormal metabolism in the liver and flaws in the heart's electrical channels, he says.

The electrical or ion channels are proteins critical to orchestrating the electrical signals that prompt the heart to squeeze (beat) and refill between each heartbeat, says Ackerman, who is also director of the Mayo Clinic's sudden death genomics lab and the long Q-T syndrome clinic.

Ackerman's team performed a genetic autopsy on every unexplained infant death investigated by the Arkansas State Crime Laboratory between September 1997 and August 1999 - a total of 93. Researchers extracted DNA from frozen heart tissue and studied the five genes linked to long Q-T syndrome.

The researchers found 21 different mutations in the five candidate genes in 32 percent (30 children). About 5 percent (4) of SIDS cases had genetic anomalies that were absent in the genes of 200 healthy, racially matched control subjects.

"Long Q-T syndrome is sometimes called the perfect killer, because it leaves no clues," says Ackerman. "Neither does SIDS. Our goal is to discover the truth. SIDS will probably turn out to have 20 different underlying causes," he says. "If we can figure out what they are, we can screen for them and hopefully one day, prevent future cases of SIDS."

Although these findings are beginning to shed light on the causes of SIDS, there is no routine clinical test to screen for such cardiac causes, Ackerman explains. He says parents should continue to follow simple preventive measures that have decreased the frequency of SIDS: 1) don't place a baby on his/her stomach to sleep, 2) don't expose a baby to cigarette smoke and 3) don't cover a baby with heavy blankets.

He says medical examiners must begin to collect and store tissue in a way that enables a molecular autopsy in sudden infant deaths.
Co-authors are David J. Tester; Carla M. Bell; Jeffrey A. Towbin, M.D.; Craig T. January, M.D., Ph.D.; Jonathan C. Makielski, M.D.; and William Q. Sturner, M.D.

American Heart Association

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