November 19, 2002
IL (AHA) – 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 at the American Heart Association's Scientific Sessions
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.
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.
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.
can be fatal within minutes unless the heart’s electrical
pattern is restored spontaneously or with the aid of a
defibrillator, he says.
suggest long Q-T syndrome may affect as many as one in 5,000,
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.
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.
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.
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."
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.
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.