Babies who die of sudden infant death syndrome have abnormalities in the part of the brain that helps control functions like breathing, blood pressure and arousal, says a study being published in Wednesday's issue of the Journal of the American Medical Association.

The syndrome, known as SIDS, involves the sudden and unexplained death of an infant under one year of age. Typically, a baby is found dead after having been put to sleep and shows no sign of having suffered. Although studies have identified risk factors for SIDS, such as putting infants to bed on their stomachs, there has been little understanding of the syndrome's biological causes.

According to the National Institutes of Health, which funded the study, the new finding is the strongest evidence to date suggesting that innate differences in a specific part of the brain may place some at increased risk for the syndrome. To reach that conclusion, researchers examined the brains of 31 babies who had died of SIDS and 10 who had died from other causes.

They found that abnormalities in the brain stem appear to affect the ability to use and recycle a chemical called serotonin, which is responsible for regulating mood as well as vital body functions.

When babies sleep face-down or have their faces covered by bedding, they are thought to breathe in the just-exhaled carbon dioxide, therefore taking in less oxygen. Normally, the rise in carbon dioxide activates nerve cells in the brain stem that stimulate respiratory and arousal centers in the brain. A normal baby would wake up, turn over and start breathing faster, but one with a defective serotonin system wouldn't receive the warning signals.

"The findings show that SIDS is not a mysterious occurrence that happens and nobody really knows why," said the lead author of the study, Dr. David Paterson, of the Children's Hospital Boston and Harvard Medical School.
He said this conclusion is important, particularly for parents who often blame themselves for the infant's death.
"This data here is something that really says 'No, (parents) didn't do anything to cause this.' This is a disease and they are not responsible for the disease."

Paterson, however, said results from the study suggest that known risks for SIDS contribute to the deaths. About 48% of the SIDS victims in the study were found sleeping on their stomachs, while 29% were found face down and 23% were sharing a bed at the time of death.

According to the researchers, the results also help explain why the syndrome occurs twice as often in males than females, as male SIDS victims studied had smaller numbers of a type of serotonin receptor than did female SIDS babies.
Paterson said the next step is to develop a diagnostic test to identify infants at risk for the syndrome.
He acknowledged, however, that treatment is far from becoming a reality because it isn't yet known what kind of defect is present in the serotonin system of those who die of the syndrome, and even whether they produce more or less of the chemical than normal.

Antidepressants such as Prozac address serotonin imbalances, but Paterson said "it is far too early to say that it will be something like Prozac that we would use, because we don't really know what is going on."
In the meantime, the study suggested that "prenatal insults" like smoking and alcohol use may influence the development of the serotonin system in babies, and that parents should follow all guidelines available to ensure they are raised in a healthy environment.

SIDS is the leading cause of death in U.S. infants after the newborn period, affecting one out of every 1,500 live-born babies.

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