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Low Serotonin Levels May Be Key to SIDS

Study Shows Link Between Sudden Infant Death Syndrome and Deficiency of Hormone Serotonin
WebMD Health News
Reviewed by Louise Chang, MD

Feb. 2, 2010 -- Lower levels of the hormone serotonin may help explain why some infants succumb to sudden infant death syndrome (SIDS), according to a new study.

In the U.S., SIDS deaths have declined by more than 50% since 1990. Experts say that's partly due to practices believed to minimize the risk, such as putting infants to sleep on their backs rather than their stomach and avoiding soft bedding, which could lead to asphyxiation.

But SIDS is still the leading cause of death among infants age 1-12 months, accounting for about 2,750 U.S. deaths annually. It's defined as the death of an infant before his or her first birthday that can't be explained even after a complete autopsy, investigation of the death scene and circumstances, and a review of the medical history of the child and family.

Now, the new research suggests that a deficiency of serotonin in the brain stem (which controls vital functions during sleep, such as breathing, heart rate, and blood pressure) may help explain most of the deaths, says study researcher Hannah Kinney, MD, a professor of pathology at Harvard Medical School and a neuropathologist at Children's Hospital Boston.

"It is not going to explain all SIDS deaths," Kinney tells WebMD. However, she adds, "it will explain the majority." Her study is published in the Journal of the American Medical Association.

Explanations for SIDS

SIDS research is a ''controversial area," Kinney says. Many experts look to the "triple risk" model to explain it, believing that SIDS results from an underlying vulnerability, a critical developmental period, and an outside stressor.

''The real risk period is the first six months," Kinney says of the critical period in which most deaths occur.

But experts disagree on what the vulnerability is. Kinney's research suggests low levels of the neurotransmitter serotonin, and probably other brain chemicals yet to be identified, are what make infants vulnerable. Other experts suspect other vulnerabilities, such as infections.

Yet others say SIDS is due simply to suffocation, she says. "We say, yes, some babies will die if they are severely asphyxiated," Kinney tells WebMD. But she adds, "what we are saying is in the majority of cases, the babies have an underlying defect that puts them at risk that makes them unable to respond to a stressor, such as having their face compressed [while sleeping on the stomach or becoming tangled in soft bedding]."

In previous research, Kinney and her colleagues found defects in the serotonin system of SIDS babies, including defects in the serotonin receptors, which are crucial for serotonin to work.

''But we never knew if there was too little or too much serotonin," she says. "In this study, we actually measured the levels of serotonin and the enzyme that makes serotonin."

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