SIDS Infants Show Brain Abnormalities

Sudden infant death syndrome (SIDS) is the sudden and unexpected death of an infant under one year of age that can’t be explained after an autopsy, an investigation of the scene and circumstances of the death, and a review of the medical history of the infant and family. Typically, the infant is found dead after having been put to sleep and shows no signs of having suffered. Researchers have now found that infants who die of SIDS have abnormalities in the brainstem, a part of the brain that helps control such basic functions as breathing, heart rate, blood pressure, body temperature and arousal.

Researchers had hypothesized that abnormalities in the brainstem may make an infant vulnerable to life-threatening challenges during sleep such as high carbon dioxide and low oxygen levels or elevated body temperature. Dr. Hannah Kinney at Children’s Hospital in Boston and her colleagues found evidence in previous studies that the brainstems of SIDS infants had alterations in their receptors for serotonin. Serotonin is one of the neurotransmitters, which serve to relay messages between neurons (nerve cells). It’s best known for its role in regulating mood, but it also plays a role in regulating vital functions like breathing and blood pressure.

Dr. David Paterson, a researcher in Kinney’s laboratory, led a group that set out to further investigate the role of serotonin in SIDS. The group examined tissue from the brainstems of 31 infants who died of SIDS and ten who died of other causes. The tissue was provided by the office of the chief medical examiner in San Diego, California. The study was supported by NIH’s National Institute of Child Health and Human Development along with other sources.

In the November 1, 2006, issue of Journal of the American Medical Association, the team reports that brainstems from SIDS infants contained more neurons that manufacture and use serotonin than the brainstems of comparison infants. At the same time, however, there are lower levels in those neurons of two key proteins involved in receiving and recycling serotonin.

The researchers also found that male SIDS infants had fewer serotonin receptors than either female SIDS infants or the comparison infants. This finding may provide insight into why SIDS affects roughly twice as many males as females.

"These findings provide evidence that SIDS is not a mystery but a disorder that we can investigate with scientific methods and, some day, may be able to identify and treat,” Kinney said.

Dr. Duane Alexander, Director of NICHD, said, “This finding lends credence to the view that SIDS risk may greatly increase when an underlying predisposition combines with an environmental risk — such as sleeping face down — at a developmentally sensitive time in early life.”

Research has shown that placing an infant to sleep on his or her stomach greatly increases the risk of SIDS. The NICHD-sponsored “Back to Sleep” campaign urges parents and caregivers to place infants to sleep on their backs to reduce SIDS risk