Brain abnormality tied to sudden infant death

updated 8:28 p.m. ET Oct. 31, 2006

CHICAGO - An abnormality in part of the brain that controls breathing, arousal and other reflexes may be what causes Sudden Infant Death Syndrome, a finding that could lead to a preventive treatment, a study said on Tuesday.

The discovery could explain why babies lying face down are more likely to die, because in that position an infant's reflexes, including head turning and arousal, are harder to trigger when breathing is challenged, the report from Children's Hospital Boston and Harvard Medical School said.

"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," said Dr. Hannah Kinney of the Boston hospital, an author of the paper.

The study, published in this week's Journal of the American Medical Association, was based on autopsy data from 31 infants who had died from SIDS and 10 who had died from other causes between 1997 and 2005 in California.

In the SIDS victims, a look at the lowest part of the brainstem, the medulla oblongata, found abnormalities in nerve cells that make and use serotonin, one of the chemicals in the brain that transmit messages between nerve cells.

Serotonin and how it is processed in the brainstem may help coordinate breathing, blood pressure, sensitivity to carbon dioxide and temperature, the report said. When babies sleep face down or have their faces covered by bedding, they are thought to breathe exhaled carbon dioxide back in, depriving them of oxygen.

When that happens the carbon dioxide increase would normally trigger nerve cells in the brainstem, which in turn stimulate respiratory and arousal centers in the brain.

Impaired reflex to breathe
"A normal baby will wake up, turn over, and start breathing faster when carbon dioxide levels rise," said Kinney. But babies with the defect die because the reflexes are impaired, she said.

Since 1994 public health officials have advised parents to put infants to sleep on their back. The campaign has cut the number of SIDS deaths in the United States in half. Despite that there were 2,162 U.S. SIDS deaths in 2003, and it is the leading cause of death in the first few months of life.

Parents have also been advised to avoid soft bedding, sharing a bed with an infant, smoking during pregnancy and smoking around a baby after birth to reduce the risk.

More education needed on back sleeping
Among the SIDS infants in the new study, 65 percent were sleeping prone or on their side at the time of death — indicating a need for continued public information on the problem, the study said.

The findings may spur development of a diagnostic test to identify infants at risk, or perhaps some day a drug or other type of treatment to protect infants with abnormal brainstem serotonin systems, the authors 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," said Duane Alexander, director of the National Institute of Health's Institute of Child Health and Human Development, which helped pay for the study.

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