Abnormalities Found in the Brains of SIDS Babies

Researchers in Boston and San Diego have found brain abnormalities in babies who've died of Sudden Infant Death Syndrome. They report in the Journal of the American Medical Association that the abnormalities appear in a part of the brain that controls breathing, heart rate and temperature.

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Each year, more than 2,000 babies under 12 months of age die of SIDS, Sudden Infant Death Syndrome. The cause is unknown. A team of researchers now has pinpointed a specific abnormality in the brains of babies who died of SIDS that may have put them at high risk for sudden infant death.

Michelle Trudeau has this report.

MICHELLE TRUDEAU: For over 20 years now, Hannah Kinney, a neuropathologist at Children's Hospital Boston, has been examining the brains of babies who've died of SIDS, trying to find a biological cause for these unexplained infant deaths. Early on, Kinney knew about a common characteristic in SIDS deaths.

Dr. HANNAH KINNEY (Neuropathologist, Children's Hospital Boston): Usually, typically, a seemingly healthy baby is found dead after sleep period, either in the early morning or after naptime.

TRUDEAU: So Kinney focused on the part of the brain called the brainstem, critical for the control of breathing, heart rate, blood pressure, temperature. It's the autopilot of our vital functions.

Dr. KINNEY: We look at it under the microscope, and we'd look for differences between SIDS and babies who've died of known causes like accidents and infection.

TRUDEAU: In the study, there were 31 SIDS cases and 10 control cases.

Dr. KINNEY: And as a group, on average, the SIDS cases have significant differences from those control groups.

TRUDEAU: The significant differences seen in the brainstem involved what's called the serotonin system, a network of nerve cells that produce the chemical messengers serotonin. In the brainstems of SIDS babies, the serotonin systems had run seriously amok in a number of ways. There were too many serotonin secreting cells, some serotonin cells hadn't matured properly and other defects. And this was particularly true in baby boys who died of SIDS.

Their serotonin receptors had even greater defects than baby girls. This may help explain why more boys die of SIDS. So overall, the serotonin system in the brainstem of SIDS babies, boys and girls, seem to have been poorly built and not working well. Marian Willinger directs the government's SIDS program at the National Institute of Child Health and Human Development.

Dr. MARIAN WILLINGER (SIDS Expert, National Institute of Child Health and Human Development): This is the best data that that we have that says here is a biologic abnormality in the SIDS baby that could make it vulnerable to an environmental risk.

TRUDEAU: Over the years, several environmental risks have been identified. Mothers who smoke or drink is one. An infant co-sleeping with parents is another. But the most potentially deadly risk factor is putting a baby to sleep on its stomach or side. Hannah Kinney reports in her study that 75 percent of the SIDS babies were on their stomachs or sides when they died.

Dr. KINNEY: If a baby has a serotonin defect, is lying on its stomach with its face down in soft bedding, it would re-breathe stale air. These chemical changes would not signal the baby to wake up and turn its head like a normal baby, and the baby would go on to die of SIDS.

TRUDEAU: The study suggests that a defective serotonin system in a baby's brainstem plus sleeping prone maybe a lethal combination for some infants. Yet, the full chain of events that leads to a SIDS death requires much more research to unravel. For in this study, a quarter of the SIDS babies with brainstem abnormalities nevertheless died while sleeping on their backs. This study is published in the Journal of the American Medical Association.

For NPR News, I'm Michelle Trudeau.

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