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David Baxter PhD

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Clues to sudden infant death found in brain
CBC News
Wednesday, February 3, 2010

The brains of babies who died of sudden infant death syndrome show low levels of a chemical that helps regulate breathing, researchers say.

Sudden infant death syndrome (SIDS), also known as crib death, refers to the sudden and unexpected death of an apparently healthy infant under one year of age.

The latest findings, published in Wednesday's issue of the Journal of the American Medical Association, underscores the importance of sleep position.

Dr. Hannah Kinney of Harvard Medical School in Boston and her colleagues examined small tissue samples from the medulla oblongata in the brain stem, which regulates breathing, body temperature, blood pressure and heart rate. The researchers found that serotonin levels were 26 per cent lower in tissue from 34 infants who died of SIDS than in tissue from five infants of the same age who had died unexpectedly of other known causes.

No single factor
Measurements of an enzyme needed to make serotonin were also 22 per cent lower in the SIDS cases compared with the controls, the researchers found. The abnormality appeared to fit into the model that says three elements must come together in SIDS:

  1. An underlying vulnerability, possibly from low serotonin levels.
  2. Timing during the first year of life, when vital functions such as breathing are stabilized.
  3. An external stress, such as sleeping face down.
The researchers speculated that serotonin acts like an alarm clock and is a messenger that helps regulate breathing.

"Our research suggests that sleep unmasks the brain defect," Kinney said in a release. "When the infant is breathing in the face-down position, he or she may not get enough oxygen. An infant with a normal brain stem would turn his or her head and wake up in response. But a baby with an intrinsic abnormality is unable to respond to the stressor."

Prevention steps
There was no single risk factor, and in 88 per cent of the SIDS cases, there were two more risk factors, such as the infant's sleep position, an illness or exposure to cigarette smoke.

Scientists don't know why some babies have low serotonin levels. Serotonin levels can only be detected by researchers after death. Kinney hopes the findings will one day lead to a test that measures infants' serotonin levels in the blood or other tissues, but there is no such test available now.

"The current findings provide important clues to the biological basis of SIDS and may ultimately lead to ways to identify infants most at risk as well as additional strategies for reducing the risk of SIDS for all infants," added Dr. Alan Guttmacher, director of the U.S. National Institute of Child Health and Human Development, which funded the study.

Kinney advised parents to continue to remove SIDS risk factors when possible, such as:

  • Not drinking alcohol.
  • No first or secondhand smoke.
  • Putting babies on their back in a crib on a firm mattress without toys, soft pillows, excessive blankets or clothing until 12 months of age.
Each week, three babies die of SIDS in Canada, according to Health Canada.
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