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Hormone Deficiency Could Cause Sudden Infant Death Syndrome01:49

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Sudden Infant Death Syndrome is the leading cause of death for babies between one month and 12 months old. But why some infants who seem totally healthy suddenly die in their sleep has mystified researchers for years. Now, a new study out of Children's Hospital Boston finds a possible reason.

Sudden Infant Death Syndrome seems like a bolt out of nowhere. A happy, active baby falls asleep and just doesn't wake up.

But Dr. Hannah Kinney, a neuropathologist at Children's Hospital, led a group of researchers who studied the brain stems of babies who had died of SIDS and found something striking: they had abnormally low levels of serotonin. Serotonin is a neurotransmitter that helps regulate breathing, heart rate and blood pressure during sleep.

Low serotonin levels aren't a problem when a baby is awake, "but when the baby goes to sleep, we feel there's something that unmasks the serotonin defect with sleep itself," said Dr. Kinney, who is also a professor at Harvard Medical School.

What Parents Need To Know

Dr. Hannah Kinney, the lead researcher on a new study of Sudden Infant Death Syndrome, says parents should follow national recommendations to reduce the risk of SIDS.

  • Put a baby to sleep on its back
  • Use a safety-approved crib, with a firm mattress and fitted sheet
  • Don't put a baby to sleep on a chair, sofa, water bed, cushion or sheepskin
  • The safest place for a baby to sleep is within an arm's reach of the parent's bed
  • If bumper pads are used, they should be thin, firm and well-secured
  • If blankets are used, they should be tucked in and not reach higher than a baby's chest
  • Keep pillows, quilts, comforters, sheepskins and stuffed toys out of the crib
  • Use light sleep clothing so that a baby doesn't get too warm
  • Pacifiers may help, but shouldn't be forced upon a baby. If breastfeeding, wait until baby is one month old before pacifier use
  • Give a baby plenty of "tummy time" while awake to strengthen neck muscles and avoid flat head spots
  • Avoid smoking and drinking during pregnancy
  • Share sleep information with anyone who cares for a baby

SOURCE: American Academy of Pediatrics

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Babies with too little serotonin can have trouble when they sleep. They're at risk, for example, of re-breathing their own carbon dioxide if they're sleeping in a face-down position.

When a normal baby starts to inhale its carbon dioxide, "the baby raises its head, it stirs, it wakes up and its airway is protected," Dr. Kinney explained. "But if there's a defect in the neurotransmitter system, then the baby can't arouse and goes on to die."

Dr. Kinney said that's why putting babies to sleep face-up is safer than letting them sleep on their bellies.

Low serotonin levels can also be deadly if a baby is bundled too tightly in a blanket, because a normal baby can cool off by sweating, but a baby without enough serotonin can overheat and die.

Dr. Kinney now wants to find out why some babies have low serotonin levels. She also wants to devise a method for testing if living infants don't have enough serotonin, and a method for treating that problem.

Finally, she wants to develop a diagnostic test that could be done during autopsies of babies who die while sleeping so that medical examiners can determine if their deaths were due to a serotonin deficiency.

"But all those things are decades away from where we are now," Dr. Kinney said.

Still, some steps can be taken now to reduce the risk of Sudden Infant Death Syndrome.

Marian Willinger, who oversees SIDS research at the National Institutes of Health, said parents can take preventive measures, such as placing babies to sleep on their backs, avoiding soft bedding and avoiding so-called bed-sharing.

"You can bring the baby into bed to cuddle or to breast feed," Willinger explained, "but then, when you're ready to go to sleep, you should place your baby in a proximate but safe sleeping environment."

Some doctors also recommend using pacifiers because they may keep a baby's airway open. And pregnant women should avoid drinking or smoking, because some studies show that alcohol and nicotine can lower a developing baby's serotonin levels.

In addition, the American Academy of Pediatrics recommends that babies sleep on a firm mattress and a fitted sheet, and that a baby's crib should not contain pillows, quilts, comforters or stuffed toys because they can cover an infant's face.

Willinger said she hopes this new serotonin research will help soften some of the pain that comes with losing a baby to Sudden Infant Death Syndrome.

"If you talk to parents, they're always second-guessing themselves: 'Well, the baby cried, maybe I should have picked up the baby,' all kinds of things," Willinger said. "Because not knowing what actually the baby died from is very difficult for them."

But now that the Children's Hospital study shows that SIDS could be due to a hidden medical disorder, doctors may one day find a way to make that problem obsolete.

"I've already talked to a number of parents in the last 24, 48 hours as this story has been evolving," Kinney said, "and I think the major thing that they've told me is that it brings them hope; that, some day, there will be a way to prevent this on a medical model, and that nobody will suffer this like they did."

This latest research should reassure parents that SIDS is not caused by "something they did because they didn't check the baby an extra time that night," she added. "It's a disease process that's taking its toll."

The study appears in the current issue of the Journal of the American Medical Association.

This program aired on February 2, 2010.

Sacha Pfeiffer Twitter Host, All Things Considered
Sacha Pfeiffer was formerly the host of WBUR's All Things Considered.


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