Brain chemical serotonin may play a role in SIDS: U. S. study

Posted by Pacific J Med Sci on February 3, 2010 at 10:29 AM

Brain chemical serotonin may play role in SIDS: U.S. study



FEBRUARY 2, 2010


After two decades of work and in a finding that could help explain why some babies die mysteriously in their sleep, a Boston doctor and her collaborators believe they have evidence that abnormally low level of a chemical in the brain that helps control breathing during sleep plays a role in causing sudden infant death syndrome (SIDS).


Dr. Hannah Kinney, a Children's Hospital Boston neuropathologist, says she has never been satisfied with the idea that normal babies sometimes die, that SIDS is a mystery, a "bolt out of the blue."

"I found that unacceptable," she said. Now, in a study published this week in the Journal of the American Medical Association, Kinney and her colleagues are linking SIDS with low production of serotonin deep in the brainstem.


Serotonin helps regulate breathing, heart rate and blood pressure during sleep.

The finding may one day lead to a test to screen babies at birth for a serotonin brainstem defect — the same way infants are now screened for hypothyroidism and other diseases — and, ultimately, treatments that would correct the hormone deficiency. "It adds one further piece of evidence that SIDS is a biological disorder," says Dr. Ernest Cutz, a senior staff pathologist and senior associate scientist at the Hospital for Sick Children in Toronto.


"The forensic community, they still look at these as suspicious deaths. I think it strengthens the argument that this is a natural disease, that there's something intrinsically wrong with the baby." Low serotonin alone may not lead to SIDS, he said. But if "biologically vulnerable" babies are exposed to risks, such as being put to sleep face down, "this may then trigger SIDS." Sudden infant death syndrome is the leading cause of death in the first year of a child's life; every week in Canada, three babies die of SIDS. In medical terms, SIDS is defined as the sudden and unexpected death of an infant in whom a complete autopsy and death scene investigation fails to reveal the cause of death.


Typically, an apparently perfectly healthy baby is found dead after having been put to sleep.

"It's devastating," says Dr. Michael Rieder, a professor of pediatrics at the University of Western Ontario in London. "Whether you have six kids or one child, a death is a devastating blow. But especially when people are having babies late, and often not many of them . . . it's really a huge blow for otherwise healthy babies to be suddenly found dead."


Rates of SIDS have fallen by half since the 1990s, when "Back to Sleep" awareness campaigns urged parents to put babies to sleep on their backs, and not their tummies. But the campaigns didn't abolish it; the rates have plateaued over the last decade, and SIDS remains the leading cause of post-neonatal infant death, affecting about one in every 2,000 live births. About 20 years ago, Kinney and her colleagues started working on the idea that SIDS was a problem in the brainstem, that some kind of defect prevented babies from responding to "challenges" or stressors during sleep, such as low oxygen, or re-breathing their own breath if babies are sleeping face down. Their hypothesis was that certain babies may not be able to detect high carbon dioxide or low oxygen during sleep, and don't wake up or turn over.


The researchers systematically searched the regions of the brainstem involved in breathing, heart rate, blood pressure and arousal during sleep. They looked at a slew of neurotransmitters systems, and the one with the most significant changes was in the serotonin system. Serotonin is best known for its role in regulating mood; it's the brain chemical targetted by Prozac and drugs like it. It's also found in the brain circuits that govern breathing, sleep and arousal from sleep.


Three years ago, Kinney and her group found abnormalities in the receptors for serotonin in the brainstem, but it wasn't clear whether the problem was too much, or too little serotonin. In the new study, the group measured the levels of serotonin, as well as an enzyme that makes serotonin, in tissue samples taken during autopsies of 35 infants who died from SIDS, provided by research partners at the San Diego County medical examiner's office in California. Levels of serotonin, and the enzyme that makes it, were, on average, lower in the SIDS babies compared to babies who died of other causes.


"There's something about sleep that unmasks the defect," Kinney says. A blood test to detect low serotonin levels in newborns "would be the ultimate goal", she said, "something that was readily accessible that pediatricians could do in their office. I think we're decades from that. (But) it's what we work at." In the meantime, the study strengthens messages about safe sleeping positions.

"You're told to put the baby on his back, but that doesn't make sense. What difference would that make? Our research says that if you have a baby who has a defect in circuits in serotonin, you put this baby face down, and it's in soft bedding, and it starts to re-breathe carbon dioxide around its face, or drops its oxygen around its face, a normal baby would respond to that challenge and stir and rouse and wake up, and that would protect its airway," Kinney says. "A baby who has a defect in the serotonin system who is in the face-down or prone position, wouldn't do that, and would go on to die."


Quick tips:

How to keep babies safe when sleeping:

- Always place a baby on his or her back for every sleep — at night time and nap time

- Infants should sleep in a crib for the first year of life

- Provide the baby with a smoke-free environment — both before and after birth.

Mothers who smoke during pregnancy increase their baby's risk of SIDS. Passive exposure to tobacco smoke in the environment is also associated with an increased risk of SIDS

- Use a crib that is empty of all toys and bedding (except a fitted sheet) and meets current safety regulations. Cribs should be free of quilts, comforters, bumper pads, pillows and pillow-like items. Dressing infants in sleepers eliminates the need for any covers over the baby, other than a thin blanket.

- Have a baby sleep in a crib next to a parent's bed for the first six months

- Breastfeeding may give some protection against SIDS

- Sleeping with an infant on a sofa is associated with a particularly high risk of sudden unexpected death in infancy


Sources: Public Health Agency of Canada; Canadian Paediatric Society

© Copyright (c) Canwest News Service

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