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Low Serotonin Levels May Be Key to SIDS

Study Shows Link Between Sudden Infant Death Syndrome and Deficiency of Hormone Serotonin

Measuring Serotonin Levels

Kinney and colleagues evaluated serotonin and tryptophan hydroxylase (TPH2), the enzyme that helps make serotonin, in 35 infants who died from SIDS.

They compared these measurements with those from two groups -- five infants who died suddenly for whom a cause of death was established and five infants who died while hospitalized for having insufficient oxygen to the tissues.

They retrieved tissue samples from the autopsies to measure the enzyme and hormone levels.

They found that:

  • Serotonin levels were 26% lower in the SIDS babies than in the infants who died suddenly with a known cause of death, and the enzyme levels were 22% lower. The serotonin and enzyme levels were also lower in the SIDS babies than in the group of hospitalized infants.
  • Levels of binding to the serotonin receptors were also lower in the SIDS babies.

Finding the deficiency in serotonin levels isn't the whole story, Kinney says. "We think there are probably several neurotransmitter systems involved in SIDS."

Second Opinion

The new research seems to verify the suspicions of many experts who have thought abnormalities of respiratory control contribute to SIDS, says Richard Martin, MD, director of neonatology at Rainbow Babies and Children's Hospital and professor of pediatrics at Case Western Reserve University in Cleveland.

"Serotonin is important for arousal," he says. "If serotonin production is diminished in patients at risk for SIDS, that all makes sense.

"I think the message is there is something inherently wrong in some of these babies," he says. "On the other hand, in no way should that subtract from the public health message -- to avoid prone position, avoid fluffy bedding and pillows, avoid exposure to cigarette smoking, and don't overheat your baby."

While researchers have been focusing on brain stem abnormalities to explain SIDS for many years, the new research ''tells us more about what is wrong with that part of the brain, the brain stem," says Marian Willinger, PhD, special assistant for SIDS at the Eunice Kennedy Shriver National Institute of Child Health and Human Development at the National Institutes of Health.

She calls the finding an important development. "This is another piece in the puzzle in terms of understanding what is wrong in the brain."

Eventually, she says, it may help researchers develop ways to intervene or to develop screening tests for SIDS.

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