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    Clue to Sudden Infant Death Syndrome

    Brain Stem Abnormality Seen in SIDS Babies, Study Shows

    Brain Abnormality continued...

    Multiple defects in the serotonin system of the SIDS babies were identified, including abnormally high numbers of neurons that make and release serotonin and deficiencies in certain serotonin receptor binding sites.

    "Our hypothesis right now is that we're seeing a compensation mechanism," Paterson says. "If you have more serotonin neurons, it may be because you have less serotonin and more neurons are recruited to produce and use serotonin to correct this deficiency."

    Male babies who died of SIDS had less serotonin receptor binding - necessary for serotonin to work -- than either female babies who died of SIDS or the babies who died of other causes. This may help explain why SIDS is twice as common in males as in females.

    Identifying At-Risk Infants

    The next step, Paterson says, is to confirm that the serotonin system abnormalities reported in this study play a role in SIDS.

    The hope is that the discovery of a biological trigger will lead to better ways to identify at-risk infants and intervene to protect them.

    Even though much is still unknown, the identification of a specific biological link to SIDS is a huge step forward, says Marian Willinger, PhD.

    Willinger is special assistant for SIDS at the National Institute of Child Health and Human Development, which funded the study.

    "This research is important because it gives us a specific place to look in our future research," she tells WebMD. "We still don't have the whole story. But it is getting pieced together little by little."

    Despite public health efforts to urge parents and caregivers to put infants to sleep on their backs, roughly half the infants in the study who died of SIDS were found sleeping on their stomachs or sides. About one in four were bed sharing, which is another suspected risk factor for SIDS.

    Putting babies to sleep on their backs, alone in a crib, with little bedding, can help reduce SIDS risk, but these interventions don't eliminate the risk, Willinger says.

    "Back sleeping is an effective intervention, but there are still babies who die of SIDS after being placed on their backs," she says.

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