Washington, Feb 3 (IANS) The brains of infants who die of sudden infant death syndrome (SIDS) produce low levels of serotonin, a brain chemical that conveys messages between cells and plays a vital role in regulating breathing, heart rate and sleep, says a new research.
SIDS is the death of an infant before his or her first birthday that cannot be explained after a complete autopsy, an investigation of the scene and circumstances of the death, and a review of the medical history of the infant and of his or her family.

SIDS is the third leading cause of infant death, claiming more than 2,300 lives in 2006 in the US, according to the National Centre for Health Statistics.

Researchers theorise that this newly discovered serotonin abnormality may reduce infants’ capacity to respond to breathing challenges, such as low oxygen levels or high levels of carbon dioxide (CO2).

These high levels may result from re-breathing exhaled CO2 that accumulates in bedding while sleeping face down.

“We have known for many years that placing infants to sleep on their backs is the single most effective way to reduce the risk of SIDS,” said Alan E. Guttmacher, acting director of Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), the NIH institute that funded the research.

“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.”

NICHD’s Back to Sleep campaign urges parents and caregivers to place infants to sleep on their backs. Following the campaign’s launch in 1994, the rate of SIDS dropped by more than 50 percent.

Senior author Hannah C. Kinney, Harvard Medical School and Children’s Hospital Boston, and her colleagues analysed brain tissue from infants who died from SIDS and controls who died of other causes.

Included in the analysis were 35 infants who died of SIDS, five infants who died unexpectedly of other causes, and five infants who were hospitalised and died for reasons associated with a lack of oxygen, said a NICHD release.

The researchers found that serotonin levels were 26 percent lower in tissue from infants who died of SIDS than in tissue from the group of infants who had otherwise died unexpectedly.

Measurements of tryptophan hydroxylase, an enzyme needed to make serotonin, also were 22 percent lower.

The findings appeared in the Wednesday issue of The Journal of the American Medical Association.