SAN JOSE, Calif. - Researchers say they have unlocked the mystery behind sudden infant death syndrome, or SIDS, the leading cause of death for infants in the United States.
Horrifying to parents, SIDS is a silent stalker that usually catches babies while they sleep, killing 2,500 infants younger than 1 in the United States each year.
Providing the strongest evidence yet that SIDS has a concrete biological basis, a study published Tuesday in the Journal of the American Medical Association reveals an abnormality in the brain stem that impairs a baby's ability to regulate breathing.
Scientists hope the information will lead to early detection and treatment for infants at risk, bolster recommendations to put babies to sleep on their backs and offer some answers to parents struggling to understand their unfathomable loss.
The research is "a big deal," said Stanford pediatrician Dr. Ronald Ariagno, who has studied SIDS since 1975. "It provides us anatomical information that can perhaps explain how a baby can die suddenly and not have any signs of health problems."
The eight-year study, led by Dr. Hannah Kinney at Children's Hospital Boston and funded in part by the National Institutes of Health, compared autopsy data from 31 infants in San Diego County who died of SIDS and 10 who died unexpectedly from other causes between 1997 and 2005 .
Researchers focused on the brain stem, the stalk at the bottom of the brain that connects to the spinal cord and controls basic functions such as heart rhythm and breathing. Babies who died from SIDS had abnormalities in nerve cells that make and use serotonin - a chemical best known for regulating mood, but also critical for regulating breathing and blood pressure.
When babies sleep face-down or have their faces covered by bedding, they are thought to breathe carbon dioxide that they have just breathed out. As a result, they take in less oxygen.
"A normal baby will wake up, turn over and start breathing faster when carbon dioxide levels rise," Kinney explains in a statement.
But in babies who die from SIDS, she said, defects in the serotonin system could impair these reflexes.
"It definitely reinforces and confirms what we have seen in previous studies in that there's a problem with the serotonin system," said Children's Hospital Boston researcher David Paterson, who worked on the study.
Paterson said more research is needed to explain what causes the abnormalities and how they can be prevented. For now, the results offer new clues to a mystifying event that leaves mothers and fathers wracked with guilt, wondering whether they did something wrong.
"For all the parents who have experienced this horrible, horrible death it gives them something to hold onto," said Laura Reno, spokeswoman for one of the study's primary funders, First Candle/SIDS Alliance, a national organization based in Baltimore.