SIDS Linked With Serotonin, Brainstem Abnormalities
Infants who die of sudden infant death syndrome have abnormalities in their brainstems that disrupt their ability to process the neurotransmitter serotonin and impair control of their own breathing, heart rate and arousal, according to study published in the Journal of the American Medical Association, the New York Times reports. NIH funded the study (Carey, New York Times, 11/1).
More than 2,000 U.S. infants die annually from SIDS. The number of SIDS cases has decreased by 50% since 1994, when NIH launched a campaign that urges parents and caregivers to place infants on their backs to sleep.
Although studies have shown that infants who are placed on their stomachs to sleep are at a higher risk for SIDS, it had been unknown if there is also a biological component to the correlation between stomach-sleeping and the disease (Naik, Wall Street Journal, 11/1).
For the new study, researchers from Children's Hospital Boston and Harvard Medical School examined data from autopsies of 31 infants who died of SIDS and 10 who died from other causes between 1997 and 2005 in California (Washington Post, 11/1). Among the infants who died of SIDS, 65% were sleeping on their stomachs or sides at the time of death (Wall Street Journal, 11/1).
Researchers examined an area of the brainstem called the medulla, which regulates breathing and sleep-wake cycles. The brainstem supports the autonomic nervous system, which helps awaken a sleeping person who is breathing too little oxygen, according to the study (New York Times, 11/1).
The study found that most of the infants who died of SIDS had abnormalities in brainstem nerve cells that produce and process serotonin, which helps the brain regulate breathing, blood pressure, temperature and sensitivity to carbon dioxide (Washington Post, 11/1). The infants with the abnormalities had about twice as many nerve cells with serotonin defects as the other infants, the study found (Tanner, AP/Philadelphia Inquirer, 11/1).
About three-fourths of the infants who died of SIDS had the abnormalities, according to the study (Goldberg, Boston Globe, 11/1). The study also found that male infants who died of SIDS had more defective nerve cells than female infants who died of SIDS or the control group, which the authors said could help explain why SIDS affects about twice as many male infants and female infants (Howard Price, Washington Times, 11/1).
The study sample included only white and Hispanic infants, so the findings might not apply to infants of other races, lead author Hannah Kinney, a professor of pathology at Harvard Medical School, said (New York Times, 11/1). Serotonin defects probably cause about half of all SIDS cases, she said (AP/Philadelphia Inquirer, 11/1).
The study adds, "Despite intensive research, the causes of SIDS remain unknown."
Debra Ellyn Weese-Mayer, a pediatrician at Chicago's Rush University Medical Center, writes in an editorial accompanying the study that more research is needed on SIDS in black infants. The rate of SIDS among black infants is almost three times higher than the rate among white infants, the Washington Times reports (Washington Times, 11/1).
Weese-Mayer said, "This is the most sophisticated, most impressive study so far looking at the serotonin system." She added that it is "going to drive genetic studies to find out what's behind this." (New York Times, 11/1).
Kinney said the study suggests that many infants who die of SIDS have not properly developed an internal "alarm system" that would prompt them to breathe harder or turn their heads if their carbon dioxide levels rise while sleeping on their stomachs. "The most important thing about this work is that it gives biological plausibility to the 'Back to Sleep' campaign," she said (Boston Globe, 11/1).
"I think this abnormality probably begins during gestation, in the womb, as the brainstem is developing," Kinney added (New York Times, 11/1). Kinney said she and her colleagues would like to develop a diagnostic test that could identify infants at higher risk for SIDS, adding, "You could then give the baby a serotonin drug at the time of highest risk" (Wall Street Journal, 11/1).
Such a test would take at least 10 years to develop, she noted, adding, "These findings provide evidence that SIDS is not a mystery but a disorder that we can investigate with scientific methods, and some day, may be able to identify and treat."
Duane Alexander, director of the National Institute of Child Health and Human Development, said, "This finding lends credence to the view that SIDS risk may greatly increase when an underlying predisposition combines with an environmental risk, such as sleeping face down, at a developmentally sensitive time in early life" (McVicar, South Florida Sun-Sentinel, 11/1).
William Fifer, a professor of psychiatry and pediatrics at Columbia University, said the study "gives people evidence that smoking, stress and other toxic exposures in the mother gets passed on to the fetal brain." He said that in conducting future studies, "[n]ow we have a clear direction for where we should look for markers" (Wall Street Journal, 11/1).
Carmen Steigman, medical director of pediatric pathology at Broward General Medical Center, said, "It's interesting and puts us onto something that could lead to further study, but it doesn't mean that every susceptible baby will have SIDS. Other things have to come together, sort of like Jupiter aligning with Mars."
Steigman said maternal smoking, soft sleep surfaces or loose bedding, overheating, illness and prematurity can increased SIDS risk (South Florida Sun-Sentinel, 11/1).
Several broadcast programs reported on the study:
- CBS' "Evening News": The segment includes comments from Kinney and U.S. parents (LaPook, "Evening News," CBS, 10/31). Video of the segment is available online.
- NBC's "Nightly News": The segment includes comments from Kinney and U.S. parents whose infant died from SIDS (Bazell, "Nightly News," NBC, 10/31). Video of the segment is available online.
- NPR's "Morning Edition": The segment includes comments from Kinney and Marian Willinger, special assistant for SIDS at NIH's National Institute of Child Health and Human Development (Trudeau, "Morning Edition," NPR, 11/1). Audio of the segment is available online.