New study suggests cause of sudden infant deaths [Archives:2006/998/Health]

November 13 2006

Preliminary research suggests that brainstem abnormalities involving certain serotonin pathways in the brain may play a more important role in Sudden infant death syndrome (SIDS) than previously thought.

The new findings, appearing in The Journal of the American Medical Association, provide the strongest evidence yet that a physical abnormality ) probably genetic in origin ) can help explain what until recently was a matter of speculation for scientists and deep anxiety for new parents: SIDS.

Researchers have found that many of the deaths occurred while the babies, most of them boys, were sleeping on their stomachs, often on soft bedding, or bundled in blankets.

Researchers suspect these abnormalities might affect the ability of babies to wake up when threatened by external problems such as excessive heat or carbon dioxide when they are face down in bed.

Dr Hannah Kinney, the lead author of the study, said: 'A normal baby will wake up, turn over and start breathing faster when carbon dioxide levels rise.

'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.'

Suspicions of child abuse also cloud many sudden infant deaths, though recent research suggests that abuse is responsible in less than 5 percent of such deaths.

The new study confirms that a far more important cause is defects in the way neurons process serotonin, a brain chemical associated with mood and arousal. Experts said the findings could help doctors develop a diagnostic test for SIDS risk, and possibly preventive treatments.

“This is the most sophisticated, most impressive study so far looking at the serotonin system,” said Dr. Debra E. Weese-Mayer, director of pediatric respiratory medicine at Rush University Medical Center in Chicago, “and it's going to drive genetic studies to find out what's behind this.” Dr. Weese-Mayer wrote an editorial accompanying the journal article.

The research team, led by doctors at Children's Hospital Boston, compared brain tissue from 31 infants who died of SIDS from 1997 to 2005 with samples from 10 babies who had died of other causes. They focused on an area of the brain stem called the medulla, which regulates breathing, sleep-and-wake cycles and other vital functions.

They found, among other oddities, that cells in this region of SIDS babies' brains were significantly less sensitive to serotonin than those in the other brains. The brain stem supports the autonomic nervous system, which helps arouse people if they are breathing in too little oxygen, the authors said; and serotonin keeps the system responsive. The defects were particularly striking in male brains, which could account for boys' higher risk of SIDS, they said.

Previous studies had pointed to similar defects, but the new research pinpointed their location.

“I think this abnormality probably begins during gestation, in the womb, as the brain stem is developing,” said Dr. Hannah Kinney, the senior author of the study, which was financed by the National Institutes of Health and a coalition of SIDS advocacy groups, including the CJ Foundation for SIDS in New Jersey.

The study findings are based on tissue from white and Hispanic infants provided by the medical examiner's office in San Diego. They may not apply to blacks or other ethnic groups, Dr. Kinney said.