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Researchers find key clue for Sudden Infant Deaths
INGRID PERITZ

Researchers have found evidence linking crib deaths to an abnormality in the brains of stricken infants, findings that may help unravel an enduring medical mystery.

The findings suggest that the seemingly random deaths may have a biological cause, and, down the road, infants would be tested and treated before tragedy strikes.

Sudden Infant Death Syndrome (SIDS) is a leading cause of death among infants between the age of one month and 12 months. Because the cause has been unknown, parents have been left guilt-stricken and without insight into what befell their apparently healthy baby.

"To a certain extent, this demystifies SIDS and indicates that it's a disease process," said David Paterson, a neuroscientist at the Children's Hospital Boston and Harvard Medical School.

"It's not this mystical event that happens for no apparent reason."

Researchers in the study, published in the Journal of the American Medical Association, located defects in the area of the infant brain that controls breathing, blood pressure and arousal from sleep.

They studied brain autopsies from 31 infants who died of SIDS in California between 1997 and last year, and compared them to 10 infants who died of other causes.

They found that the SIDS babies had an abnormality in their brain stems that might impair vital reflexes such as breathing. The defect appeared to affect the brain stem's ability to regulate serotonin, the chemical that helps control these vital body functions.

In a normal baby, a rise in carbon dioxide would activate nerve cells to send a signal to wake up and breathe faster. Babies with abnormalities wouldn't get such activation.

In effect, the babies' alarm systems don't function properly.

"If the alarm system doesn't work, and doesn't detect or effectively cause a change in their breathing, then they could be in real trouble," Dr. Paterson said in an interview.

He said serotonin defects may be linked to as much as 75 per cent of all SIDS cases.

Ernest Cutz, a pediatric pathologist at the Hospital for Sick Children in Toronto who has studied SIDS, said brain abnormalities have been suspected for years as a possible cause of crib deaths, but it has been hard to pinpoint a specific abnormality.

"This brings it out of the realm of mystery toward a rational explanation," Dr. Cutz said yesterday. "It gives us hope that we will eventually solve it, and possibly prevent it."

With no known cause of SIDS, health professionals have run campaigns to reduce its likelihood, counselling parents to put their babies on their backs to sleep, use a pacifier, and abstain from having babies sleep in parents' beds.

The campaigns have been effective. In Canada, the number of crib deaths has declined from about 400 a year a decade ago to a little more than 100 annually today.

While SIDS used to be the leading cause of death among one-to-12-month-olds, it is now tied with congenital malformations.

Aurore Côté, a specialist at the Montreal Children's Hospital and an authority on SIDS, said that while the new U.S. study remains "another piece of the puzzle," she cautioned that the number of cases examined -- 31 -- is small.

She emphasized that the most important risk factors for SIDS are already known -- smoking during pregnancy, and putting babies to bed belly down.

Of the SIDS infants in the new U.S. study, 65 per cent had been sleeping prone or on their side at the time of death, suggesting that public education on the problem was still needed, the study says.

The study also uncovered a biological explanation for SIDS striking twice as many infant boys as girls. Males who died of SIDS in the study had significantly fewer serotonin receptors than females who died of SIDS.

Marian Willinger, a SIDS researcher at the U.S. National Institute of Child Health and Human Development, which paid for the study, said that while all babies should sleep on their backs, it's impossible to target high-risk babies because they can't be identified.

"There are still babies who die of SIDS after being placed on their backs," she said in a statement released with the study.

"Eventually, we hope to have an understanding of the developmental disease process underlying SIDS, so that we can identify infants at highest risk and provide them with appropriate intervention."