While there are steps parents can take to help protect their babies from sudden infant death syndrome (SIDS), such as putting babies to sleep on their backs, these measures can't stop all cases of this syndrome, characterized by the sudden and unexplained death of an infant younger than one year old.

That's likely because some children have abnormalities in the serotonin system in their brains that make them more susceptible to SIDS, according to a new study by researchers at Children's Hospital Boston.

"This study confirms that SIDS is a disease process that's biologically based and not this mystery," said one of the study's authors, Dr. David Paterson, an instructor at the Harvard Medical School-affiliated hospital.

As to what might cause these abnormalities, Paterson said, "I think it's going to be a complex combination of factors. I don't think these problems are exclusively genetic or environmental."

The Serotonin System

The serotonin system is located in an area of the brain stem called the medulla oblongata, and it's believed to regulate many vital body functions, including heart rate, breathing, blood pressure and temperature regulation, according to Paterson.

So, an abnormality in this critical area might stop a baby from having a normal response when not getting enough air. For example, if a baby is sleeping face down, he may be breathing in exhaled air and getting high levels of carbon dioxide. When the brain's serotonin system is working normally, it signals the baby to wake up and move his head to get fresh air. In babies that succumb to SIDS, however, it appears that the serotonin system doesn't send the right signals to the rest of the body, Paterson said.

Paterson said the new study builds on previous research that he and his colleagues have done that found serotonin-receptor defects in two other populations of SIDS babies.

"Now that we've confirmed these abnormalities in a third data set, we're confident there's a problem in the serotonin system," he said.

New Study

The new research included tissue samples from 31 babies who died of SIDS, and 10 babies who died of other causes. The researchers found that babies who died of SIDS had abnormalities in their serotonin-receptor cells, that they had more serotonin-producing cells, and that they had too few serotonin-transporter cells when compared with the control group of babies.

"Now that we know there's a problem here in the biology of the brain stem, hopefully we can do something about this," Paterson said.


"This is a very good study. It takes us one step further in terms of focusing on the role of serotonin and SIDS," said Dr. Debra Weese-Mayer, director of pediatric respiratory medicine at Rush University Medical Center in Chicago.

But, she added, the study does have limitations, such as its small size and the underrepresentation of black infants. Like Paterson, she said she believes that the ultimate cause of SIDS will likely be multifactorial. The serotonin system will likely play a large role, though she said she thought it would probably be serotonin abnormalities along with other factors, such as genetics and environment.


Both experts said there needs to be a renewed focus on getting parents to have babies sleep on their backs. The majority of the infants included in this study were sleeping on their stomachs or sides.

Babies should sleep by themselves on a firm crib mattress with no soft bedding, Paterson said. Also critical is that parents don't smoke around their babies and don't allow anyone else to do so, either. Pregnant women shouldn't smoke or drink any alcohol, Paterson cautioned.

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