Brain stem linked to sudden infant death syndrome

Back in the old days, I put my babies to sleep on their tummies. We worried that if they slept on their backs, they might choke on some regurgitated milk or baby food. Turns out we were wrong about that, and in 1992, after some extensive research showing that sudden infant death syndrome, or SIDS, was more common in babies who slept on their tummies, the American Academy of Pediatrics recommended that we put our babies to sleep on their backs.

The Back to Sleep campaign resulted in a dramatic drop in SIDS deaths. Before 1992, 7,000 infants a year died of SIDS in the United States. In 1999, the number had dropped to 2,648.

For parents who face the tragedy of the sudden death of a healthy infant, the question has always been, “Why?” We know associations and risks, but any underlying “cause” has eluded us, most likely because there is no one “cause,” but a constellation of circumstances that come together to create a tragedy.

Researchers reporting in the most-recent Journal of the American Medical Association may have identified a biological abnormality that makes infants more susceptible to SIDS. Following on their earlier research, they concentrated on a part of the brain stem called the medulla oblongata.

The brain stem is the primitive part of our brain, sitting right above the spinal cord. The medulla oblongata, a part of the brain stem, controls many of the automatic functions of our body. We don’t have to remember to breathe or make sure our heart beats because the medulla takes care of that for us.

The researchers, from Harvard, the New England Research Institutes, and the University of California at San Diego, studied autopsy samples from the medullas of 31 infants who died of SIDS and compared them to 10 samples from infants who died of other causes.

Based on their earlier research, they suspected that an abnormality existed in the serotonin nerve pathways in the medulla of children who died from SIDS. Serotonin is one of the brain chemicals that transmits information from one nerve cell to another.

Using sophisticated staining techniques, they found that compared to infants who died of other causes, the SIDS babies had more serotonin-producing cells, but the receptor cells were not normal and there were too few “transporter cells.” (Things are complicated up there!)

These researchers have speculated in the past that SIDS results from a combination of genetic and environmental factors. In their small sample of 31 SIDS infants, eleven of the infants were born prematurely, fifteen were found lying on their stomachs, nine were found face down, and seven were bed sharing at the time of death. All of these are considered risk factors for SIDS, and all 31 of the SIDS babies examined had at least one risk factor.

This research is quite preliminary, and the sample size studied is small. But the fact that all SIDS babies showed the abnormalities while none of the other infants did certainly supports the theory that an underlying flaw in brain anatomy and function may combine with environmental factors (like tummy sleeping) to cause SIDS.

Since the medulla is responsible for controlling so many of the functions that keep us going, it was an obvious place to look. The researchers surmise that babies who have this abnormality are vulnerable to the decreased oxygen intake or increased carbon dioxide levels that might result from sleeping face down. Because of the altered serotonin pathways, they may not be able to respond normally by turning their heads or waking up.

These findings need to be confirmed by larger studies. And there is no test available (yet) looking for this abnormality. But it gives us a biological basis that may make babies vulnerable, and it confirms the value of the Back to Sleep campaign.

For more information about SIDS, check out one of the many informative web sites like www.sids.org.