For many years, Sudden Infant Death Syndrome (SIDS), the leading cause of death among infants in the United States, was a mysterious disease. It is only in the past decade or so that researchers have begun to understand the condition on a molecular level. Now, a new study has further unraveled some of the disease's dark secrets by showing that defects in a chemical messenger pathway in the brain are at the heart of the problem. The findings may help pave the way for identifying at-risk babies and developing ways to prevent SIDS-related deaths.
Babies with SIDS suffocate while asleep, usually when they lie face-down and breathe in too much carbon dioxide. Normal infants would survive by reflexively gasping for air, but something about SIDS victims prevents them from doing this. That's why SIDS researchers have been focusing on serotonin, a chemical messenger in the brain that controls breathing and gasping. Autopsies have shown that SIDS babies have less serotonin bound to their serotonin receptors than did babies who died of other causes, but the exact nature of the serotonin problem in SIDS remained unclear.
To find out more, neuropathologist Hannah Kinney of Harvard Medical School in Boston and her colleagues autopsied the brains of 31 SIDS children. They found a lower concentration of a kind of serotonin receptor that specifically controls respiration (other serotonin receptors control sleep, anxiety, and a variety of other functions). The researchers also found nearly twice as many cells that make serotonin in the brain stem as in controls. That made sense: Studies with other chemical messengers often find a higher amount of the messenger can lower the number of its receptors. Furthermore, SIDS boys appeared to have less serotonin bound to serotonin receptors than did the SIDS girls, the team reports today in the Journal of the American Medical Association.
That may explain the higher rate of SIDS deaths in boys, says developmental psychobiologist Michael Myers of Columbia University. Overall, he says, the study further supports the role of serotonin in SIDS, and it's the first report that has zeroed in on a particular receptor. By clarifying how the system is disturbed, Myers says, the study will help physicians develop ways to identify SIDS babies at birth or during the first few weeks, so that their parents can take extra care.