Babies who die of sudden infant death syndrome (SIDS) have abnormalities in the brain stem, an area that helps control breathing, heart rate, blood pressure, temperature and arousal from sleep, new federally funded research has found.
The abnormalities seem to affect the brain stem’s ability to use and recycle the chemical serotonin.
Serotonin — best known for regulating mood — also has a role in regulating vital functions such as breathing and blood pressure, according to authors of the report published in today’s issue of the Journal of the American Medical Association (JAMA).
These findings are the strongest evidence to date that inherent brain-stem differences might place some infants at increased risk for SIDS, the leading cause of postneonatal infant mortality in the United States. In 2003, nearly 2,200 infants died of SIDS in the United States, according to the National Center for Health Statistics (NCHS).
SIDS suddenly and unexpectedly kills children younger than 1 year, usually after they have been put to bed. Typically, a SIDS infant shows no signs of having suffered. SIDS has an overall incidence of 57.1 deaths per 100,000 live births, according to NCHS. The SIDS rate among black infants is nearly three times higher than among whites.
“Despite intensive research, the causes of SIDS remain unknown,” said the JAMA report’s authors, who included researchers from the departments of pathology and pediatrics at the Harvard Medical School and Children’s Hospital in Boston.
The research was financed by the National Institute of Child Health and Human Development, part of the National Institutes of Health.
The findings bolster scientific arguments that brain-stem irregularities might hinder an infant’s ability to sense high levels of carbon dioxide and low levels of oxygen. Such impairment would put an infant at risk if he breathed in his own exhaled breath, depriving him of oxygen. This hypothesis holds that certain infants are not able to detect such vital changes and do not wake up.
In the study, researchers examined tissue from the brain stems of 31 infants who had died of SIDS and 10 infants who had died of other causes. SIDS babies had nearly double the number of nerve cells displaying serotonin defects.
Lead author Dr. Hannah Kinney, professor of pathology at Harvard Medical School, said the study “strengthens the hypothesis” that brain-stem “dysfunction is associated with SIDS and may lead to death by a failure of respiratory and autonomic responses to homeostatic stressors during sleep.”
The researchers also found that male SIDS infants had fewer serotonin receptors than did either female SIDS infants or the control infants. They said this could help explain why SIDS affects roughly twice as many boys as girls.
In an accompanying editorial, Dr. Debra Ellyn Weese-Mayer, a pediatrician at the Rush University Medical Center in Chicago, called for more study of SIDS among black infants.
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