Investigators at Boston Children’s Hospital (Boston, USA) report that many infants dying suddenly and unexpectedly, in all kinds of sleep environments, have underlying brainstem abnormalities and are not all normal prior to death.
The researchers also highlight to the need to detect and treat this underlying vulnerability early, the focus of their current work. They report their findings in the December issue of Pediatrics.
The investigaton, led by Hannah Kinney, a neuropathologist at Boston Children’s, has shown over the past two decades that infants who die suddenly, unexpectedly and without explanation—whose deaths are generally attributed to sudden infant death syndrome (SIDS)—have differences in brainstem chemistry that set them apart from infants dying of other causes.
These abnormalities impair brainstem circuits that help control breathing, heart rate, blood pressure and temperature control during sleep, and, the researchers postulate, prevent sleeping babies from rousing when they rebreathe too much carbon dioxide (due to inadequate ventilation), breathe too little oxygen or become overheated (from overbundling).
Epidemiologic studies have shown that infants dying suddenly and unexpectedly are often found sleeping face down with their face in the pillow, or sleeping next to an adult in the bed—environments that have the potential to lead to smothering and death by asphyxia.
In the new study, Kinney and colleagues re-examined their data and reviewed the cases of 71 infants who died suddenly and unexpectedly. The infants were autopsied at the San Diego County Medical Examiner’s office from 1997 to 2008 and had brainstem samples available for analysis. The researchers grouped the infants according to sleep circumstances—those that were considered likely to generate asphyxia and those that were not—based upon death-scene investigation reports.
They compared 15 infants with SIDS whose deaths were deemed not to involve asphyxia (group A), 35 SIDS infants whose deaths were possibly asphyxia-related (group B) and nine infants who clearly died from other causes (controls). They excluded the other infants, who either had insufficient data or had evidence of other clear risk factors for death, such as exposure to drugs or extremes of temperature.
Brainstem neurochemical abnormalities—involving serotonin, serotonin receptors, GABA receptors and 14-3-3 (a protein that regulates serotonin)—were found in both group A and group B. Infants in these two groups, with and without environmental risk factors for asphyxia, had the same brainstem abnormalities and both groups differed significantly from the controls.
“Even the infants dying in a potentially asphyxia-generating situation had an underlying brainstem abnormality that likely made them vulnerable to sudden death if there was any degree of asphyxia,” Kinney says. “The abnormality prevents the brainstem from responding to the asphyxial challenge and waking.”
The investigators believe say these findings confirm that sudden unexplained death in infants is associated with underlying vulnerabilities, and that not all infants who die in compromised sleep environments are normal.
“Certainly, there are compromised sleeping environments that can cause any baby to die, such as entrapment in the crib, but if it is just sleeping face down, the baby who dies may have an underlying brainstem vulnerability,” says Kinney. “We have to find ways to test for this underlying vulnerability in living babies and then to treat it. Our team is focused now upon developing such a test and treatment.”
