Researchers at Boston Children's Hospital report that infants dying suddenly and unexpectedly - in both safe and unsafe sleep environments - have underlying brainstem abnormalities. The research, led by neuropathologist Hannah Kinney, appears in the journal Pediatrics.
Kinney said that her findings showed that infants 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, she explained, impair brainstem circuits that help control breathing, heart rate, blood pressure, and temperature control during sleep.
These factors, she believes, prevent sleeping babies from rousing when they rebreathe too much carbon dioxide (due to inadequate ventilation) or become overheated (from overbundling).
This could possibly explain why epidemiologic studies have previously shown that SIDS infants are often found in unsafe sleep environments, such as sleeping face down with their face in the pillow, or sleeping with another person in the bed.
Kinney and her colleagues based their new work on 71 infants who died suddenly and unexpectedly and were autopsied at the San Diego County Medical Examiner's office between 1997 and 2008. The researchers grouped the infants according to sleep circumstances - those considered safe (asphyxia not likely) or unsafe (asphyxia likely) based upon death-scene investigation reports.
They finally compared 15 SIDS-classified infants whose deaths were deemed not to involve asphyxia (group A), 35 SIDS-classified infants whose deaths were possibly asphyxia-related (group B) and 9 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.
Kinney says 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. Neurochemical measures didn't differ significantly between these two groups, but each group differed significantly from the controls.
"Even the infants dying in unsafe sleep environments 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."
Kinney's team believe 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 unsafe sleeping environments that can cause any baby to die, such as entrapment in the crib, but if it's just sleeping face down, the baby who dies may have an underlying brainstem vulnerability," Kinney concluded. "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."
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Source: Boston Children's Hospital