Brainstem Abnormalities in Infant Deaths Linked to SIDS

Infants who die suddenly and unexpectedly tend to have underlying brainstem abnormalities that researchers have linked to SIDS, or sudden infant death syndrome, according to a new study in the journal Pediatrics.

The brainstem abnormalities, which include factors that impair breathing, blood control, heart rate and body temperature, were found to be typical in SIDS babies that died in both safe and unsafe sleeping environments, researchers from Boston Children's Hospital report.

Babies who die of SIDS tend to have differences in brainstem chemistry that sets them apart from infants dying of other causes, the researchers said.

"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," said Dr. Hannah Kinney, a neuropathologist at Boston Children's and lead author of the study. "The abnormality prevents the brainstem from responding to the asphyxial challenge and waking."

Often infants who die suddenly and unexpectedly are also found in unsafe sleeping situations such as sleeping face down into a pillow or sleeping with another person in the bed. In the new study, Kinney and her colleagues reexamined the cases of 71 infants who died suddenly and unexpectedly; each of the infants received an autopsy from the San Diego County Medical Examiner's office sometime between 1997 and 2008 and still had brainstem samples available for analysis.

Based on the death-scene investigation reports, the 71 infants were grouped into two categories, those where asphyxia was likely (an unsafe sleep environment) and cases where asphyxia was unlikely (a safe sleeping environment).

Kinney and her colleagues compared 15 infants with SIDS whose deaths were deemed not to involve asphyxia, 35 SIDS infants whose deaths were possibly asphyxia-related and nine infants who clearly died from other causes (used as controls). The other 12 infant death cases either had insufficient data or had evidence of other clear risk factors for death, such as exposure to drugs or extremes of temperature, and were factored out of the study.

In groups where there was a possibility of infant asphyxia and there was no clear signs of any asphyxia, the researchers found brainstem neurochemical abnormalities. Neurochemical measures didn't differ significantly between the two groups, but each group differed significantly from the controls, the researchers said.

This led them to conclude that SIDS 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 said. "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.

"Safe sleep practices absolutely remain important, so these infants are not put in a potentially asphyxiating situation that they cannot respond to," she added.