For years, it has been known that babies who sleep face-down are at greater risk of sudden infant death syndrome (SIDS), especially if they were premature. But no one knew exactly why. Now Australian researchers at the University of Adelaide think they may have found the answer.
The researchers have uncovered a developmental abnormality in babies — especially in premature babies and in boys — that for the first time has been directly linked to cases of SIDS. The abnormality, in the brain’s control of head and neck movement, breathing, heartbeat and the body’s responses to deprivation of oxygen supply, could be the reason why some babies sleeping on their front are more at risk of SIDS.
“Our studies have now discovered a significant abnormality within key regions of the brain stem in SIDS babies, specifically in parts of the brain stem that control breathing and movements of the head and neck. This abnormality is directly linked to SIDS cases,” said Dr. Fiona Bright. “While the exact cause of death in SIDS has not been identified, multiple studies have pointed to a subset of SIDS babies that are not entirely ‘normal’ before death. These infants all seem to have some form of underlying vulnerability, exposing them to increased risk.”
The abnormality is in the transmission in the brain of a neuro-peptide, known as “substance P”, and its binding with an associated neuroreceptor, “neurokinin-1” (NK1R). Until now, worldwide investigations of the role of substance P in SIDS have been inconsistent and inconclusive.
“Substance P and the NK1R neuroreceptor play a critical role in the brain’s control of the respiratory system, the cardiovascular system, and in how the body responds to hypoxia — that is, deprivation of oxygen at the cell level,” said Dr. Bright. “An infant with this abnormality is likely to have impaired respiratory and motor responses to life-threatening challenges during sleep. While they may be otherwise healthy looking, there is an inability for that child’s brain and body to respond appropriately to an event in which the child is deprived of oxygen in some way.”
SIDS risk rises in front-sleeping babies
Study supervisor Professor Roger Byard, Professor of Pathology at the University of Adelaide, says this abnormality is a key reason why it is more dangerous for babies to sleep on their front.
“We’ve known for many years that babies sleeping face down places them at greater risk of SIDS — now we have a much better understanding as to why,” Professor Byard says.
“If a child has this underlying vulnerability in its brain chemistry, and its breathing becomes compromised by sleeping on its front, that child is at greater risk of death because its body simply can’t respond in the normal way. The baby can’t lift its head, and its breathing and heartbeat will be compromised,” he said.
The research was conducted by Bright and Byard of the Adelaide Medical School, in collaboration with Professor Hannah Kinney’s lab at Harvard Medical School and Boston Children’s Hospital. The results of the study, which investigated 55 SIDS cases in the United States, are now published in the journal PLOS ONE.