Cot death babies lack a key brain chemical that regulates breathing, heart rate and sleep, research has shown.
Scientists in the US discovered abnormal amounts of serotonin in brain tissue samples taken from 35 children who died from Sudden Infant Death Syndrome (SIDS). Levels of the chemical were 26% lower in the infants than in babies who died unexpectedly for other reasons.
The samples came from the medulla, a region at the base of the brain that regulates basic body functions. Serotonin is a neurotransmitter that helps cells in the brain transmit messages to one another. It has a number of functions and may be crucial to a baby's breathing.
The discovery may help explain the link between cot death and babies sleeping face down.
“We have known for many years that placing infants to sleep on their backs is the single most effective way to reduce the risk of SIDS,” said Dr Alan Guttmacher, from the Eunice Kennedy Shriver National Institute of Child Health and Human Development, the US body that funded the research.
“The current findings provide important clues to the biological basis of SIDS and may ultimately lead to ways to identify infants most at risk as well as additional strategies for reducing the risk of SIDS for all infants.”
The research, led by Dr Hannah Kinney from the Children's Hospital, Boston, is published in the Journal of the American Medical Association.
Dr Kinney said: “There's something about sleep that unmasks the defect, which we believe is in serotonin circuits: the baby experiences some kind of stress during sleep, such as re-breathing carbon dioxide in the face-down position or increased temperature from over-bundling, that cannot be compensated for by the defective brainstem circuits. ”