Cot death may be caused by a treatable genetic brain disorder, scientists have found.
Sudden Infant Death Syndrome (SIDS) is a mysterious condition that terrifies parents and kills around 300 babies every year in the UK.
But another piece in the jigsaw which helps doctors understand why has now been found by a team of experts in the US who say they have uncovered strong evidence that victims have a brain abnormality.
It means some babies cannot tell when there is not enough oxygen in the bloodstream - leaving them much more vulnerable to being smothered.
They are particularly at risk in situations where they are inhaling in their own recycled breath, such as when they are sleeping face-down or have their faces covered by bedding.
"These findings provide evidence that SIDS is not a mystery but a disorder that we can investigate with scientific methods, and some day, may be able to identify and treat," said senior author Hannah Kinney of the Boston Children's Hospital.
"Our goal is to find a way - a diagnostic test - to identify these defects in living infants and then find a way to correct these defects by drugs or other means as the infant passes through the first six months of life, the period of greatest risk for SIDS."