An enzyme in the blood of babies is linked to the risk of sudden infant death syndrome

Scientists may have come a step closer to discovering the causes of sudden infant death syndrome in a study hailed as a significant breakthrough by the British scientist whose work underpinned the Back to Sleep campaign of the 1990s.

The study is the first to identify a biochemical marker in the blood that is linked to the risk of SIDs, sometimes called sudden death, when an apparently healthy baby dies in its sleep. Although the test is not accurate enough to be used for newborn screening, it suggests that abnormally low levels of a chemical related to the brain’s arousal system could be involved in the sudden death of these babies while they sleep.

“This is a very important observation,” said Professor Peter Fleming of the University of Bristol, whose work is credited with preventing tens of thousands of baby deaths in the UK after the Back to Sleep campaign launched in the 1990s. “If this tells us something new about the mechanism, then that’s very important.”

The investigation was led by Dr. Carmel Harrington, an honorary research fellow at Children’s hospital in Westmead, New South Wales, who lost her own son, Damien, to Sids 29 years ago. Harrington and her colleagues compared dried blood samples taken during heel prick testing from newborns of 655 healthy babies, 26 babies who died of Sids and 41 babies who died in infancy of other causes.

They found that infant Sids had lower levels of an enzyme called butyrylcholinesterase (BChE), which plays an important role in the brain’s arousal pathway. This could indicate an arousal deficit, which reduces the baby’s ability to wake up or respond to the external environment, such as being overheated or a blanket pulled over the face. This could cause vulnerability to Sids, the scientists said.

“Until now we didn’t know what was causing the lack of arousal,” Harrington said. “Now that we know BChE is involved, we can start to change the outcome of these babies and make Sids a thing of the past.

“A seemingly healthy baby who falls asleep and doesn’t wake up is every parent’s nightmare and until now there was no way of knowing which baby would succumb.”

However, at this stage, the BChE test would not be useful as a screening tool for newborns. Although the baby Sids had lower levels on average, there was also a lot of overlap between the groups, with about half of the baby Sids falling within the same range as half of the babies who didn’t die.

The biomarker was also not as powerful a predictor as some previously known environmental factors, such as smoking during pregnancy, which is linked to a more than threefold increase in the incidence of SIDS. Babies with low levels of BChE had a 1.1- to 1.5-fold increased risk of SID.

“What worries me, and I’ve already gotten calls from grieving families, is that at this stage it’s not usable by the individual,” Fleming said. “It’s useful at the population level.”

The findings could help explain how smoking during pregnancy leads to biological changes that put babies at higher risk for SID, for example. “Much more research is needed,” Fleming said.

Jenny Ward, CEO of the Lullaby Trust, said: “The findings of this study are interesting and more work is needed. We look forward to seeing more as this research continues and we hope it will help us understand more about SIDS.”

She added that it was important that the findings not be seen as a reason to play down safer sleep advice, which includes “always putting the baby to sleep on his or her back in a clear sleeping space on a flat, firm, waterproof mattress without bulky bedding, pillows, or bumper pads.

The findings are published in Lancet eBioMedicine Journal.