Australian researchers may have come closer to taking the mystery out of Sudden Infant Death Syndrome, the death of otherwise healthy babies, that are often ruled "undetermined".
An Australian study of about 30 babies who died from SIDS, or cot death, has discovered they have decreased levels of a protein that helps adults and babies wake up if they stop breathing from sleep apnoea.
Researchers from The Children's Hospital at Westmead, Dr Rita Machaalani and doctoral student Nicholas Hunt, found a 20 per cent decrease in a protein called orexin in the babies who had died of SIDS compared with a control group of 12 babies.
Not all babies who died of SIDS had the decreased level of orexin, the original study by Mr Hunt found. But when the levels of orexin were averaged among the SIDS babies, they were lower than in the control group, Dr Machaalani explained.
"This response to tell them to wake up is not as strong as it would be [in other babies without SIDS]," said Dr Machaalani, a senior clinical lecturer at the University of Sydney and manager of the sleep unit at The Children's Hospital.
The breakthrough coincides with the announcement on Wednesday that Brenda King, a mother whose son nearly died from suspected SIDS more than five years ago, has been awarded the 2016 Research Australia Advocacy Award after raising $130,000 for SIDS research at Westmead.
"Ryan was basically dead on my lap and, after we revived him via CPR, we went to casualty and then back many times to the specialist facility at Westmead," Ms King said.
"We left the hospital extremely grateful and with our son, but without answers; we didn't know what happened, why it happened or if it would happen again.
"We had to go to the Children's Hospital every fortnight to monitor his breathing and heart rate, and through that contact we realised how little research and funding they had."
Ms King's son Ryan is now five, and on Wednesday attended orientation day to start school next year.
Orexin is a neuropeptide that regulates wakefulness and arousal, and research has found adults with narcolepsy, a sleep disorder that causes chronic sleepiness and involuntarily sleep, often have less of this neuropeptide than other people.
It is the second protein that researchers have discovered is associated with SIDS, which killed as many as 500 Australian babies a year until researchers found that putting children to sleep on their backs decreased the risk. Before this discovery, many women were accused of killing or smothering their babies for the lack of any other explanation.
American researchers also found lower levels of serotonin in babies who had died from SIDS. Serotonin is a brain chemical - a neurotransmitter - that conveys messages between cells and plays a vital role in regulating breathing, heart rate, and sleep, researchers funded by the National Institutes of Health reported.
The discoveries have raised hopes that babies could be screened for this risk in the future. But Dr Machaalani said the research - published in Acta Neuropathologica - was just the "tip of the iceberg" and screening was at least 10 to 15 years away.
Much more needed to be known first.
"It could be used as a screening tool, but first we need to know if this [protein] is changed in the blood, and those changes are seen in the brain. And then we need to look at genetics to see if it is inherited," Dr Machaalani said.
But Dr Machaalani said she hoped the discovery would give hope to parents whose children's deaths were ruled "undetermined" by forensic pathologists.
She said many of these experts were increasingly giving a diagnosis of undetermined, which could be heartbreaking for a parent.
The next effort was to go back and give these parents a diagnosis and "say these cases are SIDS".
Dr Machaalani said the US research into serotonin found that only 10 to 15 per cent of children with the decreased levels of serotonin had a genetic marker.
In Australia in 2013, 117 babies died suddenly and unexpectedly; of those deaths, 54 were identified as SIDS.
Brenda King's SIDS Stampede fun run was started in 2011 after her son's near-miss. It is one of only two main sources of funding for SIDS.
The chief executive of Research Australia, Nadia Levin, will present the award to Ms King at a black-tie function in Sydney on Wednesday night.
"We are thrilled to award the 2016 Research Australia Advocacy Award to Brenda," said Ms Levin. "Not only do advocates like Brenda raise funding for research, but her work in raising awareness in the community is beyond any dollar measure. Advocacy and giving is part of what makes scientific advancement and research possible, and Brenda's SIDS Stampede is testament to her passion and commitment to this cause."
Other award winners include Dr James Little, Professor Ian Hickie and Ita Buttrose.