About 3,400 babies die of sudden infant death syndrome (SIDS) each year in the U.S., according to the Centers for Disease Control and Prevention (CDC).
Now, a new study led by researchers at Boston Children’s Hospital and Harvard Medical School suggests that some of the unexplained deaths may be caused by an abnormality in the medulla, which connects the brain stem and the spinal cord.
The study was published in the Journal of Neuropathology & Experimental Neurology on May 25.
"We found abnormalities in a particular receptor (the serotonin receptor 2A/C) in the medulla oblongata, part of the lower brain stem that regulates autonomic and respiratory function, in a subset of SIDS infants," lead author Dr. Robin Haynes, PhD, who is a principal associate at Harvard Medical School, told Fox News Digital via email.
When a baby isn’t getting enough oxygen, the serotonin receptor 2A/C triggers the baby’s natural instinct to gasp for air, the doctor explained.
When the receptor has an abnormality that doesn’t allow it to function correctly, it doesn’t send the signal to the baby to "reoxygenate the brain."
"This places them at greater risk in unsafe sleep conditions, such as prone sleep and bedsharing, when the levels of oxygen around the infant’s airway may be lower than normal," Haynes said.
The researchers analyzed brain tissue from 70 infants who died. All 58 of the babies who died from SIDS were shown to have the altered serotonin receptor 2A/C.
Previous studies also linked abnormalities in the brain and nervous system to a higher risk of SIDS, Haynes said.
Older SIDS infants showed more of these abnormalities than younger infants, which surprised the researchers.
"This suggests the possibility that there are different pathological mechanisms in younger versus older SIDS infants," said Haynes.
"More research is necessary to better understand these mechanisms and how they relate or interact with the specific environmental risk factors that infants may face."
‘No way to identify risk’
While the study sheds light on one potential cause of SIDS, there is currently "no way to identify an infant at risk for SIDS," Haynes said — as babies who die of SIDS appear healthy up until the unexplained death.
"Abnormalities in this neurotransmitter system are undetectable in a living infant," she said. "Because of this, it is critical at all times to follow safe sleep practices."
"It is critical at all times to follow safe sleep practices."
Dr. Chandani DeZure, a board-certified pediatrician in Palo Alto, California, who is also a member of the BabyCenter Medical Advisory Board, was not involved in the study but shared her opinion of the findings.
"Research shows that inadequate levels of serotonin found in the brain stem of 70% of babies who passed away from SIDS may make an infant more vulnerable," DeZure told Fox News Digital.
Serotonin is important during sleep as it affects heart rate, breathing and blood pressure, the doctor explained.
"While this study adds to the growing body of evidence about the potential role of serotonin in SIDS, we still don't know how to identify babies who may have an underlying vulnerability," she added.
Some factors do put babies into a higher risk category, however.
A SIDS diagnosis is made only when no other cause of death is identified after a full investigation.
Babies between 2 and 4 months old are most likely to experience SIDS, with 90% of cases occurring in infants under 6 months old, DeZure noted.
"Further, babies born prematurely, babies with a family member who died of SIDS, those who have smoke and alcohol exposure in the womb and/or home, and children with underlying physical vulnerabilities (such as certain heart conditions or breathing issues) are high at-risk groups," she went on.
There has been a trend of disproportionately high cases of SIDS in Black and Native American/Alaskan Native families, DeZure said.
"It’s important that research help address these health disparities in marginalized communities," she said.
Safe sleep habits key to prevention
A SIDS diagnosis is made only when no other cause of death is identified after a full investigation, according to the Cedars Sinai website.
Although studies like this one point to possible causes of SIDS cases — including brain abnormalities, respiratory illness and heart function — there is no way to predict which babies might be more susceptible, experts say.
"Until we have more research, the best things for parents to do is try to minimize the risk of SIDS by using proven methods like safe sleep habits and breastfeeding (if possible), especially during the first few months of life, when newborns are the most vulnerable of dying from SIDS," said DeZure.
The American Academy of Pediatrics (AAP) launched its Back to Sleep campaign in the early 1990s; that program has since been renamed Safe to Sleep.
The AAP’s guidelines call for putting babies to sleep on their backs on a firm, flat surface at naptime and bedtime, with no pillows, loose bedding or other objects that could interfere with breathing.
While it’s recommended that babies sleep in the same room as parents or caregivers, they should not share the same bed, the AAP says.
Breastfeeding, giving babies pacifiers and having daily "tummy time" sessions have all been shown to lessen the risk of SIDS.
Using home baby monitors shouldn’t be regarded as a means of preventing SIDS, the AAP states.
"There is no data to suggest this works and, if anything, it can cause harm by increasing parental anxiety or giving false reassurance," DeZure said.
Since the AAP’s campaign launched, SIDS cases have been reduced by nearly half, the doctor said.
"However, after 2001, SIDS cases in the U.S. remain the leading cause of death for infants under 1 year old, so there is a vital role for research that can help find additional ways to reduce the risk of SIDS," she added.
If parents have questions about how to prevent SIDS, they should speak to their baby's pediatrician or primary care physician for more information, said DeZure.