New Research Offers Clues as to Why Some Babies Die of SIDS

Scientists in Australia have found that some babies at risk of sudden infant death syndrome, or SIDS, have low levels of an enzyme called butyrylcholinesterase (BChE) in their blood.

Their study, published May 6 in the journal eBioMedicine, could pave the way for newborn screening and interventions if the results are corroborated by further research.

“It’s the first time we’ve ever had a potential biomarker for SIDS,” said Dr. Carmel Harrington, who led the research at the Children’s Hospital at Westmead, in Sydney, Australia.

Researchers have been trying to chip away at the biological underpinnings of the puzzling syndrome for decades. And while public health campaigns have drastically reduced the incidence of SIDS, it remains a leading cause of sudden and unexpected death in infants under the age of 1 in Western countries. In the United States, about 3,400 babies die suddenly and unexpectedly each year, according to the Centers for Disease Control and Prevention.

This includes infants who die suddenly from a known cause, such as suffocation, as well as those who die without a clear cause, such as from SIDS. Nearly half of the sudden and unexpected infant death (SUID) cases in the U.S. are due to SIDS.

What the new study found

One of the reasons that SIDS remains so tragic and mysterious is because it is likely not caused by a single biological mechanism, but a combination of factors that come together in a perfect storm, said Dr. Thomas Keens, a pediatric pulmonologist at Children’s Hospital Los Angeles. Previous studies have pointed to low activity or damage in parts of infants’ brains that control heart rate, breathing and arousal from sleep, for instance, as well as to environmental stressors such as soft bedding or secondhand smoke.

“The thinking among researchers is that some babies die from SIDS because they don’t wake up in response to a dangerous situation when they’re asleep,” Dr. Keens said.

To test if there were something inherently different in SIDS babies, Dr. Harrington and her colleagues compared dried blood samples from the newborn heel prick test of 655 healthy babies, 26 babies who died from SIDS and 41 babies who died from another cause. They found that about nine out of ten babies who died of SIDS had significantly lower BChE levels than did the babies in the other two groups.

“I was just stunned,” said Dr. Harrington, who has been searching for clues and crowdfunding for her research for nearly 30 years, ever since she lost one of her own children to SIDS. “Parents of SIDS babies carry a huge amount guilt because essentially their child died on their watch. But what we’ve found with this study is that these infants are different from birth, the difference is hidden and nobody knew about it before now. So it’s not parents’ fault.”

The new findings add support to researchers’ hypothesis that babies who die from SIDS have problems with arousal, said Dr. Richard Goldstein, a pediatric palliative care specialist at Boston Children’s Hospital. BChE plays a role in the availability of important neurotransmitters in the brain’s arousal pathway. Low levels of the enzyme could indicate that the brain is not able to send out signals telling a baby to wake up and turn her head or gasp for breath. “But we need a lot more research before we can understand its actual significance,” Dr. Goldstein said.

What parents should know

While the study identifies an important chemical marker in a small group of infants, it is too soon to say if widespread testing for BChE will be helpful.

For one, scientists and doctors do not know what a “normal” level of the enzyme looks like. And because the Australian researchers did not have access to fresh blood samples for BChE, they did not measure absolute levels of the enzyme. There was also overlap between the infants. Some of the babies who died from SIDS had BChE levels within the same range as the babies who did not die.

“If you’re going to test every baby who’s born, you want the results to stand out as abnormal only for babies who are at very high risk,” Dr. Keens said. Even if further studies helped fine-tune the test for BChE to accurately distinguish between babies who might die from SIDS and those who might go on to live healthy lives, doctors and parents would still be faced with a dilemma: What to do next? Currently, there is no intervention or treatment for low BChE levels.

Much of the advice for preventing SIDS remains the same, Dr. Keens said. Make sure that you follow safe sleep recommendations like laying your baby down on her back — both at nap time and at night. Remove loose sheets, blankets, pillows, bumper pads and soft toys from your baby’s sleep area. And consider keeping your baby in the same room as you at night for at least six months, or, ideally, until your baby turns a year old.

The American Academy of Pediatrics also recommends avoiding exposure to smoke, alcohol and illicit drugs during pregnancy; breastfeeding; immunizing routinely; and using a pacifier to reduce the risk of SIDS.

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