Did we find the “cause” of SIDS?

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As a pediatrician who has seen cases of infant death, the idea of finding a biomarker or solution for SIDS is undeniably appealing.

Recent headlines make the claim that the “cause of SIDS has been found” based on a study from a research team in Australia. But is that really what the research shows?

Here are my thoughts.

For those who want just the summary…

As a pediatrician who has seen cases of infant death, the idea of finding a biomarker or solution for SIDS is undeniably appealing. This research may provide an avenue for further investigation, but I don’t think it tells us a whole lot yet.

And (importantly) it doesn’t change that we know of certain interventions that decrease the risk of infant death:

• Put your infant on their back to sleep (even for naps) — no inclined sleeping!

• Avoid loose sheets, blankets, pillows, BUMPERS, stuffies, or anything else in the crib

• Use approved firm crib mattresses without additional layers & a fitted mattress cover. Our adult mattresses and bedding are too soft.

• No co-sleeping. I am sorry, but the risks here trump any benefits.

• No exposure to second-hand smoke, alcohol and illicit drugs

• Pacifier at sleep onset

• Keep up with preventive care, immunizations, etc

• Breastfeeding

  • On this one, I don’t want those of you who are unable to or choose not to breast-feed to feel guilty. Everything is a balance, and focusing on the factors that you can control is more important here. And recognizing that a birthing parent’s sanity and well-being are also critical for infant well-being.

Here’s the long version :)

Any infant death is awful. Little is known right now about why some infants are more susceptible to SIDS than others. The truth is that this research is promising, but it doesn’t change much from a practical perspective.

SUID and SIDS

About 3400 infants a year die unexpectedly, according to the CDC. But many articles, and parents, confuse SIDS (Sudden Infant Death Syndrome) with SUID (Sudden Unexplained Infant Death) but they are not exactly the same thing.

SUID includes all unexpected infant deaths (for example, from SIDS, suffocation, entrapment, strangulation etc).  SIDS is the term used when an infant dies without any clear explanation.

The study

The study (PMID: 35533499) looked at dried blood samples from 722 infants. The samples were taken 2-4 days after birth but not analyzed immediately.

The infants were categorized into one of three groups: those who died from SIDS (26 infants), those who died of other known causes (41 infants), and the remaining 655 living infants. 

Researchers compared levels of an enzyme called Butyrylcholinesterase across the groups and found that the levels of this enzyme were lower in the SIDS cases than in the other groups.

What is Butyrylcholinesterase?

This enzyme works in the nervous system to help regulate blood pressure, breathing, and arousal—so it makes sense that it may play a role in SIDS.

Issues with the study

This study adds to the body of knowledge, but it is far from conclusive. Some issues with the study design include:

• Small sample size

• Blood samples were dried (some even up to 2 years old!)

• There was actual overlap in the blood levels in the different groups

  • As you can see from the graph below: the levels of enzyme in babies who died (the red bars) overlapped with babies who did not die (the blue or control group).

  • Although the trend here is suggestive, if you have a baby with a low level of this enzyme, you cannot necessarily predict which group they would be in.

• Assessment of which babies died of SIDS was based on coroners’ diagnoses, rather than autopsies.

So what causes SIDS?

Most clinicians and experts see SIDS as a multi-factorial issue. Although this enzyme may play a role, there are almost certainly other factors that matter too.

The leading hypothesis is that infants who die of SIDS have underlying issues with arousal, and don’t always wake in response to dangerous situations.

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I can remember every single baby I’ve taken care of that has died. Thankfully, there aren’t many, but there is a very specific anguished cry that you hear from a parent who has lost their child. It is a fate I wouldn’t wish upon anyone.

I wish, so much, that we could find (and address) the causes of SIDS. And perhaps this study is a step in that direction. But we aren’t there yet.

So for now, I implore you to make sure you adhere to our data-based recommendations so we can minimize those conditions that make SUID more likely.