A team of researchers in Australia may have identified a biomarker for Sudden Infant Death Syndrome (SIDS) in new research that was published in eBioMedicine. The team was led by Dr. Carmel Harrington at Children’s Hospital at Westmead in Australia, a researcher and mother whose son died from SIDS 29 years ago.

What is Sudden Infant Death Syndrome (SIDS)?

Sudden Infant Death Syndrome (SIDS) is a category of Sudden Unexpected Death in Infancy (SUDI). Although some SUDI can be explained, others cannot. The unexplained infant deaths are classified as SIDS. SIDS is the death of a healthy baby that cannot be determined by post-mortem for a conclusive cause of death and typically occurs during the sleep periods of babies under 1-year-old.

What are the SIDS Statistics?

In the United States, according to the Centre for Disease Control (CDC), every year there are about 3,400 SUDIs. In 2019 there were 3376 SUDIs, of this number, 1248 were SIDS deaths, 1173 deaths were due to unknown causes, and 955 deaths were accidental suffocation and strangulation deaths. 

From the data, it is clear that deaths from SIDS were the highest in 2019 at 37% of SUDIs. This is an improvement from decades ago, as SIDS deaths have been on the decline since 1990, moving from 130.27 per 100,000 live births to 33.3 per 100,000 live births in 2019. The reduction in SIDS is attributed to the release of The American Academy of Paediatrics’ safe sleep recommendations in 1992.

However, despite the progress, CDC data shows SIDS death rates for 2014-2018 were twice as high for American Indian/Native (89.5) and Non-Hispanic Black babies (72.7) per 100,000 live births than for Non-Hispanic White (36.7) babies. Hispanics (20.7) and Asian/Pacific Islanders (13.8) had the lowest rates of SIDS per 100,000 live births.

Overview of the SIDS Research

Dr. Harrington’s research tried to find out if babies who had died from SIDS had different levels of Butyrylcholinesterase (BChE) at birth than babies who had not died from SIDS or babies who were alive at the time of the study.

Butyrylcholinesterase (BChE) is a protein of the cholinergic system which is responsible for regulating brain functions like sensory processing, attention, sleep, and arousal. The reason why this is important is that it has long been speculated that the cholinergic system was involved in SIDS deaths. Since SIDS deaths occur during sleep, the reasoning is that there is a dysfunction in SIDS infants’ arousal system which would stop them from waking up if something is not right. A low level of BChE is believed to impair the functions of the cholinergic system.

To test this hypothesis, Dr. Harrington and her team tested dried blood samples that were taken 2-4 days after birth from 26 babies who had died from SIDS; 30 babies whose death were not from SIDS and 545 surviving babies who were born at the same time as the study group. The aim was to see if there would be a difference in the BChE levels of the babies who died from SIDS from the other babies in the control groups.

What did the SIDS Research Find?

The results of the study showed that SIDS infants had significantly lower levels of BChE than non-SIDS infants and the control group. Additionally, the results showed that lower levels of BChE were associated with SIDS deaths. However, there was no link between lower levels of BChE and non-SIDS deaths.

Why is this Research Important?

This research is important because it is believed that SIDS is caused by a combination of factors known as the Triple Risk Model.

The Triple Risk Model aims to help researchers better understand the risk factors for SIDS. The model suggests that there are three factors when combined can cause SID deaths. The factors include:

1.  A vulnerable infant with underlying defects or abnormal brain activity
2. A critical development period is within the first 6 months of the baby’s life characterised by rapid growth and development
3. Outside stressors which are environmental, including baby’s sleep position, overheating and second-hand tobacco smoke

Based on Dr. Harrington’s research, the identification of BChE as a possible biomarker or biological indicator for SIDS could be the missing part of the puzzle to answer the question: What makes infants vulnerable to SIDS? That is, BChE could explain the underlying defect or abnormal brain activity that puts babies at risk of dying from SID when the other two factors are present.

Knowing this can help in the development of screening infants for specific risk factors with targeted prevention strategies for SIDS.

What are the Limitations of the Sudden Infant Death Research?

Although very important, this research had a few limitations. Firstly, the sample size of the study was small. The researchers only sampled 29 SIDS infants. This fact makes it hard to generalise the findings to the wider population.

Secondly, the researchers noted that AChE is also a part of the cholinergic system and low levels could possibly be implicated in its dysfunction, but ACHE levels were not tested and compared in the trial.

Additionally, SIDS death rates vary by and within countries. The study did not compare samples from other countries. How could future research address these discrepancies? For example, SIDS death rates are higher in the USA than in the UK.

Further, within the United States, data show that SIDS death rates are higher for Native Americans and African Americans than for other ethnic groups. Are these groups at the centre of the perfect storm of the Triple Risk Model, or is there another explanation? Why are SIDS death rates higher in America than in other developed countries?

Now that the findings of this research have been released, future research will need to address all these questions and more for a better understanding of SIDS.