“It’s a good first study,” says Felderhoff-Müser. It might be worth pursuing the clues further. However, it is only a pilot study and SIDS is also a relatively rare phenomenon. This entails limitations that must be taken into account when interpreting the data. “If you take a closer look at the results, there is not enough selectivity between the individual groups,” she says.
The study has a number of weaknesses
The researchers from Sydney and Westmead examined blood samples taken on days two to four after birth. In fact, they found significantly lower levels of BChE activity in infants who died from SIDS compared to babies who died from a known cause and to a control group of more than 500 living children.
Sudden infant death in the delivery room
Sudden infant death occurs when an infant dies before the age of one year from unknown causes. “The original definition of SIDS actually excludes the perinatal period,” says Christoph Bührer, Director of the Charité Berlin Clinic for Neonatology. This applies to the time up to the seventh day of life of the newborn; SIDS cases are usually only counted as such from the 21st day of life. However, this neglects the time in the first hours after birth, says the doctor. In 2020, 2,373 children died in their first year of life in Germany, more than half of them within the first seven days after birth.
Christian Poets, Head of the Department of Neonatology at the University Hospital in Tübingen, agrees: “For a number of years, it has been recognized that sudden infant death can also occur directly after birth.” Studies confirm this. Several classic risk factors for SIDS come together: the child lies on its stomach, usually on its mother. She, in turn, is exhausted from the birth and sometimes does not notice when the newborn’s airways are not clear. “These cases stayed under the radar for a long time and were therefore not included in the prevention recommendations,” says Poets. All you have to do is instruct the parents to make sure that their noses are always free when cuddling.
Better monitoring of newborns, especially primiparae, could prevent some of the early cases of SIDS that may occur.
However, the values of all groups showed a large scatter. Since the blood samples were also taken so shortly after birth, only very limited statements can be made about the BChE activity at the time of death. Further information about the child and parents is also missing, because there was only a drop of blood and the diagnosis of a forensic doctor.
In addition, the activity of the “sister” cholinesterase AChE was missing in the data, an analysis was not possible due to methodological difficulties. Previous studies had found an increased amount of AChE and an acetylcholine receptor in the hearts of SIDS children. This can cause blood pressure to drop and people may faint.
The greatest limitation of the current study, however, is the study design: The researchers compared 26 children who died of cot death at the maximum age of 35 weeks with 30 children who died early for other reasons. Not only are these very small samples, the ages also vary greatly. Some of the »non-SIDS« children were almost two years old when they died. In addition, six values were removed from the “non-SIDS” group after the measurements were completed because, according to the study authors, they were repeatedly below the standard curve. Taken together, these limitations massively weaken the validity of the study results.
“The enzyme is therefore unsuitable as a biomarker with predictive power.”(Christoph Bührer, neonatologist)
Accordingly, SIDS experts are surprised by the euphoric headlines in the media. “The overlap between the case and control values is so great that I don’t know where the difference is,” says Christoph Bührer, director of the Charité Berlin’s neonatology clinic, making it even clearer than his colleague from the Essen Children’s Hospital. The medians of the measured values may differ significantly, but the scatter of the values is too large. “A child cannot be assigned to the SIDS or control group based on an individual measured value,” explains the President of the Society for Neonatology and Pediatric Intensive Care Medicine (GNPI). “The enzyme is therefore unsuitable as a biomarker with predictive power.”