Where do we stand with understanding sudden unexplained infant deaths?

May 26, 2022  |  General

There is no question that our understanding of sudden infant death syndrome (SIDS) has advanced significantly over the past couple of decades. But it still accounts for about 10 % of deaths in children under 1 year of age. The syndrome has also been renamed and its description broadened. It’s now generally called sudden unexplained infant death, or SUID. The current thinking is that SIDS is really a subset of SUID, although it is the largest subset. Trends in this are shown in the graph below, taken from this recent essay in the New England Journal of Medicine.

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As you can see, the number of deaths from SIDS has been steadily dropping, being now only a third of what the number was in 1990. This has been attributed to the recognition that sleep position, particularly prone, influences the risk of SIDS. Hence the widely adopted “back to sleep” program of the American Academy of Pediatrics. But there are more complex things going on, and it’s clear we shouldn’t think of SIDS or SUID as only a problem of poor sleep hygiene. Modern medicine promotes a mixed, logically inconsistent message regarding SIDS: authoritative statements imply that SIDS is a consequence of unsafe sleep in biologically normal children, but there is vague acknowledgment that important biologic factors are involved in these deaths. What are these factors?

Observations from cardiorespiratory monitoring led to the association of serotonin and other neurotransmitter abnormalities in the brain stems of infants who died from SIDS with failures in autoresuscitation and arousal. Neuropathology associated with epilepsy has been observed in a substantial number of infants who died from SIDS. Numerous studies have revealed genetic differences between infants who died from SIDS and surviving, healthy infants; one study identified causative variants and plausible contributors to death in 11% of cases. Research on heritability in the back to sleep era revealed that younger siblings of babies who had died from SIDS were four times as likely as other babies to also die from SIDS; moreover, the risk of SIDS among first- through third-degree relatives was nine times as high as the risk in nonaffected families. So there’s a lot more going on here than sleep hygiene.

And another thing. After an infant dies from SIDS, often no standard medical care is provided to the family. Along with often failing to respond to families’ emotional pain and confusion, we permit postmortem assessment to focus primarily on the legalistic question of manner of death, rather than on the medical question of biologic and environmental causes. The current approach may answer questions about mistreatment, but it leaves any effort to know more about etiologic factors, including possible risks to siblings, to bereaved family members. Medicine doesn’t exhaustively attempt to explain these deaths, even though doing so would be routine in other disease areas.

So although it’s gratifying that the rate of SUID as decreased over the past decades, we appear to have reached a plateau. It is time of focus on molecular and physiologic mechanisms that might help explain the deaths that still occur. It’s probably complicated, but our capabilities now are far more sophisticated than when prone positioning was first shown to be a risk factor.

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