Following a series of recent investigations, performed by researchers at Boston Children’s Hospital, sudden infant death syndrome (SIDS) cases, also known as crib deaths, could be linked to brainstem abnormalities in young patients that were reared in both “safe and unsafe sleep environments.”
The research was led by Hannah Kinney, M.D., a neuropathologist based at Boston Children’s Hospital, with the findings published in the latest issue of the journal Pediatrics.
It has been two decades since the American Academy of Pediatrics launched a campaign to educate parents on the best sleeping practices for vulnerable, young infants. The “Back to Sleep” campaign highlighted the importance of putting newborn babies to sleep on their backs to reduce the risk of sudden infant death syndrome. With statistical evidence showing the number of deaths from SIDS to have halved since the scheme’s inception, researchers have proclaimed the program to have been a success.
What is Sudden Infant Death Syndrome?
SIDS is the unexpected, sudden death of a child under the age of one, whereby ensuing forensic autopsy, clinical history and assessment of the scene of death reveals no explicable cause of death.
Nonetheless, medical practitioners and researchers have theorized a number of factors to contribute towards increased risk of SIDS. It has been suggested that the baby’s sleep arousal is affected, alongside the body’s inability to detect accumulation of carbon dioxide within the bloodstream.
According to the Centers for Disease Control and Prevention (CDC), SIDS is the leading cause of death among infants between the ages of one month to one year and, in the United States, is the third leading cause of death for infants, overall.
According to a previous study, performed by Kinney and Bradley T. Thach, M.D., entitled The Sudden Infant Death Syndrome, a Triple-Risk Model is associate with SIDS pathogenesis. The model suggests that SIDS typically takes place when the infant is exposed to three simultaneous risk factors:
- Factor 1: underlying vulnerability in infant
- Factor 2: the incident takes place around a crucial developmental period
- Factor 3: can include one of any number of intrinsic (e.g. genetic, developmental) and extrinsic risk factors (e.g. sleeping position, infection)
Ultimately, however, according to the U.S. National Library of Medicine, the following risk factors have been suggested to contribute towards increasing an infant’s risk of SIDS:
- Sleeping on stomach
- Exposure to illicit drugs and cigarette smoke during and after pregnancy
- Co-sleeping (e.g. in same bed as parents)
- Soft bedding in crib
- Multiple baby births (twins etc.)
- Having a sibling who suffered from SIDS
- Premature birth
- Teenage pregnancies
- Short time period between births
- Poor prenatal care
- Living in poverty
Abnormal Brainstem Chemistry and SIDS Risk
Kinney and colleagues set out to determine whether there were obvious neurochemical differences between infants that had died suddenly and without warning, who had been subjected to safe and unsafe sleeping environments. Those infants deemed to have unsafe sleeping arrangements were at greater risk of dying from asphyxiation, relative to those infants that appeared to have safe sleeping environments.
The group revisited 71 cases of infants who had died suddenly and unexpectedly. These infants had been autopsied at the San Diego County Medical Examiner’s office, from 1997 to 2008. Brainstem specimens were acquired from the subjects, allowing more in-depth analysis.
Certain infants were categorized, based upon their risk of asphyxia-related mortality – a deficiency of oxygen supply to body, caused by abnormal breathing. 15 SIDS subjects were classified as having no risk (group A) and 35 separate SIDS subjects were classified as having deaths that were, quite conceivably, asphyxia-related (group B). The remaining 21 infants were excluded from the study, as the researchers considered that insufficient data was available to reliably categorize these individuals; additional risk factors were also thought to play a part in these children, ranging from contact with drugs to exposure to unsuitable temperatures.
Interestingly, the group discovered marked differences in neurochemical balance between normal infants and groups A and B SIDS infants. Brainstem neurochemical aberrations were associated with 14-3-3, GABA receptors, serotonin and serotonin receptors.
In reasoning how these neurochemical changes bring about SIDS, the researchers suggest that they impair neurological circuitry within this particular part of the brain. The brainstem includes the medulla oblongata, pons and midbrain and is involved in a number of basic physiological processes, ranging from cardiac and respiratory function to regulation of the sleep cycle. As a consequence, the research team consider that disruption to this region of the brain could prohibit slumbering babies from rousing when they rebreathe too much carbon dioxide, or became too hot.
There was no significant statistical difference in mortality risk between group A and group B infants; however, there was obvious difference between groups A and B, relative to normal infants. During a recent press statement, Kinney talked about his group’s novel findings:
“Even the infants dying in unsafe sleep environments had an underlying brainstem abnormality that likely made them vulnerable to sudden death if there was any degree of asphyxia… The abnormality prevents the brainstem from responding to the asphyxial challenge and waking.”
Kinney went on to discuss how unsafe sleeping environments, including entrapment within the crib, contribute towards SIDS infant mortality. However, he also suggests – even in circumstances where the infant’s environment may have been unsafe – there to be a link between irregular brainstem neurochemistry and incidence of SIDS.
She adds that safe sleep practices are of the highest priority, and parents should do everything within their power to ensure a “potentially asphyxiating situation” is avoided. Infants should always be placed on their backs in a safe and secure crib. Firm, tight-fitting crib mattresses should also be employed, with a light sheet used to cover the child. Pillows, comforters and quilts should all be avoided and the room maintained at a temperature that is not too excessive.
In the meantime, Kinney and her colleagues are now aiming to research a test that might identify these underlying vulnerabilities, alongside potential treatment methods, thereby preventing SIDS:
“We have to find ways to test for this underlying vulnerability in living babies and then to treat it. Our team is focused now upon developing such a test and treatment.”
By James Fenner