SIDS: Is Hope Finally on the Horizon?

For years now, research into SIDS has come up with similar findings based on the following three hypostheses:

First, researchers suggest that some babies have a physical abnormality that makes their breathing systems unable to respond protectively when under stress;

Second, they hypothesize that the brain centres that control breathing and heart rate are immature and continue to develop during the first year of life. So they are not yet capable of overcoming threats to breathing; and

Third, the researchers theorize that the baby is under a stressor that renders breathing more difficult, whether from sleeping on his / her belly or side, or in very soft bedding; or from having a viral infection or having been born premature.

For most babies, when they suddenly face a challenge to breathe, their nervous system detects this sudden change and sends distress signals to the brain that then increase the baby’s level of arousal and breathing effort – so the baby rescues himself or herself. Yet so many infants experience such conditions but they do not die from SIDS. So it seems that these risk factors alone don't form 'the whole picture'.

A new study confirms that infants who die of sudden infant death syndrome (SIDS) have a serotonin abnormality in the brainstem that affects responses to breathing and carbon dioxide, as well as to temperature, blood pressure, and heart rate. This study was conducted by a team of doctors from the Department of Pathology, Children’s Hospital Boston and Harvard Medical School who compared brain autopsies of 41 babies: most who died from SIDS, and the rest who died from other known causes.

The Feb. 3 2010 edition of JAMA (The Journal of the American Medical Association) described this research into the brain chemicals that help communication in the brain for monitoring breathing, changing the level of arousal, and responding to external stress.

The researchers, led by children's neuropathologist Dr. Hannah Kinney, found that one chemical was significantly less in the brains of babies who had died from SIDS. The researchers compared autopsies of the brains of SIDS victims to those of the babies who had died from known causes, and measured the amount of serotonin in each.

The investigators found that the level of serotonin in SIDS babies was 26% lower than in babies who had died from other causes. They also looked at compounds that would be created if serotonin was broken down too quickly. These levels were the same for all of the babies. So they determined that low levels of serotonin did not occur because the chemical was being destroyed, but rather because there was never enough there in the first place.

They also found that the SIDS babies lacked the normal number of receptor sites in the brain to which the serotonin could attach and transmit neurological messages throughout the system.

The researchers hypothesised that the SIDS babies couldn’t rescue themselves when their breathing was under stress due to low levels of serotonin: a vital messenger in the brain’s warning and self-protection system

Serotonin is thought to help coordinate breathing and sensitivity to carbon dioxide. When babies sleep face down, it is believed they breathe in exhaled carbon monoxide; taking in less oxygen. A rise in carbon dioxide activates nerve cells in the brainstem, to stop most babies from asphyxiating.

Therefore, the researchers believe that babies who die from SIDS have defects in their serotonin system -- impairing their reflex to wake up and turn over.

These doctors now hope to develop a diagnostic test to identify infants at risk for SIDS. They also hope to develop a treatment to protect infants who have these abnormalities.


SOURCES:

The Journal of the American Medical Association:  2010 Feb 3;303(5): 430-7

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