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What Really Causes SIDS?

Since the 1960′s, when sudden infant death syndrome (SIDS) was recognized as a distinct condition, doctors have been perplexed by its cause. Myths have cropped up in the absence of medical explanations, and the disease has been attributed to everything from toxic mattresses to negligent parenting. But over the decades, researchers have been uncovering concrete evidence of SIDS’ biological roots. This year, data was released that pinpoints a specific brain region and hints at a possible treatment down the road.

Abnormalities in the Brainstem

A recent study in the Journal of the American Medical Association found that babies who died of SIDS had lower levels of serotonin, a crucial neurotransmitter, in the medulla oblongata, the part of the brainstem that controls breathing, temperature, blood pressure, and heart rate. The lead author on the study, Hannah Kinney of Harvard, thinks that low levels of serotonin compromise the medulla’s ability to regulate these functions, making the babies unable to detect when they don’t have enough oxygen.

The idea that a brain abnormality underlies SIDS is not a new one. The first signs of faulty wiring were identified in 2006 when Kinney and her team saw another distinctive pattern in the brainstems of SIDS victims. They had more serotonin-using neurons, which the researchers now think is to compensate for the low neurotransmitter levels. An out-of-balance chemical network was seen more in male babies, which might explain why SIDS affects twice as many boys as it does girls.

It’s a promising line of research, and it folds into what doctors are calling the “triple-risk model” of SIDS:

  • an underlying biological vulnerability
  • a critical period of life (usually the first six months)
  • one or more environmental stressors (such as tummy-sleeping, over-bundling, or loose bedding).

The condition seems to strike only when all these elements come together. The underlying vulnerability might be the brainstem issue that Kinney and her team have discovered, but scientists believe there may be multiple health conditions at play – heart irregularities have also been implicated. And in 88 percent of the SIDS cases in Kinney’s research, the baby had been exposed to two or more environmental stressors, for example, lying on its stomach and having loose bedding in the crib.

Myths of SIDS

The fact that SIDS was cloaked in mystery for so many decades has made it ripe for speculation and theory. Explanations like smothering, infanticide, and vaccines (which the CDC says have no connection to the disorder), have been posited as the cause. The toxic mattresses theory, proposed in the 1980′s, argued that SIDS is caused by gases released when flame-retardant chemicals in baby mattresses are broken down by fungus. The theory got a lot of press, but doctors don’t give it much weight, saying that there are no replicated, peer-reviewed studies showing a connection between mattresses and sudden death.

As the biology of SIDS becomes clearer, it seems we’ve taken the first step towards being able to identify and treat the babies at risk. The Harvard researchers hope one day to be able to test a baby’s blood for indications that the brainstem’s serotonin system is off. In the best-case scenario, a drug might be able to correct the functioning of the baby’s medulla, but at the very least, parents could be warned to take extra precautions. For now, nobody knows which of our babies has the biological snag – infants with these brainstem differences look and act just like any other. That’s why we’re all supposed to follow the safe sleeping practices, like back-sleeping, no loose bedding, using fans, and not overheating the room or over-bundling the child – all of which have cut the incidence of SIDS in half since being implemented in the 1990′s. Until we know which of our little ones are vulnerable, we should all play it safe.

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