Animal experiments point to a possible cause of Sudden Infant Death Syndrome (SIDS).
Getting to the bottom of SIDS. I'm Bob Hirshon and this is Science Update.
Scientists still don't know what causes Sudden Infant Death Syndrome, or SIDS. But animal studies in Italy suggest that a brain chemical called serotonin may be the key.
Neuroscientist Cornelius Gross of the European Molecular Biology Laboratory and his team found that mice with serotonin regulation disorders suffered SIDS-like deaths. As to why, Gross notes that serotonin helps maintain involuntary functions like heart rate and body temperature. But he says genetic deficiencies in infants would probably be mild compared to those of their mice.
A combination of factors will then be important to determine if and when an infant will have one of these crises and might actually die.
For example, breathing obstructions like crib bumpers may fatally tip the scales for vulnerable babies. I'm Bob Hirshon for AAAS, the Science Society.
Making Sense of the Research
Sudden Infant Death Syndrome (SIDS) is a term scientists use to describe the unexplained death of a healthy infant under one year of age. It's sometimes called “crib death,” because in most cases, parents put their baby to bed and return to find the child dead. According to the Centers for Disease Control, about one in 2,000 American babies born alive died from SIDS in 2005. That's down from about one in 650 in 1980, but it still translates to over 2,000 SIDS deaths in the U.S. alone every year.
Since the only real symptom of SIDS is death, it's very difficult to figure out what causes it. Over the past few decades, however, scientists have identified a number of factors which reduce the risk of SIDS. Babies whose mothers ate well, got regular medical care, and avoided alcohol, tobacco, and drugs during pregnancy had lower rates of SIDS. Avoiding teen pregnancy and frequent births (less than one year apart) also can reduce a child's SIDS risk. During the first year, the risk of SIDS can be reduced by avoiding anything that might obstruct the baby's breathing while he or she sleeps. Doctors recommend putting babies to sleep on their backs (rather than face down) in a crib without pillows, blankets, stuffed animals, and soft bumpers that could stifle breathing. Avoiding secondhand smoke and respiratory infections can also protect children from SIDS. Keeping children from overheating also helps.
Still, only a small fraction of babies with these risk factors will actually die of SIDS. For example, just imagine how many babies were exposed to cigarette smoke in the 1960s, when smoking was about twice as common as it is today. Until recently, parents usually put babies to sleep on their stomachs, because they tend to sleep more soundly—even though stomach sleeping is one of the biggest risk factors for SIDS. Are some children just unlucky? Or are some children biologically pre-disposed to SIDS, and more vulnerable to risk factors like these?
This study touches on several clues that may help answer this question. Many risk factors for SIDS relate to breathing and body temperature, which are regulated, in part, by a brain chemical called serotonin. Furthermore, autopsies of SIDS babies have shown abnormalities in brain cells that produce serotonin, although it's not clear what effect, if any, these abnormalities may have. However, when Gross' team was studying mice with genetically engineered serotonin disorders, they discovered that the mice often died during a period of development that corresponds to a human baby's first year of life. These deaths were often preceded by sudden, unpredictable changes in heart rate and body temperature.
Based on these clues, Gross' team suggests that serotonin regulation disorders may increase the risk of SIDS in human babies. Although the serotonin deficiency alone was enough to kill the mice in his experiments, Gross suspects that human versions of the disorder may be less dramatic. In fact, he suggests, many babies may get through infancy with no major problems—but if their heart rate and body temperature suddenly change at a time when their breathing is already partially blocked, it could be fatal.
It's important to note that this is just a hypothesis, and that even if it's correct, babies with normal serotonin regulation aren't necessarily immune from SIDS. However, it may lead scientists to look more closely at the role of serotonin in SIDS, and eventually, to identify babies who may need to be watched more closely.
Now try and answer these questions:
- What is SIDS? Why is it hard to understand?
- How do Gross' findings point to a possible cause of SIDS?
- What kinds of follow-up studies could determine whether or not this hypothesis is correct?
- How do you make sure studies of SIDS in humans are ethical? How does that limit the progress of scientific knowledge?
- Do you think the use of animals in this study—or any medical study—is ethical? Why or why not?
You may want to check out the August 8, 2008, Science Update Podcast to hear further information about this Science Update and the other recent programs. This podcast's topics include: the science of magic, the hormone behind the mind-body connection, and the brain chemical that could be responsible for sudden infant death syndrome (SIDS).
The American SIDS Institute has information and statistics about Sudden Infant Death Syndrome.
More details on the relationship between SIDS and serotonin can be found in SIDS Infants Show Abnormalities In Brain Area Controlling Breathing, Heart Rate, from the National Institutes of Health.
In the Access Excellence activity Genetic Ethics Debate, students select topics relating to bioethical questions to research and debate.