What we know so far

Despite the challenges, SIDS research goes on. And though much remains to be learned, scientists do have some answers (see "4 Other Ways to Protect Your Baby"). For instance, theyknow that certain infants, such as African-American, Native American, and premature babies, are at particular risk, and that certain situations (including sleeping on a soft surface and exposure to secondhand smoke) raise the odds for all babies. They also know that babies who sleep on their stomachs or sides face the biggest danger: They have twice the risk of dying from SIDS as babies who sleep on their backs. When a baby's face is turned toward the bedding, he's in a position to re-breathe the carbon dioxide he exhales, which limits the amount of oxygen he takes in. "When they aren't getting enough oxygen, most babies will do something to change their environment -- they'll turn their heads, or they'll sigh, or they'll yawn," says Rachel Moon, M.D., an associate professor of pediatrics at George Washington University School of Medicine in Washington, DC. "But babies who die of SIDS don't wake up when they get into trouble, and we don't fully understand why."

One of the most plausible theories may be a brain-stem abnormality that affects the brain's ability to make and use serotonin -- a theory corroborated by a new Italian study that found that serotonin overproduction caused SIDS-like deaths in mice -- and it may be responsible for well over half of all cases. Along with its role affecting mood, serotonin helps regulate breathing and arousal. If that arousal center isn't functioning properly, a baby sleeping in a position that limits his oxygen may not wake up in time. This discovery, made by researchers at Children's Hospital Boston, helps explain why SIDS rates drop dramatically after 6 months and disappear entirely at one year: The brain stem continues to mature, and even abnormal brain stems are eventually able to process serotonin appropriately.

The many sides of SIDS

As encouraging as this research is, it's become increasingly clear that the syndrome likely has several biological explanations, with different babies dying for different physiological reasons -- and that complicates the mystery even more. Along with brain-stem problems, researchers are also looking into undiagnosed genetic anomalies that cause no symptoms but are ultimately fatal. A metabolic disorder called MCADD (medium chain acyl-CoA dehydrogenase deficiency), for instance, impairs the baby's ability to process fatty acids, eventually causing a sudden and fatal interruption in heart function. Another condition is long QT syndrome, an electrical disorder in the heart that causes sudden bursts of extremely rapid heartbeats and can lead to cardiac arrest. MCADD and long QT syndrome account for fewer than 15 percent of SIDS cases, but both disorders can be successfully treated if caught in time by a blood test; unfortunately, these tests aren't routine in most states.

Although some infants seem to be at greater genetic risk for SIDS, it's also possible that all babies are susceptible if the factors are strong enough at the time of greatest vulnerability. "It probably takes more of a stressor to tip a baby who has no predisposition over into SIDS than it takes for a genetically susceptible baby, but it could still happen," says Dr. Moon.

Preliminary research also suggests that babies who begin daycare before 4 months of age, like Jake Haberzettl, may be at increased risk as well. In the most recent AAP analysis, about 20 percent of all SIDS deaths occurred while the baby was in the care of someone other than a parent. One third of the infants died during the first week of childcare, and half those deaths occurred on the very first day. "It may be that starting a new routine interrupts the baby's sleep cycle, so that when he finally does fall asleep, he sleeps too deeply," says Dr. Moon. It may also be that some providers don't recognize the risks of tummy sleeping. The danger? Babies who are accustomed to sleeping on their backs are 18 times more likely to die from SIDS when put down to sleep on their stomachs. That's why it's important for parents to emphasize safe-sleeping practices with their providers, and try to use only a licensed facility.

Eventually, researchers hope that it will be possible to create a diagnostic test to identify the babies most at risk for SIDS. "But our real dream is to develop some sort of protection to use through the risk period," says Dr. Krous. Reaching that goal will take a lot more funding, a lot more research, and more accurate information from death-scene investigations. As Dr. Krous says, "That's a long way off, but that's the dream. To save lives."

Melissa Haberzettl shares this dream. In March, she gave birth to a second son, Dylan Jacob, whose middle name is a tribute to the older brother he'll never know. "I was nervous about trying to get pregnant again," says Melissa, "but Rudy and I both said to ourselves, 'We have to try.' " (To make sure his risk was low, Dylan was tested for both MCADD and long QT syndrome, but he has neither.) And she continues to keep up with SIDS research. "I'm hopeful that in my lifetime, people will say, 'SIDS? What's that?' And no other family will have to go through what we did when Jake died."

Margaret Renkl is a contributing editor.

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