Solving the SIDS Mystery
New clues reveal that sudden infant death syndrome may be a disease-not a tragic mistake
Sudden infant death syndrome, better known as SIDS, is a cruel killer, striking infants as they sleep. More than 2,000 babies in the United States die of SIDS each year. Autopsies reveal no infection or other hidden health problem. Over the years, many suspects have been put forward, as benign as too-soft pillows that smother the child or as sinister as child abuse. Scientists have been struggling for decades to discover a physical cause. Now, they have unearthed the strongest evidence yet that the brain region that controls breathing develops abnormally in many infants who die of SIDS.
Researchers at Children's Hospital Boston and Harvard Medical School, working with colleagues at the University of California-San Diego School of Medicine and other institutions, autopsied the brains of 31 infants in San Diego who died of SIDS and 10 who died of other causes. They zeroed in on the medulla, an area in the brain stem that controls involuntary actions like breathing, blood pressure, and heart rate and that has been the focus of scrutiny. Their findings, reported in last week's Journal of the American Medical Association, showed that the medullas of SIDS babies were far more likely to have abnormalities in nerve cells that respond to serotonin, a chemical that plays a key role in regulating breathing and sleep. "SIDS is not a mystery," says Hannah Kinney, an associate professor of neuropathology at Children's Hospital Boston and Harvard Medical School and coauthor of the JAMA study. "It's not something that parents did. SIDS is a disease. It's a scientific problem, and it can be tackled with scientific methods."
The irregularities Kinney and her colleagues found were more extensive than had been discovered in earlier studies. What's more, the SIDS baby boys in the study had more deficiencies than the SIDS girls, which may help explain why boys are twice as likely to die of SIDS as girls. If these flaws do indeed cause SIDS, perhaps a test could be developed to identify babies at risk in the first weeks of life. But any such test is many years away, according to John Kattwinkel, a professor of pediatrics at the University of Virginia, because no one has yet pinpointed an early-warning signal for SIDS. "You've got to figure out how to detect it."
When Kyra Oliver Hitzeman heard news reports about the SIDS study, she was thrilled-and overwhelmed by the memories it revived. Her son Hayes died in 2002, while he took a nap at his day-care provider's home. He was 4
Indeed, no one knows what prompts seemingly healthy babies to suddenly die in their sleep. Most SIDS deaths occur between 2 and 4 months of age. Epidemiological data gathered over the years has shown that babies are more likely to succumb to SIDS if they are put to sleep face down, if they sleep with an adult, or if there are toys or soft bedding in the crib. The thought has been that SIDS babies don't rouse themselves when the bedding traps carbon dioxide near the face, and they suffocate.
At the same time, researchers have hunted biological causes and have found genetic variations in some SIDS babies that suggest a hereditary component. Other scientists have found metabolic problems in the liver that may account for 3 to 5 percent of SIDS cases. Michael Ackerman, a pediatric cardiologist at the Mayo Clinic, has examined 93 SIDS cases, and found that 9 percent of the babies had a genetic defect that causes Long Q-T syndrome, a heart defect that can result in sudden, fatal arrythmia. Last week's JAMA study brings the most concrete evidence yet that SIDS is a disease, not just the result of a tragic mistake.
Multiple causes. Kinney, who has been trying to solve the SIDS riddle since the early 1980s, thinks the aberrations in the brain's serotonin system develop in utero and can be caused by maternal cigarette smoking, which impairs fetal brain development. Other researchers think the problems could be caused by a genetic predisposition, or by lack of oxygen or other stress at birth. In the end, many prominent researchers believe SIDS will turn out to have multiple biological causes that make babies more susceptible to environmental risks like soft bedding or cigarette smoke.
Kinney says that her group's findings reinforce the "Back to Sleep" program, created by a consortium led by the National Institute of Child Health and Human Development and introduced in 1992. It aims to reduce the risk of SIDS by telling parents and caregivers to put infants to sleep face up and to keep soft bedding like quilts and pillows out of the baby's crib. A child without the brain variations would have no problem sleeping face down, but a SIDS-prone child might. "Why would putting a baby on its back save a life?" asks Kinney. If that baby has a defect in its brain arousal system, it might asphyxiate if laid face down. "A normal baby would sense the low oxygen and turn its head and wake up."
Although the Back to Sleep campaign is credited with reducing SIDS deaths by 50 percent since its inception, 77 percent of the children who died of SIDS in Kinney's study were sleeping on their stomach or side, shared a bed with an adult, or both. Kattwinkel, who is chairman of the American Academy of Pediatrics's SIDS Task Force, says the fact that the bulk of SIDS deaths are related to risk factors like cosleeping, soft bedding, or sleeping face down is actually encouraging. "We can do something about it," he says. Thanks to the Back to Sleep program, the number of newborns put to sleep on their stomachs has shrunk to 12 to 14 percent. But that number increases when babies are 2 to 3 months old-right when many mothers go back to work. "We think a fair amount of the reason for the increase is secondary caretakers, like grandmothers and day-care centers," Kattwinkel says. As a result, he says, Back to Sleep has been targeted more toward caretakers in the past decade. The situation is improving, he says, "but it's still not where it should be."
Hitzeman knows that all too well. Hayes's babysitter put him to sleep on his stomach before he died, even though she had asked that her baby be put to sleep on his back. She says she doesn't blame the sitter for not recognizing the seriousness of the request. After her son's death, Hitzeman and her husband created a foundation to support SIDS research and awareness. And she has given the foundation's public face a flourish making use of her talents as a designer: a onesie embellished with a smiling, sleeping baby that reads, in English or in Spanish, "This Side Up."
This story appears in the November 13, 2006 print edition of U.S. News & World Report.