CHICAGO -- Researchers and doctors across the nation are digging deeper into the mystery of Sudden Infant Death Syndrome and finding clues that suggest many of the deaths labeled as SIDS are instead other rare maladies that have been overlooked or inadequately diagnosed by doctors. And they're still arguing -- loudly -- over how many are murders.
As the debate rages, the federal Centers for Disease Control and Prevention has launched in Chicago one of the largest and most comprehensive studies of environmental and social risk factors for SIDS. The $1 million study is aimed at pinpointing a baby's risks from such things as exposure to cigarette smoke, sleeping position and room temperature.
Chicago has one of the highest rates of such deaths in the nation, a statistic that experts find as inexplicable as SIDS itself.
Every year, SIDS kills about 7,000 infants nationally. It is a leading cause of infant mortality -- and one of the most perplexing -- because it leaves no tell-tale marks on body organs that would allow pathologists to trace a fatal chain of events. Autopsies reveal nothing; critical organs, such as the heart and brain, appear healthy.
"SIDS is probably not a single entity," said Dr. Charles Strom, director of medical genetics at Illinois Masonic Medical Center in Chicago, voicing an opinion shared by many experts.
"It's probably a combination of many things, and theories come and theories go. It's like an onion. You peel away one layer at a time."
One of the latest and most sensational theories comes from Dr. Michael Bennett, a clinical biochemist and associate professor at Baylor University Medical Center in Waco, Texas. Since last year, Dr. Bennett has been examining tissue and blood samples of suspected SIDS victims in 20 Illinois counties.
His research, he said, indicates that as many as 5 percent of deaths labeled SIDS here were actually caused by a rare metabolic problem called Medium-Chain Acyl-CoA Dehydrogenace, or MCAD. Another 15 percent of SIDS deaths, he said, are caused by other genetic errors of metabolism, which, like MCAD, prevent victims from correctly processing food and ridding their bodies of waste.
"This means that babies' lives can be saved down the road," with early detection and treatment, said Kane County (Ill.) Coroner Mary Lou Kearns, who has changed her SIDS ruling on several cases in which Dr. Bennett later found that the babies had died from metabolic defects.
Rare metabolic deficiencies can be missed when babies die because county pathologists generally do not test for the defects. The tests are expensive, and the current autopsy methods of preserving blood and tissue destroy the enzymes that must be analyzed to make the diagnosis.
Unlike SIDS babies, most babies with inborn metabolism problems are sick before they die. They are lethargic, have fevers and infections and problems with feeding and gaining weight, experts say.
But others who have the defect appear to be healthy until they suddenly die.
Even though his findings have yet to be confirmed, Dr. Bennett's research is prompting some authorities to change the way they investigate infant deaths, particularly a series of deaths in a single family.
In recent years, police and medical examiners have believed that the statistical odds of three babies dying of SIDS in one household are almost infinitesimal. They usually suspect homicide when a third baby dies and no explanation is found.
But such cases can be explained by genetic metabolic defects, said Dr. Bennett, noting that if both parents carry the gene, each child has a one-in-four chance of being born with the defect.
As research and interest in SIDS have mounted in recent years, )) authorities have begun to call for more stringent medical and forensic examinations of infant deaths.
Dr. Millard Bass, a private New York pathologist, has claimed in widely disputed research papers that he has investigated SIDS deaths only to find that they were actually caused by leaky gas vent pipes, defective furnaces, drunken mothers who fell asleep on their babies or homicides.
Recent studies in Britain, New Zealand and Australia showed marked decreases in SIDS deaths after public awareness campaigns urged parents to put babies on their backs in bed.