McLEAN, VA—Despite remarkable advances in health care and the study of medicine in recent decades, scientists remain baffled by Sudden Elder Death Syndrome, a disorder that cuts long lives short and leaves aggrieved loved ones wondering why.

Also known as Craftmatic Adjustable Bed Death, SEDS is the sudden, unexplained passing of an elderly person. In many SEDS cases, even a full autopsy and a review of 80-plus years of health records cannot account for the mysterious death.

"We have no forensic explanation for it," said Dr. Martin Gerrard, chairman of the SEDS Institute. "These seemingly healthy elders—some of whom are performing such normal activities as eating liquefied food, trying to stand up, or taking frequent naps—just stop breathing."

According to a study published by the SEDS Institute, Sudden Elder Death Syndrome is the leading cause of death among people over the age of 85. Nicolai Korsgaard, author of the most comprehensive SEDS investigation conducted in the past decade, said scientists have been unable to replicate his results because study participants often succumb to SEDS before the studies are complete.

"Over 99 percent of elders between the ages of 100 and 105 die of SEDS," Korsgaard said. "As a researcher and caregiver, I can't think of a scenario more gut-wrenching than that of a healthy and contented centenarian slipping into a deep slumber and never awakening."

The earliest recorded SEDS fatality occurred on American soil in 1661, when 58-year-old English-born colonist Jonas Clay died in his sleep in his cabin. While advances in mattress technology and elder care have raised the average age of SEDS victims from 54.5 in 1700 to 78.6 today, the mysterious syndrome kills at exactly the same rate it did three centuries ago.

"Doctors haven't isolated any genetic anomalies or behavior patterns among elders afflicted with SEDS," Gerrard said. "The one constant in the SEDS community is age. We do know that the older one gets, the greater the risk of becoming a victim."

However, independent research group SEDS Prevention Alliance has detected patterns among SEDS victims.

"Nearly 80 percent of SEDS deaths occur in a home setting, such as a nursing home or assisted-living facility," said SEDSPA director Melinda Byrnes. "Inactive elders who lie in their beds all day ingesting prescription medicines are especially susceptible."

For many loved ones of SEDS victims, however, these and other theories offer little comfort. Atlanta resident Mary-Beth Soltis, 34, lost her grandmother Esther, 91, to SEDS in 2003.

"Every day, I think, 'There must have been something I could have done to save Nana,'" Soltis said. "When I left the hospital the night before, I never thought that it would be the last time I saw her. What did I do wrong? I'm a terrible granddaughter."

Byrnes recommends putting elders to sleep on their backs, checking on them regularly, and monitoring them with a device called an electrocardiograph, which emits a sustained electronic tone if your elder is in danger of succumbing to SEDS.