There's no cure for Alzheimer's disease, and no effective treatment.
One reason might be that there is no reliable way to detect the disease before its devastating symptoms, including memory loss and functional decline, become apparent.
A new study, however, might have discovered such a detection system: a blood test that researchers say can predict, with greater than 90 per cent accuracy, whether a healthy person will develop Alzheimer's within three years.
"This has sort of been the holy grail for a lot of years: even finding a blood test to tell the difference between a person who has Alzheimer's disease and someone who's normal," said Dr Claudia Kawas, a professor of neurology at UC Irvine Medical School who is among 17 co-authors of a new study on the blood test.
The study, conducted at several university hospitals, was published online Sunday in the April issue of the journal Nature Medicine.
Over the course of five years, 76 of the 525 test subjects were diagnosed with either Alzheimer's or a condition called amnestic mild cognitive impairment, which is associated with memory loss. Patients who had a set of 10 lipids, or fats, were more likely to develop the mild cognitive decline or Alzheimer's.
Other tests that look for certain "biomarkers" associated with Alzheimer's, such as magnetic resonance imaging, are limited because they are invasive or prohibitively expensive. Trials that examine the role of amyloids, proteins that build up in the brain, have been inconclusive.
Developing a blood test that could give people advance warning would be huge, Kawas said.
"The thing that distinguishes this paper is we appear possibly to be identifying a marker that's apparent before the person has the disease," she said. "Eventually, that will be unbelievably important."
The blood test won't be ready for further clinical trials for two more years. The test must be replicated to make sure it works, Kawas said.
Even if it's confirmed to be effective, getting a heads-up won't be enough for patients: They'll want a drug, like a vaccine, that will prevent or delay onset of the disease.
"We're not there yet," Kawas said.