Researchers have identified a specific biomarker signature that can predict the onset of Alzheimer's disease with 100 percent accuracy.

The findings by Geert De Meyer of Ghent University in Belgium and colleagues in the Alzheimer's Disease Neuroimaging Initiative are published in the American Medical Association's Archives of Neurology. It is based on a study comparing groups of adults with and without Alzheimer's.

In the study, the samples consist of 114 normal older adults, 200 older adults with mild cognitive impairment, and 102 who had the disease. A common biomarker was found in 90 percent of adults with Alzheimer's, 72 percent among those with mild cognitive impairment and 32 percent in the group of normal adults.

The results were cross-checked against two smaller data sets. In one group of 68 patients, 64 or 94 percent had the biomarker related to the disease.

In the other group of 57 patients with mild cognitive impairment and the biomarker, their condition progressed to Alzheimer's after five years of checking.

The fact that the biomarkers were present in more than one-third of cognitively normal subjects suggested that Alzheimer's disease pathology is active and detectable earlier than has heretofore been envisioned, authors of the study said.

Symptoms of Alzheimer's do not show up until 10 years later.

Medicine