Examining spinal fluid samples and health data from 201 study participants, researchers have identified Alzheimer's biomarkers that prove to be accurate predictors of decline years before symptoms develop. A biomarker, or biological marker, is a biological molecule found in blood, other body fluids, or tissues that is a sign of a normal or abnormal process, or of a condition or disease.

"We wanted to see if one marker was better than the other in predicting which of our participants would get cognitive impairment and when they would get it," said Catherine Roe, Ph.D., research assistant professor of neurology at Washington University School of Medicine. "We found no differences in the accuracy of the biomarkers."

The researchers evaluated markers, such as the buildup of amyloid plaques in the brain, now visible with an imaging agent developed in the last decade; levels of various proteins in the cerebrospinal fluid, such as the amyloid fragments that are the principal ingredient of brain plaques; and the ratios of one protein to another in the cerebrospinal fluid, such as different forms of the brain cell structural tau protein.

The markers were studied in volunteers, ranging in age from 45 to 88, at the Charles F. and Joanne Knight Alzheimer's Disease Research Center. The researchers found that all of the markers were equally good at identifying subjects who were likely to develop cognitive problems and at predicting how soon they would become noticeably impaired. Next, the scientists paired the biomarkers data with demographic information, testing to see if sex, age, race, education, and other factors could improve their predictions.

"Sex, age and race all helped to predict who would develop cognitive impairment," Roe said. "Older participants, men and African Americans were more likely to become cognitively impaired than those who were younger, female and Caucasian."

In its report, "Changing the Trajectory of Alzheimer's Disease: A National Imperative," the Alzheimer's Association reported that the number of Americans age 65 and older who have or will have Alzheimer's disease is projected to increase from 5.1 million in 2010 to 13.5 million in 2050. By 2050, an estimated 16 percent of Americans age 65 and older will have the condition. Total annual costs for the care of people with the disease and other dementias will increase from $172 billion in 2010 to $1.08 trillion in 2050.

Roe described the findings as providing more evidence that scientists can detect Alzheimer's disease years before memory loss and cognitive decline become apparent. Clinical trials are already underway to determine if treatments prior to symptoms can prevent or delay inherited forms of Alzheimer's disease. Reliable biomarkers for Alzheimer's should one day make it possible to test the most successful treatments in the much more common forms of Alzheimer's.

A treatment breakthrough that delayed the age of onset of Alzheimer's disease by five years and began to show its effects in 2015, Alzheimer's Association reports, would decrease the total number of Americans age 65 and older with Alzheimer's disease from 5.6 million to four million by 2020. In addition, five years later, in 2025, 2.7 million Americans - 42 percent of the 6.5 million people who would be expected to have Alzheimer's in that year - would be disease-free. The biggest effect would be in 2050 when 5.8 million people - 43 percent of the 13.5 million Americans who would be expected to have Alzheimer's without the breakthrough - would not have the condition.

The Washington University School of Medicine study, supported in part by the National Institute on Aging, appeared in Neurology.

Roe, CM, Fagan, AM, Grant, EA, et al. Amyloid imaging and CSF biomarkers in predicting cognitive impairment up to 7.5 years later. Neurology. 2013; DOI 10.1212. Accessed May 14, 2013.