Researchers Identify New Brain Marker for Alzheimer's Disease

by Medindia Content Team on Oct 31 2007 5:09 PM

Researchers have discovered a new marker that may help identify those at maximum risk for cognitive decline and the development of Alzheimer's disease.

Duke University Medical Center researchers used functional magnetic resonance imaging, also known as fMRI, on people with mild cognitive impairment (MCI), to track regions of the brain that become active or inactive when participating in tasks that involve memory.

People with MCI are at increased risk for developing Alzheimer's disease in the future and approximately 30-50 percent of MCI subjects will develop Alzheimer's if followed over a three- to five-year period.

"A single baseline fMRI measure of deactivation could help predict which individuals will convert to Alzheimer's over the next several years," said the study's lead author, Jeffrey R. Petrella, M.D.

"On the other hand, the fMRI scans of MCI subjects who did not convert looked more like those of healthy normal people, and could therefore be reassuring," said Dr. Petrella, who is director of the Alzheimer's Imaging Research Laboratory and associate professor of radiology at Duke.

According to him, the findings focus on an area of the brain known as the posteromedial cortex, which has recently been implicated in personal memory.

"Our theory is that the posteromedial cortex may be our brain's 'cruise control' that normally deactivates when we are trying to remember things, so resources can be sent to other areas of the brain that encode memories. However, in people with mild cognitive impairment or Alzheimer's disease, the deactivation does not happen and the posteromedial cortex remains active," he said.

In this study, researchers conducted fMRI scans on 75 people, including 34 with mild cognitive impairment, 13 with Alzheimer's disease and 28 with normal cognition. Study participants completed standard neuropsychological testing and were monitored with fMRI while performing a memory task matching names and faces. Patients were then followed for three and a half years to determine how their cognition changed over time.

The researchers found that approximately a third of the MCI subjects converted to Alzheimer's in three and half years after their initial scans. The conversion to Alzheimer's was determined by study doctors using routine clinical and memory tests. fMRI level of deactivation was found to significantly predict which MCI subjects converted to Alzheimer's.

Study authors said that while other works have focused on the brain's ability to turn on certain regions, their research determined that losing the ability to turn off a region of the brain might be a more sensitive marker of future cognitive decline.

"The Holy Grail in this field is to predict with 100 percent accuracy whether a 50-year old who forgets names will get dementia or not. We are not there yet but are inching closer and closer everyday. The combination of genetic, biochemical and imaging biomarkers will soon become the gold standard," said study co-author P. Murali Doraiswamy, M.D.

The findings are published in PLoS ONE.