Normal levels of glucose metabolism in a PET scan (left), indicated in yellow and red. The levels of glucose metabolism in the brain are decreased in patients with mild cognitive impairment (middle) and with Alzheimer's disease (right). (Cindee Madison and Susan Landau/UC Berkeley)

Brain scans and memory tests may work as an early warning system for Alzheimer's disease, researchers said Tuesday.

At an Alzheimer's Association annual meeting in Vienna, Austria, researchers presented their findings on diagnosing the disease in its earliest stages, among people with mild cognitive impairment — a precursor to the disease that slowly leads to memory impairment, behavioural changes and dementia.

"Not all people with mild cognitive impairment go on to develop Alzheimer's, so it would be extremely useful to be able to identify those who are at greater risk of converting using a clinical test or biological measurement," the lead author of one study, Susan Landau, a post-doctoral fellow at University of California, Berkeley, said in a release.

Landau and her colleagues studied 85 people with mild cognitive impairment. People who did poorly on recall tests and showed less glucose in their brains during PET scans were 15 times more likely to progress to Alzheimer's within two years.

Researchers are trying to determine whether treating people with drugs before severe symptoms appear will be more effective.

"The idea is if there could be biological markers identified that tracked what was going on in the brain, this would give you a better idea of whether a drug was having a biological effect," Neil Buckholtz, who heads the U.S. National Institute on Aging's Alzheimer's Disease Neuroimaging Initiative, or ADNI, said in a telephone interview with Reuters.

A biomarker is a substance or characteristic that can be objectively measured and evaluated as an indicator of normal body function, disease or the body's response to therapy. For example, high blood pressure is a biomarker indicating risk of cardiovascular disease.

Landau's team also looked at other measurements that showed promise as biological markers for the disease, such as hippocampus volume, but it was the combination of PET and memory recall that were the most consistent predictors.

Aiming to preserve memory

Another study by Irish researchers of 345 people with mild cognitive impairment found three memory tests plus MRI measurements of brain volume in the left hippocampus, which is linked to memory, also helped predict disease progression.

It's widely believed that changes in the brain in Alzheimer's disease, such as amyloid plaques and tangles, begin many years before symptoms are seen, said Dr. Ronald Petersen, chair or the Alzheimer's Association Medical & Scientific Advisory Council.

"It is critical to identify affected individuals while they are still relatively cognitively healthy so that future therapies can preserve healthy memory and thinking function," Petersen said. "And, in order to develop those new therapies, we need to identify 'at risk' individuals now in order to steer them to clinical trials."

A third study, presented at the meeting by Dr. Allen Roses of Duke University in North Carolina, suggested a gene called TOMM40 predicted the age of Alzheimer's disease within a five- to seven-year window among people over the age of 60.

"It now looks fairly clear that there are two major genes — APOE4 and TOMM40 — and together they account for an estimated 85-90 per cent of the genetic effect," Roses said in a release.

The Duke team, and others, are planning a five-year study of the genes along with drug trials to assess prevention or delay in the onset of Alzheimer's disease.

Alzheimer's is the most common form of dementia and affects one in 20 Canadians over 65 — about 290,000 people.