Alzheimer's researchers have proposed a radical change in the way the disease is defined, focusing on biological changes in the body rather than clinical symptoms such as memory loss and cognitive decline.

The new research framework, released today by the Alzheimer's Association and the National Institute on Aging, is meant to provide scientists with a common language for describing the disease in research studies based on measurable changes in the brain that set Alzheimer's apart from other causes of dementia.

"Much of the general public views the terms dementia and Alzheimer's disease as interchangeable, but they are not," said Dr Clifford Jack of the Mayo Clinic in Rochester, Minnesota, who helped craft the guidelines published in the journal Alzheimer's & Dementia: The Journal of the Alzheimer's Association.

The proposed changes follow guidance announced earlier this year by the US Food and Drug Administration and the European Medicines Agency to encourage the testing of new Alzheimer's medicines based on biomarkers, rather than on clinical symptoms.

The moves would allow companies to test drugs in people before symptoms appear, offering a better chance of intervening before the disease has destroyed too many brain cells.

Under the proposed research framework, Alzheimer's would be characterized by three factors: evidence of two abnormal proteins associated with Alzheimer's - beta amyloid and tau - and evidence of neurodegeneration or nerve cell death, all of which can be seen through brain imaging or tests of cerebral spinal fluid. It also incorporates measures of severity using biomarkers and a grading system for cognitive impairment.

The hope is that the new definition will help researchers pick better subjects on which to test new Alzheimer's treatments, which may help improve drug companies' search for treatments.

So far, experimental Alzheimer's drugs have had a dismal track record, with more than 100 failures, including most recently a treatment from Merck, while Pfizer said in January it was quitting the field.

Most of these drugs have focused on removing beta amyloid from the brain. Recent imaging studies have shown that about 30 percent of the people who have taken part in clinical trials for Alzheimer's drugs did not have beta amyloid in their brains.

Jack said the new framework puts Alzheimer's more in line with other diseases, such as hypertension or diabetes, and it will allow researchers to study interventions that interfere with the underlying changes that lead to Alzheimer's dementia.