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Blood test shows promise as possible diagnostic tool for Alzheimer's: study

Canadian researchers have developed a blood test that one day may help diagnose Alzheimer’s, even in its early stages, potentially providing a longer window of opportunity for drug therapy aimed at halting progression of the disease.

Scientists have been trying for years to come up with a definitive diagnostic test for Alzheimer’s, a progressive form of dementia that currently can only be confirmed by analysis of brain tissue after death.

But researchers at McGill University Health Centre have created a test that measures blood levels of DHEA, a hormone naturally produced by the body that’s been touted for possible anti-aging properties.

“Our clinical study shows that a non-invasive blood test, based on a biochemical process, may be successfully used to diagnose Alzheimer’s at an early stage and differentiate it from other types of dementia,” said Vassilios Papadopoulos, director of the MUHC Research Institute.

The test involves performing a chemical reaction, called oxidation, on a sample of blood. Oxidation causes production of DHEA, or dehydroepiandrosterone. Papadopoulos said additional amounts of the steroid must be produced from a DHEA precursor that’s present in the blood, although the researchers have not yet identified what it is.

In a study published in this month’s issue of the Journal of Alzheimer’s Disease, the researchers detail how they tested blood samples from 86 people. About half had suspected Alzheimer’s disease, based on cognitive and other clinical symptoms, while about an equal number were healthy control subjects matched for age and sex.

When exposed to oxidation, the blood of healthy controls showed a rise in DHEA levels, suggesting the unidentified precursor was present. But the chemical reaction did not elicit any appreciable increase in DHEA in blood from Alzheimer’s patients.

In patients with severe disease, there was no rise in DHEA, Papadopoulos said Wednesday from Montreal. “If you move into moderate or mild (Alzheimer’s), you will find a little bit, but not the same level as in the normal (subject).”

What’s more, he said, there’s a clear correlation between the lack of ability to produce DHEA through oxidation in the blood and the degree of cognitive impairment found in patients.

“We demonstrated we could accurately and repetitively detect Alzheimer’s disease with small samples of blood. This test also allowed for differential diagnosis of early stages of Alzheimer’s disease, suggesting this can be used as a test to diagnose the disease in its infancy.”

Papadopoulos and his team have begun collecting more blood samples — they already have about 400 from other Alzheimer’s patients — and will recruit an equal number of cognitively healthy control subjects for a larger study of their test, to see if they can replicate the initial results.

But he said there are many steps before such a test could be brought to market and used to screen people for the devastating, eventually fatal disease.

If the test turns out to be a valid diagnostic tool for Alzheimer’s, it could also be used in drug trials to see if experimental medications are having an effect, using increased DHEA levels in subjects as a yardstick and “to see if it correlates to any changes with stabilization of the disease or the efficacy of the treatment.”

Papadopoulos said people often wonder what is the point of a person knowing they have Alzheimer’s when there is no cure or any drugs that effectively halt the disease in its tracks.

“And I think the best response is to go back into history,” he said, noting that breast cancer was almost universally fatal 30 years ago but now has a high cure rate; 50 years ago, little could be done to stop hardening of the arteries that led to heart attack and stroke, yet today medications like statins can prevent or at least slow blood vessel damage.

A test to identify the disease is a critical step in understanding when Alzheimer’s begins and what triggers its onset, he said. “And then, potentially treatments (can be developed) that maybe will not bring you back to normal but will be able to stabilize, stop the progression of the disease where it is.”

In the future, the DHEA-based test could be one of several used to diagnose Alzheimer’s, in the same way blood is tested for different substances to determine a patient’s risk for cardiovascular disease, he said.

“So this is how I see it: you go to the doctor, you have to have triglicerides, cholesterol, HDL, LDL before they tell you you have to take this kind of therapy. I think we’re going in this direction too,” said Papadopoulos.

“Whether somebody at 50 years old would have a test, I don’t know. Time will show us when this would have to be done.”