Predicting Alzheimer’s Disease With Blood Tests: Early Detection, Ethical Concerns

If you could take a blood test that could detect — with nearly 100% accuracy — whether you were genetically destined to get Alzheimer’s disease, would you take that test?

Regardless of whether you’d want to know or prefer to stay unaware, here’s the deal: The test isn’t publicly available unless you’re taking part in a clinical trial to help find a treatment for the disease.

Now the direction of Alzheimer’s research indicates that this is certainly a potential reality.

A new blood test appears to detect the disease a decade before diagnosis, according to research published in the Journal of the Federation of American Societies for Experimental Biology (FASEB) and presented at the recent Society for Neuroscience conference in Washington, DC.

Still in its early stages of development — it’s only been evaluated in 174 people — the blood test measures levels of a single protein in the brain involved in insulin signaling, called IRS-1, which seems to be defective in people who have Alzheimer’s.

Researchers found that patients with Alzheimer’s had higher amounts of the inactive form of this protein and lower amounts of the active form than healthy people. These levels were so consistent that the team predicted, with no errors, whether a blood sample came from an Alzheimer’s patient or a healthy person — and this proved true even when the samples from Alzheimer’s patients were taken 10 years before they were ever diagnosed.

The findings, while promising, "need replication and validation,” said Dimitrios Kapogiannis, lead author and a neuroscientist at the National Institute on Aging (NIA). “But I’m very optimistic this work will hold.”

Targeting more than one biomarker

Kapogiannis’ team are also looking at other proteins. “This disease process is far too complicated for a single magic bullet,” said Dr. Ed Goetzl of the NIA. “We’re trying to mine all these different pathogenic mechanisms because I think there’s going to be at least two, or maybe three, targets against which a drug is directed.”

Two other potential Alzheimer’s blood tests were announced this year that measure different biomarkers to predict disease. A team from Georgetown University screened for 10 lipids in the blood, and was 90% accurate in predicting disease in three years. Another test out of Oxford University measured 10 proteins in the blood to predict onset with 87% accuracy within one year.

The hope is that targeting a biomarker, or several, will identify earlier-stage Alzheimer’s disease patients and allow for early intervention, years before impairments in memory or cognition have a chance to show up.

Ethics of genetic testing

The APOE gene, the strongest genetic risk factor for Alzheimer’s, provides a blueprint for a protein that carries cholesterol in the blood. Everyone inherits one form of the APOE gene — ε2, ε3 or ε4 — from each parent. The ε4 form increases the risk of developing Alzheimer’s disease, and those who inherit two ε4 genes hold an even higher risk, particularly women. It is estimated that between 40% and 65% of people diagnosed with Alzheimer’s have one or two copies of the APOE- ε4 gene, according to the Alzheimer’s Association.

Similar to the other Alzheimer’s blood tests, the APOE- ε4 gene test is mainly used in clinical trials to identify those at higher risk of developing Alzheimer’s. And carrying this gene mutation only indicates greater risk, not whether a person has, or will, definitely develop Alzheimer’s disease.

Although it will take years for any of these tests to make it on the regular rotation at doctors’ offices, this controversial question has been brought up: Should people without symptoms be told that they could be 15 years away from the inevitable diagnosis?

To know or not to know

The development of biomarker tests means health care professionals will have the chance to select patients who have early disease and determine if early treatment helps.

But without the availability of effective treatments, the knowledge of knowing you have a higher risk of developing Alzheimer’s disease could have more cons than pros. In a study in The American Journal of Psychiatry that looked at the effect of telling people that they carry a genotype that puts them at high risk of developing Alzheimer’s, those who learned they tested positive judged their memories more critically and performed worse on memory tests than those who hadn’t been told. 

In a 2013 CNN article, Rudy Tanzi, professor of neurology at Harvard Medical School and leading Alzheimer’s researcher, said, “Medically and socially, we have to get ready for this era of using biomarkers and imaging for early detection.”