Screening for Alzheimer’s Disease: Some Progress

In developed nations, human life expectancy has increased steadily for over a century. One of the few negative consequences of this trend has been a marked increase in the prevalence of Alzheimer’s disease, an age-related untreatable condition that has driven enormous health spending on a national scale and wrecked the finances of millions of families in the US alone. Now, with the oldest Baby Boomers just reaching age 65, Alzheimer’s disease seems destined to become a true national health crisis.

Two of the most vexing problems with this nasty disease are determining who has it and diagnosing it early enough (so scientists can understand how it progresses and someday, intervene to either cure it or halt its progression).

With current technology, the only way to accurately diagnose Alzheimer’s disease is at autopsy. Special tests of the deceased’s brain reveal the sine qua non of Alzheimer’s disease: amyloid plaques.

But last week, 2 studies appearing in JAMA provided rays of hope in this otherwise dismal state of affairs. We review them both below:

Brain Scan Detects Plaques
In the first study, scientists injected a radioactive dye known as Flobetapir F 18 into the blood of elderly volunteers, and then used PET scans to image their brains.  Florbetapir F 18 had been designed by Christopher Clark and colleagues at Avid Radiopharmaceuticals to bind to amyloid proteins—which are the main constituents of amyloid plaques—and thus make them visible in vivo using the PET scan.

The PET scans correctly identified amyloid plaques in 97% of the volunteers that actually had them, as proven at autopsy. In addition, PET scans performed after the dye had been injected into young, healthy volunteers revealed no plaques.

Scientists believe the Florbetapir F 18 PET scans could be helpful as a means to exclude the diagnosis of Alzheimer’s. If no plaques are found in a patient with symptoms of dementia, physicians would be compelled to consider other causes of the symptom complex. The PET scans could also potentially be used to test drugs designed to remove amyloid from the brain.

A Blood Test for Alzheimer’s
The second study showed that blood levels of amyloid protein, as detected by a new blood test, were correlated with memory problems.

The study was directed by Kristine Yaffe at UCSF. Her group recruited 997 elderly volunteers and followed them with memory tests and amyloid blood tests for 9 years. 

Yaffe’s group found that subjects with the highest blood levels of amyloid protein were less likely to experience declining mental abilities, a result that seems counterintuitive but is in fact consistent with what scientists had expected based on their knowledge of amyloid protein physiology as the disease progresses.

Interestingly, the inverse relation between blood amyloid protein levels and mental capacity was less apparent in subjects with higher educational levels at study onset. Yaffe’s group was careful not to suggest that people who remain mentally active could be spared from Alzheimer’s disease, but suggested that the finding demands further study.

Quick Take
Yaffe’s test is, unfortunately not accurate enough to be useful in clinical settings right now, and the PET scanning approach mentioned above is too expensive for routine clinical use. Nevertheless, these 2 studies represent progress in an area where it is badly needed. We’ll take what we can get and keep our fingers crossed that the science moves as fast as the epidemic.