For the first time, a test that detects 10 types of lipids, or fats, circulating in a person's blood has been shown to predict accurately whether he or she will develop the memory loss and mental decline of Alzheimer's disease over the next two to three years. A screening test based on the findings could be available in as little as two years, said the researchers who identified the blood biomarkers.
The effort to identify predictors of Alzheimer's disease that are reliable, easy and inexpensive to detect was described Sunday in the journal Nature Medicine. Blood biomarkers for Alzheimer's could make it possible to identify those at risk before they develop symptoms, the authors suggested.
While no treatments for Alzheimer's have proven effective in slowing or reversing its progress, the authors declared that earlier detection may open new treatment options. Interventions to head off or slow cognitive decline before it is evident might be more effective than intervening later, when dementia has already set in.
The researchers -- from the University of Rochester, Georgetown University and UC Irvine -- did not start with a list of possible biomarkers, but recruited 525 subjects at least 70 years old. The team scoured their blood for possibilities while waiting to see which subjects would develop dementia symptoms.
Forty-six subjects were diagnosed with Alzheimer's disease upon entry into the study. And 28 went on to develop mild Alzheimer's or amnestic mild cognitive impairment, a condition that often progresses to full-blown Alzheimer's. The researchers compared the blood of 53 of those 74 subjects with that of 53 matched subjects who had developed no cognitive abnormalities. The analysis allowed them to identify measurable differences between the groups in 10 different lipids.
The 10 lipids identified as harbingers of Alzheimer's appear to be the result of the breakdown of neural cell membranes, a process that accelerates as the disease takes hold.
Once they had the list of revealing lipids, the study authors gathered 41 of their recruits: 21 who had developed early Alzheimer's in the course of the study and 20 who had not. Blinded to the subjects' status, the researchers tried to see if they could use the 10-lipids panel to sort the subjects correctly on the basis of their blood tests alone. They found they could do so, with over 90% accuracy.
That's an accuracy level on a par with tests that measure the cerebrospinal fluid for evidence of abnormal proteins that are a hallmark of Alzheimer's disease. But because a blood test would be much cheaper and less invasive than a spinal tap, it would make screening large populations of people far more practical.
Among the issues still to be sorted out: how revealing the 10-lipids blood panel would be in a larger and more diverse population of patients; and how sensitive and specific such a screen would be. Many tests are able to identify 100% of people who are sick with a particular disease (they're highly sensitive), but they also falsely identify many as sick who are not (they're not very specific).
If patients test positive for impending Alzheimer's, many may accept treatments that are expensive and risky in a bid to head it off. As a result, it's important to establish that the 10-lipids test does not have a very high "false positive" rate.