Nature Medicine published a new article, Plasma Phospholipids Identify Antecedent Memory Impairment in Older Adults, that introduces a blood test that may show promise in predicting the risk of developing Alzheimer’s disease. The disorder, the most common form of dementia, and the sixth leading cause of death, is a devastating neurodegenerative disorder that attacks and progressively destroys the nerve cells of the brain.
Beginning with mild memory lapses and difficulty in concentrating, the disease worsens over time, leading to the inability to think abstractly and perform complex tasks, and eventually leaves its victims incapacitated, both mentally and physically. One in nine people, 65 and older, has the disease and the prevalence increases to 32 percent for those over 85 years old. Alzheimer’s exacts a huge emotional toll on the families of patients and may account for over $100 billion in annual U.S. healthcare costs. That number will continue to rise as Americans live longer, surviving beyond today’s average age of mortality. Although medications exist that temporarily slow the worsening of symptoms, including Aricept and Namenda, no cure for the disease has yet been discovered.
Federoff’s enthusiasm for the promise of the new blood test lies in its predictive value for Alzheimer’s disease. Although presently available tests, like genetic evaluation, can identify certain biomarkers associated with the disease, the only test with any predictive power requires a lumbar puncture, or spinal tap, in order to obtain and examine cerebral spinal fluid. But for people with no symptoms, a simple blood test would make far more sense than undergoing such an unpleasant procedure. The ApoE4 gene, a known marker for the disease, can be identified in blood, but its mere presence in an individual’s genetic makeup does not necessarily mean that Alzheimer’s will manifest as a phenotype. A blood test that can predict the disease has profound implications for the research and development of potential cures, according to Federoff.
The study followed 525 healthy community-dwelling people over 70 years old for up to five years with yearly examinations. At the end of three years, the researchers analyzed blood samples from 106 of the subjects, 53 who showed signs of cognitive impairment and 53 who remained cognitively intact.
The team decided on biomarker panel of 10 phospholipids, as they posited that these fatty molecules represented breakdown of neuronal (nerve) cell membranes. These lipids turned up either significantly positive or significantly negative in the cognitively impaired subjects, while remaining in a steady range in non-impaired individuals. The authors claim that, per the study, the blood analysis had a 90 percent accuracy rate. “We were surprised, but it turns out that it appears we were looking in the right place.” said Mark Mapstone, an author of the study and a neuropsychologist at the University of Rochester Medical Center.
Critics say the study’s data does not entirely support the conclusions. For one thing, the study included as subjects individuals with mild to moderate cognitive impairment, some diagnosed with Alzheimer’s disease and some not. This brings the specificity of the blood test into question. Keith L. Black, MD, a neurosurgeon and researcher at Cedars-Sinai Medical Center in Los Angeles, referring to the biomarkers stated, “it’s difficult to understand how they can be specifically linked to Alzheimer’s disease versus some sort of diffuse neuronal abnormality.” According to John Gever, deputy managing editor of MedPage Today, its possible that, in the real world, the predictive value of the test falls to the unacceptable level of 35 percent.
In summary, although a new blood test may show promise in predicting Alzheimer’s disease, more research is needed to support the optimism of the authors.
By Robert Wisnewski