Potential Screening Tool for Alzheimer's

Levels of two key indicators in spinal fluid were able to distinguish clinically diagnosed Alzheimer's patients from controls with 89-92% efficiency in a study conducted by scientists at the US National Institute of Mental Health (NIMH;). The results were reported in the April 23, 2003, issue of the Journal of the American Medical Association (JAMA).

The scientists examined cerebrospinal fluid (CSF) levels of two protein fragments found in the brains of Alzheimer's patients: beta-amyloid and tau. Beta-amyloid clumps together to form brain-damaging plaques, while tau strangles neurons in tangled filaments. Findings showed that as CSF beta-amyloid levels dropped, tau levels rose. Taken together, the two markers revealed a sensitivity of 92% and a specificity of 89% in the 131 Alzheimer's patients and 72 controls. These results match or exceed current clinical diagnostic methods, such as a doctor's evaluation, cognitive testing, and brain scans.

The study also included a meta-analysis of world literature, which showed the same patterns for the two protein fragments. For both measures, however, the researchers found considerable overlap in levels between the Alzheimer's and control groups. They concluded that the diagnostic sensitivity and specificity of the beta-amyloid and tau assays are not sufficient to warrant general use as biomarkers for individuals until long-term studies under way are completed.

"Perhaps the most important future use for such biomarkers is in the prospective study of people at risk for developing Alzheimer's disease,” noted Trey Sunderland, M.D., chief, NIMH Geriatric Psychiatry Branch, who conducted the study with colleagues. "By establishing a person's baseline and tracking levels over time, we might be able to interpret gradual changes as a sign that the disorder is developing.”