A new molecular dye might eventually help diagnose Alzheimer's disease much earlier, which could prove vital to developing effective treatments and preventative measures. The molecule binds to amyloid plaques, the neurological hallmark of Alzheimer's disease, and can be detected in the living human brain with PET imaging.  Previously, the only definitive way to detect amyloid in the brain, and hence diagnose the disease, was via an autopsy.

"Now we can see this Alzheimer's lesion in living people, and that's a big step," says John Morris, director of the Alzheimer's Disease Research Center at Washington University. Morris was not involved in the study. "Ultimately, we would like to move diagnosis to the preclinical stage [before symptoms appear] and see if we can devise strategies to prevent the brain damage that produces dementia. But it will be years before we get to that stage."

An advisory committee for the U.S. Food and Drug Administration will meet on Thursday to decide whether to recommend that the new tracer, developed by Avid Radiopharmaceuticals, be approved to help doctors diagnose the disease or to rule it out. Pharmaceutical giant Eli Lilly acquired the company last December. Avid's tracer is one of several amyloid binding compounds under development, and the first to complete large-scale clinical trials.

Researchers say the most promising near-term use of the tracer, which is detected via positron emission tomographic (PET) imaging, is in drug development. The ability to detect signs of the disease prior to the development of obvious cognitive problems lets pharmaceutical companies test therapies designed to prevent the development of plaques early on. "It's enormously important for drug development research," says Paul Aisen, director of the Alzheimer's Disease Cooperative Study at the University of California, San Diego. Aisen was not involved in the study. "It allows us to test therapies at the stage of disease where they are most likely to be clinically useful—when people have amyloid deposition but not major cognitive dysfunction."

Pharmaceutical companies are currently using the type of amyloid imaging used in the study to gauge the effectiveness of experimental drugs designed to reduce buildup of the protein. (Whether or not drugs that block the buildup of amyloid improve memory loss is still an open question. It's also not clear whether the plaque buildup is a cause of Alzheimer's or an effect of it.)