Biomarkers for Alzheimer's disease: showing the way or leading us astray?

The indolent nature of Alzheimer's disease, coupled with burgeoning interest in a "presymptomatic" stage of disease, has motivated efforts to identify, validate, and exploit surrogate disease markers for trials of disease-modifying or preventive strategies. Many of these efforts have been productive, and biomarkers are now routinely applied in selection of study subjects and evaluation of outcomes in clinical trials. On the other hand, biomarkers also have the capacity to lead to bad therapeutic outcomes when they determine "go- no go" decisions in early drug development. This paper reviews several reports of biomarker studies which illustrate the great potential, for both good and ill, of biomarkers of Alzheimer's disease.