By Jason Karlawish, M.D.

The earliest maps of a new land, when viewed beside contemporary maps, often have the look of a child's drawing. The borders are rough, whole regions are missing, others misrepresented. If people followed such a map, they might get terribly lost. And yet, some map is better than none at all.

This week, at the Alzheimer's Association International Conference in Vancouver, researchers from the Mayo Clinic reported results of their study of potential biomarkers for preclinical Alzheimer's disease. "Biomarker," a relatively new term in medicine, is a kind of shorthand for any of the various hints that clue us in to the complex ways in which a disease develops. In Alzheimer's disease research, the most studied biomarkers include MRI and PET scan images of the brain.

Their results suggest that among cognitively normal older adults there is a potentially large population who occupy an uncharted territory. Their biomarker results are neither normal, nor clearly abnormal. Dr. David Knopman, the investigator who presented the results, admitted that he and his colleagues "hadn't expected to encounter this result."

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