From the Journals

Alzheimer’s: Biomarkers, not cognition, will now define disorder

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A logical and modern approach

The biologically defined amyloid beta–tau–neuronal damage (ATN) framework is a logical and modern approach to Alzheimer’s disease (AD) diagnosis. It is hard to argue that more data are bad. Having such data on every patient would certainly be a luxury, but, with a few notable exceptions, the context in which this will most frequently occur is within the context of clinical trials.

While having this information does provide a biological basis for diagnosis, it does not account for non-AD contributions to the patient’s symptoms, which are found in more than half of all AD patients at autopsy; these non-AD pathologies also can influence clinical trial outcomes.

Dr. Richard J. Caselli, professor of neurology at the Mayo Clinic in Scottsdale, Ariz., and associate director and clinical core director of Mayo’s Alzheimer’s Disease Center.

Dr. Richard J. Caselli

This expensive framework might unintentionally lock out research that does not employ all these biomarkers either because of cost or because of clinical series–based studies. These biomarkers generally can be obtained only if paid for by a third party – typically a drug company. Some investigators may feel coerced into participating in studies they might not otherwise be inclined to do.

It also seems a bit ironic that the only meaningful manifestation of AD is now essentially left out of the diagnostic framework or relegated to nothing more than an adjective. Yet having a head full of amyloid means little if a person does not express symptoms (and vice versa), and we know that all people do not progress in the same way.

In the future, genomic and exposomic profiles may provide an even-more-nuanced picture, but further work is needed before that becomes a clinical reality. For now, the ATN biomarker framework represents the state of the art, though not an end.

Richard J. Caselli, MD, is professor of neurology at the Mayo Clinic Arizona in Scottsdale. He is also associate director and clinical core director of the Arizona Alzheimer’s Disease Center. He has no relevant disclosures.



The second, a six-stage numerical clinical staging scheme, will apply only to those who are amyloid-positive and on the Alzheimer’s continuum. Stages run from 1 (unimpaired) to 6 (severe dementia). The numeric staging does not concentrate solely on cognition but also takes into account neurobehavioral and functional symptoms. It includes a transitional stage during which measures may be within population norms but have declined relative to the individual’s past performance.

The numeric staging scheme is intended to mesh with FDA guidance for clinical trials outcomes, the committee noted.

“A useful application envisioned for this numeric cognitive staging scheme is interventional trials. Indeed, the NIA-AA numeric staging scheme is intentionally very similar to the categorical system for staging AD outlined in recent FDA guidance for industry pertaining to developing drugs for treatment of early AD … it was our belief that harmonizing this aspect of the framework with FDA guidance would enhance cross fertilization between observational and interventional studies, which in turn would facilitate conduct of interventional clinical trials early in the disease process.”

The entire system yields a shorthand biomarker profile entirely unique to each subject. For example an A+T-(N)+ MCI profile suggests that both Alzheimer’s and non-Alzheimer’s pathologic change may be contributing to the cognitive impairment. A cognitive staging number could also be added.


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