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.



A new definition of Alzheimer’s disease based solely on biomarkers has the potential to strengthen clinical trials and change the way physicians talk to patients.

The paradigm recasts Alzheimer’s from a symptomatic syndrome validated by biomarkers to a strictly biological construct defined by the presence of amyloid beta (AB), tau, and neuronal damage.

AB is the key to this classification paradigm – any patient with it (A+) is on the Alzheimer’s continuum. But only those with both amyloid and tau in the brain (A+T+) receive the “Alzheimer’s disease” classification. A third biomarker, neurodegeneration, may be either present or absent for an Alzheimer’s disease profile (N+ or N-). Cognitive staging adds important details, but remains secondary to the biomarker classification.

Courtesy Mayo Clinic

Dr. Clifford Jack

Jointly created by National Institute on Aging and the Alzheimer’s Association, the system – dubbed the NIA-AA Research Framework – represents a new, common language that researchers around the world may now use to generate and test Alzheimer’s hypotheses, and to optimize both epidemiologic studies and interventional trials. It will be especially important as Alzheimer’s prevention trials seek to target patients who are cognitively normal, yet harbor the neuropathological hallmarks of the disease.

This recasting adds Alzheimer’s to the list of biomarker-defined disorders, including hypertension, diabetes, and hyperlipidemia. It is a timely and necessary reframing, said Clifford Jack, MD, chair of the 20-member committee that created the paradigm. It appears in the April 10 issue of Alzheimer’s & Dementia.

“This is a fundamental change in the definition of Alzheimer’s disease,” Dr. Jack said in an interview. “We are advocating the disease be defined by its neuropathology [of plaques and tangles], which is specific to Alzheimer’s, and no longer by clinical symptoms which are not specific for any disease.”

One of the primary intents is to refine AD research cohorts, allowing pure stratification of patients who actually have the intended therapeutic targets of amyloid beta or tau. Without biomarker screening, up to 30% of subjects who enroll in AD drug trials don’t have the target pathologies – a situation researchers say contributes to the long string of failed Alzheimer’s drug studies.


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