A New Biological Definition of Alzheimer's Disease: Introduction of 2018 National Institute on Aging-Alzheimer's Association Research Framework

ABSTRACT

Diagnostic guidelines for the preclinical, mild cognitive impairment, and dementia stages of Alzheimer's disease (AD) were released by the National Institute on Aging and Alzheimer's Association (NIA-AA) in 2011. Promoted by the subsequent scientific progress, a unifying update, the ‘NIA-AA Research Framework', was published in 2018. This new research framework shifts the definition of AD from syndrome to biological construct based on biomarkers in living people. The biomarkers were grouped into β amyloid deposition (A), pathologic tau (T), and neurodegeneration (N) related, termed the ‘AT(N) classification system#x2019;, which could be extended with new biomarkers as they become available in the future. For the staging of cognitive impairment, three syndromal stages for observational studies and six numeric stages for clinical trials were also suggested. This biomarker-based classification combined with clinical staging is expected to enhance the understanding of AD as well as aid in precise targeting for interventional clinical trials. This review focused on the introduction of the new 2018 NIA-AA Research Framework. Although this framework has been proposed for research purposes, it is expected to be adopted into general clinical practice with thorough examination and validation in the future.