A new biomarker classification system for AD, independent of cognition: Agnosticism is a start

Clinicians and researchers interested in Alzheimer disease (AD) are confronted with an expanding number of biomarkers that can be derived from brain imaging and CSF analysis. But how do we make sense of specific and nonspecific disease indicators that increasingly coexist in normal and diseased older people? In this issue of Neurology®, Jack et al.1 present us with a scheme that indicates the binary presence or absence of 7 biomarkers in 3 categories of amyloid (A), tau (T), and neurodegeneration (N): the A/T/N classification system. The rationale for such a new descriptive system for categorizing multidomain biomarkers is 4-fold: (1) the advent of tau PET tracers providing an imaging biomarker of tau neuropathology; (2) the uncertainty regarding the temporal relationships among current β-amyloid (Aβ) and tau biomarkers; (3) independence from diagnostic classification schemes that are not directly related to biomarkers, particularly independence from diagnostic classification based on cognition; and (4) the need to include all biomarker profiles that are found in all members of the population. The rationale is laudable, but how far does the proposed A/T/N classification scheme go toward achieving this?