The three-part key: A/T(N)
The NIA-AA research framework yields eight biomarker profiles with different combinations of amyloid (A), tau (T), and neuropathologic damage (N).
“Different measures have different roles,” Dr. Jack and his colleagues wrote in Alzheimer’s & Dementia. “Amyloid beta biomarkers determine whether or not an individual is in the Alzheimer’s continuum. Pathologic tau biomarkers determine if someone who is in the Alzheimer’s continuum has AD, because both amyloid beta and tau are required for a neuropathologic diagnosis of the disease. Neurodegenerative/neuronal injury biomarkers and cognitive symptoms, neither of which is specific for AD, are used only to stage severity not to define the presence of the Alzheimer’s continuum.”
The “N” category is not as cut and dried at the other biomarkers, the paper noted.
“Biomarkers in the (N) group are indicators of neurodegeneration or neuronal injury resulting from many causes; they are not specific for neurodegeneration due to AD. In any individual, the proportion of observed neurodegeneration/injury that can be attributed to AD versus other possible comorbid conditions (most of which have no extant biomarker) is unknown.”