In 2018, the National Institute on Aging-Alzheimer's Association (NIA-AA)'s clinical research criteria reconceptualized AD as a biologically defined entity, diagnosed in vivo by biomarker evidence of the 2 core hallmarks of the disease: β-amyloid (Aβ) proteinopathy (A) and hyperphosphorylated tau (T).1 Rigorous research has continued to consolidate and expand the role of AD biomarkers, particularly those that are blood-based, facilitated by advances in ultrasensitive assay techniques. This evidence concerns the gene MAPT and Alzheimer disease.