While amyloid-ß42 (Aß42), either as a ratio with Aß40 (Aß42/40) or tau phosphorylated at amino acid 181 (pTau181/Aß42), remains the most commonly used biomarker in cerebrospinal fluid (CSF) to identify AD pathology1,2, its use as a blood-based biomarker has been more limited. The gene discussed is MAPT; the disease is Alzheimer disease.