Participants with diagnosed primary tauopathies (n = 10) were recruited to the Human CNS Tau Kinetics in Tauopathies study and a cohort of cognitively unimpaired or with mild cognitive impairment (Clinical Dementia Rating score ≤0.5; n = 22) to the Tau Stable Isotope Labelling Kinetics study. The gene discussed is MAPT; the disease is tauopathy.