Many studies report similar accuracy of plasma P-tau levels to that of CSF P-tau and tau PET in diagnosing Alzheimer’s disease and differentiating Alzheimer’s dementia from other neurodegenerative dementias (Janelidze et al., 2020, Karikari et al., 2020, Palmqvist et al., 2020, Thijssen et al., 2020). This evidence concerns the gene MAPT and early-onset autosomal dominant Alzheimer disease.