In apolipoprotein E (APOE) ε4-carriers, linear relationships were found between greater cognitive decline/year and higher tau; Mini-Mental State Examination score – T-tau (rs = − 0.257, p = 0.014) and Alzheimer’s Disease Assessment Scale–cognitive subscale – P-tau (rs = − 0.242, p = 0.022). This evidence concerns the gene APOE and early-onset autosomal dominant Alzheimer disease.