The diagnostic certainty after the tau PET scan was lower in participants with a pre-PET non-AD diagnosis compared with a pre-PET AD diagnosis (6.7 [SD, 2.6] vs 8.2 [SD, 2.0]; P < .001), but there was still a significant, yet subtle, increase in certainty in the non-AD group after receiving the tau PET result (6.3 [SD, 2.5] vs 6.7 [SD, 2.6]; P < .001; eFigure 6 in Supplement 1). The gene discussed is MAPT; the disease is Alzheimer disease.