MAPT and Alzheimer disease: Using the Hulstaert index, a variation of the Aβ1–42/t‐tau ratio, for AD classification of the three cohorts we obtained largely the same, but fewer statistically significant potential marker proteins compared to our uniform AD classification (Appendix Fig S6A–D, Materials and Methods) (Hulstaert et al, 1999; Molinuevo et al, 2013; Vos et al, 2013).