MAPT and Alzheimer disease: Some studies reported no effect of APOE ε4 carrier status on metabolite levels, and their association with AD biomarkers (Aβ and tau load), but others reported that APOE ε4 allele carrier status affects the metabolite levels and/or the relationship between the metabolites and AD biomarkers [50,58,60,66,67,70,71,72,73,79,80].