APOE and Alzheimer disease: Odor familiarity (AUC = 0.81) and the combination of odor familiarity plus odor identification (AUC = 1.0), but not odor identification or MMSE alone, were significant predictors of conversion from MCI to AD in the Apoe ε4 carriers, suggesting the potential for the combination of odor identification and familiarity to serve as a biomarker.