BACE1 and Alzheimer disease: Other studies have also shown that absent APOE4 alleles may predict MCI stability for at least 3 years36, plasma homocysteine and serum brain-derived neurotrophic factor may predict MCI-to-AD conversion in patients with the APOE ε4 genotype37, and plasma beta-secretase 1 activity is significantly increased in MCI converters38.