The significant difference of serum BDNF among groups (AD, MCI, and controls) was confirmed in carriers of BDNF Val/Val genotype (p = 0.026); patients with BDNF Val/Val homozygous had significantly lower serum BDNF levels (11.78 ± 2.40 pg/mL compared with Val/Val homozygous controls (13.21 ± 1.19 pg/mL p = 0.01), in particular when considering the female subsets (11.63 ± 2.66 pg/mL p = 0.001). This evidence concerns the gene BDNF and Alzheimer disease.