Moreover, the concentration of Ng in blood plasma exosomes of patients with AD and MCI was lower than that of healthy control subjects (SMD: −6.657 [95% CI: −10.558 to −2.755], P = 0.001; and SMD: −3.64 [95% CI: −6.50 to −0.78], P = 0.013), and which in patients with AD and MCI-AD were also lower than those in patients with sMCI (P < 0.001). This evidence concerns the gene NRGN and Alzheimer disease.