Many studies have found that there are differences in blood BDNF levels by sex (women higher than men), age (decrease with age), plasma/serum (serum higher than plasma), disease stage (increase in the early stage and decrease in the late stage), cognitive impairment severity, depressive symptoms, medication and other factors that also affect blood BDNF levels (Lommatzsch et al., 2005; Laske et al., 2006; Fukumoto et al., 2010). The gene discussed is BDNF; the disease is Cognitive impairment.