BDNF levels were negatively related with CDR scales, suggested that low levels of BDNF were related with AD risk since the BDNF levels were higher in lower CDR scores compared to those in higher CDR scores (χ2 = 214, P < 0.01) while CDR scores have been used to evaluate the severity of AD (Clark et al., 2014). The gene discussed is BDNF; the disease is Alzheimer disease.