BDNF and Alzheimer disease: Finally, proBDNF and BDNF have been associated with cognitive impairment (Michalski and Fahnestock, 2003; Peng et al., 2005) with several studies showing decreased levels in patients with MCI and AD dementia (Yasutake et al., 2006; Laske et al., 2007) and others showing conflicting results with increased levels in AD patients (Angelucci et al., 2010; Faria et al., 2014).