NGF and Alzheimer disease: However, the levels of NGF transcripts are unaffected (Goedert et al., 1986; Jette et al., 1994; Fahnestock et al., 1996) and the protein levels of the NGF precursor, proNGF, are greatly elevated in AD post-mortem brain samples (Fahnestock et al., 1996, 2004; Peng et al., 2004; Pedraza et al., 2005; Al-Shawi et al., 2008; Bruno et al., 2009a).