Moreover, studies have established a correlation between the incidence of single nucleotide polymorphisms (SNPs) in the genes NGF, BDNF, NTRK1, NTRK2 and the susceptibility to paranoid schizophrenia (Arévalo et al., 2004, 2010; Lin et al., 2013; Kranz et al., 2015). Here, NTRK1 is linked to schizophrenia.