BDNF and schizophrenia: Although the majority of studies report decreased circulating BDNFlevels (Pirildar et al.2004; Tan et al.2005; Grillo et al.2007; Rizos et al.2008), some find increased levels (Gama etal.2007; Reis et al.2008), and one study reports no significantdifference in plasma BDNF levels in people with schizophrenia compared to healthy controls(Lee & Kim, 2009).