Pan et al. (1998) concluded that there is a positive correlation between serum and central BDNF levels. Serum BDNF levels gradually decline in the later stages of BD episodes (Kapczinski et al., 2008a; Kauer-Sant’Anna et al., 2009). Studies have also reported lower serum BDNF levels during manic and depressive episodes, and higher levels during remission (Kapczinski et al., 2008b; Lin, 2009). Here, BDNF is linked to Behcet disease.