BDNF and agoraphobia: Our main findings in this current study included: (a) BDNF plasma levels of PD patients were significantly lower than those of healthy controls, and BDNF plasma levels of Met/Met genotype were significantly lower than those of Val/Met genotype in PD patients; (b) Trait anxiety in PD patients was associated with BDNF Val66Met polymorphism and comorbid agoraphobia, but not with BDNF plasma concentration; (c) No significant differences were found in BDNF allele frequencies and the BDNF genotype distributions between PD patients and health control subjects.