BDNF and post-traumatic stress disorder: When veterans with PTSD were subdivided according to smoking status, the ROCF copy test scores did not differ significantly in smokers with PTSD subdivided into BDNF rs56164415 genotype carriers (H = 0.306; df = 2; p = 0.858), T vs. CC genotype carriers (U = 175.5; p = 0.771) or T and C allele carriers (U = 433.0; p = 0.886).