BDNF and post-traumatic stress disorder: While some candidate gene study sample sizes have simply been too small (n < 20) to adequately represent the three BDNF genotypes (see [1,28,46]), other moderate samples (n > 100) (see [24,26,29,32]) have been able to demonstrate the influence of the gene on PTSD when other environmental conditions within and between experimental groups have been adequately controlled.