Despite this preliminary evidence, a recent model relating genetic risk factors associated with impaired fear extinction such as the BDNF val66met polymorphism, potential epigenetic-modifications associated with early-childhood adversity and trauma, and adulthood trauma has emerged to implicate a role for BDNF function in the comorbidity of PTSD and bipolar disorder (Rakofsky et al., 2012). The gene discussed is BDNF; the disease is bipolar disorder.