These findings suggest that FKBP5, which has a central function in stress-hormone regulation, could be a useful marker for susceptibility to severe nicotine withdrawal and could help to identify individuals at greatest risk for relapse to smoking following a quit attempt. FKBP5 may also be useful in understanding the link between stress-related disorders, such as PTSD, and the severe nicotine withdrawal that often accompanies it. Treatment of these co-occurring disorders is especially difficult and when they are comorbid, negative health effects may be amplified.3, 4 Risk for ND and PTSD is influenced by genetic variation, with a significant proportion of this risk being common to both disorders.52 FKBP5 could be a common factor involved in facets of each trait. Also, given its role in modulating withdrawal severity, variation in FKBP5 has implications for smoking cessation. This possibility is supported by a study showing that glucocorticoid agonists may reduce cigarette craving and satisfaction in smokers.53 The subjects in the gene expression study (n=48) were also transcriptome-analyzed after the final injection of nicotine (data not shown). Relative to the pre-saline condition, we
