FKBP5 and post-traumatic stress disorder: A study of primates implicated FKBP5 as one of the main determinants of glucocorticoid resistance.78 A study in humans examined gene-environment interaction between a risk allele associated with enhanced gene expression and ELS exposure.71 The researchers reported that ELS-exposed, risk-allele carriers showed loss of intronic methylation near a glucocorticoid response element that affected glucocorticoid-induced activation of FKBP5. Another study reported that FKBP5 alleles interacted with ELS to increase the risk for PTSD.91