FKBP5 and post-traumatic stress disorder: This study was extended to include SNP analyses of the FKBP5 gene, as well as a sample of recovered PTSD patients and it was found that any of the four PTSD risk-related SNPs was a negative predictor of FKBP5 expression, which in turn was related to lower levels of plasma cortisol and higher PTSD symptom severity [147].