FKBP51 has emerged asa promising drug target for chronic pain,36 obesity,37,38 and depression.39,40 The major challenge in FKBP51 drug development is selectivity towardits closest homologue FKBP52, as the binding pockets of both proteinsare very similar, but the biological functions are opposite. This evidence concerns the gene FKBP4 and depressive symptom measurement.