Supplementary material

Our study explored the relationship between standard glucocorticoid (GC) replacement and methylation levels of FKBP5 in patients with adrenal insufficiency (AI), aiming at identifying reliable parameters of glucocorticoid (GC) exposure. The observed dose-dependent effect of the GC replacement on FKBP5 methylation and the good alignment with clinical evaluation scores underline the potential of FKBP5 methylation as a biomarker for therapy response. Furthermore, the lower methylation levels observed in AI patients compared to patients with cortisol-producing adrenal adenomas suggest exposure to recurrent supraphysiological cortisol peaks under standard therapy, especially under a single-dose regimen. The alignment between methylation and clinical evaluation encourages further investigations in a prospective, interventional setting focused on re-evaluating the concept of physiological replacement with GC.