Supplementary material

Our study explored the relationship between standard glucocorticoid (GC) replacement and methylation levels of <i>FKBP5</i> 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 <i>FKBP5</i> methylation and the good alignment with clinical evaluation scores underline the potential of <i>FKBP5</i> 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.