The lack of increase of 11beta-HSD1 expression in Cushing's syndrome could suggest downregulation of the enzyme as a result of long-term overstimulation.
We have described a case of Cushing's disease that failed to present with a classical phenotype, and we postulate that this is due to a partial defect of 11beta-HSD1 activity, the defect in cortisone to cortisol conversion increasing cortisol clearance and thus protecting the patient from the effects of cortisol excess.