Glucocorticoids (GC) such as cortisol regulate multiple physiological functions, notably those involved in development, metabolism, inflammatory processes and stress, and exert their effects upon binding to the glucocorticoid receptor (GR, encoded by NR3C1 gene in humans). GC signaling follows several consecutive steps leading to target gene transactivation, including ligand binding, nuclear translocation of ligand-activated GR complexes, DNA binding, and recruitment of functional transcriptional machinery. Generalized glucocorticoid resistance syndrome, due to GR loss-of-function mutations, may be related to the impairment of one of the GC signaling steps. To date, 31 NR3C1 loss-of-function mutations have been reported in patients presenting with various clinical signs such as hypertension, adrenal hyperplasia, hirsutism or metabolic disorders associated with biological hypercortisolism but without Cushing syndrome signs and no negative regulatory feedback loop on the hypothalamic-pituitary-adrenal axis. Functional characterization of GR loss-of-function mutations often demonstrates GR haploinsufficiency and a decrease of GR target gene induction in relevant cell types. The main signs at presentation are very variable from resistant hypertension, bilateral adrenal hyperplasia likely related to increased ACTH levels but not exclusively, hirsutism to isolated renin-angiotensin-aldosterone system abnormalities in a context of 11βHSD2 deficiency. Some mutated GR patients are obese or overweight together with a healthier metabolic profile that remains to be further explored in future studies. Deciphering the molecular mechanisms altered by GR mutations should enhance our knowledge on GR signaling and ultimately facilitate management of GC-resistant patients. This review also focuses on the criteria facilitating identification of novel NR3C1 mutations in selected patients.
Géraldine Vitellius and Marc Lombes
Géraldine Vitellius, Séverine Trabado, Christine Hoeffel, Jérôme Bouligand, Antoine Bennet, Frederic Castinetti, Bénédicte Decoudier, Anne Guiochon-Mantel, Marc Lombes, Brigitte Delemer and investigators of the MUTA-GR Study
Recently discovered mutations of NR3C1 gene, encoding for the GR, in patients with glucocorticoid resistance and bilateral adrenal incidentalomas prompted us to investigate whether GR mutations might be associated with adrenal hyperplasia.
The multicenter French Clinical Research Program (Muta-GR) was set up to determine the prevalence of GR mutations and polymorphisms in patients harboring bilateral adrenal incidentalomas associated with hypertension and/or biological hypercortisolism without clinical Cushing’s signs.
One hundred patients were included in whom NR3C1 sequencing revealed five original heterozygous GR mutations that impaired GR signaling in vitro. Mutated patients presented with mild glucocorticoid resistance defined as elevated urinary free cortisol (1.7 ± 0.7 vs 0.9 ± 0.8 upper limit of normal range, P = 0.006), incomplete 1 mg dexamethasone suppression test without suppressed 8-AM adrenocorticotrophin levels (30.9 ± 31.2 vs 16.2 ± 17.5 pg/mL) compared to the non-mutated patients. Potassium and aldosterone levels were lower in mutated patients (3.6 ± 0.2 vs 4.1 ± 0.5 mmol/L, P = 0.01, and 17.3 ± 9.9 vs 98.6 ± 115.4 pg/mL, P = 0.0011, respectively) without elevated renin levels, consistent with pseudohypermineralocorticism. Ex vivo characterization of mutated patients’ fibroblasts demonstrated GR haploinsufficiency as revealed by below-normal glucocorticoid induction of FKBP5 gene expression. There was no association between GR polymorphisms and adrenal hyperplasia in this cohort, except an over-representation of BclI polymorphism.
The 5% prevalence of heterozygous NR3C1 mutations discovered in our series is higher than initially thought and encourages GR mutation screening in patients with adrenal incidentalomas to unambiguously differentiate from Cushing’s states and to optimize personalized follow-up.