Background: The glucocorticoid receptor (GR) consists of two alternatively spliced isoforms: GRα, which activates gene transcription, and GRβ, a dominant-negative receptor. Theoretically, inactivating variants of GRβ could result in glucocorticoid hypersensitivity.
Design: A 46-year-old woman presented for evaluation of adrenal insufficiency prompted by low plasma cortisol levels and multiple unexplained symptoms but without clinical evidence of glucocorticoid insufficiency. To explain these findings, extensive clinical, genetic, and molecular studies were performed.
Methods: Standard clinical methods assessed the patient's hypothalamic-pituitary-adrenal axis. Validated molecular techniques were used for receptor sequencing, stable transfections, stimulation of candidate genes, cDNA arrays, Ingenuity Pathway Analysis, volcano analysis, and isolation and analysis of the patient's mononuclear cells.
Results: Clinical studies excluded primary or secondary adrenal insufficiency, established consistently low basal cortisol levels, and demonstrated hypersensitivity to ultra-low-dose dexamethasone. Receptor sequencing identified two variants of GR9β (A3669G and G3134T) as well as the known Bcl1 polymorphism. Reductionist studies using stable osteosarcoma cell lines transfected with the GRβ variants demonstrated glucocorticoid hypersensitivity of transcribed genes on cDNA array analysis. The patient's monocytes responded to hydrocortisone with exaggerated stimulation of the candidate genes GILZ and FKBP5.
Conclusion: Two variants of the dominant-negative GRβ, in conjunction with a common Bcl1 intron variant, resulted in hypersensitivity to endogenous and exogenous glucocorticoids and, as a reflection of severity, low circulating cortisol levels without clinical evidence of glucocorticoid insufficiency. This prismatic case exemplifies the unique effects of variants of a dominant-negative receptor.