A Novel Patient-Derived Mutation in Glucocorticoid Receptor Reveals an Essential Role for DNA binding in Development and Endocrine Regulation

Glucocorticoid receptors (GRs) are vital transcription factors regulating stress responses, metabolism, and development. We report here a novel heterozygous NR3C1 c.1310C>T (p.T437I) variant within the GR DNA-binding domain found in a family exhibiting clinical and hormonal manifestations of partial glucocorticoid resistance. Patient-derived fibroblasts demonstrated an overall suppression in dexamethasone-induced transcription. To comprehensively assess the significance of the variant, we engineered a knock-in mouse model (Nr3c1+/T444I mice) using CRISPR-Cas9, providing an in vivo model of the patient-derived GR mutation at the orthologous residue. Heterozygous mice exhibited partial glucocorticoid resistance, dysregulated HPA axis activity and impaired dexamethasone suppression, closely recapitulating the patient phenotype. Homozygous Nr3c1T444I/T444I embryos were recovered at embryonic day 12.5 (E12.5) but did not survive to term, indicating mid-gestational lethality. Transcriptomic profiling of primary mouse embryonic fibroblasts revealed dosage-dependent effects with heterozygotes showing an intermediate response to dexamethasone compared to wild-type, while homozygotes showed a markedly blunted response. Our results challenge prior assumptions by demonstrating that GR DNA-binding is essential for embryogenesis, while offering a new preclinical platform to investigate glucocorticoid resistance pathophysiology and therapeutic interventions.