Molecular basis of glucocorticoid-resistant syndromes

Generalized inherited glucocorticoid resistance (GIGR) is a rare syndrome characterized by elevated levels of plasma cortisol but lacking the symptoms of Cushing's syndrome. Biochemically, the condition is characterized by a relative resistance to glucocorticoids that can be compensated for by the elevated levels of cortisol. The inheritance pattern of GIGR is incompletely understood, and one of the central questions is whether there is a correlation between genotype and phenotype. Analysis of mutations within the receptor resulting in relative glucocorticoid resistance has identified two regions of clustered mutations in the proximity of previously identified affinity-labeled residues, the putative steroid-binding site. In the majority of cases, the mutation affects steroid binding and transactivation to the same degree, with the exceptions suggesting an explanation for the variability of the clinical manifestations. From a clinical point of view, in addition to preexisting genetic resistance to glucocorticoids, it is important to consider acquired changes in glucocorticoid receptor (GR) gene structure and organization, including alterations of noncoding sequences, and the importance of the resultant mutations, deletions, and other changes affecting receptor function. Finally, studies of New World primates and cell lines derived from hematologic malignancies constitute animal and human models for the molecular basis of glucocorticoid resistance where a number of inherited and acquired mutations in the GR gene have been demonstrated.