Familial glucocorticoid resistance 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. Analysis of mutations within the receptor resulting in relative glucocorticoid resistance both familial glucocorticoid resistance and directed mutagenesis, has identified two regions of clustered mutations in the proximity of previously identified affinity-labeled residues In the majority of cases, the mutation affects steroid binding and transactivation to the same degree, but this is Mot always the case.