A MUTATION OF THE GLUCOCORTICOID RECEPTOR IN PRIMARY CORTISOL RESISTANCE

The precise molecular abnormalities that cause primary cortisol resist ance have not been completely described. In a subject with primary cor tisol resistance we have observed glucocorticoid receptors (hGR) with a decreased affinity for dexamethasone. We hypothesize that a mutation of the hGR glucocorticoid-binding domain is the cause of cortisol res istance. Total RNA isolated from the index subject's mononuclear leuko cytes was used to produce first strand hGR cDNAs, and the entire hGR c DNA was amplified in segments and sequenced. At nucleotide 2,317 we id entified a homozygous A for G point mutation that predicts an isoleuci ne (ATT) for valine (GTT) substitution at amino acid 729. When the wil d-type hGR and hGR-Ile 729 were expressed in COS-1 cells and assayed f or [H-3]-Dexamathasone binding, the dissociation constants were 0.799/-0.068 and 1.54+/-0.06 nM (mean+/-SEM) (P < 0.01), respectively. When the wild-type hGR and hGR-Ile 729 were expressed in CV-1 cells that w ere cotransfected with the mouse mammary tumor virus long terminal rep eat fused to the chloramphenicol acetyl transferase (CAT) gene, the hG R-Ile 729 conferred a fourfold decrease in apparent potency on dexamet hasone stimulation of CAT activity. The isoleucine for valine substitu tion at amino acid 729 impairs the function of the hGR and is the like ly cause of primary cortisol resistance in this subject.