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Immunoreactive AR and Genetic Alterations in Subjects with Androgen Resistance and Undetectable AR Levels in Genital Skin Fibroblast Ligand-Binding Assays

Departments of Internal Medicine (D.M.A., C.M.W., N.N., J.E.G., M.J.M.) and Pharmacology (C.M.W.), University of Texas Southwestern Medical Center, Dallas, Texas 75390-8857

Address all correspondence and requests for reprints to: M. J. McPhaul, M.D., Department of Internal Medicine, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390-8857. E-mail: michael.mcphaul{at}utsouthwestern.edu

Defects of the AR cause a wide range of abnormalities of male development, ranging from individuals with mild defects of virilization to those with complete female phenotypes. In parallel with this phenotypic spectrum, a large number of different mutations have been identified that alter the synthesis or functional activity of the receptor protein. This report aims to categorize the alterations of immunoreactive AR (IRAR) expression and the underlying genetic changes in a single category of patient: those in whom ligand binding is undetectable in genital skin fibroblasts. Our study found a wide range in the levels of IRAR that are detectable in fibroblast strains established from 27 such individuals. A large proportion (19 of 27) express significant amounts of AR protein, as detected using a sensitive Western blot technique. In a smaller number (8/27), AR expression was undetectable. Intact IRAR was identified in16 of the 19 fibroblast strains in which AR expression could be detected. The AR gene was analyzed in 14 strains from this group. In 13 instances, single amino acid substitutions were identified within the ligand-binding domain of the receptor protein. In three of the remaining patients (3 of 19), truncation of the receptor protein was suggested by the rapid migration of the IRAR in SDS-polyacrylamide gels. In those three patients, production of the shortened immunoreactive receptor was traced to mutations that interrupted the AR open reading frame. By contrast, only one of the eight patient samples with no detectable IRAR carried a mutation that resulted in a single amino acid substitution. An interruption of the AR open reading frame was identified in six of the eight strains in which immunoreactive receptor was absent. In the remaining strain, no mutation was present within or surrounding the eight coding exons. This study serves to define the effects that mutations of the AR have on the levels of expressed immunoreactive receptor protein. In addition, it demonstrates the type of information that can be obtained if an immunoblot assay were to be used as a component of a screening method to analyze samples from patients with defects of the AR. Finally, the study suggests that in some androgen-resistant patients, defects outside the AR open reading frame may result in major alterations of AR expression.

This work was supported by Grant DK-03892 from the NIH and Grant I-1090 from The Robert A. Welch Foundation. Portions of this work were presented at the 75th Annual Meeting of The Endocrine Society, Las Vegas, Nevada, June 9–12, 1993.

Abbreviations: CAIS, Complete androgen insensitivity syndrome; Gln, glutamine; IRAR, immunoreactive AR; LBD, ligand-binding domain.

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