CLINICAL AND BIOCHEMICAL INVESTIGATIONS AND MOLECULAR ANALYSIS OF SUBJECTS WITH MUTATIONS IN THE ANDROGEN RECEPTOR GENE

OBJECTIVE Androgen insensitivity syndromes (AIS) in subjects with 46,X Y karyotype and normal or even elevated androgen brood levels are char acterized by various aberrations in male differentiation and virilizat ion. AIS is often accompanied by a broad spectrum of abnormal binding characteristics of the androgen receptor (AR). in order to investigate the correlation between the degree of virilization defect and the typ e of androgen binding abnormalities and/or the nature of the mutation in the AR gene, we determined androgen binding characteristics of the AR protein and the sequence of the AR gene in clinically and biochemic ally well characterized patients with various degrees of androgen resi stance. DESIGN AND PATIENTS The activity of 5 alpha-reductase and the binding of androgen to its receptor (K-D-values, B-max, thermolability ) were determined in genital skin fibroblasts from 20 patients with va rious degrees of defects in virilization (2 CAIS, complete AIS; 18 PAI S, partial AIS patients). The AR gene of these 20 subjects was charact erized by PCR-SSCP analysis. In case of aberrant electrophoretic mobil ity the corresponding exon was sequenced. RESULTS The 2 patients with CAIS and 7 with PAIS showed a mutation in the AR gene. In two, the mut ation was in the DNA binding domain, and in all others in the ligand b inding domain. In 11 patients with severe virilization defects no abno rmal behaviour was detected in the PCR-SSCP. Transcriptional activatio n studies of two mutant ARs revealed that an approximately tenfold hig her androgen concentration (methyltrienolone) is necessary to achieve maximal response as compared to the wild type AR. CONCLUSIONS There is no obvious relation between the degree of androgen resistance and the binding parameters of the AR and/or the nature of mutation in the AR gene. Androgen insensitivity syndrome can occur despite normal androge n binding and presumably non-mutated AR genes. Even if there is abnorm al binding of androgen and/or a mutation in the AR gene there is no cl ear-cut relationship between these parameters and the degree of virili zation defects. Thus, in a proportion of patients, neither the determi nation of binding parameters of the AR nor the detection of mutations in the AR gene are sufficient to understand the mechanisms underlying the androgen insensitivity syndrome.