Characterization of mutant androgen receptors causing partial androgen insensitivity syndrome

The androgen insensitivity syndrome (AIS) is an X-linked disorder caused by mutations of the androgen receptor (AR) gene resulting in a spectrum of sex phenotypes that ranges from complete female (complete AIS) to nearly complete male (partial AIS). Using the polymerase chain reaction and denaturing gradient gel electrophoresis, we have analyzed the AR gene in three 46,XY individuals with partial AIS. In one subject whose androgen insensitivity was manifest at birth by clitoromegaly, posterior labial fusion, and a urogenital sinus, androgen-binding affinity in genital skin fibroblasts was similar to that of the control. In this subject, a mutation was identified in exon C encoding the second zinc finger of the androgen receptor. The mutation converted a leucine residue at position 616 to arginine, causing greatly reduced binding of receptor to an androgen-response element DNA sequence. However, the mutant AR retained a low level of transcriptional activity at physiological androgen concentrations in keeping with the subject's phenotype of partial AIS. In the second subject, who also had an ambiguous external genital phenotype, a single base mutation was identified in exon G, converting arginine at position 840 to histidine. Androgen-binding affinity in genital skin fibroblasts of this subject was 7-fold lower than control, and the mutant receptor had reduced transcriptional activity. In the third subject, who had a female phenotype with normal pubic hair reflecting a low degree of androgen responsiveness, the valine residue at position 889 was replaced by methionine. This mutant receptor had apparent normal androgen-binding affinity but reduced androgen-binding capacity when examined by expression of the recreated mutant AR in COS 7 cells. These results demonstrate the clinical, functional, and molecular heterogeneity in the syndrome of partial androgen insensitivity.