A single amino acid substitution (Met786----Val) in the steroid-binding domain of human androgen receptor leads to complete androgen insensitivity syndrome.

Androgen receptors (ARs) in two Japanese siblings with complete androgen insensitivity syndrome were characterized, and their molecular bases were investigated. Androgen binding was undetectable in cultured pubic skin fibroblasts from the patients by whole cell assay. Sequence analysis of exons B-H, which encode the DNA- and steroid-binding domains, of the AR gene from these patients using polymerase chain reaction revealed a single nucleotide substitution in exon F, resulting in an amino acid change at 786 from methionine (ATG) to valine (GTG) within the steroid-binding domain of AR. Reconstruction of this mutation by site-directed mutagenesis into human AR cDNA followed by expression in COS-1 cells led to production of the same amount and the same molecular mass of immunodetectable AR protein as those found with expression of the normal human AR cDNA. However, in contrast to wild-type AR expressed in COS-1 cells, the mutant AR showed markedly low affinity of androgen binding by whole cell assay. These results suggest that androgen resistance in these patients is due to the point mutation in the steroid-binding domain of the AR.