Molecular Analysis of the Androgen-Receptor Gene in a Family with Receptor-Positive Partial Androgen Insensitivity: An Unusual Type of Intronic Mutation

Abstract

In the coding part and the intron-exon boundaries of the androgen-receptor gene of a patient with partial androgen insensitivity, no mutation was found. The androgen receptor of this patient displayed normal ligand-binding parameters and migrated as a 110-112-kD doublet on SDS-PAGE in the absence of hormone. However, after culturing of the patient's genital skin fibroblasts in the presence of hormone, the slower-migrating 114-kD protein, which reflects hormone-dependent phosphorylation, was hardly detectable. Furthermore, receptor protein was undetectable in the nuclear fraction of the fibroblasts, after treatment with hormone, which is indicative of defective DNA binding. By sequencing part of intron 2, a T-->A mutation was found 11 bp upstream of exon 3. In our screening of 102 chromosomes from unrelated individuals, this base-pair substitution was not found, indicating that it was not a polymorphism. mRNA analysis revealed that splicing involved a cryptic splice site, located 71/70 bp upstream of exon 3, resulting in generation of mRNA with an insert of 69 nucleotides. In addition, a small amount of a transcript with a deleted exon 3 and a very low level of wild-type transcript were detected. Translation of the extended transcript resulted in an androgen-receptor protein with 23 amino acid residues inserted between the two zinc clusters, displaying defective DNA binding and defective transcription activation.