Androgen receptor point mutations as the underlying molecular defect in 2 patients with androgen insensitivity syndrome.

PURPOSE: We have detected androgen receptor (AR) gene mutations as the underlying molecular defect in male pseudohermaphroditism patients. The functional properties of these mutant receptors regarding hormone binding and transactivation were characterized in 2 patients and offered a possible treatment modality for a male pseudohermaphroditism newborn. MATERIALS AND METHODS: Specific binding of dihydrotestosterone, thermostability of the receptor-hormone complex and 5alpha-reductase activity were measured in their genital skin fibroblasts. AR gene mutations were detected by direct sequencing. The ability of the mutant receptors to activate androgen responsive elements in the deoxyribonucleic acid was determined by transactivation experiments. Screening techniques that distinguish between normal and mutant ARs were developed for rapid detection of the mutation in other family members. RESULTS: The 2 patients showed a qualitative and quantitative binding defect. In both patients, point mutations in the ligand binding domain were identified as the underlying cause. Transactivation assays demonstrated that in the newborn increasing androgen concentrations can restore the mutated receptor's function completely, whereas in the patient with complete androgen insensitivity, excessive amounts of synthetic androgens were necessary. Therefore, the newborn received androgen stimulation and underwent surgical correction in the male direction. These experiments revealed that the functional difference between a mutant AR that causes a partial and one that causes a complete androgen insensitivity may be very small. CONCLUSIONS: Identification of the molecular mechanisms that cause the various forms of sex ambiguity will greatly improve both diagnosis and therapy in affected patients. Exact characterization of AR activation and function may offer a possible treatment modality in affected patients.

CAG-repeat expansion in androgen receptor in Kennedy's disease is not a loss of function mutation.

Expansion of CAG trinucleotide repeats in androgen receptor gene is present in patients with a rare X-linked inherited form of motor neuron disorder termed Kennedy's disease or spinal and bulbar muscular atrophy (SBMA). This is a late onset progressive disease often associated with mild signs of androgen insensitivity. Defects in androgen receptor (AR) action have been linked to the expansion of the CAG trinucleotide repeats and postulated to be the cause of the disease. We have identified a trinucleotide repeat of 45 in the N-terminus of the AR in two brothers with SBMA and several members in their family (range in the general population is 11-35). Treatment of the patients with androgens failed to improve their clinical symptoms and provided no hint of an anomalous function of the AR. Consistently, functional analysis of the mutant receptor showed hormone binding, transactivation and transrepression potentials identical to that of the wild-type receptor. These results together argue against SBMA being a loss of function mutation of the AR.

A single amino acid exchange abolishes dimerization of the androgen receptor and causes Reifenstein syndrome.

A single exchange of an alanine to a threonine at amino acid position 596 in the androgen receptor has been identified as an inheritable trait in patients with Reifenstein syndrome. This exchange is a result of a germ line mutation in the genomic DNA sequences that make up the D-loop of the receptor. The D-loop and sequences in the hormone binding domain together provide the interacting surfaces for receptor dimer formation and subsequent binding to DNA. Here we show that the single amino acid exchange abolishes dimerization of the receptor. With this finding we demonstrate that the destruction of dimerization of the androgen receptor is one of the causes of Reifenstein syndrome.

Androgen receptor alterations in patients with disturbances in male sexual development and in prostatic carcinoma.

The androgen receptor, a ligand-activated nuclear transcription factor belonging to the large superfamily of nuclear receptors, mediates the intracellular action of androgens. It plays a central role in male sexual development and in prostatic carcinoma as a target of endocrine therapy. We have looked for androgen receptor mutations as a cause of male sexual ambiguity and as a possible reason for failure of androgen ablation therapy on prostatic carcinoma. In 5 patients of 2 families with perineoscrotal hypospadia and undescended testes, we have identified a mutation ala596-->thr in the DNA-binding domain of the androgen receptor. This mutation interferes with DNA binding of the receptor. Reactivation of this mutant receptor by binding of an antibody or by interaction with other proteins and by exchange of the amino acid thr602-->ala indicates that the dimerization step is affected. A point mutation ser703-->gly was detected in a newborn male child with perineoscrotal hypospadias. This mutation decreased receptor-hormone affinity. As a consequence its transactivation activity was dependent on the androgen concentration. Although the molecular mechanisms of these two mutations are completely different, both resulted in partial androgen insensitivity and interfered with virilization in the affected patients. A different kind of mutation was present in a tumor specimen derived from an advanced therapy-resistant prostatic carcinoma. This point mutation resulted in exchange of valine-->methionine at amino acid position 715 in the receptor protein. In contrast to the former two mutations this receptor showed a gain in function.(ABSTRACT TRUNCATED AT 250 WORDS)