Introduction

Androgens are key regulators of male sexual differentiation and development of a normal male phenotype. In the adult they are required for maintenance and function of male genital organs and spermatogenesis. In addition, they are involved in a large number of physiological processes such as stimulating muscle and hair growth, bone development, erythropoiesis as well as controlling male psychosocial behavior. The two main androgens in the human body are testosterone and dihydrotestosterone, the 5α-reduced derivative of testosterone. Each of them has its distinct role and target tissues. During development, testosterone produced in the testis triggers the development of the Wolffian duct structures which results in the development of the seminal vesicles, vas deferens and urethra, whereas dihydrotestosterone, synthesized in the periphery through the action of the enzyme 5α-reductase, is crucial for development of external genitalia and the prostate from the urogenital sinus.

At the cellular level, androgen action is mediated by a high affinity receptor, the androgen receptor (AR) that functions as a ligand-activated transcription factor. This receptor is a member of the large superfamily of ligand-inducible transcription factors that share the structural and functional organization in three domains (transactivation, DNA-binding and ligand-binding domains). Binding of androgens induces a cascade of activation steps that finally result in a transcriptionally active AR capable of regulating the transcription of genes by binding to target sequences in the chromatin, termed androgen response elements.

The gene encoding the AR is located on the long arm of the X-chromosome close to the centromere region.