Androgen receptor (AR) is a protein that belongs to family of nuclear receptors. AR is activated by binding of androgen hormones and functions as a transcription factor that regulates gene expression. Genes regulated by androgens are essential for the development and maintenance of the male phenotype. Since the AR gene is located on X chromosome, molecular-genetic pathologies are manifested almost exclusively in men. Mutations in the AR gene affect all its exons and the consequences of these mutations are variable serious with a wide range of phenotypic abnormalities. Mutations in the AR gene may cause androgen insensitivity syndrome, but AR also affects the physiology of a nervous system and is defective in a disorder known as spinal and bulbar muscular atrophy (Kennedy disease). In addition, point mutations and polymorphisms of trinucleotide repeats are associated with a number of other diseases such as prostate cancer. To date, more than 1000 different mutations were identified in the AR gene, most of which cause androgen insensitivity and are presented mainly as substitutions in the ligand-binding domain of the AR.

For AR mutations diagnostics, two major molecular-genetic methodological approaches are principally used. For diagnostics of androgen insensitivity syndrome and prostate cancer, sequence analysis of exons of the AR gene is used, which will reveal any point mutation that may cause these diseases. Spinal and bulbar muscular atrophy is confirmed by fragmentation analysis, which analyzes the length of the amplified fragment containing CAG repeats in the first exon of the AR gene.