The main function of the androgen AR receptor is as a DNA-binding transcription factor that regulates gene expression; however, the androgen receptor has other functions as well. Androgen regulated genes are critical for the development and maintenance of the male sexual phenotype.
The study group included 112 male to female transsexuals and 258 non-transsexual males and associations in repeat lengths of the aforementioned genes were examined.
The conclusion found was that the transsexual group showed longer repeat lengths of the AR gene than the non-transsexual group with no association for transsexualism found in the EB or CYP19 genes. No links to the interaction between the three sets of genes and transsexualism were found. Therefore the only link to the condition was the androgen receptor.
The researchers found that the reduced androgen signalling might contribute to a female gender identity in male to female transsexuals. The longer repeat lengths signified a reduced binding ability with a protein co-activator which was responsible for testosterone signalling in the brain.
Females lack the testosterone surge and so their AR gene is not activated. The report concludes that it is possible that the reduced testosterone levels during development could result in incomplete masculinisation and thus a partially or fully feminised brain.