Polymorphism link in transsexualism

Melbourne researchers have found a genetic link between a gene for the androgen receptor and male-to-female transsexualism.

The small study, conducted on 112 male-to-female transsexuals and 258 non-transsexual males, found an association between the repeat lengths in the AR allele, with transsexuals having longer repeat lengths than control subjects.

The study was led by Associate Professor Vince Harley of the Prince Henry’s Institute of Medical Research and Monash University PhD student Lauren Hare.

The researchers studied three sex steroid genes to test their hypothesis that these may be responsible for under-masculinisation or feminisation in the fetal brain.

They looked at the androgen receptor, which regulates testosterone; the oestrogen receptor (ER-beta), which regulates oestrogen, and CYP19, a gene coding for aromatase, an enzyme that catalyses the conversion of testosterone to oestrogen.

While the team found a significant association between transsexualism and longer repeats in the AR gene, they found no correlation with ER-b or CYP19.

They conclude that the study provides evidence that male gender identity may by partly mediated through the androgen receptor.

The researchers are planning larger studies to investigate a wider range of genes involved in gender dysphoria.

“Androgen receptor repeat length polymorphism associated with male-to-female transsexualism” is published in Biological Psychiatry [doi:10.1016/j.biopsych.2008.08.033].