The largest ever genetic study of male to female transsexuals has found a significant genetic link between gender identity and a gene involved in testosterone action.

DNA analysis from 112 male-to-female transsexual volunteers showed they were more likely than heterosexuals to have a longer version of the androgen receptor gene.

Professor Vincent Harley, who led the team at Prince Henry’s Institute in Melbourne that produced the report published in Biological Psychiatry, said:

“There is a social stigma that transsexualism is simply a lifestyle choice, however our findings support a biological basis of how gender identity develops.”

The receptor gene controls testosterone signals.

The longer version that was detected in male-to-female transsexuals could weaken those signals as the foetus develops in the womb.

“We think that these genetic differences might reduce testosterone action and under masculinise the brain during foetal development.” said researcher Lauren Hare.

For decades, there has been debate over the causes of transexuality.

Early theories included psychosocial factors such as childhood trauma.

More recent studies have indicated that family history and genetic aspects are linked to the development of gender identity.

Terry Reed from the Gender Identity Research and Education Society, said:

“This study appears to reinforce earlier studies which have indicated that, in some trans people, there may be a genetic trigger to the development of an atypical gender identity.

“However, it may be just one of several routes and, although it seems extremely likely that a biological element will always be present in the aetiology of transsexualism, it’s unlikely that developmental pathways will be the same in all individuals.”