Major new finding: Will the discovery of a possible gene linked to transssexualism help break down some of the stigma attached to transsexuals? Image shows the official transgender symbol.

Credit: MIT OpenCourseWare

SYDNEY: The first genetic link to male-to-female transsexualism provides new evidence of its biological nature, say Australian researchers.

"There is a social stigma that transsexualism is simply a lifestyle choice, however our findings support a biological basis of how gender identity develops," said Vincent Harley a geneticist from Prince Henry's Institute in Melbourne and co-author of a new study detailing the find.

Gender identity

Gender identity, an inner feeling of being male or female, is usually identified at an early age. Transsexuals, however, identify with the sex that is opposite to their biological sex.

Early theories as to the cause of transsexuality suggested that it could stem from childhood trauma, but more recent research has pointed to family history and a possible genetic aspect. A study released earlier this year by researchers at the University of Vienna, Austria, hinted at a gene that may be involved in female-to-male transsexualism.

The new study, published today in the journal Biological Psychiatry, builds on previous research that highlighted some similarities in the brain structures of women and male-to-female transsexuals.

For the study, Harley and his team took DNA from 112 male-to-female transsexuals and 258 non-transsexual men. They looked at the sequence of three genes known to be involved in the action of sex hormones, and found that some male-to-female transsexuals carry a different form of a gene, called an androgen receptor, which modifies the body’s response to testosterone.

Androgen receptor

The researchers found that, on average, the form of the gene found in the transsexual group had a larger number of repeats of a short, repetitive sequence of DNA - making the gene significantly longer than the form found in the control group of non-transsexual men.

Though the researchers admit that the average difference in the length of the gene between the two groups was small, they said that the size of the study population was limited by the rarity of transsexualism. Nevertheless, "we think that these genetic differences might reduce testosterone action and under-masculinise the brain during foetal development," said co-author Lauren Hare, a geneticist from Monash University in Melbourne.