HONG KONG, Oct 26 (Reuters) - Scientists in Australia said they have identified a gene which may explain why some people are transsexuals.

For decades, there has been debate over the origins of transexuality, with some recent studies indicating that family history and genetics may be linked to gender identity.

In the largest genetic study involving transsexuals to date, researchers in Australia said they found that transexuality may be linked to the androgen receptor (AR) gene -- which is known to modify the effect of the male sex hormone testosterone.

"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 lead researcher Vincent Harley of Monash University's Prince Henry's Institute of Medical Research.

The scientists collected DNA samples from 112 male-to-female transsexuals and found that they were more likely to have a longer version of the AR gene than another group of 258 non-transsexual men.

The longer AR gene was found in 55.4 percent of people in the transsexual group and 47.6 percent of the non-transsexual men, they wrote in an article published in Biological Psychiatry.

Samples were also analysed for two other genes, but no significant differences were found between both groups.

The researchers said the longer AR variant gene may have resulted in less effective testosterone signalling, a mechanism that masculinises the brain during early development.

"It is possible that a decrease in testosterone levels in the brain during development might result in incomplete masculinisation of the brain in male-to-female transsexuals, resulting in a more feminized brain and a female gender identity," they wrote.

One of the researchers, Lauren Hare, said: "We think that these genetic differences might reduce testosterone action and under masculinise the brain during foetal development."

The researchers called for more such studies in other populations to replicate the findings. (Reporting by Tan Ee Lyn)

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