Thursday, October 30, 2008
Gene Linked To Transsexualism?
TransGriot Note: The Human Genome Project is the gift that keeps on giving. I always suspected as a reality based real-science person that there was a biological cause to transsexuality. Now an Australian study may have found the first evidence of a genetic link to the biological nature of transsexuality.
Deal with that right-wing Know Nothings.
by Melanie Macfarlane
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, 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.
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.
“This research suggests that extra-long copies of the androgen receptor (AR) gene potentially affect testosterone function in the brains of male-to-female transsexuals," said Andrew Sinclair, a geneticist at the Murdoch Children’s Research Institute in Melbourne who was not involved with the study.
Sinclair, who agreed with the authors as to the possible mode of action of the gene variant, said that, "these defective copies of the AR gene could severely reduce normal testosterone levels, resulting in a more female-like brain."
"This [study] supports the notion that transsexualism has a biological basis rather than being due to psychosocial factors in early childhood,” he added.
Limitations of study
Other experts, however, argued that the small study population limited the conclusions that could be drawn from the results.
"The investigators themselves point out that numbers in association studies are important and while the numbers in their study are modest, they are still potentially quite low," said Ron Trent, a geneticist at University of Sydney. "While statistically significant, [the results are] only just so and this is a weakness."
“This is still a small sample and the effects of the difference in androgen receptor are not black and white, so obviously there is much more to be done," agreed Jennifer Graves, head of the Comparative Genomics Research Group at the Australian National University in Canberra.
"However, I am perfectly sure it will turn out that there are important genes involved in sexuality," she said.
Call to replicate findings
Juliet Richters, a professor in sexual health at the University of New South Wales, in Sydney, said that while the study does not identify the gene as a cause of transsexualism it might provide some comfort for those with the condition.
“It may be a matter of relief for transsexuals to have their condition identified as genetic, rather being blamed for making an awkward lifestyle choice,” she commented.
Despite the debate, the findings provide a good clue to go hunting for the many factors likely to be involved in transsexualism, said Harley, who now invites other research teams to attempt to replicate his findings.