It's all in the genes for a transsexual; HEALTH.
The discovery was made by scientists who examined DNA from 112 male-tofemale transsexuals.
In many cases there was a longer version of a gene known to modify the action of testosterone.
This may "under-masculinise" the brain's development in the womb.
The Australian study leader, Dr Vincent Harley, 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 report is published in the journal Biological Psychiatry.