Trans rights campaigners and their allies have long argued that being transgender is not a lifestyle choice but rather the resolution of a deep-rooted conflict between mind and body.

The new study, led by John Theisen at Augusta University in Georgia, may be the strongest vindication of this argument to date. The scientists sequenced the DNA of 14 female-to-male and 16 male-to-female transgender people and looked for genetic variants that were common in these groups but turned up in fewer than one in 10,000 people in the wider population. They found 30 such variants, nine of which were in genes known to be implicated in the growth of brain cells or the production of sex hormones such as oestrogen and testosterone.

Dr Theisen stressed that his team’s research was in its early days, with a relatively small number of subjects involved and no proof as yet that any individual variant was involved in gender dysphoria.

The study, which was presented this month at a meeting of the Society for Reproductive Investigation in San Diego, California, has yet to go through peer review and some of its findings may be down to chance. Nevertheless, its preliminary results tally with more than half a dozen other papers that suggest there is something distinctive about the neurobiology of transgender people.

MRI scans carried out by several groups of neuroscientists suggest that some structures and mechanisms in trans people’s brains resemble those of the gender with which they identify more closely than those of their birth sex. Others indicate that the areas of the brain implicated in the perception of self are less well connected to regions that process the perception of the body in trans men and women than in cisgender people, who identify with their birth sex.

Ten years ago a team led by Vincent Harley, a molecular geneticist at the Hudson Institute of Medical Research in Victoria, Australia, found that male-to-female transgender people were much more likely to have a particular variant in the CYP19 testosterone receptor gene than cisgender men. Professor Harley said that it would be exciting if the new findings could be confirmed in a larger study.

Bernard Reed, a founder and trustee of the Gender Identity Research and Education Society, said: “There is a growing amount of scientific evidence that, within the brain, there is a biological basis for these unusual gender identities, just as there is for being right or left-handed. Already, this has led to acceptance within the World Health Organisation and NHS England that the development of an unusual gender identity is not a mental illness.

“Nor is it a lifestyle choice or the result of a person’s experiences, for example being mistreated. The biological factors that influence gender identity development are varied and none of them may be used diagnostically. You can’t conduct a physical test on somebody and say this person’s gender identity is unusual. The only way to be certain about a person’s gender identity is to listen to them.”

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