Scientists have uncovered 20 genes linked to being transgender – supporting claims that the condition has a physical basis.

Researchers believe the gene variations may contribute to people identifying with the opposite sex.

Critics of transgender identity say the condition is ‘all in the mind’, and transgender people have a psychological problem rather than a medical one. But by highlighting genetic mutations that affect brain development, the latest findings point towards transgender identity having a physical basis.

US researchers tested 14 female-to-male and 16 male-to-female patients at gender reassignment clinics.

Presenting their research at the Society for Reproductive Investigation conference, the researchers said: ‘We identified genetic variants in 20 genes that may play a role in transgender identity.

‘The most promising of these include variants of genes involved in neurologic development and sex hormones.’

Dr Ricki Lewis, a geneticist, said: ‘These are highly reputable folks going about this exactly the right way, searching the genomes of transgender people to highlight which genes they have variants in. It lends legitimacy, if that needs to be added, that transgender is not a choice but a way of being.'