US researchers tested 14 female-to-male and 16 male-to-female patients

The latest findings point towards transgender identity having a physical basis 

Dr Ricki Lewis, a geneticist, said: 'It lends legitimacy, if that needs to be added, that transgender is not a choice but a way of being'

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.

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.