A gene variant has been identified that could explain female-to-male transexuality.

The variation is found within the gene for an enzyme called cytochrome P17, which is utilised in the metabolism of sex hormones. According to researchers it leads to a high tissue concentrations of the hormones which could then influence the development of the brain.

Clemens Tempfer and his tram at the University of Vienna discovered the variant within DNA samples from 49 female-to-male transsexuals and 102 male-to-female transsexuals as 1,669 samples.

The proportion of male-to-female transsexuals and non-transsexual male control samples carrying the gene was around the same. But with women 44% of transsexuals carry the gene compared to 31% non transsexual women.

Linda Geddes writing in the New Scientist said: “While there are many women with the variant who are not transsexual and many female to male transsexuals who lack it, the finding raises the possibility that the variant makes women more likely to feel that their bodies are of the wrong sex, and that this is a result of their brains having been exposed to higher than average levels of sex hormones during development.”

Mikael Landén of the Karolinska Institute in Stockholm told the publication: “The present study found that a mutant gene that ultimately results in higher testosterone levels is overrepresented in female-to male transsexualism.

“This is in line with what we previously know about masculinisation of the brain and is therefore less likely to be a chance finding.

“Hence, the study is important and adds to the notion that gender identity is influenced by sex hormones early in life, and that certain gene combinations make individuals more vulnerable to aberrant effects.”

Janett Scott, formerly the president of transsexual support group, the Beaumont Society said: “Nature may have made us the way that we are, but nurture is what gives us a problem.”