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'Transsexuality gene' boosts male hormones

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  • Chris King
    Transsexuality gene boosts male hormones * 16:13 29 July 2008 * NewScientist.com news service * Linda Geddes A gene variant has been identified that appears
    Message 1 of 1 , Jul 30, 2008
      'Transsexuality gene' boosts male hormones

      * 16:13 29 July 2008
      * NewScientist.com news service
      * Linda Geddes

      A gene variant has been identified that appears to be associated with
      female-to-male transsexuality – the feeling some women have that they
      belong to the opposite sex.

      While such complex behaviour is likely the result of multiple genes,
      environmental and cultural factors, the researchers say the discovery
      suggests that transsexuality does have a genetic component.

      The variation is in the gene for an enzyme called cytochrome P17,
      which is involved in the metabolism of sex hormones. Its presence
      leads to higher than average tissue concentrations of male and female
      sex hormones, which may in turn influence early brain development.

      Clemens Tempfer and his colleagues at the Medical University of
      Vienna in Austria discovered the variant after analysing DNA samples
      from 49 female-to-male (FtM) and 102 male-to-female (MtF)
      transsexuals, as well as 1669 non-transsexual controls.

      The variant was more common in men than women, although it doesn’t
      seem to be implicated in MtF transsexuality as the proportion of MtF
      transsexuals with it was similar to that in non-transsexual men. In
      women, however, there were some differences: 44% of FtM transsexuals
      carried it, compared with 31% of non-transsexual women.
      Testosterone boost

      While there are many women with the variant who are not transsexual
      and many FtM 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.

      "It may increase the likelihood that people will become transsexual,"
      says Tempfer. But he stresses that their cultural environment is also
      important.

      "The present study found that a mutant gene that ultimately results
      in higher testosterone levels is overrepresented in female-to male
      transsexualism, says Mikael Landén of the Karolinska Institute in
      Stockholm, Sweden.

      "This is in line with what we previously know about masculinisation
      of the brain and is therefore less likely to be a chance finding", he
      says. "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."
      Motive fears

      However, Janett Scott, former president of the Beaumont Society, a UK
      support group for transgender people, is concerned that positing a
      biological basis for transsexuality may encourage people to try and
      cure it.

      "Nature may have made us the way that we are, but nurture is what
      gives us a problem," she says.

      Tempfer strongly denies any such motive for his research: "That is
      completely out of the question," he says.

      Nonetheless, he says, if other gene variants with a stronger
      association to transsexuality are identified, establishing a
      diagnosis might become easier. This might allow gender reassignment
      surgery or hormone therapy to start earlier in life.

      Journal reference: Fertility and Sterility (DOI: 10.1016/j.fertnstert.
      2007.05.056)
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