Transsexualism, Left-Handedness May Share Origins

NEW YORK (Reuters Health) - Left-handedness may be more common among transsexuals than in the general population, suggesting that the two conditions might share a common developmental origin, according to UK researchers.

``Both male and female transsexuals were more often non-right-handed'' compared with non-transsexual males or females, according to Dr. Richard Green and Robert Young of Charing Cross Hospital in London.

Some researchers believe that handedness may be determined by prenatal exposure to male hormones, or androgens, in the womb. Green and Young note that a fetal preference for one hand over the other ``has been observed as early as week 15 of gestation.'' One theory is that this hormonal exposure influences the structural development of the brain, which later helps determine which hand a person favors.

Similarly, according to the British authors, many experts speculate that homosexuality is linked to androgen exposure during fetal development. And past research has suggested that structural differences between the brains of men and women, as well as homosexual and heterosexual men, may occur early in brain development.

All of this speculation has triggered ``considerable recent attention'' to the possible link between handedness and sexual orientation, Green and Young note in the December issue of Archives of Sexual Behavior.

Their study of 443 male-to-female transsexuals and 93 female-to-male transsexuals showed that these individuals were less likely to be exclusively right-handed compared with a ''control'' group of 284 volunteers.

Presented with six everyday tasks--including cutting, throwing or writing--about 48% of non-transsexuals said they performed the tasks with their right hands only, compared with 44% of female transsexuals and just over 38% of male transsexuals. Even when the investigators looked only at transsexuals whose family members were solidly right-handed, the association remained.

Although it is possible that altered levels of prenatal sex hormones could play a role in this association, the UK team notes that other developmental factors--such as the mother's immune response to the fetus--could be involved.

Dr. Anne Lawrence, a Seattle clinical sexologist with a majority transsexual clientele, agreed, noting that ''developmental instability could occur in the womb, it's just not necessarily associated with variations in the hormonal environment.''

And what about transsexuals who are solidly right-handed? ''One of the things we know about transsexuality is that it develops differently in different persons; this suggests that there might be more than just one cause,'' Lawrence--herself a transsexual--said in an interview with Reuters Health.

``There are a lot of different conditions that we believe might make someone choose a transsexual solution to their life-dilemma,'' she said. Developmental influences might play a role, but they might not necessarily be ``the whole answer.''

She believes that research into human sexuality--including transsexualism--is valuable for several reasons. Right now, she said, ``we don't really have a consistent theory for transsexual orientation and gender identity development.'' And she notes that individuals also tend to be more accepting of non-traditional sexual orientations when they believe these preferences have their roots in biology, as opposed to some kind of ``choice.''

Finally, she added, Green and Young's research could point to possible ways of preventing or treating gender identity problems. ``Of course that's very controversial,'' she said, ``and I take no firm position on that except to say that this path is not easy for individuals--many transsexuals themselves will tell you that if their condition could have been prevented they would have preferred that.''

SOURCE: Archives of Sexual Behavior 2001;30:565-574.