Genes behind transsexualism possibly found
Genes behind transsexualism possibly found
http://www.world-science.net/exclusives/050511_transfrm.htm
WORLD SCIENCE
Genes behind transsexualism possibly found
May 11, 2005
Special to World Science
Scientists say they may have found genes that help explain why a tiny percentage of men see
themselves as women, cruelly trapped in the wrong body.
The researchers say the findings are very preliminary and should be ³interpreted with the utmost
caution,² due to the small sample size used in their study.
Nonetheless, they say, the results might shed some light on the rare condition, transsexualism.
It is estimated to afflict about one in 30,000 men, some of whom follow through on their sense
of their correct gender by getting sex-change operations.
More broadly, the research could help clarify one of the most contentious and poorly understood
questions in biology: what creates ³gender identity²
The feeling is normally rather deep-seated; people don¹t need to examine their body shapes to
confirm it. It is also considered distinct from the issue of whom a person is sexually attracted
to.
The question is how genes, culture or both conspire to produce gender identity.
Transsexualism ³raises important questions as to how the gender identity is moulded in humans,²
wrote the researchers, who included Susanne Hennigsson of Göteborg University and Mikael Landén
of the the Karolinska Institute in Göteborg and Stockholm, Sweden, respectively.
They describe the research in the August issue of the scientific journal
Psychoneuroendocrinology.
If their findings are correct, the risk of becoming a transsexual may depend partly on
variations in the length of certain segments of DNA where the genetic code ³stutters,² that is,
a few ³letters² of the code repeat themselves in the same order many times.
Notably, scientists found in a study published last December that these repeat sequences may be
the sites of some of the most common genetic mutations, and thus may underlie some of the
fastest evolutionary changes in life¹s history. Evolutionary theory holds that mutations produce
evolution, because the occasional mutations that are advantageous spread through populations,
changing these populations¹ characteristics, and over time gradually create new species.
In that study of last year, researchers found that the muzzle length of dogs depends on the
length of certain repeat sequences.
In the transsexualism study, the researchers examined a repeat sequence in each of three genes
known to affect the sexual development of the brain, in hopes that one or more of these might
shed light on transsexualism. They studied several common variants affecting the length of these
repeats in different people.
These variants ³are all much more common than is transsexualism² itself, they wrote. ³Hence, the
goal of this study was not to reveal the primary cause of transsexualism,² but rather to help
explain ³whether the studied genes may facilitate or prevent² it.
One particular variant seemed significantly associated with the frequency of transsexualism,
they found. This variant was in a gene responsible for producing a molecule called ER-Beta.
ER-Beta acts as a minuscule gateway that controls the flow of estrogen, a hormone, through the
brain during fetal development.
Estrogen is thought to be responsible for wiring the brain in a ³masculine² way in healthy males
before birth
The gene that produces the ER-beta receptor contains a section called a CA repeat sequence, so
called because C and A are names for two ³letters² of the genetic code which, here, are repeated
many times in a row.
The researchers found that longer CA repeats were associated with a greater risk of
transsexualism in the the study, which included 29 male-to-female transsexuals (men who wish
they were women) and 229 healthy males.
It is unknown exactly how this change in the ER-beta gene might contribute to transsexualism,
the researchers said. The gene may produce different variants of the molecular gateway, which
transmit estrogen more or less easily; but it¹s unknown whether one of these might be the reason
for the effect, or whether the reason is something else.
Moreover, the researchers found that the two other genes that they studied also seem to
influence the risk of becoming a transsexual. But neither of these genes on its own predicted
that risk, they found. Rather, specific combinations of all three variants seemed to be more
common among transsexuals.
The other two genes studied were genes encoding the production of molecules called aromatase and
androgen receptor. These genes, too, are believed to help determine how ³masculine² the brain
becomes.
More masculine, in this context, means that certain brain structures are relatively smaller or
larger in males than in females, possibly reflecting the relative importance of those brain
structures in each sex.
Researchers have found that parts of the frontal cortex, the seat of many reasoning functions,
and the limbic cortex, involved in emotions, are bigger compared to other brain areas in women
than in men. Parts of the parietal cortex, which contributes to spatial perception, and the
amygdala, which responds to emotionally arousing information, are bigger in men. A part of the
hypothalamus, a brain region that regulates reproductive behavior, is also believed to be bigger
in males.
At least one brain region has also been found to be different in male heterosexuals and
homosexuals, also a part of the hypothalamus. And more recently, gay and straight men have been
found to differ in how their brain responds to a scent in male sweat.
But scientists don¹t know whether homosexuality and transsexualism have anything in common
biologically, beyond the fact that some people view both as aberrations
The idea that genes underlie transsexualism, at least among men who want to be women, has gained
support from reports on twin and non-twin siblings who both have ³this very rare condition, and
from reports on families with more than one member² having it, Henningsson and colleagues wrote.
Gender identity is typically established by 18 to 24 months of age, when ³boys come to know they
are boys, and girls come to know they are girls,² according to the Merck Manual of Diagnosis and
Therapy, 17th Edition.
Some people act in ways typically considered more appropriate for the other sex, but this
doesn¹t make them transsexuals, as long as they¹re comfortable with their physical gender.
Rather, transsexuals ³believe that they are victims of a biologic accident,² the book says, ³and
that they are cruelly imprisoned within a body incompatible with their gender identity.²
So maybe when Arnie calls other politicains "girliemen" he is right!
thoughts
Keep the Faith
🙂