Genes May Contribute to 'Gender Identity'

[JesusA (imported)]

It’s very interesting that two different scientific studies, by different research groups, studying very different phenomena, both published this week, have reached the same conclusion that gender preference seems to be determined before birth. The article previously posted as Startling Study Says People May Be Born Gay (http://www.eunuch.org/vbulletin/showthread.php?t=4244) was based on differences in the “startle reflex” which babies already have at birth and which doesn’t change with age. The study below looks at genetic variance that kicks in before the sex hormones are first produced.

Enough of this and maybe (but not likely) the religious fanatics will finally decide that gender preference is NOT a choice. “God created it!” Let us delight in our diversity, not condemn it!

Genes May Contribute to 'Gender Identity'

Hormones might be just one player in process

By Randy Dotinga

HealthDay Reporter

WEDNESDAY, Oct. 22 (HealthDayNews) -- Researchers say they've discovered genes that may help determine sexuality in the early days of life, weeks before hormones kick in and force fetuses to develop into males or females.

In some cases, the genes may go one way -- affecting the development of the brain -- while the hormones head in the opposite direction, says study co-author Dr. Eric Vilain, an assistant professor of human genetics at the University of California at Los Angeles. If the brain and hormones are at cross-purposes, that could shed light on why transgendered people feel as though they are trapped in the body of the wrong sex, he explains.

The findings "may explain the mechanism of gender identity, why we feel that we're male or female," Vilain adds. "What we're saying, and we're not the only ones to say this, is that [hormones] are not whole story. There also might be genetic influences independent from hormones."

Researchers have long assumed the hormones estrogen and testosterone are responsible for gender development in humans, Vilain notes.

At about six weeks of life, the hormones kick in and create testes or ovaries in humans. Before that time the fetus is physically sexless. The hormones also supposedly affect brain development, which is slightly different in males and females.

In his study, Vilain and his colleagues examined mice before they reached a similar stage of development. They wanted to see if certain genes in the mice "switched on" in accordance with their gender, which only became obvious later during physical development.

The results of the study appear in the October issue of Molecular Brain Research.

The researchers found 54 genes that seem related to gender. Eighteen were produced at higher levels in males; the 36 others were produced at higher levels in females.

In addition to possibly explaining why transgendered people feel as though they're men trapped in women's bodies (or vice versa), the findings could lead to genetic testing to help parents decide how to raise babies who have sex organs of both genders, Vilain says. Parents often have problems deciding whether these children should be raised as boys or girls and whether they should have surgery to "correct" their bodies.

Vilain thinks sexual orientation is a different matter, however, and he's not as certain these genes could contribute to homosexuality.

Bruce McEwen, head of the neuroendocrinology laboratory at Rockefeller University, says the ideas behind the study aren't new, but the research is still "very worthwhile."

But he cautions against assuming genes alone are responsible for different types of sexuality. "It's a nature-nurture type of thing in the extreme," he says. "Environment will play a role, genes will play a role. It would be dangerous to be simplistic."

The next step for researchers is to tinker with the genes of mice and see how they behave, Vilain says. Male and female mice act differently, with males being more aggressive. (There's no word yet on whether they're less likely to ask for directions, too.)

SOURCES:ssssssssssssssssssss Eric Vilain, M.D., assistant professor, human genetics and urology, University of California, Los Angeles; Bruce McEwen, Ph.D., head, neuroendocrinology laboratory, Rockefeller University, New York City; October 2003 Molecular Brain Research

DrKoop.com

Copyright © 2003 ScoutNews, LLC. All rights reserved.

Last updated 10/22/2003.

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[JesusA (imported)]

Below is another journalistic report on this research and a copy of the ABSTRACT of the original article. The article itself is available on-line, but is written in pure Academic.

Genes Organize Male, Female Brain Differently

Dwayne Hunter

Betterhumans Staff

Monday, October 20, 2003

More than 50 genes have been linked to the organization of female and male brains, refuting 30 years of scientific theory that sexuality is entirely determined by hormones, offering a genetic basis for gender assignment of babies born with ambiguous sexual organs and undermining the notion that homosexuality and gender dysphoria are matters of choice.

Since the 1970s, scientists have believed that

the hormones estrogen and testosterone

were wholly responsible for sexually organizing the brain—a fetal brain under the influence of more testosterone became male and under the influence of more estrogen became female.

But a study conducted at the David Geffen School of Medicine and the Mattel Children's Hospital, part of the University of California Los Angeles, indicates that hormones cannot explain everything about the sexual differences between male and female brains.

More than 50 points of difference

Eric Vilain,

assistant professor of human genetics a

nd urology at David Geffen, says that sexual identity is rooted in every person's biology before birth and springs from a variation in the genome.

Using two genetic testing methods that compared genes in male and female brains in embryonic mice—long before the animals developed sex organs—Vilain and colleagues explored whether genetic influences could explain brain variations.

The researchers found 54 genes in different amounts in male and female mouse brains prior to hormonal influences. Eighteen of the gene

s were produced at higher levels in

the male brains and 36

were produced at higher levels in

the female brains.

"We didn't expect to find genetic differences between the sexes' brains," says Vilain. "But we discovered that the male and female brains differed in many measurable ways, including anatomy and function."

Combined influence

In one example, the team found that two hemispheres of the brain appeared more symmetrical in females than in males. Villain believes the symmetry may improve communication between both sides of the brain—an anatomical difference that may explain why women can sometimes articulate their feelings more easily than men.

The research implies that genes account for some of the differences between male and female brains, and that one's genes, hormones and environment exert a combined influence on sexual brain development.

"From previous studies, we know that transgender persons possess normal hormonal levels," says villain. "Their gender identity likely will be explained by some of the genes we discovered."

Villain expects the discovery to lend credence to the idea that gender dysphoria—feeling that you have been born into the body of the wrong sex—has biological origins.

Gender assignment and homosexuality

The findings may also ease the plight of parents with children who have ambiguous genitalia and help physicians assign gender to the children with greater accuracy.

Mild cases of malformed genitalia occur in one percent of all births and severe cases occur in about one in every 3,000 births.

"If physicians could predict the gender of newborns with ambiguous genitalia at birth, we would make less mistakes in gender assignment," said Vilain.

Vilain also proposes that the findings help explain the origin of homosexuality.

"It's quite possible that sexual identity and physical attraction is 'hardwired' by the brain," he says. "If we accept this concept, we must dismiss the myth that homosexuality is a 'choice' and examine our civil legal system accordingly."

The scientists will pursue further studies to distinguish specific roles in the brain's sexual maturation for each of the 54 different genes they identified.

The identification of the 54 genes is reported in the journal Molecular Brain Research

------------------------------------------------------------------------

Copyright © 2002-2003 Betterhumans

http://www.betterhumans.com/News/news.a ... 03-10-20-7

************************

Molecular Brain Research

Volume 118, Issues 1-2 , 21 October 2003, Pages 82-90

Abstract

Copyright © 2003 Elsevier B.V. All rights reserved.

Sexually dimorphic gene expression in mouse brain precedes gonadal differentiation

Phoebe Dewinga, Tao Shia, b, Steve Horvatha, b and Eric Vilaina, c, d, ,

a Department of Human Genetics

, University of California, Los Angeles,

CA, USA

b Department of Biostatistics

, University of California, Los Angeles,

CA, USA

c Department of Pediatrics and Mattel Children's Hospital

, University of California, Los Angeles,

CA, USA

d Department of U

rology, University of California, Los Angeles,

CA, USA

Accepted 31 July 2003. ; Available online 17 September 2003.

Abstract

The classic view of brain sexual differentiation and behavior is that gonadal steroid hormones act directly to promote sex differences in neural and behavioral development. In particular, the actions of testosterone and its metabolites induce a masculine pattern of brain development, while inhibiting feminine neural and behavioral patterns of differentiation. However, recent evidence indicates that gonadal hormones may not solely be responsible for sex differences in brain development and behavior between males and females. Here we examine an alternative hypothesis that genes, by directly inducing sexually dimorphic patterns of neural development, can influence the sexual differences between male and female brains. Using microarrays and RT-PCR, we have detected over 50 candidate genes for differential sex expression, and confirmed at least seven murine genes which show differential expression between the developing brains of male and female mice at stage 10.5 days post coitum (dpc), before any gonadal hormone influence. The identification of genes differentially expressed between male and female brains prior to gonadal formation suggests that genetic factors may have roles in influencing brain sexual differentiation.

Author Keywords: Brain sexual development; Microarray; Sex differences

Neuroscience classification codes: Development and regeneration, Developmental genetics

Corresponding author. Department of Human Genetics, UCLA, 695 Charles E. Young Drive South, Gonda 6357, , Los Angeles, CA 90095, , USA. Tel.: +1-310-267-2455; fax: +1-310-794-5446.

http://www.sciencedirect.com/science?_o ... 6de64e86ee

[Kelly_2 (imported)]

Thank you very much for the information! I very much enjoy these studies and appreciate your posting of them. I do not agree fully with their assumptions, though.

The article on mouse brains is interesting, but humans are different. It can be more complicated with humans. First, gender identity and sexual preference are separate issues. Second, yes, people are born homosexual or transsexual--these are not choices. Thirdly, in humans, gender identity seems to reside in the hypothalamus region of the brain. The hypothalamus forms much later in fetal development than the genitalia.

A correlation between the BSTc region of the hypothalamus and gender identity has already been established. Please see:

http://www.symposion.com/ijt/ijtc0106.htm

and

http://jcem.endojournals.org/cgi/content/full/85/5/2034

"In the present study, we show regardless of sexual orientation: 1) a sex difference in SOM neuron numbers in the human BSTc, with males having almost twice as many SOM neurons as females; 2) a number of SOM neurons in the BSTc of male-to-female transsexuals in the female range; and 3) an opposite pattern in the BSTc of a female-to-male transsexual with a SOM neuron number in the male range."

Although the original article speculates that there are genes that can cause gay mice, gender identity in humans is more likely due to hormones effects on the development of the brain. For instance, I have three full brothers (sharing the same genes). None of them are transsexual. I am, but my mother took DES (a synthetic estrogen that, according to empirical evidence, can cause boys to be born with a female gender identity) when she was pregnant with me.

And note that even genitalia are not gene specific--the presence or absence of testosterone and DHT is what causes males, females, or intersexes to be formed. Usually, these correspond to the XX or XY karyotype, but not always. There are XX males, XY females, intersexes of various karyotypes, and XXY, and other karyotypes.

Again, thank you for stimulating this conversation.

Hugs,

Kelly

[An Onymus (imported)]

To use a mathematical analogy, the more that is discovered about sexuality, the more it appears to be a tensor phenomenon, rather than a scalar phenomenon. You can't simply describe somebody as "male" or "female," and be telling the whole story.

[Kelly_2 (imported)]

This thread seems to be about gay or transsexual mice and what makes them that way. Here is a recent study that showed that sexual differentiation of mouse brains is due to hormones rather than genes, and shows that estrogen, especially late in development, creates the differences of male and female mouse brains:

http://www.bbsonline.org/documents/a/00/00/05/57/

Short Abstract:

Historically, studies of the role of endogenous hormones in developmental differentiation of the sexes have suggested that mammalian sexual differentiation is primarily mediated by testicular androgens, and that exposure to androgens in early life leads to a male brain as defined by neuroanatomy and behavior. The female brain has been assumed to develop via a hormonal default mechanism, in the absence of androgen or other hormones. The role of ovarian hormones in female sexual differentiation may be complementary to androgen-mediated masculinization because the feminizing effects of ovarian steroids are only found in the absence of perinatal androgen. Ovarian hormones have significant effects on the development of a sexually dimorphic cortical structure, the corpus callosum, which is larger in male than female rats. In the females, removal of the ovaries as late as Day 16 increases the cross-sectional area of the adult corpus callosum. Treatment with low-dose estradiol starting on Day 25 inhibits this effect. Female callosa are also enlarged by a combination of daily postnatal handling and exogenous testosterone administered prior to Day 8. The effects of androgen treatment are expressed early in development, with males and testosterone-treated females having larger callosa than control females as early as Day 30. The effects of ovariectomy do not appear until after Day 55. These findings are consistent with other evidence of a later sensitive period for ovarian feminization than androgenic masculinization.

Hugs,

Kelly