Study of Gay Brothers May Show It’s Genetic

by Peter Cassels

EDGE Media Network Contributor

Wednesday September 27, 2006

Researchers are recruiting gay brothers to participate in a study that hopes to map genes that may determine sexual orientation.

While no one has yet identified a "gay gene," many scientists believe it may be a group of genes that help determine whether someone is gay. That's what researchers led by Dr. Alan Sanders, associate professor of psychiatry at Northwestern University, seek to corroborate. The study is funded by the National Institutes of Health.

The Evanston Northwestern Healthcare Research Institute is recruiting 1,000 sets of gay brothers to participate in the study, in which participants are having their DNA analyzed through blood samples and completing questionnaires that are being used to determine how their sexual orientation was developed.

If science can show that being gay is a biological trait, like eye color, the public likely would be more accepting of gays, Timothy Murphy, a University of Illinois at Chicago bioethicist and paid consultant to the study told the Chicago Sun-Times.

Earlier studies of so-called familial sexual orientation have included families that had gay or lesbian members extended over several generations, identical twins and smaller samples of gay brothers, Sanders reported in an EDGE interview Sept. 27.

In 1993, an NIH research team led by Dr. Dean Hamer conducted a study of families that showed a pattern of cross-generational male homosexuality containing evidence that the trait is to some degree inherited through the maternal line. The Hamer study also showed that through a genetic linkage analysis of 40 pairs of gay brothers, a particular genetic region on the X chromosome (Xq28) was shared between gay brothers at a significantly higher rate than between gay men and their heterosexual brothers. Several others studies of gay brothers were done in the 1990s, but they involved other small samples, usually of about 50 pairs, and they had different findings, according to Sanders.

Studies of families that had gay men with older heterosexual brothers showed that the chances of a man being gay increased by about a third for each older heterosexual brother in his family.

In the 1990s Sanders said researchers figured out that methods relying on trying to find one gene that determines sexual orientation "did not work out so well."

The larger sample size provides "more statistical power" and may help scientists determine if there is one gay gene or, what is more likely, a group of genes that determine sexual orientation, Sanders said. "If there is any one or a few genes that are responsible, there's a pretty good chance that we'll pick that up," he explained. "It would tell us that this linkage mapping approach is not the way to go to find it. It's up in the air. We'll see what the data show us."

"If there is any one or a few genes that are responsible, there's a pretty good chance that we'll pick that up."

It's also possible that maybe there's many genes--dozens--that contribute, each just a tiny amount, the researcher acknowledged. "If that is the case, our linkage study would not be able to get at those because of the noise factor."

Sanders emphasized that the objective of his research is to find out more about the role genetics plays in determining sexual orientation, but the scientists will look at other factors, hence the reason for having subjects complete a detailed questionnaire that looks at, among other things, early childhood influences.

"We know that environmental contributions are very important," he explained. "Environment also includes very early biological influences that are not genetic." Those are prenatal hormonal influences, for which there have been animal studies, but not much in the way of human studies. "It certainly doesn't appear to be a difference in adults," Sanders explained. "Testosterone levels are the same [regardless of sexual orientation]."

Sanders and his associates are looking for gay brothers who share both biological parents, half brothers who share one biological parent, or fraternal twins. Other family members need not participate, but can if they wish to. Identical twins are ineligible because it is already known that their DNA is the same. Subjects are eligible regardless of HIV status or any other medical condition.

The study does not include lesbian siblings, although there is some evidence to suggest that genetics may play a role in female sexual orientation, according to the researchers. However, there is no evidence suggesting that a particular genetic region is involved in the sexual orientation of women, as there is for men. In fact, studies have shown that a particular genetic region that might influence sexual orientation in males shows no evidence of that effect in women. Family and twin studies have also shown indications that male and female sexual orientation may have different genetic influences from each other.

Sanders reported that the study began in 2004 and analyses of several hundred families who have volunteered for the study have been completed. "There are several hundred more where the first brother has turned in his questionnaire, but the second brother hasn't. We may have identified 2-3,000 potential families over the past 2 1/2 years, but we have a fair amount to go." Even if they don't have quite 1,000 pairs of brothers by the spring of 2007, they will continue with the analysis, which could take another year, and "there's a good chance our first major paper will come out in 2008."

The study is confined to English-speaking brothers and most thus far have been from the United States and Canada, Sanders said. Also eligible are families from the United Kingdom, Ireland, Australia and New Zealand

Visit to find out more about the research project. Gay brothers who wish to participate in the study can e-mail [email protected] or phone toll-free 866-364-7571.

Peter Cassels is a recipient of the National Lesbian and Gay Journalists Association's Excellence in Journalism award. His e-mail address is [email protected].

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