May 06, 2005  |  By: EARTHA MELZE  | COMMENTS     

A recent study by researchers at the National Institutes of Health has added to the body of knowledge on the relationships between genes and sexual orientation, according to a recent issue of Human Genetics.

Although the research was concluded two years ago, the small number of people working on the issue resulted in a delay of two years before the research was published, lead investigator and D.C. resident Dr. Dean Hamer said this week.

The investigation builds on studies that have suggested that there tend to be clusters of gays within a family. In 1993, a group of researchers under the direction of Hamer, who was also a researcher on the recent study, examined DNA from gay men and their family members and found that gay men within a family share a segment of DNA on the X chromosome, which men inherit only from their mothers.

“This told us that genes play a role,” said Brian Mustanski, one of the researchers on the genomescan. “But it doesn’t tell us where the genes are or what they do.”

To develop a more precise picture of what genes might be involved in sexual orientation, researchers examined the genes of 456 individuals from 146 unrelated families — 137 families with two gay brothers and 9 families with three gay brothers.

Researchers reasoned that brothers are expected to share an average of 50 percent of their genes but that genes that influence sexual orientation would be shared more than 50 percent of the time by gay brothers.

Mustanski compared the process of scanning gay brothers for sexual orientation-related genes to looking for doctors in a town of 40,000 people, a number that corresponds to the number of human genes.

“You could take a guess that [a doctor] probably lives in a six bedroom brick house … and only go to a few houses that meet this criteria,” Mustanski said.

“Alternatively, you could go to every street in the town and knock on one door in the neighborhood and ask them if a doctor lives on their street. We used this second approach and narrowed it down to a few streets that are likely to have a doctor on them. When we say ‘chromosomal regions,’ it is akin to the street. The next step is to discover which specific gene within these newly discovered chromosomal regions, is related to sexual orientation,” he said.

The researchers placed 403 markers across the genome.

This strategy revealed three chromosomal areas that are shared by the gay brothers around 60 percent of the time. This frequency of shared markers is not a “significant link,” according to Mustanski but it does rise to the level of “suggestive link.”

Mustanski said that the idea that these chromosomal regions are related to sexual orientation is very compelling because the areas identified through the scan are known to contain genes involved in sexual orientation.

“I think it’s important because it reinforces the theory that sexual orientation is at least partially genetic and that there are many different genes, not just one or two,” Hamer said. “I think it is important knowledge because homophobes often argue that sexual orientation is a choice, which simply isn’t true. It is important to have concrete data showing that it is not simply a choice.”

Research into genetic aspects of homosexuality is controversial. Hamer said that the effect of politics on science can be seen in the fact that there have only been five papers on the subject in 10 years.

“In 1994 our lab discovered a gene involved in anxiety, and there have been 850 papers on that.” Hamer said.

The Council for Responsible Genetics, a 21-year-old Cambridge, Mass.-based group founded by scientists to educate the public on genetics issues, has issued a position paper on the hunt for the genetic basis of sexual orientation.

Eartha Melzer can be reached at emelzer@washblade.com.