Discovery of "Gay Gene" Questioned
Six years ago, scientists at the National Cancer Institute (NCI) in Bethesda, Maryland, predicted that there was a gene somewhere on the tip of the
X chromosome that influences a male's chances of becoming homosexual. But in tomorrow's issue of Science, a team of Canadian researchers says that they can't find evidence for such a genetic link.
The possible "gay gene" was located in 1993 by a team led by Dean Hamer of the NCI. They noticed a preponderance of gay relatives on the maternal side of the families of the gay men they studied. A closer look at the X chromosomes of 40 pairs of gay brothers from the families with maternal gay relatives showed that the brothers were far more likely to share certain
DNA signposts, or markers, on the Xq28 region of the chromosome than would be expected by chance. The researchers concluded that the snippet must contain a gene predisposing men to homosexuality. A second study published in 1995 led them to the same conclusion.
But a new study by clinical neurologists George Rice and George Ebers at the University of Western Ontario in London, Ontario, and their colleagues takes issue with those findings. Rice and Ebers's team examined DNA from 52 pairs of gay brothers for four markers in region Xq28, using methods similar to Hamer's. They found that the brothers were no more likely to share the Xq28 markers than would be expected by chance. A statistical analysis ruled out the possibility of any gene in Xq28 having a major genetic influence on a male's chances of being gay. "What is troubling is that there is no hint or trend in the direction of the initial observation," says Ebers.
Hamer is not persuaded by the new evidence, however. He points out that his group claimed that the gene only influences those cases of male homosexuality that are transmitted maternally. And Hamer says the Ontario team did not select families based on the presence of maternal transmission. "Maybe there was an X chromosomal linkage in some families, but those families weren't analyzed," Hamer says.
Elliot Gershon, a psychiatric geneticist at the University of Chicago, calls the Ontario team's finding "interesting and important" but would like to see more data. "Failure to find linkage in this study does not mean it doesn't exist," he says.
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