There is additional evidence for a genetic component to homosexuality, but not proof, say the authors of a new study of gay brothers published online today.
The study, published on the Psychological Medicine Web site, indicates that genes on a region of the X chromosome are associated with homosexuality and that genes on a different chromosome, called chromosome 8, may play a role as well. It does not identify, however, which genes are involved
This “is not proof, but it’s a pretty good indication” that genes in these areas influence sexual orientation, lead author Alan Sanders, MD, told the Associated Press. Sanders is a behavioral genetics researcher with the NorthShore University HealthSystem Research Institute in Evanston, Ill.
In the study, funded by the National Institutes of Health, researchers looked at DNA samples from 409 pairs of gay brothers. It replicates findings by NIH scientist Dean Hamer’s 1993 “gay gene” study in that it implicates the same region of the X chromosome in homosexuality, notes Science magazine.
“When you first find something out of the entire genome, you’re always wondering if it was just by chance,” Hamer, who is now retired from the NIH, told Science. The new study “clarifies the matter absolutely,” added Hamer, who shared the Science coverage on Twitter.
— Dean Hamer (@deanhamer) November 17, 2014
The Science article notes that Hamer, who was attacked by activists on the left and right for his work on a gay gene, “feels vindicated,” but some scientists are skeptical about the significance of the findings by Sanders and his colleagues. The new information is “intriguing but not in any way conclusive,” Harvard Medical School geneticist Robert Green, MD, told the AP. And Neal Risch, a geneticist at the University of California, San Francisco, told Science the linkages found in the new study are not statistically significant.
Study participant Chad Zawitz, MD, a Chicago physician, was encouraged. The study, he told the AP, is “a giant step forward” in advancing the understanding that being gay “is sort of like having certain eye color or skin color — it’s just who you are.” He added, “Most heterosexuals I know didn’t choose to be heterosexual. It’s puzzling to me why people don’t understand.”
Sanders and collaborator J. Michael Bailey, a psychologist at Northwestern University in Evanston, are undertaking further research. They now will look at information from the study published today plus DNA samples from more than 1,000 more gay men, and the results could provide further evidence of a genetic link or cast doubt on it. “It looks promising for there being genes in both of these regions,” Bailey told Science, “but until somebody finds a gene, we don’t know.”