Through a study of more than 400 pairs of gay brothers, researchers led by Northwestern University's Michael Bailey identified two regions of the genome that appear to be associated with sexual orientation in men.
As they report in Psychological Medicine, Bailey and his colleague homed in on a region of chromosome 8 and one on the X chromosome through a genome-wide linkage scan. That region on the X — Xq28 — had been linked in previous, smaller studies to sexual orientation, the researchers note.
While they didn't drill down to specific genes in the 8q12 and Xq28 regions, the researchers say that that there are a number of genes located nearby.
First author Alan Sanders from NorthShore University HealthSystem tells the Associated Press that this "is not proof but it's a pretty good indication" that genes on those two chromosomes influence sexual orientation. "It erodes the notion that sexual orientation is a choice," he adds in the New Scientist.
Medical geneticist Robert Green from Harvard Medical School tells the AP that the results are "intriguing but not in any way conclusive," while the University of California, San Francisco's Neil Risch says the data are statistically too weak to demonstrate any genetic link.
Sanders, Bailey, and their colleagues note in their paper that further investigation including through re-sequencing studies is warranted. Sanders tells the New Scientist that they've already begun work comparing SNPs in the regions they've highlighted between gay and straight men.
"Through this study, we have the potential to narrow down to fewer genes," he says.