Chemical DNA Tags can Predict Homosexuality

Researchers from UCLA David Geffen School of Medicine have discovered that certain chemical DNA tags or epigenetic tags can predict a man's sexual orientation with 67% accuracy.

Results of this unpublished study were presented on October 8, 2015 at the annual meeting of the American Society of Human Genetics. Comparing one type of epigenetic tag known as DNA methylation in pairs of twins in which one brother is gay and the other straight revealed patterns that distinguish one group from the other about 67 percent of the time, computational geneticist Tuck Ngun and colleagues say.

Several researchers who are not involved in the study are skeptical on the authenticity of the results because the study was only tested on a small sample of men.

Some also thinks that the research could be misinterpreted as an effort to "cure" homosexuality. "None of us see homosexuality as a disorder or something to be fixed," Ngun said. "We're just interested in what makes us tick."

Ngun says that the research is just still new and he has no intention of making a commercial test to predict sexuality. He has decided to leave the academe last week and plans to research in an industry that has nothing to do with the biology of sexual orientation.

"It kind of, honestly, became a little bit troubling to me, what I was actually doing," Ngun said. "Having done this now, I could sort of foresee a not-so-happy outcome."

The researchers measured methylation levels in the saliva of 37 pairs of identical twins in which one twin self-identified as homosexual and the other as heterosexual. 10 pairs of gay twins also participated in the study. A computer program called the FuzzyForest algorithm examined data from half of the gay and straight twins to learn how their DNA methylation patterns differed from each other. The initial data gathering found 6,134 spots in the genome where the twins differed, but together those sites could correctly identify gay twins in the remaining pairs only 44 percent of the time. The number of sites decreased to nine improved accuracy to 67 percent.

Ngun started to do this research because he wanted to understand himself. "I was kind of curious about myself - why I turned out like I did," he said.

Peng Jin, a human geneticist at Emory University in Atlanta said that he's just not sure the researchers have gone about it correctly. He also doubts that a study of less than 100 men has the statistical power to predict sexual orientation.

Jin also studied epigentetic tags in autism. He said that genes are regulated differently in different parts of the body; it's difficult to use epigenetic marks in blood or saliva to glean insights about complex behaviors rooted in the brain.