The big news yesterday, sparked by a yet-to-be-published study of twins and a related news release from the American Society of Human Genetics (ASGH), is that scientists can now predict male sexual orientation “with 70% accuracy” using a genetic test.
The headline about the study in the ASGH news release put it this way: Epigenetic algorithm accurately predicts male sexual orientation.
And here’s a sampling of the news headlines that may have been influenced by that news release:
But a closer look at the study itself raises some questions about these bold claims of accuracy and whether these headlines should have been better calibrated. Many experts have expressed skepticism and say larger studies beyond the 47 pairs of twins are needed to prove that a molecular marker can predict sexual orientation.
A story in Science by Michael Balter picked up on this:
“They were able to reach almost 70% accuracy, although the presentation makes clear that—in contrast to what a provocative ASHG press release about the study suggested—this predictive ability applies only to the study sample and not to the wider population.”
BuzzFeed News also featured some very skeptical takes on the research, both in terms of the study size and the applicability of using saliva to make determinations about processes that take place in the brain. And their coverage nods to the uncertainty surrounding the test right in the headline: “Epigenetic Test Can Predict Homosexuality, Controversial Study Claims.”
“The sample size is very small,” Peng Jin, a professor of human genetics at Emory University, told BuzzFeed News. For a study of this kind, he added, you’d need a lot more twin pairs to ensure that the epigenetic differences observed between straight and gay twins were not just due to chance.
Jin’s own research studies epigenetic markers involved in autism. Because genes are regulated differently in different parts of the body, he said, it’s difficult to use epigenetic marks in blood or saliva to glean insights about complex behaviors rooted in the brain.
Healthline’s coverage, by contrast, exemplifies several stories that treat readers like a ping-pong ball, veering from boundless enthusiasm in the headline to near-dismissal of the claims in the body text. Their story embarks with a promise of “Real-Life ‘Gaydar’: Gene Scan Predicts Who’s Gay with 70 Percent Accuracy,” then gives way several paragraphs later to an expert’s overwhelming skepticism: “There is absolutely nothing that’s well accepted that defines a genetic basis of homosexuality.”
Let’s recall that researchers have been looking for so-called “gay genes” for decades, particularly following the completion of the Human Genome Project in 2003.
“We already know there is no ‘gay gene’,” William Rice, an evolutionary geneticist at the University of California, Santa Barbara, told Nature in a discussion of the new study.
If there were, he says, it would have turned up in one of the massive studies that scan the whole genome for variants shared between gay people. The largest such study, led by Sanders, looked at 409 pairs of gay brothers including some non-identical twins. The researchers found that gay men shared similarities in two areas of the genome: the X chromosome and chromosome 8. But Sanders says that he and his colleagues are still trying to determine which particular genes or other components in these regions contribute to sexual orientation.”
Tim Spector, professor of Genetic Epidemiology, King’s College London, diplomatically summed up research interest in the study this way:
“It has always been a mystery why identical twins who share all their genes can vary in homosexuality. Epigenetic differences are one obvious reason and this study provides evidence for this. However the small study needs replicating before any talk of prediction is realistic.”
Hat tip to Ivan Oransky, MD, publisher of Retraction Watch, for pointing us to the ASHG news release.