A saliva test can predict with 67% accuracy whether a man is gay or not – in male twins at least, say researchers.

The test, designed by scientific researchers from the University of California, Los Angeles, uses clues from tiny modifications to a person’s genome to determine sexual orientation, reports New Scientist.

To investigate a potential role for epigenetics, Tuck Ngun and his colleagues looked for epigenetic modifications made to the genes of 47 sets of male twins. Thirty-seven of the twin pairs were both gay, while 10 pairs differed, with one brother identifying as gay and the other as straight. Researchers ended up with a giant spreadsheet showing the levels of methylation across the genome of each twin, says Ngun.

Using the test results from 20 of the pairs, researchers developed a model to predict if a person is straight or gay based on the methylation patterns of their genes. When they tested their model on the remaining pairs of male twins, they found it correctly predicted sexual orientation 67 percent of the time.

Other scientists remain cautious about the results of the test. “Studies that associate biomarkers with particular traits are notoriously prone to false positive results due to the tendency of these studies to find spurious associations that are down to sheer chance,” Johnjoe McFadden, a molecular geneticist at the University of Surrey, told New Scientist.

Worries over the possible misuse of such findings have troubled the team responsible for the discovery. “I’m gay,”says Ngun, “and I’ve always wondered why I am the way I am. But once you have this information, you can’t control how it’s used or disseminated.”

“I don’t believe in the censoring of knowledge, but given the potential for misuse of the information, it just didn’t sit well with me,” he added.