Researchers have revealed details of a saliva test that has enabled them to predict the sexual orientation of sets of male twins with 67% accuracy.

The lead researcher, who is gay, is so concerned about the possible consequences of the research that he has now decided to not pursue it further.

Working at University College Los Angeles’ Center for Gender-Based Biology, postdoctoral scholar Tuck C. Ngun and his colleagues have followed up previous research that found that gay brothers share a sequence of five genetic markers in the region of the X chromosome, reports New Scientist.

Other research has also found that there is an increased chance of women giving birth to a son who grows up to be gay with each subsequent male boy born – rising from a 2% chance for her first boy to a 6% chance for a third male child.

It has been theorized that the male pregnancy may leave behind some sort of marker that affects subsequent pregnancies – most likely leading to the addition or subtraction of methyl groups to specific genes. Methyl is a specific type of hydrocarbon molecule group.

Ngun and colleagues looked at the genetic make-up of 47 pairs of male twins; 37 sets of twins were both gay, while the other ten sets differed in their sexuality. They also analyzed the genes of heterosexual and homosexual volunteers.

They specifically looked at methylation patterns between gene codes.

They found several genetic sites of interest – one of which has previously been identified as having an influence on sexual orientation.

Ngun presented his findings yesterday at the University of Baltimore in Maryland at the 2015 meeting of the American Society of Human Genetics.

He said that having identified a particular gene code of interest, the team took things further and tested whether some of the twins were gay or straight based on the methylation patterns of their genes. They found their results to be accurate 67% of the time.

The findings have yet to have been published in a peer-review journal.

New Scientist has said that other researchers are extremely cautions of the results – particularly as the testing was carried out on a specific sample of the population; male twins.

‘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,’ said Johnjoe McFadden, molecular geneticist at the University of Surrey, UK.

‘The nub of the problem with studies like these is that when you see methylation changes, you don’t know whether methylation is the prime event or if it’s reflecting some other event. Methylation might be reflecting a state rather than driving it,’ added Gavin Kelsey, an epigeneticist at the Babraham Institute in Cambridge, UK.

Darren Griffin, professor of genetics at the University of Kent, told the Western Daily Press, ‘To claim a 70% predictive value of something as complex as homosexuality is bold indeed. I wait with bated breath for a full peer-reviewed article.

‘While there is strong evidence in general for a biological basis for homosexuality my personal impression has always been one of a multiple contributory factors, including life experiences.’

Psychologist Michael J. Bailey of Northwestern University told the Los Angeles Times that although genes are likely to affect a man’s sexuality, the fact that identical twin pairs can contain gay and straight brothers would, ‘conclusively suggest that genes don’t explain everything.’

Ngun, who is himself gay, has expressed caution over the implications of the research – to the extent that he has decided to abandon the research for the time being.

‘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.’

He told New Scientist that he was concerned about people potentially wanting to screen developing fetuses for methylated gene markers, even though reproducing the studies with fetuses would be extremely difficult.

‘Assuming the marks were placed early enough in fetal development, the potential for a [screening] test is there,’ he said, before explaining that these particular gene patterns differ between cells within the same person, and asking, ‘Which embryo cells would correspond to adult saliva?’

Asked if he worried about people abusing the information to punish or persecute gay people, Ngun said, ‘I honestly don’t think it’s that far-fetched.’

‘I just left the lab last week,’ he said, commenting on the fact that he had decided to withdraw from the project.

‘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.’

Ngun has been approached for further comment.