According to a controversial new study, homosexuality is not a lifestyle choice but is rooted in a person’s biology.
Scientists from NorthShore University in Illinois looked at the DNA of more than 2,000 people. They located two regions of chromosomes that may be linked to sexuality. Their research claims to have found genetic markers that reveal if a man is gay.
Independent scientists have described the study as ‘weak.’ The study’s authors admit the link is ‘speculative.’
However, the research could help them get closer to finding so-called ‘gay genes.’
The ongoing debate among the scientific community is over whether sexual orientation is biologically determined, the result of environmental causes or a combination of factors.
The latest study will not settle this debate, but scientists have claimed since the 1990s that homosexual men share a ‘gay gene.’
American geneticist Dean Hamer in 1993, found families with several gay males on the mother’s side, suggesting a gene on the X chromosome. Dr. Hamer showed that pairs of brothers who were openly gay shared a small region at the tip of the X. He proposed that it contained a gene that predisposes a male to homosexuality.
It vindicated the claims that ‘I was born this way’ but opened frightening new possibilities for detection and discrimination. Gay men were divided on this conclusion.
NorthShore University (NSU) HealthSystem’s Research Institute, based in Evanston, researchers made the findings after conducting a genome-wide association study (GWAS). Their latest study examined the sexual orientation of 1,077 homosexual and 1,231 heterosexual men.
The participants in the study said their sexual orientation was rated based on their self-reported sexual identity and sexual feelings.
While men were asked to provide DNA by blood or saliva samples, it was then analyzed for variations in their genetic code. The scientists found two regions with multiple genetic variants most strongly associated with sexuality.
The genetic variants were located on chromosomes 13 and 14, close to genes that have functions relevant to the development of sexual orientation.
Alan Sanders, a psychiatrist who studies behavioral genetics at NSU who led the study, said: ‘Because sexuality is an essential part of human life, for individuals and society, it is important to understand the development and expression of human sexual orientation.
‘The goal of this study was to search for genetic underpinnings of male sexual orientation and thus ultimately increase our knowledge of biological mechanisms underlying sexual orientation.
‘What we have accomplished is the first step for GWAS on the trait, and we hope that subsequent larger studies will further illuminate its genetic contributions.’
Chromosome 13 was located between the genes, SLITRK5 and SLITRK6, having the strongest associated region.
SLITRK6 is a neurodevelopmental gene in a region of the brain called the diencephalon. This contains a region previously reported as differing in size in men depending on their sexual orientation.
Chromosome 14, the thyroid stimulating hormone receptor (TSHR) gene was found to span the most significant region that may offer clues into sexual orientation. Genetic variants in TSHR may help explain past findings linking thyroid function and sexual orientation.
The authors note that their study had only a modest sample size in for a trait with complex genetics and is a limitation. Also, their focus on men of European ancestry, as well as limiting the study to just men.
Although the top two association regions provide interesting and perhaps trait-relevant examples with their closest genes, researchers emphasize that the potential connections remain speculative.
Professor Robin Lovell-Badge, group leader at The Francis Crick Institute biomedical research center in London, who was not involved in the study, said: ‘Genome-Wide Association Studies (GWAS) are problematic and are frequently underpowered, meaning that the sample sizes are too small to allow any robust conclusions.
‘This is particularly so for traits like being gay that are likely to involve many genes and where “environmental” influences, perhaps both in utero and postnatally, can have a strong effect.
‘Moreover, correlation does not mean causation.
‘The new data on genetic associations they report here does not show sufficient statistical significance to make any formal link between a gene or chromosome region and being gay or heterosexual.
‘However, their data does tend to reinforce some previous findings of associations, which were also relatively weak, with a region of Chromosome 8 and the X chromosome.
‘Regions of chromosome 13 and 14 also appear from the new work to be worth paying attention to in future studies.’
Professor Gil McVean specializes in statistical genetics at the University of Oxford, added: ‘The researchers have found weak evidence for genetic variation that influences self-reported sexual preferences in men.
The sample size is small, the results have not been replicated in an independent study, and the level of evidence presented doesn’t meet the threshold of significance typically required within the field.
‘I do not think the work would have been published if it were on a less controversial topic. It is, at best, preliminary.’
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