US scientists have published results in the Scientific Reports that hint towards the existence of genetic links to homosexuality.
Researchers, hailing from NorthShore University in Illinois to the University of Miami in Florida (and one from the UK), decided to conduct this study, because genome-wide association studies (GWAS) for male sexual orientation are sparse and often simplistic. As such, they took matters into their own hands.
The team of researchers analyzed the DNA of 1,109 homosexual and 1,231 heterosexual men (most being white/of European ancestry). The sexualities of these men were classified based on both how they identified themselves and on how they scored on the Kinsey scale.
Once the whittling down of genetic outliers was done, the DNA of the remaining men was analyzed.
The results found prominent single nucleotide polymorphism or SNP regions (basically a difference or variation in the DNA between the straight and gay men) on chromosomes 13 and 14.
On chromosome 13, the strongest SNP region found was located between SLITRK6 and SLITRK5. These areas are associated with neuronal outgrowth, survival, and synapse formation.
As stated in the report:
“Gene families, such as the SLITRK family that are important for neurodevelopment and are implicated as candidate genes for various neuropsychiatric phenotypes, are also of potential relevance to behavioral phenotypes such as sexual orientation.”
Meanwhile, the strongest region on chromosome 14 was the thyroid stimulating hormone receptor or TSHR.
As you might suspect from the name, this genetic area influences hormones/cells connected to the thyroid and sends for autoantigen in Graves’ disease. That said, TSHR also connects to other areas of the body such as the hippocampus in the brain.
The researchers then theorized that there may be a genetic link between thyroid function and sexual orientation in men.
“Females with Graves’ disease have been reported to manifest biased X chromosome inactivation, and skewed X chromosome inactivation has also been reported in mothers of homosexual men compared to age-matched mothers of heterosexual men.”
The researchers also converged earlier findings, such as a review of 790 adolescents (8 to 17-years-old) which found “15 mothers with a history of thyroid dysfunction during pregnancy, 16 adolescents with a history of same-sex attraction and/or gender nonconformity, and 12 overlapping mother-offspring pairs with both.”
That said, the researchers also realized that this study has its own problems.
They admit that the sample size may have been too small. In addition, exclusive focus on males of European ancestry could limit a true understanding of the complex topic that is how genetics affect male sexual orientation.
As such, they realize more studying is needed and a larger sample pool will be required for further analysis.
While this study found new areas of interest concerning the connection between genetics and male sexual orientation (and even backs up earlier findings on the subject), the researchers on this specific study reminded us that the potential connections are best characterized as speculative until more information can be found.