Gene Variants Identified That May Influence Sexual Orientation in Men And Boys

Source: NorthShore University; Scientific Reports

Summary: Researchers have found two gene variants that appear to be more prevalent in gay men than straight men, adding further evidence of sexual orientation having a biological component.

In 1993, An American geneticist – Dean Hamer’s study triggered an uproar with the discovery of a “gay gene” – a stretch on the X-chromosome (Xq28) which is likely associated with homosexuality. Many subsequent studies did not agree with his findings, but in 2014, a large study by Michael Bailey looked at DNA from 409 pairs of gay brothers, fingers the same region on X and confirms Hamer’s findings. A new study by a large team of researchers (Alan R. Sanders, Gary W. Beecham, Shengru Guo et al,) from several institutions in U.S have found two gene variants that appear to be more prevalent in gay men than straight men, adding further evidence of sexual orientation having a biological component which suggests a specific genetic influence on sexual preference. The research findings were published in the journal Scientific Reports.

Manhattan Plot for Male Sexual Orientation

Manhattan Plot of GWAS for Male Sexual Orientation. A plot of negative log10 of the p-values for the single SNP association analysis of 1,077 homosexual and 1,231 heterosexual men, ordered along the x-axis for each chromosome by chromosomal position. Credit: Alan R. Sanders et al/ Scientific Reports

The research team looked at DNA from 1077 gay and 1231 straight men and scanned the entire genome, searched for single-letter variations rather than whole chromosomes. Doing so, it allowed them to identify two gene variants that seemed to be linked to sexual orientation. One such gene variation was found in the gene SLITRK6 on chromosome 13 in the brain’s region, the diencephalon which contains the hypothalamus (prior research has shown that the hypothalamus of heterosexual men is nearly twice the size it is in homosexual men). The other gene variant was found in the gene TSHR (prior research has shown it is mainly involved with the thyroid and might also be involved in sexual orientation) on chromosome 14. In this study, the number of samples tested was too small, which do not offer a conclusive evidence, larger studies will have to be undertaken to solidify the evidence.

Dean Hamer said, “The latest findings open the prospect to identifying the whole pathway of genes involved in both homosexual and heterosexual orientation” and further added, “It adds yet more evidence that sexual orientation is not a ‘lifestyle choice’. But the real significance is that it takes us one step closer to understanding the origins of one of the most fascinating and important features of human beings.”

More Information: Alan R. Sanders et al, “Genome-Wide Association Study of Male Sexual Orientation”, Scientific Reports (2017). DOI: 10.1038/s41598-017-15736-4

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