SoSoGay – November 19th 2014

A genetic analysis of 409 pairs of gay brothers, including sets of twins, has demonstrated new findings on the nature versus nurture debate – providing the strongest evidence yet that gay people are born gay. According to the New Scientist, the study linked sexual orientation in men with two regions of the human genome that have been implicated before – one on the X chromosome and one on chromosome 8.

The finding is an incredibly important contribution to mounting evidence that being gay is biologically determined rather than a lifestyle choice as there are still countries, such as Uganda, that criminalise homosexuality and some religious groups still believing that gay people can be ‘treated’.
‘It erodes the notion that sexual orientation is a choice,’ says Alan Sanders, the study leader from the NorthShore Research Institute in Evanston, Illinois.

Over the past five years, Sanders has collected blood and saliva samples from 409 pairs of gay brothers, including non-identical twins, from 384 families. This compares, for example, with 40 pairs of brothers recruited for a previous study on a similar subject by Dr Dean Hamer.

The team combed through the samples, looking at the locations of genetic markers called single nucleotide polymorphisms (SNPs), differences of a single letter in the genetic code, and measuring the extent to which each of the SNPs were shared by the men in the study. The only trait unequivocally shared by all 818 men was being gay. All other traits, such as hair colour, height and intelligence, varied by different degrees between each brothers in a pair and between all sets of brothers. Therefore, any SNPs consistently found in the same genetic locations across the group would most likely be associated with sexual orientation.

Only five SNPs stood out and, of these, the ones most commonly shared were from the Xq28 and 8q12 regions on the X chromosome and chromosome 8 respectively. But this doesn’t mean the study found two ‘gay genes’. Both regions contain many genes, and the next step will be to home in on which ones might be contributing to sexual orientation.

Sanders says he has already completed the work for that next step: he has compared SNPs in those specific regions in gay and straight men to see if there are obvious differences in the gene variants, and is now preparing the results for publication. Whatever the results, Sanders stresses that complex traits such as sexual orientation depend on multiple factors, both environmental and genetic. Even if he has hit on individual genes, they will likely only have at most a small effect on their own.

‘This study knocks another nail into the coffin of the “chosen lifestyle” theory of homosexuality,’ says Simon LeVay, a neuroscientist and writer who, in 1991, claimed to have found that a specific brain region, within the hypothalamus, is smaller in gay men. ‘Yes, we have a choice in life – to be ourselves or to conform to someone else’s idea of normality – but being straight, bisexual or gay, or none of these, is a central part of who we are, thanks in part to the DNA we were born with.’

Read the article on the SoSoGay site here.