ESPEYB17 15. Editors’ choice (1) (18 abstracts)
To read the full abstract: Science 2019;365:eaat7693.
These authors performed a genome-wide association study on 493 001 participants of European-ancestry from the USA, UK, and Sweden to identify genes associated with sexual orientation. They found multiple loci implicated in same-sex sexual behavior indicating that, like other behavioral traits, non-heterosexual behavior is polygenic.
As many as 4% to 10% of US individuals report ever engaging in same-sex sexual behavior. It is commonly believed that same-sex orientation and sexual behavior runs in families and has a genetic basis. Twin studies and models to estimate inheritance indicate that same-sex sexual behavior has a significant genetic component that explains 18% of the phenotype in women and 37% in men. Other factors include shared environments of family or school, and legalization or norms regarding same-sex sexual behavior. However, previous searches for the specific genes involved had been underpowered.
This is the largest genetic study to date on this topic. They discovered 5 loci robustly associated with same-sex sexual behavior: 2 loci across both sexes, 2 only in males, and 1 only in females. However, these 5 loci together account for a small fraction (<1%) of the phenotypic variation. Thus, a combined genetic score cannot be used to predict same-sex sexual behavior of an individual.
A notable finding was that these loci were also associated with more heterosexual partners (among those reporting only heterosexual partners) suggesting the traits measured here indicated a promiscuous tendency rather than sexual orientation or preference. They did not find evidence of any specific cells and tissues related to this trait. Yet, male-specific loci were associated with olfactory receptor genes, sensitivity to certain scents, and regulation of testosterone and estrogen.