Closing in on Gay Genes

A new study has found several more interesting linkages between the human genome and sexual orientation. You can read the original paper from the journal Human Genetics HERE. The researchers' press release is a little lighter reading, probably more appropriate for a site like this:

CHICAGO, Illinois, USA, January 12, 2005— A new genetic study helps explain why some men are gay and other men are heterosexual. The first research project that examines linkage between male sexual orientation and genes across the human genome was published this month in the prestigious biomedical journal, Human Genetics. The culmination of several years of research, the report identified three new chromosomal regions of interest.

One hundred forty-six families that had two or more gay brothers participated in the study. The largest finding was a statistically suggestive linkage to a region on chromosome 7 called 7q36, and the second largest link was found on chromosome 8, in a region called 8p12. There was also an interesting finding on chromosome 10, in the region called 10q26, where the linkage to sexual orientation only occurred if that region was inherited from the mother. This is likely a result of the recently discovered phenomenon that geneticists call "genomic imprinting." Given the complex nature of sexual orientation it is not surprising that multiple genetic regions were implicated.

According to the lead author of the study, Dr. Brian Mustanski, "Our study helps to establish that genes play an important role in determining whether a man is gay or heterosexual. It expands upon previous research with twins, which has consistently found evidence for genetic influences on sexual orientation. The next steps will be to see if these findings hold up in a new sample and then identify the particular genes within these newly discovered chromosomal regions." Dr. Mustanski emphasized that finding the specific genes would have implications beyond uncovering the cause of homosexuality. Their identification would also greatly advance our understanding of human variation, evolution, and brain development. Press Release

In a separate FAQ document, the lead author answers the question: Did you find the "gay gene?"

His answer:

For several reasons the answer to this question is no. First, sexual orientation is such a complex phenotype that no one gene could ever explain it. Instead, our best guess is that multiple genes, acting and interacting with environmental influences, explain variability in sexual orientation. Therefore, a better question is, "did you find one of the genes that influence male sexual orientation?"

He also answers the question, Does your study prove that homosexuality is genetic?

We found 3 new chromosomal regions that showed some linkage to male sexual orientation. This suggests that within these chromosomal regions are genes that influence male sexual orientation. If genes did not influence male sexual orientation it is unlikely that we would have found linkage to these regions. Our study builds upon previous twin and family studies which have consistently found evidence for genetic influences on sexual orientation. As with all scientific research, it is important that our results are replicated in another lab with a new sample of participants to guarantee that they are not due to unlikely random chance. At this point, the best evidence suggests that genes play an important role in determining if a man is gay or heterosexual.

Anti-gay groups have frequently argued that there is no gay gene. It seems that the implication is that people can choose their sexual orientation, since it's not hard-wired at conception. In that light, it is interesting to learn from these researchers about twin and family studies which have consistently found evidence for genetic influences on sexual orientation. We would not expect to find one site on the chromosome that explains all variation in sexual orientation, but these researchers have narrowed it down to a small number of locations. This is a young science, we can be sure that more will be learned as time rolls along.