The largest study yet conducted on gender identity and genes has identified genetic differences between a group of transwomen and a control group of men. Although the research has only scratched the surface of the topic, it is the strongest evidence yet that gender dysphoria sometimes has a genetic basis. The authors hope the work will both improve basic understanding and reduce discrimination against trans and gender-diverse individuals.

It's not long since the medical community regarded people whose gender identity did not align with the one they were assigned at birth as suffering from a mental illness, probably brought on by childhood trauma and abuse. Although most psychologists have moved on, much of the rest of the population has not. Widespread stigmatization about increasing rates of adolescents publicly identifying as trans often relies on explicit or implicit denial of a genetic contribution to gender identity.

Some studies have already indicated an association between gender identity and genetics, but these have mostly had small samples and looked at only a few genes. Professor Vincent Harley of the Hudson Institute of Medical Research in Australia has led the largest study on the topic to date, publishing the findings in the Journal of Clinical Endocrinology & Metabolism.

Harley tested 12 genes, five of which had never been investigated in this context before. He compared the forms of these genes in 380 transwomen undergoing hormone treatment or confirmation surgery in Australia and the United States, and a control group of 344 men.

Certain variations for these genes were found to be significantly more common among the transwomen than the controls.

Harley stressed to IFLScience he is in no way claiming to have found a universal cause of gender diversity. Not all trans people experience gender dysphoria, but Harley's sample was restricted to some who do. His sample was also exclusively made up of people with predominantly European ancestry, in recognition that some of the gene variations he was investigating are more frequent among certain ethnicities. “When you're doing genetic studies, you want to start with the most homogeneous population you can,” Harley told IFLScience.

Harley explained to IFLScience that the 12 genes were chosen because they are part of a common pathway, involving the production and reception of sex hormones, and that each is known to exist in humans in functionally different forms.

The associations, while statistically significant, were not strong enough to predict a person’s gender identity based on these genes alone. “I don't think we have discovered the only, or probably even the most important, genetic factors,” Harley said. He added that, across a population, environment probably plays a larger part than genetics.

Other researchers are investigating the influence of additional genes, as well as using samples drawn from different ethnic populations, likely contributing to a more complete picture. However, their work still relies on testing genes someone thought were likely prospects in the first place. Harley and colleagues would like to do a genome-wide study, removing the bias in the genes chosen. However, at an estimated cost of $10 million, Harley isn’t expecting funding soon.

Even if our knowledge of the genes shaping gender identity remains limited, Harley hopes the demonstration that there is a genetic component will reduce stigmatization.

“While it should not hinge on science to validate people’s individuality and lived experience, these findings may help to reduce discrimination, lend evidence towards improving diagnosis or treatment, promote greater awareness and acceptance and reduce the distress experienced by transgender people in our communities,” Harley said in a statement.