Wednesday, 15 April 2015

Correlation between differences in genetic make-up and transsexualism

Heya everybody,

something just hot off the press – Brazilian researchers Cunha, Bachega, et al. presented their latest findings about genetics and transsexualism at the Endocrine Society’s 97th annual meeting in San Diego, USA, in March 2015. They found a correlation between female-to-male transsexualism and fewer repeats of the trinucleotide CAG on the androgen receptor gene.

My understanding is that on the androgen receptor gene, places have been identified where the nucleotides cytosine (C), adenine (A) and guanine (G), three of the four basic blocks of our genetic information, repeat themselves several times in that particular order. In their sample of 35 female-to-male transsexuals, the authors of the study found that the number of these CAG repeats was significantly lower than in the control group of cisgender females.

This is significant for two reasons: firstly, longer CAG repeats on the androgen receptor gene had been linked in an earlier study to male-to-female transsexualism, and secondly, modifications of the androgen receptor gene can directly influence the processing of sex hormones by the body, which in turn have been shown to shape gender identity, especially before and around birth. In other words, if this discovery is true, we seem to have a clear a and consistent pathway to transsexualism.

Excited? Yes, me too. However, it has been very, very difficult to link most illnesses and other health conditions to a specific gene. Think about conditions such as diabetes, schizophrenia, autism, homosexuality, Alzheimer’s, etc.[1] Genes probably are implicated in all of these conditions, but many more factors also play a role. Transsexualism is most likely also caused by a multitude of factors, with genes playing only one part. This is also supported by twin and family studies that show transsexualism has a heritable component, but is not fully explained by heredity.

So, a lot more research has to be done to see whether this result holds up, and how much of a factor it is in causing transsexualism. However, this is another piece of the puzzle that points more and more clearly to a biological basis of gender dysphoria.

If I have time over the next few days, I might wrote more about studies on genes and transsexualism. Take care and have fun!

[1] No, I’m not saying homosexuality or transsexualism are illnesses, like schizophrenia or autism. This is also not a value judgement. I’m just looking at how certain conditions of human experience come into existence, and whether there is a genetic component or not. For a full discussion on whether transsexualism is an illness, please see: Is transsexualism an illness?