Gay men : two genes identified for the first time

stevanovicigor / Epictura

Published the 10.12.2017 to 18h56

A A

Keywords :

génétiquegénesorientation sexuellehomosexualiténeurosciencesexualitégénomiquegénomecerveau

This would be the first time that genes related to sexual orientation are identified. The find, if confirmed, is so important. Published in Scientific Reports, it is the result of a study conducted by the team of Pr Alan Sanders, of the department of behavioral neuroscience, university NorthShore (near Chicago), on a sample of 2308 men of european origin, of which 1231 declaring themselves to be gay.

As much to lift the hare from the outset : the researchers have not discovered ” genes for homosexuality “. If such genes existed, such as for eye color, they would have been discovered long ago. In all likelihood, the sexual orientation is the result of an interaction between a set of genes and the environment, biological and cultural. But we know that part of it is transmitted, with a heritability of 30% to 40% according to the studies, and it results in men with a predisposition to strong for a heterosexuality or homosexuality often exclusive.

Two genes related to brain

The first identified gene, carried on chromosome 13 (SLITRK6), likely plays a role in sexual differentiation in the hypothalamus, a structure deep in the brain that varies in size (in English) based on sexual orientation. The second, present on chromosome 14 (TSHR), encodes a receptor in the thyroid, the gland responsible for secreting the thyroid hormone, which is suspected to also be linked to sexual orientation through the mother (in English).

To identify these two genes, researchers have had recourse to the first study of genome-wide association in the field. Emerged thanks to high-throughput sequencing, these studies allow to analyze the entire genome of subjects, without a priori regions of interest. If the genetic analysis was a war, the genome wide approach would be a weapon of mass destruction. Remains a catch : in order to be valid, such studies require very large samples.

Results to confirm

With only 2300 subjects when it would take probably ten times more, the results of Sanders and colleagues are questionable, and will need to be replicated to be considered as definitive. Genetics, which is based on statistically significant associations that attempt to explain traits of highly complex, lends itself to the announcement of results is sometimes expected, especially in a field that arouses as much passion as that of sexual orientation.

Many researchers in neuroscience and genetics believe that male homosexuality can be explained first of all by factors of a biological order – a point of view often seen as controversial, but based on a significant body of evidence (in English). But the determination of the underlying mechanisms, hereditary and environmental, is very difficult. A theory in vogue, popularized in France by professor Jacques Balthazart, sees the prenatal exposure to testosterone as one of the major determinants of the future sexual orientation of a fetus. If the role of genes SLITRK6 and TSHR is confirmed, this theory could well be enhanced.