Researchers are now attempting to find genetic factors that could explain the differences in several traits between men and women.
They analyzed thoroughly the commonly occurring genetic variation in chromosome X, one of the two sex-determining chromosomes, in almost 25,000 Northern European individuals with diverse health-related information available.
In addition, the researchers also investigated whether the X chromosome would contribute to some of the well-known differences between men and women in certain traits, such as height.
Hundreds of genetic variants having an effect on these traits have already been identified, but, given its unique nature, the X chromosome has been neglected in most of these previous studies.
"Studying the X chromosome has some particular challenges. The fact that women have two copies of this chromosome and men only one has to be taken into account in the analysis. We nevertheless wanted to take up the challenge since we had a strong belief that opening 'the X files' for research would reveal new, interesting biological insights", Dr. Taru Tukiainen, who is currently working at the Massachusetts General Hospital in Boston, said.
The study showed that a genetic variant close to ITM2A, a gene that has a role in cartilage development, is frequent among the people being shorter than average.
The identified variant, which is present in more than a third of Europeans, was also shown to increase the expression of ITM2A, suggesting that the more the gene is expressed the shorter the person will be. Interestingly, the effect of this variant on height was shown to be much stronger in women.
"The double dose of X-chromosomal genes in women could cause problems during the development. To prevent this, there is a process by which one of the two copies of the X chromosome present in the cell is silenced," Professor Samuli Ripatti, the principal investigator behind the study, said.
"When we realized that the height associated variant we identified was nearby a gene that is able to escape the silencing we were particularly excited", Ripatti said.
The research is published in PLOS Genetics journal.