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Opening “the X-files” helped researchers to understand why women and men differ in height
Given its unique nature, the X chromosome has often been neglected when performing large-scale genetic studies. However, identifying genetic associations with X chromosomal genes can be particularly valuable in helping us to understand why some characteristics differ between sexes.
– 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, says Dr. Taru Tukiainen who is currently working at the Massachusetts General Hospital in Boston.
The researchers from the University of Helsinki 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.
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. 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, explains Professor Samuli Ripatti, the principal investigator behind the study.
– Based on our calculations, this variant accounts for a significant, though small proportion, 1-2% of the current difference in mean height between men and women in the Finnish population.
The results were published in PLOS Genetics journal.
Text: Mari Kaunisto and Päivi Lehtinen
Ripatti Research Group