The X chromosome may explain the origin of height differences between women and men

Duplicate genes on the X chromosomes are usually silenced in women. From a study conducted by Finnish researchers on approximately 25 residents of Northern Europe, one such gene, which when overexpressed causes short height and whose silencing of one of its copies failed, is one of the causes of the distinct difference in height between women and men 

The X chromosome is often overlooked when conducting large-scale genetic studies because of its uniqueness. Since women carry two copies of the chromosome and men only one, identifying the genetics associated with the genes located on the X chromosome may be valuable and help us understand the characteristics that distinguish the two sexes. Researchers at the University of Helsinki in Finland have now discovered that a genetic variation on the X chromosome affects a person's height.
The researchers analyzed the common genetic differences in the X chromosome, one of the two sex-determining chromosomes, among about 25 people in Northern Europe whose medical information was available to the researchers. The aim of the study was to discover genetic factors that may explain individual differences in some traits such as BMI, height, blood pressure and lipid level (fats in the blood). In addition, the researchers also looked at whether the X chromosome could contribute to some of the known differences between women and men in some traits such as height. Hundreds of genetic variations affecting these traits have been identified so far, but given its uniqueness, the X chromosome has been overlooked in most previous studies.
The results of the study were published on February 6, 2014 in the journal PLOS Genetics.
X chromosome research poses unique challenges. The fact that women have two copies of the chromosome and men only one copy had to be taken into account in the analysis. However, we wanted to overcome these challenges because new biologics" says Dr. Taro Tokainen, who currently works at Boston General Hospital.
The study showed that a certain genetic version of the ITM2A gene that plays a role in the development of cartilage is common among shorter than average people. The identification of the variant, found in the bodies of about a third of Europeans, showed that the phenomenon results from overexpression of ITM2A, meaning that the more the gene is expressed, the shorter the person will be. Interestingly, the phenomenon affects height and is more pronounced in women.

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"The double dose of X chromosomes in women causes problems during development. To prevent this, there is a process in the body of silencing one of the two copies of the X chromosomes. We realized that the height depends on the fact that the gene duplicated to the one we identified (and its neighbor in the genome), avoided silencing," explained Prof. Samoli Ripati, the lead researcher in the study.
"Since both copies of ITM2A remain active, the gene is expressed at high levels in the female body. These areas are unbalanced between men and women and they can help us understand why some of the characteristics are different between the sexes" he continued.
According to the researchers' calculations, the version is responsible for about 1-2% of the differences between the average height of men and women in the Finnish population.

In addition, two other regions on the X chromosome, one of which is responsible for blood insulin levels after fasting and the other is also associated with height were identified in this study. In none of them were detected significant differences between the sexes in the strength of the genetic effect as in ITM2A.

For information on the website of the University of Helsinki