Researchers from Stanford University point to the X sex chromosome as the origin of the propensity for this type of disorders. In women, when a defect appears in one of the X chromosomes, it is silenced and its function is replaced by the intact region of the other identical chromosome.

In men, this possibility does not exist, and this lack of replacement has been associated with lower male life expectancy. Males, mice or humans, also have Xist on their X chromosome, but the gene only begins to work in the presence of a second X chromosome.