There's a longstanding belief that, on average, women are healthier than men, and with good reason. Women live longer, and studies reveal women fight off disease better than their male counterparts. But where does this advantage come from? Turns out it's all thanks to some microRNA on the X-chromosome.
At least, that's the finding of Dr. Claude Libert of Belgium's Ghent University, who has identified the specific pieces of RNA that confer this heightened immune system to women. Like its better known relative DNA, RNA is essential to the formation of life, and it's responsible for carrying genetic information throughout the cell to direct various biological reactions and expression of genes. Very short strands of RNA are known as microRNA, and a lot of these cluster in the X-chromosome, which is the female sex chromosome.
Dr. Libert explains:
"Statistics show that in humans, as with other mammals, females live longer than males and are more able to fight off shock episodes from sepsis, infection or trauma. We believe this is due to the X chromosome which in humans contains 10% of all microRNAs detected so far in the genome. The roles of many remain unknown, but several X chromosome-located strands of microRNA have important functions in immunity and cancer.
Libert and his team developed a map of all known microRNA in the X-chromosome that are known to affect the immune system. The came to the conclusion that there is indeed a strong link between the genetic material found in the X-chromosome and the larger functions of the immune system, and that the reason behind the gender difference is a phenomenon known as gene silencing. In this process, genes are essentially switched off, so that they can't pass on whatever benefits or harms they might ordinarily confer. This affects the microRNA in the X-chromosome, silencing many of the strands most useful to the immune system.
Because women have two X-chromosomes, they are better able to compensate for this lost genetic information. Even if lots of these immune-related strands are silenced, there's still a complete set of duplicates that hopefully can remain active and supply this heightened immune response. Men, on the other hand, have to make do with what the Y-chromosome can supply - and its supply of helpful microRNA is far too low to be of much use.