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The X Factor: Why Women May Be Healthier Than Men

The Reason Women Live Longer May Lie in Their Second X Chromosome
By
WebMD Health News
Reviewed by Laura J. Martin, MD

x chromosome

Sept. 28, 2011 -- “X” may really mark the spot when it comes to why women live about five to 10 years longer than men and are less likely to develop certain diseases.

Specifically, it's the X chromosome and the microRNA -- or tiny strains of ribonucleic acid -- that it contains. Men have one X chromosome and one Y chromosome, and women have two X’s. Their microRNA tells our genes what to do or not to do.

Robert G. Lahita MD, PhD,explains it like this: “How does a daffodil know to bloom in the spring?  The microRNAs are in the chromosome for blooming and are temperature sensitive so as soon as the temperature gets to be in a certain range, the gene goes into effect largely because the microRNA tells it to,” he says. He is the chairman of the department of medicine at Newark Beth Israel Medical Center in New Jersey. “Voila, we have a bloom.”

Researchers from Ghent, Belgium, mapped out all of the microRNA found on the X chromosome in both humans and mice. They were able to highlight the microRNA that plays a role in our immune system’s ability to ward off infections and cancer. Much of this microRNA is found on the X chromosome, which shows that the genetic deck may be stacked in women’s favor.

The new study appears in BioEssays.

This research is still in its infancy, says study researcher Iris Pinheiro of the Flanders Institute for Biotechnology in Ghent. “The future will tell whether X-located microRNAs are indeed contributing to gender differences in what concerns to immune response and cancer onset.  But I have no doubt that this is so.”

Are Our Genes Our Destiny?

Is it all about the X? “I would not say that all is in the 'X,' but as a geneticist I would say that a lot is in the genes,” Pinheiro says. “At the end of the day we are a product of our genome, and in many cases we cannot escape detrimental mutations which cause certain diseases, even if we have a healthy lifestyle.

“We can shape their consequences, and we can postpone or dribble the symptoms,” she says in an email.  “It is still important to maintain a healthy lifestyle. We don’t want to accelerate the process or end up with diseases for which we were not even predisposed to in the first place.”

“Women do live longer and may have fewer problems with certain infections diseases than men,” says David Pisetsky, MD, chief of rheumatology at Duke University Medical Center in Durham, N.C.

Some of the why may lie in the Y (chromosome), he says. “Women have two X and men only wind up with one,” he says. The genetic makeup of women is different from men because they have a backup X chromosome. “Maybe males get in trouble because they just have one X and no backup.”

One theory is that some genes on the X chromosome may be silenced or inactivated. This leaves men at a disadvantage because they only have one X. Pisetsky says that the extra X may be a buffer from what is defective or silenced on a single X chromosome.

Women may live longer and be less likely to develop some diseases, but they are at much higher risk for autoimmune diseases such as lupus and rheumatoid arthritis.

“It is a trade-off,” Pisetsky says.

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