X AND Y chromosome

New York: Researchers have identified that X chromosome — one of the sex chromosomes that determines whether an individual is male or female — plays a major role in the increased incidence of cancer occurrence in males. “Across virtually every type of cancer, occurrence rates are higher in males than in females. In some cases, the difference might be very small — just a few percent points — but in certain cancers, incidence is two or three times higher in males,” said Andrew Lane from at Dana-Farber Cancer Institute in Massachusetts, US.

Men outpace women in developing many cancers, including those associated with tobacco use, such as kidney, renal, bladder, and oral cancers, Lane said.  The disparity is present among boys and girls, as well as men and women. “Data from the National Cancer Institute show that males carry about a 20 per cent higher risk than females of developing cancer. That translates into 150,000 additional new cases of cancer in men every year,” Lane added.

In the study, the researchers specifically focussed on tumour suppressor genes — which protect the cells from cancer. In cancers, these tumour suppressor genes are often mutated or deleted and are no longer functional. X chromosome was the only genes that were mutated more frequently in male cancers than female cancers.

Males have an X and a Y chromosome, and females have two X. In females, one of the X chromosomes shuts down and remains inactive for life to balance out the gene expression.  The study showed that some genes on the inactivated X chromosome in female cells “escape” that dormant state and function normally.

Thus females are protected from cancer to some relative extent because they have two copies of these genes whereas males only have one, the researchers said.  So if they are going to get a cancer that those genes are involved in, they have to mutate them twice, whereas males only have to have one mutation, Lane said. The study was reported in a paper published online in the journal Nature Genetics.