1 in 500 men may carry extra chromosome, raising risk of some diseases

A comprehensive genetic analysis of over 200,000 men has found that around one in 500 have an extra sex chromosome, with most of them unaware. That’s a much higher proportion than previously thought, and it seems to increase their risk of diseases like diabetes and cardiovascular problems.

The new finding comes from data gathered by the UK Biobank project, which is comprehensively tracking the health and genetic data of half a million participants over years. For this study, researchers at Cambridge and Exeter Universities conducted an analysis of genetic data from 200,000 men in the Biobank database, searching for the prevalence of extra sex chromosomes.

Characterized as either X or Y, the sex chromosomes are, as the name suggests, those responsible for the differences between the biological sexes. Usually, females have two X chromosomes, while males normally have an X and a Y. But that’s not always the case.

In the new study, the scientists identified 213 men with an extra X, and 143 men with an extra Y, out of the 200,000 men studied. Taking into account the overall health of Biobank participants, the team calculated that about one in 500 men in the general population may carry an extra sex chromosome, which is a much higher percentage than previously thought.

The majority of the men in the study didn’t have any indication of the abnormality in their medical records. Of the 213 with the additional X, only 49 (or 23 percent) had been diagnosed with the condition, also known as Klinefelter syndrome. It typically manifests as delayed infertility or puberty, and can be discovered and diagnosed then, but often goes unnoticed. Meanwhile, just one of the 143 men with an extra Y chromosome had been diagnosed, as this condition has even fewer outward signs.

The researchers then investigated the health of these men, and compared them to the rest of the Biobank population. Men with XXY chromosomes had significantly lower levels of testosterone in their blood, and were at a three-fold higher risk of delayed puberty and four times more likely to be childless, suggesting infertility. Men with XYY, on the other hand, seemed to have normal reproductive function.

Men with extra copies of either chromosome were found to be at higher risk of a few other conditions. Their risk of developing type 2 diabetes was three times higher than usual, six times higher for venous thrombosis, three times higher for pulmonary embolism, and four times higher for chronic obstructive pulmonary disease.

The team says it’s unsure why the extra chromosome would increase these risks, or why it was similar for both types. But further study could help answer these questions, as well as whether it’s useful to start screening people for extra chromosomes as a potential way to prevent the associated diseases.

“Even though a significant number of men carry an extra sex chromosome, very few of them are likely to be aware of this,” said Yajie Zhao, first author of the study. “This extra chromosome means that they have substantially higher risks of a number of common metabolic, vascular, and respiratory diseases – diseases that may be preventable.”

The research was published in the journal Genetics in Medicine.

Source: Cambridge University

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