One in 500 men born with an extra sex chromosome

By Mark Waghorn via SWNS

One in 500 men are born with an extra sex chromosome - which can lead to a host of life-threatening illnesses, according to new research.

It raises the risk of type 2 diabetes and blood clots three and sixfold, respectively. It also makes serious lung diseases up to four times more likely.

The finding is based on over 200,000 Britons aged 40 to 70. It could lead to a screening program.

Co-author Professor Ken Ong, an epidemiologist at the University of Cambridge, said: "Genetic testing can detect chromosomal abnormalities fairly easily.

"So it might be helpful if XXY and XYY were more widely tested for in men who present to their doctor with a relevant health concern."

A child's gender is determined by chromosomes - known as X and Y. They carry our DNA. Males have XY while females have XX.

But some men also have another - XXY or XYY. Most are unaware - unless they have been genetically tested. There are few obvious signs.

Those with an extra Y tend to be taller as boys and adults, but otherwise have no distinctive physical features. A second X may delay puberty or cause infertility.

Added Prof Ong: "We would need more research to assess whether there is additional value in wider screening for unusual chromosomes in the general population.

"But this could potentially lead to early interventions to help them avoid the related diseases."

Fathers contribute the X or Y, and mothers an X. Inherit an X and Y and you are a boy. Get a pair of Xs and you are a girl.

First author Yajie Zhao, a Ph.D. student from the same lab, said: "Even though a significant number of men carry an extra sex chromosome, very few of them are likely to be aware of this. This extra chromosome means they have substantially higher risks of a number of common metabolic, vascular and respiratory diseases - diseases that may be preventable."

The study analyzed participants in the UK Biobank, a database containing anonymized genetic, lifestyle and health information on half a million people.

It found 356 men had an extra X or Y - 213 and 143, respectively. As members tend to be 'healthier' than average, the phenomenon will apply to around one in every 500.

Only a small minority had the abnormality on their medical records or self-reported - fewer than one in four (23%) with XXY and only one individual with XYY (0.7%).

By linking genetic data to routine health records, the men were three times more likely to have type 2 diabetes - the form that develops in middle age and is linked to obesity.

They were six times more likely to develop clots, or venous thrombosis - hardening of the arteries that can cut off blood and trigger heart attacks or strokes.

They were three times as likely to suffer a pulmonary embolism, a blocked vessel in the lung that can kill.

They were also four times more prone to COPD (chronic obstructive pulmonary disease) - a debilitating disorder that causes breathing difficulties.

The team also found men with XXY have much higher chances of reproductive problems.

It includes a three and fourfold higher risk of delayed puberty and being childless, respectively.

They also had much lower blood levels of testosterone, the natural male hormone. Men with XYY appeared to have a normal reproductive function.

The researchers say it is not clear why an extra chromosome should increase the risks of serious illness or why they were so similar irrespective of the duplication.

Co-author Prof Anna Murray, of the University of Exeter, said: "Our study is important because it starts from the genetics and tells us about the potential health impacts of having an extra sex chromosome in an older population, without being biased by only testing men with certain features as has often been done in the past."

Previous studies have found around one in 1,000 females have an additional X chromosome.

It can result in delayed language development and accelerated growth until puberty, as well as lower IQ levels compared to peers.

The study in Genetics in Medicine was funded by the Medical Research Council.