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One in 500 men carry extra X or Y chromosome and face higher risk of several conditions, say Cambridge and Exeter researchers

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About one in 500 men could be carrying an extra X or Y chromosome that puts them at increased risk of diseases such as type 2 diabetes, atherosclerosis and thrombosis.

Researchers at the University of Cambridge and University of Exeter say most of them will be unaware.

An illustration of X and Y chromosomes
An illustration of X and Y chromosomes

They analysed genetic data from more than 200,000 UK men aged 40-70 from the UK Biobank database, finding 356 men with either an extra X or Y chromosome.

These chromosomes determine our biological sex, with men typically having one X and one Y chromosome, while women have two Xs. Some men have XXY or XYY chromosomes, but it may not be obvious to them without a genetic test, although men with extra X chromosomes are sometimes identified during investigations of delayed puberty and infertility.

Men with an extra Y chromosome tend to be taller as boys and adults, but there are otherwise no distinctive physical signs.

Of the 213 men with an extra X chromosome found in the study, only 23 per cent had a known diagnosis, while only one of the 143 found with an extra Y chromosome was aware of it.

Connecting the data to routine health records showed men with XXY have much higher chances of reproductive problems, including a three-fold higher risk of delayed puberty and a four-fold higher risk of being childless. They also had significantly lower blood concentrations of testosterone, the natural male hormone.

Men with XYY appeared to have a normal reproductive function but men with either XXY or XYY had higher risks of other conditions.

The researchers said they were three times more likely to have type 2 diabetes, six times more likely to develop venous thrombosis, three times as likely to experience pulmonary embolism, and four times more likely to suffer from chronic obstructive pulmonary disease (COPD). The reason for this is not yet clear.

Yajie Zhao, a PhD student at the Medical Research Council (MRC) Epidemiology Unit at the University of Cambridge, the study’s first author, 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 that they have substantially higher risks of a number of common metabolic, vascular, and respiratory diseases – diseases that may be preventable.”

Professor Ken Ong, also from the MRC Epidemiology Unit at Cambridge and joint senior author of the MRC-funded study published in Genetics in Medicine, added: “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.

“We’d 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.”

Previous studies have found about one in 1,000 females have an additional X chromosome. This can lead to delayed language development and accelerated growth until puberty, as well as lower IQ levels.

Chromosomes are made of protein and single molecule of DNA, carrying our genetic information. Each human cell normally contains 23 pairs, including one pair of sex chromosomes.

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