CAMBRIDGE, United Kingdom — One in 500 men are born with an extra sex chromosome, which can lead to a host of life-threatening illnesses, a new study reveals. A team from the University of Cambridge has found that this extra chromosome raises the risk of developing type 2 diabetes by three times and blood clots by six times.
It also makes serious lung diseases up to four times more likely. The findings come from a review of over 200,000 British adults between 40 and 70. The discovery could lead to a screening program for future diseases among men.
“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,” says co-author and epidemiologist Professor Ken Ong in a university release.
How do you know if you have an extra chromosome?
Scientists explain that X and Y chromosomes determine a child’s gender. These chromosomes carry our DNA, with males having XY while females having XX. However, some men also have an extra – creating either XXY or XYY. Most are unaware of the difference, unless they undergo genetic testing.
There are few visible signs, but those with an extra Y chromosome tend to be taller. A second X may delay puberty or cause infertility.
“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,” Prof. Ong adds.
Fathers contribute the X or Y, and mothers contribute an X. Inherit an X and Y, and you give birth to a boy. Get a pair of Xs, and it’s a girl.
“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,” says first author Yajie Zhao, a PhD student from Prof. Ong’s lab.
The study analyzed participants from 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. Since participants in the UK Biobank tend to be “healthier” than the average person, researchers say the phenomenon will apply to around one in every 500 men.
Only a small minority had the abnormality listed on their medical records — fewer than one in four (23%) with XXY and only one individual with XYY (0.7%).
An extra chromosome can have wide-ranging health implications
By linking genetic data to routine health records, the men were three times more likely to have type 2 diabetes.
They were also six times more likely to develop a form of blood clotting called venous thrombosis — a hardening of the arteries that can cut off blood and trigger heart attacks or strokes. The extra chromosome makes it three times as likely for men to suffer a pulmonary embolism, a blocked vessel in the lungs that can be fatal. Men were also four times more prone to COPD (chronic obstructive pulmonary disease) — a debilitating disorder that causes breathing difficulties.
Additionally, the team found men with XXY have much higher chances of reproductive problems. It includes a three and fourfold higher risk of delayed puberty and being infertile, respectively. These men also had much lower blood levels of testosterone, the natural male hormone.
However, men with XYY appeared to have a normal reproductive function. The researchers say it is not clear why an extra chromosome should increase risks of serious illness or why they were so similar irrespective of the duplication.
“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,” concludes co-author Prof. Anna Murray from the University of Exeter.
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 is published in the journal Genetics in Medicine.
South West News Service writer Mark Waghorn contributed to this report.