Around one in 500 men could be carrying an extra X or Y chromosome — most of them unaware — putting them at increased risk of diseases such as type 2 diabetes, atherosclerosis and thrombosis, say researchers at the universities of Cambridge and Exeter.
In a study published in Genetics in Medicine, researchers analysed genetic data collected on over 200,000 UK men aged 40-70 from UK Biobank, a biomedical database and research resource containing anonymised genetic, lifestyle and health information from half a million UK participants. They found 356 men who carried either an extra X chromosome or an extra Y chromosome.
Sex chromosomes determine our biological sex. Men typically have one X and one Y chromosome, while women have two Xs. However, some men also have an extra X or Y chromosome — XXY or XYY.
Without a genetic test, it may not be immediately obvious. Men with extra X chromosomes are sometimes identified during investigations of delayed puberty and infertility; however, most are unaware that they have this condition. Men with an extra Y chromosome tend to be taller as boys and adults, but otherwise they have no distinctive physical features.
In today’s study, the researchers identified 213 men with an extra X chromosome and 143 men with an extra Y chromosome. As the participants in UK Biobank tend to be ‘healthier’ than the general population, this suggests that around one in 500 men may carry an extra X or Y chromosome.
Only a small minority of these men had a diagnosis of sex chromosome abnormality on their medical records or by self-report: fewer than one in four (23%) men with XXY and only one of the 143 XYY men (0.7%) had a known diagnosis.
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