Twice as many men carry an extra sex chromosome as previously thought, according to researchers who called for more genetic testing to identify people at greater risk of related medical problems.
Research on more than 200,000 men enrolled with the UK Biobank suggests that about one in 500 in the general population has an extra X or Y chromosome, double the number found in earlier work, though only a fraction are likely to be aware of it.
“We were surprised at how common this is,” said Prof Ken Ong, a paediatric endocrinologist at the MRC epidemiology unit at Cambridge and a senior author on the study. “It had been thought to be pretty rare.”
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Men with an additional X chromosome are often diagnosed when it has an impact on puberty and fertility, though it is also linked to higher body fat, cognitive problems and personality disorders. In the study, XXY men had substantially lower testosterone than XY men, a threefold greater risk of delayed puberty, and a fourfold higher risk of being childless. The effects of an extra Y chromosome are less well understood. XYY men tend to be taller as boys and adults, but appear to have normal reproductive function.
