A survey of more than 200,000 men registered with the UK Biobank shows that about one in 500 in the general population has an extra X or Y chromosome, twice the number found in a previous job, although only a fraction are likely to know it. While most men have an X and a Y chromosome, some are born XXY or XYY, putting them at increased risk for health problems ranging from type 2 diabetes, clogged blood vessels and chronic obstructive pulmonary disease (COPD), a lung condition, or study. were found. “We were amazed at how common this was,” said Professor Ken Ong, a pediatric endocrinologist at the MRC Epidemiology Unit in Cambridge and senior author of the study. “It was considered quite rare.” In collaboration with colleagues at the University of Exeter, the Cambridge team tested DNA from 207,067 men of European descent between the ages of 40 and 70. They identified 231 men with an extra X chromosome and 143 men with an extra Y chromosome. Those enrolled in the UK Biobank tend to be healthier than average, but from the data, scientists estimate that 1 in 500 men in the general population has an additional X or Y chromosome. Among the men identified in the study, published in Genetics in Medicine, only 23% of those XXYs and 0.7% of those XYYs had a known diagnosis of an extra chromosome, indicating that there was little awareness of the condition. Men with an extra X chromosome are often diagnosed when it affects adolescence and fertility, although it is also associated with higher body fat, cognitive problems and personality disorders. In the study, XXY men had significantly lower testosterone than XY men, three times the risk of delayed puberty and four times the risk of being infertile. The effects of an extra Y chromosome are less understood. XXY males tend to be taller as boys and adults, but appear to have normal reproductive function. Subscribe to the First Edition, our free daily newsletter – every morning at 7 p.m. BST Previous research suggests that about 1 in 1,000 women carry an extra X chromosome, which can lead to similar results, ranging from faster growth to adolescence, delayed language development and reduced IQ compared to their XX peers. Analysis of men’s health records found that carrying an extra sex chromosome increased the risks of many medical conditions. Compared to XY men, having an extra racial chromosome tripled the risk of type 2 diabetes and blocked blood vessels in the lungs, quadrupled the risk of COPD and six times the risk of blocked veins, the researchers found. It is not clear why the extra chromosomes have such an effect and why they are similar regardless of the dual chromosome. “We need to adopt more genetic tests, especially on delayed puberty and infertility, as well as some men with diabetes and coagulation problems,” Ong said. “Some of these conditions require genetic testing, but doctors may not look for it. “We need to encourage broader genetic testing when patients have these conditions.”
