A new study suggests that up to one in 500 men may carry an extra sex chromosome – an X or a Y – but very few of them probably know.
The research, published June 9 in the journal Genetics in medicine (opens in a new tab), included data from over 207,000 men who provided information to the UK Biobank, a repository of genetic and health data of half a million UK-based participants. Typically, males carry an X-shaped and a Y-shaped sex chromosome in each of their cells, but among the study participants were 213 men who carried an extra X chromosome and 143 who had an extra Y chromosome.
Very few of these men reported being diagnosed with a chromosomal abnormality or having such an abnormality noted in their medical records: of the XXY men, only 23% had a known diagnosis and only 0.7% of the XYY men had a diagnosis. (The potential symptoms of having an extra Y chromosome can be very subtle, which may somewhat explain the difference in diagnosis rates, according to the Information center on genetic and rare diseases (opens in a new tab).)
“We were surprised at how common it is,” Dr Ken Ong, pediatric endocrinologist at the University of Cambridge’s Medical Research Council (MRC) Epidemiology Unit and senior co-author of the study, he told the Guardian (opens in a new tab). “It was thought to be quite rare.”
Previous estimates suggested that about 100-200 out of 100,000 men were XXY, according to the National Human Genome Research Institute (opens in a new tab)and an estimated 18 to 100 out of 100,000 were XYY, the authors noted in their report.
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In all, about 0.17 percent of study participants had an extra sex chromosome, or about one in 580. However, the observed rate in the study may be slightly lower than that of the general population, the study authors noted. their relationship. This is because UK biobank volunteers tend to be healthier than the general population and have a lower than average incidence of genetic conditions. Based on this, the authors estimate that about one in 500 men, or 0.2%, in the general population carries an extra sex chromosome.
Having extra sex chromosomes can increase the risk of certain health conditions, and this increased risk seemed to be reflected in the health data of the Biobank volunteers, the researchers reported.
For example, Klinefelter’s syndrome (KS) – or having an extra X chromosome as a male – has been linked to reproductive problems, including infertility and delayed puberty, according to the National Human Genome Research Institute. In the study, the childlessness rate in XXY men was four times that of XY men and was three times more likely to have started late puberty, according to one. declaration (opens in a new tab).
A condition called syndrome 47, XYY – or having an extra Y chromosome as a male – was not linked to an increased rate of reproductive problems in affected study participants, the authors reported. That said, in the past, the syndrome has been linked to other symptoms, including learning difficulties, delays in the acquisition of motor and language skills, and unusually low muscle tone, according to the Information Center on Genetic and Rare Diseases. These symptoms were not specifically assessed in the Biobank study.
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However, research has revealed a possible link between extra sex chromosomes and other conditions. Compared to XY men, both XXY and XYY men showed higher rates of type 2 diabetes; accumulation of plaque in the artery walls (atherosclerosis); blood clots in the veins (venous thrombosis) and pulmonary arteries (pulmonary embolism); and chronic obstructive pulmonary disease, which obstructs airflow to the lungs.
“It is not clear why both KS and 47, XYY should show striking similarities in conferring substantially higher risks for many diseases in common,” the authors wrote in their report. The mechanisms driving this increased risk will need to be explored in future studies, they said.
The study is limited as it only included men of European descent between the ages of 40 and 70. However, “our study is important because it starts with genetics and tells us about the potential health impacts of having an extra sex chromosome in an older population, without being prevented from testing only men with certain characteristics as has often been done in past, “Anna Murray, associate professor of human genetics at the University of Exeter Medical School and senior co-author of the study, said in the statement.
Originally published in Live Science.