At most one in every 500 men can carry an extra sex chromosome – either X or Y – but very few are likely to know about it, a new study shows.
The study, published June 9 in the journal Genetics in medicine (opens in a new tab), includes data from more than 207,000 men who provided information to the UK Biobank, a repository of genetic and health data from half a million participants in the UK. Usually men wear one X- and one 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 had an extra Y.
Very few of these men either reported being diagnosed with a chromosomal abnormality or had such an abnormality noted in their medical records: Of the XXY men, only 23% had a known diagnosis and only 0.7% of XYY men had diagnosis. (The potential symptoms of having an extra Y chromosome can be very subtle, which may partly explain the difference in the frequency of diagnosis, according to Genetic and Rare Diseases Information Center (opens in a new tab).)
“We were surprised at how often this is,” said Dr. Ken Ong, a pediatric endocrinologist in the Epidemiological Department of the Medical Research Council (MRC) at the University of Cambridge and co-author of the study. told The Guardian (opens in a new tab). “It was thought to be quite rare.”
Previous estimates have estimated that approximately 100 to 200 men out of every 100,000 are XXY, according to National Institute for Human Genome Research (opens in a new tab)and it is estimated that 18 to 100 out of every 100,000 are XYY, the authors note in their report.
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Overall, about 0.17% of study participants had an extra sex chromosome, or about one in 580. However, the percentage observed in the study may be slightly lower than in the general population, the study authors noted in their study. report. This is because UK Biobank volunteers are healthier than the general population and have a lower than average incidence of genetic diseases. Based on this, the authors estimate that about one in every 500 men, or 0.2% of the total population, carries an extra sex chromosome.
The presence of extra sex chromosomes may increase the risk of certain health conditions, and this increased risk appears to be reflected in the health data of Biobank volunteers, the researchers said.
For example, Klinefelter’s syndrome (KS) – or the presence of an extra X chromosome in a man – has been linked to reproductive problems, including infertility and delayed puberty, according to the National Institute of Human Genome Research. In the study, the incidence rate of childlessness in men XXY is four times higher than in men XY and three times more likely to have started puberty late, according to statement (opens in a new tab).
A condition called syndrome 47, XYY – or the presence of an extra Y chromosome in men – was not associated with an increased rate of reproductive problems in the study participants, the authors said. However, in the past, the syndrome has been linked to other symptoms, including learning difficulties, delayed speech and motor skills, and unusually low muscle tone, according to the Genetic and Rare Diseases Information Center. These symptoms were not specifically evaluated in the Biobank study.
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However, the study reveals a possible link between extra sex chromosomes and other conditions. Compared to men XY, men XXY and XYY show higher levels of type 2 diabetes; accumulation of plaque on the walls of the arteries (atherosclerosis); blood clots in the veins (venous thrombosis) and pulmonary arteries (pulmonary embolism); and chronic obstructive pulmonary disease, which impedes airflow to lungs.
“It is unclear why both KS and 47, XYY should show striking similarities in providing significantly higher risks for many common diseases,” 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 to only men of European descent between the ages of 40 and 70. However, “our research is important because it starts with genetics and tells us about the potential health effects of having an extra sex chromosome in an older population, without being addicted just by testing men with certain characteristics, as is often the case. has done in the past, “Anna Murray, an associate professor of human genetics at the University of Exeter School of Medicine and co-senior author of the study, the statement said.
Originally published in Live Science.