Up to one in 500 men may carry an extra sex chromosome — either an X or a Y — but very few of them are likely aware of it, a new study finds.
The research, published June 9 in the journal genetics in medicine (opens in new tab), comprised data from more than 207,000 men who submitted information to the UK Biobank, a collection of genetic and health data from half a million UK-based participants. Typically, males carry an X- and a Y-shaped gender chromosome in each of their cells, but among the study participants there were 213 men who carried an extra X chromosome and 143 who had an extra Y chromosome.
Very few of these men were either diagnosed with a chromosomal abnormality or recorded one on 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 an extra Y chromosome can be very subtle, which might explain the difference in diagnosis rates somewhat, the researchers said Information Center for Genetic and Rare Diseases (opens in new tab).)
“We were surprised at how common this is,” said Dr. Ken Ong, a pediatric endocrinologist in the Medical Research Council (MRC) Division of Epidemiology at the University of Cambridge and co-senior author of the study. said The Guardian (opens in new tab). “It was thought to be quite rare.”
Previous estimates suggest that around 100 to 200 out of every 100,000 men are XXY, according to the National Institute for Human Genome Research (opens in new tab)and an estimated 18 to 100 out of 100,000 were considered XYY, the authors noted in their report.
Related: Is the Y chromosome dying out?
Overall, about 0.17% of study participants had an extra sex chromosome, or about one in 580. However, the rate observed in the study may be slightly lower than that in the general population, the study authors noted in their report. This is because UK Biobank volunteers tend to be healthier than the general population and have a lower than average incidence of genetic disorders. Based on this, the authors estimate that about 1 in 500 men, or 0.2% in the general population, carries an extra sex chromosome.
The presence of extra sex chromosomes can increase the risk of certain health conditions, and this increased risk appeared to be reflected in the biobank volunteers’ health records, the researchers reported.
For example, Klinefelter syndrome (KS) — or 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, XXY men’s childlessness rate was four times higher than XY men’s, and according to a, they were three times more likely to have started puberty late expression (opens in new tab).
A condition called 47,XYY syndrome — or an extra Y chromosome as a male — was not associated with an increased rate of reproductive problems in affected study participants, the authors reported. However, the syndrome has historically been associated with other symptoms, including learning disabilities, delays in acquiring language and motor skills, and abnormally low muscle tone, according to the Genetic and Rare Diseases Information Center. These symptoms were not specifically assessed in the biobank study.
Related: Are you more genetically similar to your mother or father?
However, research found a possible link between extra sex chromosomes and other disorders. Compared to XY men, both the XXY and XYY men showed higher rates of Type 2 diabetes; plaque build-up in 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 the lung.
“It is unclear why both KS and 47,XYY should share striking similarities in conferring substantially higher risks for many common diseases,” the authors write in their report. The mechanisms driving this increased risk would need to be explored in future studies, they said.
The study is limited in that it only included males of European descent between the ages of 40 and 70. “However, our study is important because it starts with genetics and informs us about the potential health effects of having an extra sex chromosome in an older population without being biased by only testing males with certain traits, as has often been done in the past.” was,” Anna Murray, associate professor of human genetics at the University of Exeter Medical School and co-author of the study, said in the statement.
Originally published on Live Science.
https://www.livescience.com/men-with-extra-sex-chromosomes-study One in 500 men may carry an extra sex chromosome (most without knowing it)