Many men carry an extra chromosome, without even knowing about it

A study on the extra chromosomes titled "Detection and characterization of male sex chromosome abnormalities in the UK Biobank study" has been published in the journal Genetics in Medicine.

Data from over 207,000 men included in the UK Biobank has revealed that an extra sex chromosome, either an X or Y, may be prevalent in as many as 1 in 500 men. Typically, men are born with one X chromosome and one Y chromosome, however, in the dataset, were 213 men with an extra X chromosome, resulting in the XXY genotype, and 143 men with an extra Y chromosome, resulting in the XYY genotype.

Also referred to as 47,XXY and 47,XYY, the genotypes are called Klinefelter syndrome and Jacobs syndrome, respectively. Only 23% of those with Klinefelter syndrome had a known diagnosis, while only 0.7% of those with Jacobs syndrome were diagnosed. However, the latter has much more subtle characteristics that could contribute to a lower diagnosis rate.

"We were surprised at how common this is. It had been thought to be pretty rare," said Dr. Ken Ong, a pediatric endocrinologist and a co-senior author of the study.

You can read more from the study here.