© BSIP/UNIVERSAL IMAGES GROUP VIA GETTY IMAGESA set of human chromosomes, with a pair of XY and XX chromosomes in the bottom right.
In the 1960s, doctors counting the number of chromosomes in human white blood cells
noticed a strange phenomenon. Frequently — and more frequently with age — the cells would be missing the Y chromosome. Over time, it became clear this came with consequences. Studies have linked loss of the Y chromosome in blood to cancer, heart disease, and other disorders.
Now a new study — the largest yet of this phenomenon — estimates that 20 percent of 205,011 men in a large genetic database called the UK Biobank have lost Y chromosomes from some detectable proportion of their blood. By age 70, 43.6 percent of men had the same issue. It's unclear exactly why, but the authors think these losses might be the most glaring sign of something else going wrong inside the bodies of these men: They are allowing mutations of all kinds to accumulate, and these other mutations could be the underlying links to cancer and heart disease.
Mutations are, after all, spontaneously popping up in the human body all the time. Every cell division produces errors as small as miscopying one letter or as large as losing an entire chromosome. So over a lifetime, this can lead to what scientists call "clonal mosaicism" — in which a person's body is a mosaic of distinct populations of cells, each with their accumulated mutations. This is true of everyone to some extent, but it becomes more relevant as you get older. "The more you age, the more errors have taken place in cell division," says
John R. B. Perry, a biologist at the University of Cambridge who led the recent study.
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