And still, men who had a loss of Y in their blood cells were nearly seven times more likely to develop Alzheimer’s, versus other men.
“It seems that the loss of Y is, per se, an independent risk factor for Alzheimer’s disease,” Giliberto said.
That opens up many more questions, Giliberto noted. One is, which genes on the Y chromosome — when lost — might leave a man more vulnerable to Alzheimer’s?
Another question is, when does loss of Y begin? “We speculate that whatever cellular mechanisms fail and lead to Alzheimer’s, they start in our young adult life, not in our 70s,” Giliberto said. “Is loss of Y a process that starts that early?”
If loss of Y does not begin until late in life, he added, then it may only make an “ancillary” contribution to Alzheimer’s risk.
The findings are based on blood samples from more than 3,200 European men, average age 73. Overall, 17 percent had a detectable loss of Y in some of their blood cells.
Since scientists do not fully understand the workings of Y, the reasons for the link are unclear.
But Forsberg speculated that impaired immune function could play a role — since loss of Y has been tied to cancer risk as well.
Giliberto agreed. He noted that loss of Y has also been seen in certain autoimmune diseases — where the immune system mistakenly attacks the body’s own tissue. And some researchers suspect immune function may affect Alzheimer’s risk.
“A faulty brain immune system has been proposed as a possible ‘soft spot’ for Alzheimer’s disease, allowing for the abnormal accumulation of proteins and consequent (brain cell) degeneration,” Giliberto said.
For now, though, researchers have much to learn about the connection between the Y chromosome and disease. And more studies will be needed before loss of Y can be used as a “biomarker” of Alzheimer’s risk, Giliberto said.
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