Men who lose the Y chromosome as they age have an increased risk of Alzheimer's disease, scientists have said. Around one in five men over the age of 80 loses the Y chromosome (also called LOY). Previously scientists have linked this to men having shorter lifespans than women.

Researchers from the Uppsala University in Sweden looked at over 3,200 men to assess LOY with the development of Alzheimer's. They found men with the disease were three times more likely to show LOY in some of their blood cells than those who had not lost the chromosome. Their findings were published in the American Journal of Human Genetics.

Researchers said their study does not prove that LOY directly contributes to Alzheimer's disease. Earlier research on the subject has indicated that LOY can also raise the probability of cancer in older men and is more frequently found in smokers. The team is now including these evidences for a wider range of health problems.

"Having loss of Y is not 100% predictive that you will have either cancer or Alzheimer's. But in the future, loss of Y in blood cells can become a new biomarker for disease risk and perhaps evaluation can make a difference in detecting and treating problems early," lead research Professor Lars Forsberg said.

Their findings also showed some men with LOY lived with no symptoms of Alzheimer's well into their 90s.

According to Professor Chris Lau from University of California, who was not part of the study, the research has "only highlighted the fact that the Y chromosome could serve important functions beyond male sex determination and sperm production. What exactly on the Y chromosome that increases the risk of Alzheimer's disease is the key issue."

Lau has called for more research to be done as the Y chromosome contains many genes, with some being unique to men while others are shared with women (who do not have a Y chromosome). "It depends on what is lost to determine what is important for Alzheimer's disease. Without such information, the loss of Y is just an observation," Lau said.

However, another question regarding the link between LOY and Alzheimer's is why does the loss of Y chromosome even begin? "We speculate that whatever cellular mechanisms fail and lead to Alzheimer's, they start in our young adult life, not in our 70s," Dr Luca Gilberto, a New York based neurologist said, further raising a question, "Is loss of Y a process that starts that early?"

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