Losing the Y chromosome in blood cells may affect the immune system, thereby increasing susceptibility to disease, a study of more than 3200 men suggests.

Loss of the male Y chromosome from the blood cells of older men may be linked to Alzheimer's disease, new research has shown.

A study of more than 3200 men found that loss of the Y chromosome (LOY) significantly increased the chances of developing Alzheimer's.

Previous research has linked LOY both with smoking and with cancer.

The findings may indicate that losing the Y chromosome affects the immune system, thereby increasing susceptibility to disease, scientists believe.

Lead researcher Professor Lars Forsberg, from the University of Uppsala in Sweden, said: "Having loss of Y is not 100 per cent 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."

The scientists looked at data on three populations of men, totalling more than 3200, to investigate possible links between LOY and Alzheimer's.

Participants had an average age of 73 and around 17 per cent showed evidence of LOY in blood cells, which increased the older they were.

In one group, losing the Y chromosome made it almost three times more likely that a man had been diagnosed with Alzheimer's.

Men in the two other groups, whose progress was monitored for a number of years, were nearly seven times more likely to develop Alzheimer's if they had a blood LOY.

The results appear in the American Journal of Human Genetics.

Previous research by the same team showed that smoking increased the risk of losing the Y chromosome from blood cells by as much as 400 per cent.

Lifetime-acquired LOY in blood cells was associated both with deaths from any cause, and non-blood cancers.

Co-author Professor Jan Dumanski, also from Uppsala University, said: "The blood cells we studied are involved in the immune system, and the fact that LOY in them is associated with disease in other tissues is striking. We therefore hypothesise that the loss of LOY in blood cells leads them to lose part of their immune function."

Since they do not have a Y sex chromosome - just two female X chromosomes - there can be no connection between LOY and Alzheimer's in women.

The genetic mutation that silences the Y chromosome is newly acquired in an affected individual and not inherited.

Dr Simon Ridley, science director at the charity Alzheimer's Research UK, said: "Further research may allow us to uncover more information about the molecular processes underpinning the disease, an important step in the search for treatments. It's important to note that not all men with loss of Y chromosome in this study developed Alzheimer's disease, and these results do not suggest that testing for this trait would be a reliable indicator of Alzheimer's risk."