Scientists have discovered a genetic risk factor which serves as an evidence why more women than men develop Alzheimer's disease.

Research carried out at the Mayo Clinic in Jacksonville, Florida and Rochester, Minnesota has revealed that women who inherited the same variant of the gene, known as PCDH11X, from both parents were more prone to Alzheimer's disease.

The gene is found on the X chromosome and it harbors the first sex-specific genetic variant that causes greater risk to Alzheimer's.

But a single copy in both the sexes could lead to a heightened risk towards the disease. But since only women have two X chromosomes, it makes them vulnerable to the impact of the double variant.

"Two thirds of people with dementia are women, but this is partly because women live longer and risk of developing dementia increases with age."

Neil Hunt, of the Alzheimer's Society, said research by his organisation had proved that the prevalence of dementia is twice as much as in men over the age of 65.

PCDH11X also controls production of a protein called a protocadherin. The protein molecules help cells in the central nervous system to communicate with each other. There is evidence to suggest that protocadherins may be broken down by an enzyme. This has link to some forms of Alzheimeer's.