Researchers claim to have found a particular gene variant that explains the reason behind women's high risk of developing Alzheimer's disease.

For the study, researchers at the Stanford University analysed data of 8,000 patients from around 30 Alzheimer's centers throughout the United States. Most of the people were above 60 years of age.

The experts analyzed medical reports of at least 5,000 people whose test results were normal at the beginning of the study and 2,200 people who showed signs of mild cognitive impairment.

After examining the data, the scientists discovered a gene variant called ApoE4. The ApoE4 gene affected Alzheimer's risk for both men and women. But, further examination showed that women who carried the ApoE4 variant had about twice the chances of contracting mild cognitive impairment or Alzheimer's disease.

The second set of medical reports of over 1000 patients had imaging data and measurements of various biochemical substances from the spinal fluid that serve as useful biomarkers of impending mild cognitive impairment and eventual Alzheimer's disease.

The analysis showed that ApoE4's effect was more in women than men.

"Our study showed that, among healthy older controls, having one copy of the ApoE4 variant confers a substantial Alzheimer's disease risk in women, but not in men," lead study author Michael Greicius, MD, assistant professor of neurology and neurological sciences and medical director of the Stanford Center for Memory Disorders said in a press release. "Even after correcting for age, women appear to be at greater risk."

The study was published in Annals of Neurology.