Women with a certain gene are more likely than men with the same gene to develop Alzheimer's disease, a new study suggests.

In the study, healthy older women with the gene, called ApoE4, were 81 percent more likely to develop Alzheimer's diseaseor mild cognitive impairment (a condition that can lead to Alzheimer's) over a four-year period, compared with women who didn't have the gene.

On the other hand, older men in the study with the ApoE4 gene had only a marginal increase in their risk of Alzheimer's or mild cognitive impairment (a 27 percent increase), compared with men without the gene, the researchers said. [Extending Life: 7 Ways to Live Past 100]

The ApoE4 gene is known to increase the risk of Alzheimer's: People with one copy of the gene have a 2- to 4-fold increased risk of Alzheimer's, and those with two copies of the gene have a 10-fold increased risk. But few studies have looked at whether that risk differs between men and women, and doctors today generally view men and women with the ApoE4 gene as having equal risk for Alzheimer's, the researchers said.

The new findings suggest that doctors may need to change how they interpret the finding of an ApoE4 gene in people, depending on whether the patient is a man or a woman, the researchers said.

Figuring out the reason for this sex difference may help researchers better understand what causes Alzheimer's disease, and may reveal potential new ways to treat the condition, said study researcher Andre Altmann, of Stanford University School of Medicine.

In the study, the researchers examined information from more than 5,000 healthy older adults in the United States, most in their 60s and 70s, who did not have Alzheimer's or other types of cognitive problems, and about 2,200 people with mild cognitive impairment.

During the study period, about 950 healthy older adults progressed to developing Alzheimer's disease or mild cognitive impairment.

Women who had a single copy of the ApoE4 gene had a 1.8-fold increase in their risk of Alzheimer's disease, compared with women who carried the most common form of this gene, called ApoE3. But men with a single copy of the ApoE4 gene had no increase in their risk for Alzheimer's when compared to those with the ApoE3 gene.

The researchers noted that some participants may have dropped out of the study due to cognitive problems, and this may have affected the results.

The study was published is April 14 in the journal Annals of Neurology.

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