The study also showed that female participants may be more at risk of a heavier buildup of tau protein than male participants.

“We were surprised to see that people with a father with Alzheimer’s were more vulnerable to the spread of tau in the brain, as we had hypothesized that we would see more brain changes in people with affected mothers,” said study author Sylvia Villeneuve, PhD, of McGill University in Montreal, Canada.

The study looked at 243 people who had a family history of Alzheimer’s disease but had no thinking or memory problems themselves at the average age of 68. Family history was defined as one or both parents with the disease or at least two siblings with the disease. Participants had brain scans and took tests of thinking and memory skills at the start of the study and then during the study as they were followed for an average of nearly seven years.

During that time, 71 people developed mild cognitive impairment, which is a precursor to Alzheimer’s disease.

Researchers found that people with a father with Alzheimer’s disease as well as female participants had a greater spread of tau protein in the brain. Female participants also had a heavier buildup of tau protein in the brain.

“Better understanding these vulnerabilities could help us design personalized interventions to help protect against Alzheimer’s disease,” Villeneuve said.

A limitation of the study is that white people made up the majority of participants, so the results may not apply to other groups.

The study was supported by the Canadian Institutes of Health Research, Quebec Research Fund — Health, J.-Louis Lévesque Foundation, Brain Canada Foundation, Alzheimer’s Society Canada and Brain Canada Research.