Having a parent with Alzheimer’s disease has been known to raise a person’s risk of developing the disease, but new research published in Neurology suggests that having second- and third-degree relatives who have had Alzheimer’s may also increase risk.
“Family history is an important indicator of risk for Alzheimer’s disease, but most research focuses on dementia in immediate family members, so our study sought to look at the bigger family picture,” said Lisa A. Cannon-Albright, PhD, University of Utah School of Medicine, Salt Lake City, Utah. “We found that having a broader view of family history may help better predict risk. These results potentially could lead to better diagnoses and help patients and their families in making health-related decisions.”
For the study, researchers looked at the Utah Population Database, which includes the genealogy of Utah pioneers from the 1800s and their descendants up until modern day. The database is linked to Utah death certificates, which show causes of death, and in a majority of cases, contributing causes of death.
In that database, researchers analysed data from over 270,800 people who had at least 3 generations of genealogy connected to the original Utah pioneers including genealogy data for both parents, all 4 grandparents, and at least 6 of 8 great-grandparents. Of those, 4,436 have a death certificate that indicates Alzheimer’s disease as a cause of death.
Results showed that people with 1 first-degree relative with Alzheimer’s disease (18,494 people) had a 73% increased risk of developing the disease. Of this group of people, 590 developed Alzheimer’s disease; the researchers would have expected this group to have 341 cases.
People with 2 first-degree relatives were 4 times more likely to develop the disease; those with 3 were 2.5 times more likely; and those with 4 were nearly 15 times more likely to develop Alzheimer’s disease.
Of the 21 people in the study with 4 first-degree relatives with Alzheimer’s, 6 had the disease. The researchers would have expected only 0.4 people to develop the disease.
Those with 1 first-degree relative and 1 second-degree relative had a 21 times greater risk. Examples of this would be a parent and one grandparent with the disease, or a parent and one aunt or uncle. There were 25 people in this category in the study; 4 of them had the disease when researchers would have expected 0.2 cases.
Those who had only third-degree relatives, and 3 such relatives, with Alzheimer’s disease had a 43% greater risk of developing the disease. An example of this would be two great-grandparents with the disease, along with one great uncle, but no parents or grandparents with the disease. Of the 5,320 people in this category, 148 people had the disease when researchers would have expected 103.
“More and more, people are increasingly seeking an estimate of their own genetic risk for Alzheimer’s disease,” said Dr. Cannon-Albright. “Our findings indicate the importance of clinicians taking a person’s full family history that extends beyond their immediate family members.”
She noted that among all of the study participants, 3% had a family history that doubled their risk of Alzheimer’s disease, and a little over one-half of a percent had a family history that increased their risk by ≥3 times that of a person without a family history of the disease.
Limitations of the study include that not all individuals dying from Alzheimer’s disease may have had a death certificate listing it as cause of death. Dr. Cannon-Albright said death certificates are known to underestimate the prevalence of the disease.
“There are still many unknowns about why a person develops Alzheimer’s disease,” she said. “A family history of the disease is not the only possible cause. There may be environmental causes, or both. There is still much more research needed before we can give people a more accurate prediction of their risk of the disease.”