It’s not surprising that someone whose mother or father has Alzheimer’s disease may be more prone to develop the illness than those without any close family connections. But a new study suggests that having a grandparent, aunt, cousin or other extended-family member with dementia may increase your risk.
The study, published in the journal Neurology, drew on genealogical data from more than 270,800 Utah death certificates. Using that state’s database, the researchers compared rates of Alzheimer’s deaths in a variety of scenarios involving first-, second- and third-degree relatives.
The findings give physicians and the public a “more complete picture of risk,” says study coauthor Keoni Kauwe, a biology professor at Brigham Young University. “What we add that other studies have not been able to evaluate,” he says, “is that the second-degree and even third-degree relatives give us predictive power as to your individual risk.”
First-degree relatives include parents and siblings who share both parents. Second-degree relatives are grandparents, blood-related aunts and uncles, and half-brothers and sisters. Third-degree relatives include great-grandparents, great uncles, great aunts, and first cousins.
Researchers found that people with one first-degree relative with Alzheimer’s were more than one-and-a-half times as likely to develop the disease than they otherwise would have. In general, the risk increases the more relatives you have with the disease and the closer those relatives are. For example, the study found that if someone’s mother (a first-degree relative) had Alzheimer’s and so did two second-degree relative — like a grandparent and an uncle — that person was 21 times more likely to develop the illness.
Kauwe and his colleagues also found that even in cases where parents and siblings weren’t affected, having distant family members with the disease was linked to greater risk. While Kauwe hopes that physicians, for example, ask their patients about Alzheimer’s disease in their extended family, he underscores that these numbers are not intended to alarm people. The causes of Alzheimer’s are complex, and much remains unknown about how the disease, which is estimated to affect about 1 in 10 adults age 65 and older, develops. In the overall population, he says, genetic factors account for about half of risk.
Researchers now plan to use this data to focus on the families with the highest and lowest rates of Alzheimer’s so they can better understand the genetic and environmental factors that influence why the disease does — or does not — develop. “That,” Kauwe says, “will give us the path toward prevention and cure.”