Having a first-degree relative, such as a parent, with Alzheimer's disease may affect a person's cognition, new research suggests.
In fact, it is one of the two most significant risk factors, together with age. Having a first-degree relative with Alzheimer's raises relative risk by 30%, which means that a person's existing risk goes up by almost a third.
Having a copy of the gene APOE4 that encodes the protein apolipoprotein E raises Alzheimer's risk by threefold. Having both copies of the gene — which is a rare occurrence — increases the risk by 10 to 15 times.
However, the medical research community has not given much attention to the effect that a family history of dementia has on a person's cognition throughout their lives.
So, a team of scientists set out to explore this aspect by examining the link between having a first-degree relative with Alzheimer's and cognitive performance in almost 60,000 individuals aged between 18 and 85.
Joshua Talboom, Ph.D., a postdoctoral fellow at the Translational Genomics Research Institute in Arizona, is the lead author of the new study, which appears in the journal eLife.
Alzheimer's-related cognitive risk
Talboom and colleagues asked 59,571 participants to complete an online questionnaire that inquired about their sex, educational level, age, language, country, overall health, and family history of Alzheimer's.
The researchers also tested the participants' cognitive abilities. They asked the participants to memorize 12 word pairs and then retested their memory of the new pairs by asking them to fill in the matching word that was missing.
The study found that people who had a close relative with Alzheimer's — such as a parent or a sibling — matched 2.5 fewer word pairs than people who did not have a family history of the disease.
Living with diabetes also seemed to influence the results, amplifying the cognitive impairment in people who had a relative with Alzheimer's. "It is not surprising that diabetes exacerbates the effects of [family history] on cognition," write the authors, "since diabetes has been linked to worse cognitive deficits in [Alzheimer's disease.]"
Finally, the researchers collected blood and saliva from a subgroup of 742 study participants who had a family history of Alzheimer's and tested the samples for the APOE4 gene.
"The APOE genotype is an important genetic factor that influences memory, and we found that those with the variation performed worse on the memory test than those without the variation," reports Talboom.
However, the research also revealed that a higher educational level could offset the increased risk of premature cognitive decline among people with a family history of Alzheimer's. This led the authors to draw empowering conclusions.
"Our study supports the importance of living a healthy lifestyle, properly treating diseases, such as diabetes, and building learning and memory reserve through education to reduce the cognitive decline associated with Alzheimer's disease risk factors."
"Identifying factors that reduce or eliminate the effect of a family history of Alzheimer's disease is particularly crucial since there is currently no cure or effective disease-slowing treatments," adds the study's lead author.