Scientists know that people who carry one copy of the APOE e4 gene have a greater risk of developing mild cognitive impairment (MCI) or dementia due to Alzheimer’s disease. That risk is higher for people with two copies of the APOE e4 gene.
A new study shows people with two copies of the APOE e4 gene have a 30 to 55 percent estimated risk of developing MCI or dementia due to Alzheimer’s by age 85. The study also reveals a 20-25 percent estimated risk for people with one copy of the APOE e4 gene.
What about people who have no copies of the APOE e4 gene? The study’s authors report these individuals with the most common APOE genotype of e3/e3 have a 10-15 percent estimated risk of developing MCI or Alzheimer’s by age 85. This reinforces that other genetic and environmental risk factors are involved in the development of MCI and dementia due to Alzheimer’s. Some of those risk factors include:
The study’s new estimated risk results are slightly lower than risk estimates previously reported. This is due to the fact that the new study analyzed data from more than 17,000 people who were followed over many years.
Leading Researchers Collaborate
“Except for very rare forms of the disease, at this time there’s no genetic test available that can 100 percent predict if someone will develop Alzheimer’s disease during his or her lifetime,” said Beth McCarty Wood, MS, LCGC, Senior Genetic Counselor at the University of Pennsylvania and one of the study’s authors. “But, we do know the APOE gene has been widely studied and verified as a genetic risk factor for Alzheimer’s disease. And, we also know individuals who have two copies of the APOE e4 have a higher genetic risk for Alzheimer’s disease. For this research study, the issue came down to: What exactly is that genetic risk?”
A look at the researchers involved in the new study demonstrates the widespread interest in obtaining updated genetic risk estimates. The study is a collaboration of leading Alzheimer’s research centers throughout the U.S. and Europe. It will be published by PLOS Medicine and available to all online at no cost.
The researchers involved in the new study of the APOE e4 gene determined estimated genetic risk by analyzing data collected from four observational cohort studies: National Alzheimer’s Coordinating Center, The Rotterdam Study, Framingham Heart Study and Sacramento Area Latino Study on Aging. These four studies followed people over time, starting before age 60 and through age 85. This longitudinal approach included data collected on the more than 17,000 adults stretching over decades.
Estimating Genetic Risk
How was this risk measured in the past? Previously, researchers took a snapshot of data collected at one point in time. They had to rely on statistical modeling – a mathematical formula that approximates reality to make predictions – to estimate genetic risk for MCI and dementia due to Alzheimer’s disease.
“This new study, which improves our understanding of APOE’s role as a genetic risk factor, was only possible because so many individuals were motivated to participate in research,” McCarty Wood said. “It shows the impact that motivated individuals can have to help advance science, and that kind of motivation is what will help find a prevention for Alzheimer’s disease.”