ApoE, or apolipoprotein E, is a protein with a wide variety of possible functions. The most well-studied is its role in transporting certain types of lipids (fats) throughout the body, including in the brain. The ApoE gene comes in three different forms – ApoE2, ApoE3, and ApoE4.
The exact way in which ApoE affects Alzheimer’s disease risk is not entirely clear. Many possible mechanisms have been studied and debated. However, what is clear is that one specific form – known as ApoE4 – significantly increases an individual’s risk for Alzheimer’s disease, especially when the individual has two copies of the ApoE4 form.
We all have two copies (two “alleles”) of the ApoE gene, receiving one from each parent. The ApoE4 variant is, for most people, the most important genetic factor for Alzheimer’s disease. The chart below shows approximate lifetime risk for Alzheimer’s disease based on ApoE genotype. The chart demonstrates the dramatic difference in Alzheimer’s disease risk for those who have one copy of ApoE4 (2/4 or 3/4) or especially two copies of ApoE4 (4/4), compared to the most common genotype, 3/3 (two copies of ApoE3).
*Adapted from Genin et al., Molec Psych (2011) 16:903. Risk figures shown are the average of Rochester and PAQUID incidence rates. For simplicity we show the average of male and female rates at age 85. We rounded the figures did not show the 95% confidence intervals. These figures relate to ApoE-based genetic risk independently. There are other risk factors (genetic or non-genetic) that may modify the risk in an individual. Please see original publication for exact figures and more complete details.
Most people believe that there’s nothing that can be done to reduce the risk of Alzheimer’s disease. Genetics, however, (including ApoE) are not the only determinants. There are many other factors, including diet, lifestyle, and various metabolic factors. These factors appear to play an equally important role as genetics. Many of these non-genetic factors are modifiable, meaning that you can do something about them.
Learning your APOE genotype provides you with information for one component of your risk for developing Alzheimer’s disease so that you can make informed decisions about how aggressively you want to take action towards reducing your risk in other ways.