A well-known gene is the APOE gene. This gene is the most important predictor of the risk of contracting Alzheimer’s disease.
The APOE gene comes in 3 variants: APOEe2, APOEe3 and APOEe4. You always carry 2 variants. The e4 variant confers an increased risk of Alzheimer’s disease. People who carry one e4 variant (for example APOEe4/APOEe3), have twice the risk of developing Alzheimer’s disease. People who carry both e4 variants (APOEe4/APOEe4) have a nine times increased risk of Alzheimer’s disease.
Of course, nine times a small risk still equals a small risk, especially when you are still young (‘young’ referring to 50 to 70 years). However, research shows that e4 carriers have life expectancies that are 6 years shorter on average.
Interestingly, it seems that people who carry the e4 variant(s) have strong immune systems. They can ward off infections better. This would have been a big advantage in prehistoric times, when infectious diseases were rampant.
However, in this day and age, with improved hygiene and increased survival rates into older age, the tables are somewhat turned, and the e4 variant seems to be a disadvantage because the strong immune response can accelerate the aging process and increase your risk of Alzheimer’s disease.
The APOE gene is also involved in cholesterol and fat metabolism, and e4 carriers tend to accumulate more fat and cholesterol in their blood, raising the risk of cardiovascular disease, another aging-related disease.
About 65% of people of European ethnicity carry the e3 variant, and 25% the e4 variant.
Author: Kris Verburgh, MD