APOE is a gene that provides instruction for the body to make a protein called apolipoprotein E. Everyone has the APOE gene because we all need this protein which combines with lipids (fats) to carry cholesterol and fat-soluble vitamins through the bloodstream. The protein helps transport cholesterol to areas where it’s needed and out of areas it isn’t needed. Cholesterol helps the body build cells, and make hormones and vitamin D. This is important because it supports and repairs the central nervous system.
Genes can have different forms; these are called alleles. For example, genes related to eye color have more than one allele such as brown, blue, green, etc. Parents pass on genes to their children, but siblings may have different eye colors because one received an allele for blue eyes while the other received an allele for brown eyes. Scientists have discovered that APOE is polymorphic, meaning it has more than one allele (form). APOE has three major alleles: APOE-ε2, APOE-ε3, and APOE-ε4. Each person has two copies of the APOE gene, one from each parent.
In conversations about Alzheimer’s disease risk, APOE is often thrown into the mix, but why? In 1993, Dr. Judes Poirier led a study that helped push the topic of APOE into conversations about Alzheimer’s disease. Dr. Poirier led his team to research how the combination of alleles for the APOE gene may influence a person’s risk for Alzheimer’s disease. The research team used blood tests from 91 Alzheimer’s patients and 74 people without Alzheimer’s to determine their alleles for the APOE gene. Results showed that Alzheimer’s patients often had a copy of the APOE-ε4 allele. This allele did not show up as often in the individuals without Alzheimer’s. This led to the conclusion that when a person has an APOE-ε4 allele they may be at a higher risk for Alzheimer’s disease than someone without an APOE-ε4 allele.
Continued research since 1993 shows APOE does not tell the whole story about Alzheimer’s disease. It is certainly associated with risk for the disease. But it does not determine if a person will develop Alzheimer’s because not everyone with an APOE-ε4 allele is diagnosed with the disease. Scientists are continuing to explore genetic-related questions about Alzheimer’s to increase their understanding of the involvement of genes.