The apolipoprotein E gene (abbreviated as APOE) provides instructions for making a protein which itself is known as apolipoprotein E (abbreviated as ApoE). There are at least three different variants (alleles) of the APOE gene. The major alleles are called ε2, ε3, and ε4. The most common allele is ε3, which is found in more than half of the general population. It is considered the “neutral” variant. APOE ε2 is correlated with a reduced risk of dementia, though it may increase the risk of developing a rare disorder known as hyperlipoproteinemia type III. APOE ε4 is known for conferring a much greater risk of several types of dementia, including Alzheimer’s disease, and it has been linked to other diseases as well.