Apo E genotype:  Apolipoprotein E has three different forms or alleles, E2, E3, and E4.  Depending upon the particular configuration in an individual, it can be associated with increased risk of coronary artery disease, heart attack, stroke or Alzheimer’s disease.  People with one copy of the e4 allele have an increased risk of developing type 2 Alzheimer disease, a familial late-onset form of the disease.  People who inherit two copies of the e4 allele have a still higher chance of developing type 2 Alzheimer disease. However, the relationship between APOE e4 and Alzheimer disease is not a simple direct one. APOE e4 is clearly neither necessary nor sufficient by itself to cause Alzheimer disease. It may modify the preclinical progression of the disease and accelerate the clinical onset of it in people who are already predisposed to develop Alzheimer disease.

Apolipoprotein E is also associated with several cardiovascular disorders. Most people with familial hypercholesterolemia, a condition that causes very high levels of cholesterol and an increased risk of heart attacks and strokes, have two copies of the e2 allele. This allele seems to be one of several genetic factors that play a part in this disorder. Another version of apolipoprotein E, the e4 allele, is a risk factor for coronary artery disease.