The Human APOE Gene Has Three Common Alleles, APOE*e2, APOE*e3

Short Answer

The human APOE gene has three common alleles, APOE*e2, APOE*e3, and APOE*e4, that gives rise, respectively, to the common alleles apoE2, apoE3 and apoE4 at the protein level. Which, if any, of the following statements is true?
a) The *e4 allele confers a high risk of Alzheimer disease and people with two *e4 alleles have twice the disease risk of people with one *e4 allele.
b) The *e3 allele is a protective factor, conferring reduced risk of Alzheimer disease while the *e2 allele has a disease risk that is intermediate between those of *e3 and *e4.
c) The *e4 allele is considered the ancestral APOE allele because although the chimp and gorilla also have three apoE proteins the apoE4 protein is the most frequent allele.
d) The *e4 allele has reached a high frequency because Alzheimer disease has such a late age at onset that reproductive success rates are not diminished.