ApoE: Abbreviation for apolipoprotein E, a gene that codes for a protein component of lipoproteins (complexes of fat + protein) that are normal constituents of blood plasma -- namely, chylomicrons, HDL (high density lipoprotein), LDL (low density lipoprotein), and VLDL (very low density lipoprotein).

Studies of families in which Alzheimer disease tends to develop at later ages have shown that the disease is unusually frequent in persons with a particular variant form of ApoE termed ApoE4 present in only a minority of the general population. However, family studies suggest that the ApoE gene locus is neither necessary nor sufficient to cause Alzheimer disease and may simply modify the preclinical progression, and therefore the age of onset, in people otherwise predisposed to develop Alzheimer disease.

The ApoE gene is now known to be on chromosome 19.