Initially recognized for its role in cardiovascular disease, the APOE gene also plays a role in Alzheimer's disease (AD). The protein produced by this gene transports fats (lipids) and cholesterol in the body. However, APOE has several common variants (or "alleles") whose effects vary. The e4 allele, in particular, is the most prevalent genetic factor associated with late-onset Alzheimer's disease and causes an increased risk and/or earlier onset. Its impact varies depending on whether the mutation appears on one or both chromosomes, and on a person's race and ethnicity (i.e., risk is not increased uniformly across all ethnic groups). Scientists are still trying to find out the reasons why. Some clues may lie with ApoE4 interactions with the immune system, where it influences inflammation and a type of cellular damage known as oxidation. Also, whereas ApoE helps break down amyloid-beta protein located in and around neurons, the ApoE4 version is less effective at doing so.