Alzheimer's and APOE, The Alzheimer's Library

The APOE4 allele is a risk factor for Alzheimer's. Everyone has a double set of genes, one from each parent. ApoE4 is one variant of the apoE gene, the others being the benign apoE2 and apoE3 genes. If a person's pair of apoE genes includes one apoE4, they have three times the normal risk of developing Alzheimer's disease, but if they carry two apoE4 genes the risk increases to ten times. However, people with no apoE4 genes can still get Alzheimer's disease and people with two apoE4 genes will not necessarily get the disease. Although the genes are there from birth, they can't cause Alzheimer's disease on their own. The brain has to reach a certain critical age for the disease to occur. Researchers are actively looking for evidence of other quite normal genes that predispose one to Alzheimer's disease, but it seems unlikely that these still to be discovered genes will be as important a risk as the apoE4 one.