Are You at Risk?

Research has shown that certain genes can increase or even decrease your risk of acquiring Alzheimer's disease, though in the vast majority of cases, genes do not currently predict who will or won't develop the disease.

When it comes to understanding how our genes affect our lives, it is important to distinguish between two very broad categories: risk genes, which increase our likelihood of developing a disease or condition, and deterministic genes, which guarantee a person will develop a specific disorder.

In the case of Alzheimer's disease, less than 5% of people are known to carry an identified deterministic gene, which results in what is called familial Alzheimer's. This doesn't mean that there are no other deterministic genes or gene combinations at the root of this disease - it simply points out our current understanding of genetics and Alzheimer's. However, what we know today is that certain risk genes can predispose people to developing the disorder, which makes it even more important for people with these genes to manage the risk factors within their control as best they can.

Risk genes in Alzheimer's

Scientists have so far identified one Alzheimer risk gene called apolipoprotein E-e4 (APOE-e4), though it is believed there may be as many as a dozen yet to be discovered.

There are several forms of the APOE gene, of which APOE-e4, APOE-e3, and APOE-e2 are the most common. This gene is important in the production of one of the cholesterol-carrying proteins in our blood.

In basic terms, we all inherit some form of APOE from each of our parents. The following chart shows what impact each inherited form is believed to have on our risk of developing Alzheimer's.

APOE Gene Form	Apparent effects on Alzheimer's risk
e2 (least common)	May reduce risk
e3 (most common)	Neither reduce nor increase risk
e4 (a little more common than e2)	1 gene = 3x risk 2 genes = 10x risk

Adapted from Mayo Clinic website, Alzheimer's pages (www.mayoclinic.com/health/alzheimers-genes/AZ00047)

Exactly how APOE-e4 raises risk is yet unknown. Keep in mind that someone with two copies of the APOE-e4 gene may never develop Alzheimer's, while someone with two copies of the APOE-e3 gene may end up with the disease. That is the inexact nature of dealing with risk genes.

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