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Does having a gene for Alzheimer’s mean you will get it?

In general, having a gene for any disorder puts a person at increased risk for developing that disorder but does not guarantee that that person will definitely develop it.  The same is true for Alzheimer’s disease.  There are genes that carry increased risk for developing Alzheimer’s disease but testing positive for that disease does not mean Alzheimer’s disease is definitely in your future.

Genes are what control how every cell works, whether it is the color of your hair, your height or your predispositions for getting a certain illness.

The most common gene that has been identified for late-onset Alzheimer’s disease, which begins after age 65, is called apolipprotein E (APOE). This is detected by a simple blood type.  There are three types of APOE: APOE 2 which reduces the risk of developing Alzheimer’s as compared to the general population, APOE 3 which does not alter the risk of developing Alzheimer’s, and APOE 4 which increases the risk of developing Alzheimer’s (often a more severe type).

We all inherit two copies of the gene, one paternal and one maternal.  So having one copy of APOE 4 (for example, one APOE 3 and one APOE 4) does not confer as much risk as having two copies of APOE 4. One copy of APOE 4 doubles or triples the risk of developing Alzheimer’s over the general population which two copies increases the risk by 8 to 12-fold.

However, not everyone with one or two copies of APOE 4 will develop Alzheimer’s disease. Further, some people will develop Alzheimer’s even if they don’t have any copies of APOE 4.

There are other risk factors for developing Alzheimer’s disease, such as head trauma, lifestyle and environmental. There are other late-onset genes, such as ABCA7 and CLU, but more studies need to be done before they become clinically relevant.

There have also been three genes identified that predispose people for young-onset Alzheimer’s, in which symptoms appear between the ages of 30 and 60. People who harbor these genes (Amyloid precursor protein or APP, Presenilin1 or PSEN1, and Presenilin 2 or PSEN2) have a very high likelihood of developing Alzheimer’s before age 65.

The current prevailing theory behind developing Alzheimer’s disease is an accumulation of too much amyloid in the brain which then forms clumps called amyloid plaques. The plaques often lead to the death of nerve cells which causes the symptoms of Alzheimer’s disease. The genes associated with young-onset Alzheimer’s code for the excess production of amyloid.

There are many more genes to be identified, and identification of risk genes can help in earlier detection of Alzheimer’s, earlier implementation of therapy, and, ultimately, better patient outcomes.

While testing for these genes can be helpful, they can also have negative impacts on patient lives.  Detecting an APOE4 gene in someone who will never develop the disease could alter their life decisions, and quality of their life because of heightened fear of the unknown. Further, it may impact the ability to get a job or life insurance.

A good approach is to screen for early signs of change.  BeCare Neuro Link can help you detect changes in cognition, motor and speech earlier and direct you in when it is time to get an evaluation.

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