What Is Late-Onset Alzheimer's Disease?

Most individuals with Alzheimer’s disease are diagnosed after the age of 65, which is classified as late-onset. It is generally accepted that the cause of late-onset Alzheimer’s disease isn’t known, although there are a variety of risk factors that are thought to be involved, like lifestyle behaviors, environmental factors, and genetics. There is not one specific gene that causes late-onset Alzheimer’s, but there are genes that can increase one’s risk of developing the disease.

Genes link to late-onset Alzheimer’s

The most common gene associated with late-onset Alzheimer’s disease is called apolipoprotein E (APOE), on chromosome 19.1 Having this gene does not mean that you most definitely will develop Alzheimer’s; it merely means your risk is increased. There are three forms of the APOE gene2:

  • APOE2 is rare and might have a protective effect against Alzheimer’s disease, which means it might develop later in life than it would have otherwise
  • APOE3 is the most common form of the APOE gene and it doesn’t have much to do with the development of Alzheimer’s disease
  • APOE4 increases the risk of developing Alzheimer’s disease and often means a slightly earlier onset as well; you can have zero, one, or two APOE4 genes and the more you have, the higher your risk for developing Alzheimer’s disease

Although the APOE4 gene affects one’s risk of developing Alzheimer’s disease, there are other factors that can interact with the genetic component, so it’s hard to tease out one specific cause.

There are a variety of other genes that may be involved with the development of late-onset Alzheimer’s disease, but these are still being studied.

Genetic testing is not typically recommended, especially for late-onset Alzheimer’s disease, because the tests can be tricky to interpret, and there are other ways of diagnosing late-onset Alzheimer’s disease. If you do decide to get genetic testing, talk with your doctor or with a genetic counselor about the possible impact that might have on life insurance, long-term care policies, and things like disability insurance.1

Considering genetic testing for late-onset Alzheimer's

Having the APOE4 gene doesn’t affect treatment or disease course at all, it’s just a genetic marker for risk. If you have been tested already and have been found to have APOE4, talk with your doctor about possibly participating in a research study or clinical trial, to assist researchers in finding out more about this gene, brain changes associated with the gene, and treatment effectiveness.

Many people with late-onset Alzheimer’s disease may not even know they have the APOE4 gene, since there are other ways of diagnosing the disease and late-onset is the norm for diagnosis. If you have late-onset Alzheimer’s disease and have a family history of Alzheimer’s, you might want to talk with your doctor about the possibility of a genetic risk component, and whether genetic testing would be useful or not. It wouldn’t change treatment or the disease itself, so it’s worth thinking about and discussing it with your treatment team. At its heart, it’s important to realize that the APOE4 gene is merely another risk factor, not a potential cause.

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Written by: Jaime Rochelle Herndon | Last reviewed: June 2019