Alzheimer's disease, the most common form of dementia, is a growing global health problem. It is seen in all populations and its prevalence is rising. About five million Americans currently have this devastating disease, and the number is expected to increase to more than 13 million by 2050. It's also a terrifying prospect for any person who has ever watched a loved one suffer from the disease, or who fears that every lapse in memory is sign of Alzheimer's.
As a genetic counselor specializing in assessing patients' risk for Alzheimer's disease , I am frequently asked about the role of genetic testing. My answer is that at this time, genetic testing for Alzheimer's disease has many limitations and is beneficial for only a limited number of people. I strongly encourage anyone seeking genetic testing to talk with a genetic counselor and consider all the pros and cons.
Arguments in favor of testing include planning for the future, participating and investing in research, lowering personal risk factors associated with the disease, and the potential peace of mind of learning you have no known genetic risk factors.
But there are many reasons to be cautious about genetic testing for Alzheimer's disease, and it's important to think carefully about how you will react to and use the information the testing provides.
Genes Are an Indication, Not a Guarantee for Most
Genetics plays a considerable role in our risk for Alzheimer's disease in both early and late onset types, but for most, testing for these genes may not provide the clarity one is seeking.
We know of two different types of genes that contribute to the disease.
- The most common genetic risk factor for Alzheimer's disease is a gene known as apolipoprotein E or APOE. One form of APOE -- APOE e4 -- is estimated to contribute to about 40 percent of Alzheimer's disease cases. Although it is present in about 25 percent of the population, not everyone who inherits an APOE e4 develops Alzheimer's disease, and not everyone who develops Alzheimer's disease has an APOE e4. This makes it difficult to counsel people who are tested for this gene.
- Only approximately 2 percent of people with Alzheimer's disease have a mutation in a gene known to actually cause Alzheimer's disease. Most often, these genes are seen in families with early onset disease when more than one generation is affected; for example, a grandmother with the disease and a mother with early onset. There is a direct correlation between the change in the gene and the development of Alzheimer's disease. Someone found to have a mutation in one of these genes will most likely develop Alzheimer's disease if that person lives long enough, depending on the specific gene.
Lifestyle Influence
In addition, there are susceptibility genes that don't cause Alzheimer's disease directly, but contribute to a person's risk. Lifestyle or health factor risks such as obesity, hypertension or diabetes can influence the chance of developing Alzheimer's disease due to having a mutation in one or more of these genes. These genes can be found in early or late-onset disease, and in those with or without a family history.
Treatment Options Are Limited
We still do not know for certain how Alzheimer's disease develops. No new drugs to treat Alzheimer's disease have been approved for use in more than a decade. In addition, it has been more than 20 years since the most significant genetic risk factors were identified. Considerable effort is ongoing to unravel the genetic underpinnings of this disease.
Recently, scientists have discovered they can use proteins found in the fluid that surrounds the brain and spine to predict with fairly good accuracy which individuals with mild cognitive impairment will go on to develop Alzheimer's disease. This may prove useful in future treatment studies.
Some feel that treatment needs to occur prior to the onset of dementia to be effective. However, this proves difficult without knowing who will ultimately go on to develop Alzheimer's disease. Once effective treatment options are discovered, genetic screening measures could potentially be used to intervene before dementia progresses.
Cause for Increased Anxiety
Genetic testing for Alzheimer's disease weighs heavily on the mind. Many people want information that will either put their minds at ease or help them take action. But because the genetic information available for most people concerned about Alzheimer's disease is not that clear cut, it may cause anxiety rather than clarity. Once that genetic information is known, it can't be unknown and will dangle in front of a person and that person's family well into the future.
Due to the emotional burden and limited health benefits, genetic testing for late onset Alzheimer's disease will often not be useful until scientists discover a way to prevent or delay the disorder. In addition, clinicians are concerned about the potential for patient discrimination.
Risk of Insurance Discrimination
Results from genetic testing for Alzheimer's disease could potentially put a person at a disadvantage when purchasing long-term care, life, or disability insurance coverage because the Genetic Information Nondiscrimination Act (GINA) does not protect against discrimination for these types of insurance policies. It only affords protection against health insurance and employment discrimination.
See a Genetic Counselor
As a genetic counselor, I want what is best for each and every person, and for society at large. It's my job to guide patients and their families to decide what would most benefit or influence their future health decisions. Alzheimer's disease is a condition that is devastating for both individuals and their families, and for society and our health care system. I help guide patients through decisions about what tests to consider, help determine what information they need and how best to use information to empower them. If you are interested in learning more, find a genetic counselor in your area by using NSGC's “Find a Genetic Counselor” tool.
Susan Hahn , MS, CGC, is an Alzheimer's disease expert with the National Society of Genetic Counselors, and assistant director of communications, compliance, and ethics at the University of Miami Miller School of Medicine.
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