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Published on: November 3, 2018
by Women’s Brain Health Initiative:
Once on the frontiers of science, genetic testing has in recent years moved into the mainstream. According to industry estimates, the number of people who have had their genes analyzed with direct-to-consumer (DTC) genetic genealogy tests more than doubled during 2017 and currently exceeds 12 million.
THE RESULTS OF A GENETIC TEST, ALSO KNOWN AS A DNA TEST, CAN CONFIRM OR RULE OUT A SUSPECTED GENETIC CONDITION OR CAN HELP DETERMINE AN INDIVIDUAL’S CHANCE OF DEVELOPING OR PASSING ON A GENETIC DISORDER.
Over 1,000 genetic tests are currently in use, and more are being developed. There are also a variety of health-related genetic testing services available through the Internet – some of which promise to gauge an individual’s susceptibility to cancer, diabetes or obesity, while others claim that an analysis of one’s genes can be used to develop specialized training and nutrition programs to build a leaner, stronger body.
Then there is the matter of genetic testing to measure the risk of developing dementia – a controversial subject that has generated discussion amongst both the medical community and individuals living with the disease. A recent survey conducted by Healthline Media of nearly 400 active caregivers in the U.S. found that 34% of caregivers indicated that caring for a loved one with Alzheimer’s disease has prompted them to undergo genetic testing for the disease.
THE REPORT ALSO FOUND A DEMOGRAPHIC DIVIDE, WITH MORE MILLENNIALS (49%) SEEKING TESTING THAN OLDER GENERATIONS (GEN XERS 36%, BOOMERS 17%).
At present, the relationship between genetics and dementia is not fully understood. As the Alzheimer’s Society observes, while genes play a role in the development of many forms of dementia, the extent of this role varies between dementia types. A person with a parent or sibling living with dementia has on average a higher risk of developing the same condition him or herself, although other factors such as lifestyle can also play a part.
There are two broad categories of genetic testing for dementia: predictive genetic testing and susceptibility testing. Predictive (or determinative) genetic testing is used to determine whether an individual has inherited a particular and rare genetic mutation from a relative who has been diagnosed with dementia. If the individual possesses the same mutation, he or she will most likely develop Alzheimer’s disease or frontotemporal dementia (FTP) at some point in his or her life (presuming that he or she lives long enough). In contrast, susceptibility testing aims to identify the presence of so-called “risk genes” that alter one’s risk of developing Alzheimer’s disease, as opposed to inevitability causing it.
In the vast majority of people, any genetic risk of developing Alzheimer’s disease is linked not to rare mutations but to variations in a large number of susceptibility genes that they have inherited. The most common risk gene is called Apolipoprotein E (APOE), which is the only susceptibility gene for Alzheimer’s disease that has been widely confirmed to date (although several others are currently under investigation). Risk genes such as APOE have a more subtle influence on an individual’s chances of developing Alzheimer’s disease than the genes that are used in tests for the inherited forms of dementia. Advisory committees across the globe have therefore recommended against this type of genetic testing since individuals who have an APOE gene may never develop Alzheimer’s disease and individuals with no APOE genes can still develop Alzheimer’s disease.
In Canada, there is a substantial amount of screening that patients must go through in order to be eligible for genetic testing, explained Dr. Robin Hsiung, Associate Professor in the Neurology Division of University of British Columbia’s Department of Medicine.
PATIENTS NEED TO UNDERSTAND THE DIFFERENCES BETWEEN TESTING FOR A SPECIFIC GENETIC MUTATION OR RISK FACTORS.
“If there’s a known family history [of dementia] and we can see a pattern, then they are potentially eligible,” Dr. Hsiung said in an interview with Mind Over Matter®. Dr. Hsiung noted that he does not recommend genetic testing for the presence of elevated risk factors. This type of genetic testing does not provide conclusive results and can be challenging emotionally. For those who wish to discover if they have a particular mutation, Dr. Hsiung carefully educates them on the pros and cons of undergoing genetic testing.
The knowledge that an individual will at some point in his or her life develop dementia may affect one’s life choices, such as his or her decision about having children. Individuals who exhibit symptoms of dementia often wish to understand as much as possible about the cause of their disease, and to share this knowledge with their relatives to allow them to make decisions about learning their own and any future children’s genetic status.
Dr. Hsiung noted that he also considers the potential impact on the individual’s mental health.
“We need the patients to be psychologically stable because we don’t want them to become depressed. Some people who have disposition to anxiety or depression may be burdened by the news and will carry this heavy load and make them have a much worse outlook on life.”
In a 2017 article published in the Journal of Neurology, the authors discuss the critical role of health care professionals in the ever-growing genetic testing market. As the authors observe, “the increasing complexity of the genetic landscape … presents a significant resource and physician training challenge.” It is incumbent on practitioners to ensure that individuals are adequately informed, counselled, and supported when making their decision.
Experts in the industry have expressed caution about firms that advertise genetic testing services through the Internet. The U.K. Alzheimer’s Society published a position paper warning of the implications for individuals who pay offshore companies to test saliva for the APOE gene, noting that the APOE test has “poor predictive value”— in other words, a positive result does not guarantee that the patient will actually develop Alzheimer’s disease. The paper strongly recommends
THAT ANYONE THINKING ABOUT UNDERGOING GENETIC TESTING SHOULD FIRST CONSULT A HEALTH CARE PROFESSIONAL (SUCH AS A DOCTOR OR A CERTIFIED GENETIC COUNSELLOR) – SOMETHING THAT IS NOT OFFERED WITH THE COMMERCIALLY-AVAILABLE GENETIC TESTING.
There have also been concerns about discrimination based on an individual’s genetic characteristics, particularly in the context of the insurance industry. In Canada, parliament passed Bill S-210 in 2017, which prohibits the mandatory disclosure of genetic test results as a condition of providing goods or services (namely, health and life insurance). Canada was the last member of the G7 to pass its own genetic discrimination law. The U.S. had passed similar legislation in 2008.
Dr. Michael Gordon, a leading geriatrician at Baycrest Health Sciences in Toronto, is skeptical of the benefits of genetic testing.
“If someone asks me about it, I say ‘what would you do about it [if you had a positive result]?’” he observes. “Can we do anything to change your genetic makeup? No we can’t.”
Dr. Gordon notes that, in the absence of a cure for dementia, perhaps the best advice is to live a healthy lifestyle. Indeed, as Mind Over Matter® regularly reports, there is much evidence that a healthy diet coupled with exercise, staying mentally and socially engaged, managing stress and getting a good night’s sleep can help you maintain a healthy brain, amongst other benefits.
The decision about whether to be tested is a personal and complex one. A geneticist or genetic counsellor can help by providing detailed information about the advantages and disadvantages of a particular test, as well as the social and emotional aspects of genetic testing.
A direct-to-consumer (DTC) genetic test is any DNA test for a medical or non-medical trait that provides interpretation or communication of test results directly to the consumer, rather than through a health care professional. The Internet currently enables unprecedented ease of access for DTC genetic testing, with saliva collection kits posted directly to consumer homes from anywhere in the world. There are several potential harms and consequences of poorly regulated Internet-based DTC testing, which have been well documented. If you are considering any kind of genetic testing, it is important that you speak with your doctor or a genetic counsellor beforehand.
As the Alzheimer’s Society observes, there is a lot to think about before undergoing a genetic test for Alzheimer’s disease, including:
Motivations: Why do you want to take the test? Will it change life decisions such as financial planning or having children?
Informed consent: Do you fully understand what the test results will and will not reveal? Are you aware of the possible benefits and risks of taking the test?
Confidentiality: Will your test results be kept private? Who will you share the results with?
Risks: Will the test results affect your family relationships, and/or your mental or emotional wellbeing?
Source: MIND OVER MATTER V7
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