When does it make sense to test a person for the risk of an incurable illness?
When does it make sense to test a person for the risk of an incurable illness? Andrei Tchernov/iStockphoto.com
Counselors have long cautioned about the downsides of genetic testing for Alzheimer's disease.
For one thing, the current genetic tests for late-onset Alzheimer's — the type that develops after age 60 and is responsible for more than 90 percent of cases — only indicate a probability of getting the disease. It's not definitive. And consumers' ability to buy life insurance or long-term care coverage could be jeopardized by the results.
But there's another reason some doctors and counselors have discouraged testing: Concern that if people learned that they were at higher risk for developing a serious, incurable neurological disease, it might prove profoundly distressing.
Those worries have proved unfounded so far. An ongoing series of studies has found that people manage just fine when told their results, thank you very much, even if the results indicate that their risk of developing Alzheimer's is higher than average.
Many factors likely influence the development of Alzheimer's disease, including genes, lifestyle and the environment. To date, one gene in particular has been identified as providing a strong indication of risk for the disease: the apolipoprotein E (APOE) gene on the 19th chromosome. There are three versions of the gene—dubbed E2, E3 or E4-and everyone inherits one version, or allele, from each parent. People with one or two E4 alleles have an up to 15 times greater risk of developing late-onset Alzheimer's disease.
The studies, called Risk Evaluation and Education for Alzheimer's Disease (REVEAL), got started in 2000 to test how asymptomatic people reacted to learning their genetic risk, based on the APOE gene. The first study examined 162 adult children of people with Alzheimer's. Subsequent studies tested other variables, adding more African-Americans to the subject pool, for example, or disclosing the results by phone instead of in person.
At the time of the original study, "there was a resounding consensus that no way should you be sharing APOE information with people," says Dr. Robert Green, a lecturer in genetics at Brigham and Women's Hospital in Boston and co-author of papers about the work.
But the study, which followed people for a year after they learned their results, found that people who knew their APOE genetic status were no more anxious or depressed about their chances of developing Alzheimer's than those who didn't. This was true even for subjects who had the E4 genetic variant that conferred the highest risk.
Despite limitations of the test, people in the study said there were many reasons they wanted to be tested, including arranging their personal affairs, making decisions about long-term care insurance and preparing their family for the possibility that they might become sick.
Interest in this type of testing is only going to continue to grow, says Green. "Whether we recommend tests or not, the world is changing and people are starting to want to know about their own DNA," he says.