IF people want a good example of the potential hazards of genetic testing, they need look no further than a new test linked to Alzheimer鈥檚 disease, say two American researchers. The test results are so ambiguous, they warn, that people could be unfairly discriminated against if prospective employers or insurance companies got hold of them.
In 1993, researchers led by Alan Roses at Duke University in North Carolina found that people who carry two copies of one variant of a gene for the blood protein apolipoprotein E (ApoE), called &egr;4, are about eight times as likely to develop the disease as people who do not have this variant.
Roses describes ApoE as 鈥渢he first susceptibility gene for a common disease鈥�. Eventually, it will give people an idea of their risk of developing Alzheimer鈥檚 鈥� in the same way that doctors use cholesterol levels to predict people鈥檚 risk of heart disease. But, before such a test is used routinely, scientists must devise treatments for Alzheimer鈥檚 or ways to prevent it.
Advertisement
This leaves the question of how to use the test today. 鈥淚t鈥檚 not clear that the result means anything,鈥� says Richard Mayeux of Columbia University, New York. Many people develop the disease even though they do not carry the &egr;4 variant, and many who have two copies of &egr;4 never develop the disease, he says.
This means that the test cannot be used to tell people definitively whether they will develop Alzheimer鈥檚, say Mayeux and his colleague Nicole Schupf in the American Journal of Public Health. They also doubt the value of the test for diagnosing Alzheimer鈥檚 in people who consult a doctor because their memory is failing. They argue that the test should only be used as a research tool.
Michael Boss, director of research at Athena Diagnostics, which holds the licence to make the test, says the company does not recommend using the test in people who do not have symptoms of Alzheimer鈥檚. But it is useful for diagnosing the disease in confused, elderly people, he says.
Roses, who is now a consultant with Athena, agrees. The probability that any elderly person with symptoms of dementia has Alzheimer鈥檚 disease is 0.67. Rough estimates suggest that if such a person has two copies of &egr;4, the probability rises to 0.94. Evidence is also emerging that Alzheimer鈥檚 drugs work best in patients with specific combinations of ApoE variants, says Roses.
The ambiguities surrounding ApoE testing have prompted the US National Institute on Aging to organise a conference to try to forge consensus among scientists and doctors about how the test should be used. Roses predicts that after the conference, Athena will restrict testing to elderly patients with Alzheimer鈥檚-like symptoms.
For Mayeux and Schupf, the problems with the ApoE test exemplify the potential dangers of genetic testing: dangers that will increase as more tests are devised. They argue that people should have control over which tests their DNA is subjected to and who sees the results. Employers and insurers should have only limited access to such results, say the two researchers 鈥� not just for the sake of the person tested, but also for their relatives.