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 When one of these tests indicates a "health risk," it doesn't
necessarily mean someone will develop the health problem, and
conversely, "reassuring" results may be unreliable, they caution in
the medical journal BMJ.
"We had several people come to our clinic who appeared to have a
genetic test result that put them at very high risk of developing a
condition, for example, cancer," said senior author Anneke Lucassen
of the University of Southampton.
"When we checked their result with a more detailed technique, we
found that it wasn't there," she told Reuters Health by email. "We
then realized that colleagues across the country were coming across
similar examples."
Although most manufacturers warn against making healthcare decisions
based on the results of direct-to-consumer (DTC) tests, some people
do, Lucassen added.
"I think people often expect any genetic test to be clear cut," she
said. "The marketing around DTC tests suggests people will 'find
out' about themselves and that results are accurate."
Genetic tests often promise insights into ancestry, disease risks,
personality or athletic ability, the authors write, but interpreting
genetic information is complicated. Importantly, most
direct-to-consumer tests don't sequence the complete set of a
person's genes, or genome, and instead focus on specific variants in
genes, which can lead to falsely positive results. Even tests that
do sequence the full genome often identify variants that may not
mean anything clinically, they point out.
Another limitation of these tests is that the prediction of a
disease is often incorrect when there's no family history of the
illness. The authors describe a patient whose test, purchased
online, indicated he had a gene variant that could increase his risk
for Parkinson's disease. He was upset, especially because he didn't
have a family history. In reality, many people carry genes that
could increase their risk but have other genes that protect them
from that risk, the authors explain.
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False positives are common, too, the authors note. They tell of a
patient who used an ancestry test and sent her raw genetic
information to an online interpretation service, which told her she
had a variant that could increase her risk of breast and ovarian
cancer. Although she didn't have a family history, she met with a
breast surgeon and booked a date for surgery. She also met with a
genetics scientist, who found she didn't really have the variant.
Her operation was canceled, but she still felt nervous about the
possible risk.
"Some of the examples we came across were worrying because people
were asking about risk-reducing surgery," Lucassen said. "They
thought they were at very high risk, yet such surgery would have
been inappropriate."
And reassuring results may be false negatives, the authors warn. One
patient in her 40s with breast cancer and a family history of
ovarian cancer took a test and was happy it showed no BRCA variants.
Her doctor explained, however, that most tests only screen for a few
variants. The patient then took an approved test, which found a
variant that indicated a high lifetime cancer risk. Overall,
patients with a family history of a disease should see a
professional, the authors say.
"Even in our clinical practice, when someone has a personal or
family history of inherited heart disease, it can be challenging to
definitively attribute a genetic variant to disease in an individual
or a family," said Robin Hylind, a genetic counselor at Boston
Children's Hospital in Massachusetts. Hylind, who wasn't involved
with this article, tests for heart arrhythmias.
"DTC tests may fulfill an individual's curiosity about ancestry,"
she told Reuters Health by email. "However, they are not powerful
enough to replace standard care at the present time, particularly in
individuals with increased genetic disease risk."
SOURCE: http://bit.ly/2pS15k3 BMJ, online October 16, 2019.
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