If a genetic test tells a patient that he or she is susceptible to lung cancer, will that person quit smoking?
Dr.
Eric Topol, director of the Scripps Translational Science Institute in
La Jolla, Calif., is looking for the answer to this and other similar
questions.
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For now, little is understood about how patients adjust
their lifestyle after they're tested--and if those changes matter. Until
Topol's research sheds light on this, consumers are left with anecdotes
and the Internet, which can lead them to any one of several companies
peddling bogus genetic tests or to misleading information about what
testing can achieve.
Before undergoing genetic tests of any kind,
however, it's crucial that patients fully understand their promise--and
their limitations.
The Options
Genetic testing has been offered since the 1970s, but scientific
knowledge about links between genes and certain diseases has increased
significantly in recent years.
It's now possible to perform tests
on more than 1,500 genes, according to Dr. Michael S. Watson, executive
director of the American College of Medical Genetics. While this is
only a fraction of the 20,000 to 25,000 genes contained in the human
genome, the number of tested genes has doubled in the past decade.
The
number of available tests has grown quickly as well. There are now
4,000 to 5,000 tests for heritable conditions (many of which are rare
diseases), and separate tests for certain types of cancer and leukemia.
Companies like 23andMe and Knome, based in Palto Alto, Calif. and
Cambridge, Mass., respectively, also offer genomic testing, which
gathers large swaths of information--think ancestry, inherited traits
and health conditions--from a person.
The growth of online,
direct-to-consumer companies has led to a transformation of the
industry, according to Global Industry Analysts, Inc., a market-research
company that released a comprehensive report on the subject in October.
By analyzing sales figures for genetic tests in North America, the
company determined that the market grew from $488 million in 2003 to
$1.1 billion in 2008.
The size of the market means that consumers
can obtain genetic and genomic tests from numerous sources, but aside
from a requirement that tests be done in a federally certified lab, no
regulatory body evaluates the claims of one test over another.
For
example, a patient worried about breast cancer could purchase a test
from the online company DNAdirect for a base price of $620. The customer
is then sent a kit, which he or she returns with a blood or cheek-swab
sample. Though the company offers pre-test education and access to
genetic counselors, the experience is very different from testing in a
clinical setting, where patients are closely monitored by a doctor and a
geneticist who specializes in the disease.
What You Learn
Unfortunately, there's a strong chance that some consumers aren't
learning anything useful about their health when they pursue testing.
Only
certain tests can conclusively tell a patient if he or she possesses a
gene directly related to a disease. In the cancer field, these include
genetic testing for stomach, colon, ovary and breast cancers. Many
genetic--and most genomic--tests tell patients their probability of
developing a disease at some point in the future, and not all tests are
comparable.
"Most of the 'genomic' health-risk tests being sold
directly to consumers have not been proven to be valid in the same way
we study new drugs, for example," says Dr. Kenneth Offit, director of
the Clinical Genetics Service at the Memorial Sloan-Kettering Cancer
Center in New York.
For this reason, he believes that patients
should pursue genetic testing under the supervision of a trained
geneticist--and only if the patient plans to act on the result or if a
test might resolve unanswered questions about family history and
personal health.
Similarly, Dr. Watson urges consumers to seek
out tests that have been thoroughly vetted for accuracy. The company
offering the test should be able to tell a patient two key facts: the
frequency of positive results and the number of people who test positive
but never get the disease.
"These are very general concepts,"
says Watson, "but if someone can't tell you the answer to those, they're
probably not ready for prime time.