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Most genetic medicine begins with a genetic
test.
The test itself is nothing more than a mouth swab or blood
draw that is sent to the appropriate lab. In about a week
you receive a detailed report of analysis and recommendations
specific to each patient. The tests cost in the neighborhood
of $200 to $1000 each, including the cost of the report.
The test analyzes specific sections of the patient's DNA
as well as RNA and metabolites found in the sample. The patient's
profile is correlated to the latest research that interprets
the implications in terms of specific diseases or, in the
case of pharmacogenomics, drug metabolism.
Currently gene tests can detect susceptibility to more than
1,100 diseases. More are added to the list every day. The
tests are conducted in more than 570 laboratories in the United
States, and that number is growing as well. (This data is
provided by www.Genetests.org,
a non-profit database, and an excellent source covering progress
in gene testing throughout the world.)
Genetic Testing for Diagnosis
Gene testing can lead to more informed and more accurate
diagnosis and treatment.
When a patient comes to you with symptoms, you know that
immediate and certain diagnosis is often not possible. You
gather the evidence, make an educated guess, and prescribe
measures to either effect a cure or give you more evidence.
Gene testing is a source of a new level of evidence based
on inherited tendencies and susceptibilities unique to each
patient. Test results help you flag the most likely possibilities,
reduce the guess work, and begin appropriate treatment.
Gene testing, although powerful, is only an additional source
of data for each patient. It rarely gives a definitive result
by itself. It is data to be weighed with other evidence, such
as physical and diagnostic examinations, biopsies, and more
conventional tests.
Examples of Genetic Tests for Disease
Muscular Dystrophy: A test for the deletion in the dystrophin
gene, the cause of Duchene's muscular dystrophy, can be used
to identify women who are carriers of this condition.
Hemochromatosis: A patient with hereditary hemochromatosis
can be spared cirrhosis by the early initiation of phlebotomy
treatments. Gene tests check for a mutation in the HFE gene
causing Iron overload.
Breast Cancer: Mutations in the BRCA1 and BRCA2 genes are
associated with an increased risk of breast and ovarian cancer.
Mutations in either of these genes confer a lifetime risk
of breast cancer of between 60 to 85% and ovarian cancer between
15-40%.
Genetic Testing for Prediction
A patient may ask you about an inherited disease that runs
in the family. Gene tests can confirm if the mutation associated
with the disease is carried by that family member.
Genetic counselors are trained to evaluate inheritance patterns
within families and across generations. They can help a patient
decide when a gene test is recommended and then interpret
the test results for risk of the disease in the context of
the full family history.
An example is hereditary colon cancer. A thorough family
history is done first, identifying cancer of all types and
family members with cancer, age of onset, and history of adenomas.
If molecular genetic testing verifies the diagnosis of one
family member, other relatives should be encouraged to get
tested.
1) Familial adenomatous polyposis presents as multiple
colonic polyps in the distal colon. It occurs at an early
age and patients may have a genetic mutation within the
APC germline. Patients need to be screened with flexible
sigmoidoscopy by the age of 10 to 12 years of age.
2) Hereditary nonpolyposis colorectal cancer is the most
common form of hereditary colorectal cancer. The Amsterdam
Criteria (one first degree relative, two successive generations
affected, and three relatives affected with colon cancer
of which one is before the age of 50) are used to determine
increased risk. Molecular screening is now feasible and
desirable for this cancer. It is caused by a germ line mutation
in the MLH1 and MLH2 genes. Patients need full colonoscopy
between 20 to 25 years of age annually
Genetic Testing for Better Drug Therapy
Pharmacogenomics is a type of genetic test, but requires
it 's own page, here. |
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