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Gene tests (also called DNA-based tests), the newest and most sophisticated of the techniques
used to test for genetic disorders, involve direct examination of the DNA molecule itself. Other
genetic tests include biochemical tests that look at the protein or enzyme made from the DNA
instead. We can also do Chromosome tests which look for abnormalities in entire chromosomes
(example: extra, missing, defonned) Genetic tests are used for several reasons, including:
carrier screening: determining if a person has I
copy of a "bad" gene but does not have a disease;
Can pass the disease to a child.
preimplantation genetic diagnosis (see the side bar,
Screening Embryos for Disease)
prenatal diagnostic testing: testing a fetus before it
is born to see if it has any diseases.
pre symptomatic testing: testing an adult without
any symptoms for a disease that may start later in
life like Huntigton's Disease, Cancer and
confirmational testing: testing an individual to a
disease that they are already displaying symptoms
of. Confirms a diagnosis
forensic/identity testing: solving crimes, paternity
(father) testing
In gene tests, scientists scan a patient's DNA sample for mutated sequences. A DNA sample can
be obtained from any tissue, including blood. For some types of gene tests, researchers design
short pieces of DNA called probes, whose sequences are complementary to the mutated
sequences. These probes will seek their complement among the three billion base pairs of an
individual's genome. If the mutated sequence is present in the patient's genome, the probe will
bind to it and flag the mutation. Another type of DNA testing involves comparing the sequence
of DNA bases in a patient's gene to a normal version of the gene. Cost of testing can range from
hundreds to thousands of dollars, depending on the sizes of the genes and the numbers of
mutations tested.
Gene testing already has dramatically improved lives. Some tests are used to check a diagnosis
and direct a physician toward appropriate treatments, while others allow families to avoid having
children with devastating diseases or identify people at high risk for conditions that may be
Some companies, however, are manufacturing "at home" tests which have attracted some
controversy. Alzheimer's disease is a disease that happens late in life in which people begin to
forget their friends and family, can't take care of themselves and do not remember from one
minute to the next. These at home tests claim to be able to tell if a person will develop this
disease based on a gene mutation. The problem is that many people with the mutation do not get
the disease. Scientists believe that Alzheimer's is caused by a combination of factors. These
companies may be misleading individuals in order to make some more money.
A limitation of all medical testing is the possibility for laboratory errors. These might be due to
sample misidentification, contamination of the chemicals used for testing, or other factors.
In most cases, an individual will have to contact his or her insurance provider to see if genetic
tests, which cost between $200 and $3000, are covered. Usually insurance companies do not
cover genetic tests, those that do will have access to the results. Patients must decide if they want
their insurance company to have this information. One fear is that if the insurance company finds
out that you have the gene for a disease they will cancel your insurance policy and you will be
without medical insurance. Others are concerned that insurance companies will begin to require
genetic testing BEFORE agreeing to insure a patient. They may choose to exclude people who
are at risk for serious "expensive" diseases.
emphysema and liver disease
Lou Gehrig's Disease: progressive motor function loss leading to paralysis and death
Alzheimer's disease*
Ataxia telangiectasia: progressive brain disorder resulting in loss of muscle control and cancers
Inherited breast and ovarian cancer*
Hereditary colon cancer*
Cystic fibrosis: disease of lung and pancreas resulting in thick mucous accumulations and chronic
Duchenne muscular dystrophy: severe to mild muscle wasting, deterioration, weakness
Hemophilia A and B (HEMA and HEMB; bleeding disorders)
Huntington's disease (HD; usually midlife onset; progressive, lethal, degenerative neurological disease)
Sickle cell disease (SS; blood cell disorder; chronic pain and infections)
Thalassemias (THAL; anemias - reduced red biood cell levels)
Tay-Sachs Disease (TS; fatal neurological disease of early childhood; seizures, paralysis) [3/99]