Basic
Information
FAQs
Glossary
Acronyms
Links
Genetics 101
Publications
Meetings Calendar
Media Guide
About
the Project
What is it?
Goals
Landmark Papers
Sequence Databases
Timeline
History
Ethical Issues
Benefits
Genetics 101
FAQs
Medicine
&
the New Genetics
Home
Gene
Testing
Gene
Therapy
Pharmacogenomics
Disease Information
Genetic Counseling
Ethical,
Legal, Social Issues
Home
Privacy
Legislation
Gene
Testing
Gene
Therapy
Patenting
Forensics
Genetically
Modified Food
Behavioral
Genetics
Minorities,
Race, Genetics
Human Migration
Education
Teachers
Students
Careers
Webcasts
Images
Videos
Chromosome
Poster
Presentations
Genetics 101
Genética
Websites en Español
Research
Home
Sequence Databases
Landmark Papers
Insights
Publications
Chromosome Poster
Primer Molecular Genetics
List of All Publications
Search This Site
Contact Us
Privacy Statement
Site Stats and Credits
Site Map
|
Quick Links to questions and answers on this page:
What is gene testing? How does it work?
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 for
such gene products as enzymes and other proteins and for microscopic examination
of stained or fluorescent chromosomes. Genetic tests are used for several reasons,
including:
- carrier screening, which involves identifying unaffected individuals
who carry one copy of a gene for a disease that requires two copies
for the disease to be expressed
- preimplantation genetic diagnosis (see the side bar, Screening Embryos
for Disease)
- prenatal diagnostic testing
- newborn screening
- presymptomatic testing for predicting adult-onset disorders such as
Huntington's disease
- presymptomatic testing for estimating the risk of developing adult-onset
cancers and Alzheimer's disease
- confirmational diagnosis of a symptomatic individual
- forensic/identity testing
|
|
Screening
Embryos for Disease |
Preimplantation
genetic diagnosis (PGD) is a test that screens for genetic
flaws among embryos used in in vitro fertilization. With PGD,
DNA samples from embryos created in-vitro by the combination
of a mother's egg and a father's sperm are analyzed for gene
abnormalities that can cause disorders. Fertility specialists
can use the results of this analysis to select only mutation-free
embryos for implantation into the mother's uterus.
Before
PGD, couples at higher risks for conceiving a child with a
particular disorder would have to initiate the pregnancy and
then undergo chorionic villus sampling in the first trimester
or amniocentesis in the second trimester to test the fetus
for the presence of disease. If the fetus tested positive
for the disorder, the couple would be faced with the dilemma
of whether or not to terminate the pregnancy. With PGD, couples
are much more likely to have healthy babies, Although PGD
has been practiced for years, only a few specialized centers
worldwide offer this procedure.
|
|
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.
What are some of the pros and cons of
gene testing?
Gene testing already has dramatically improved lives. Some tests are used
to clarify 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 preventable. Aggressive
monitoring for and removal of colon growths in those inheriting a gene for familial
adenomatous polyposis, for example, has saved many lives. On the horizon is
a gene test that will provide doctors with a simple diagnostic test for a common
iron-storage disease, transforming it from a usually fatal condition to a treatable
one.
Commercialized gene tests for adult-onset disorders such as Alzheimer's disease
and some cancers are the subject of most of the debate over gene testing. These
tests are targeted to healthy (presymptomatic) people who are identified as
being at high risk because of a strong family medical history for the disorder.
The tests give only a probability for developing the disorder. One of the most
serious limitations of these susceptibility tests is the difficulty in interpreting
a positive result because some people who carry a disease-associated mutation
never develop the disease. Scientists believe that these mutations may work
together with other, unknown mutations or with environmental factors to cause
disease.
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.
Many in the medical establishment feel that uncertainties surrounding test
interpretation, the current lack of available medical options for these diseases,
the tests' potential for provoking anxiety, and risks for discrimination and
social stigmatization could outweigh the benefits of testing.
For more information, see:
For what diseases are gene tests
available?
Currently, more than 1000 genetic tests are available from testing laboratories.
Some gene tests available in the past few years from clinical genetics laboratories
appear below. Test names and a description of the diseases or symptoms are
in parentheses. Susceptibility tests, noted by an asterisk, provide only an
estimated
risk for developing the disorder. Contact GeneTests
for comprehensive information on test availability and genetic testing facilities.
Some Currently Available DNA-Based Gene Tests
- Alpha-1-antitrypsin deficiency (AAT; emphysema and
liver disease)
- Amyotrophic lateral sclerosis (ALS; Lou Gehrig's Disease;
progressive motor function loss leading to paralysis and death)
- Alzheimer's disease* (APOE; late-onset variety of senile
dementia)
- Ataxia telangiectasia (AT; progressive brain disorder
resulting in loss of muscle control and cancers)
- Gaucher disease (GD; enlarged liver and spleen, bone
degeneration)
- Inherited breast and ovarian cancer* (BRCA 1 and 2;
early-onset tumors of breasts and ovaries)
- Hereditary nonpolyposis colon cancer* (CA; early-onset
tumors of colon and sometimes other organs)
-
Central Core Disease (CCD; mild to severe
muscle weakness)
- Charcot-Marie-Tooth (CMT; loss of feeling in ends of
limbs)
- Congenital adrenal hyperplasia (CAH; hormone deficiency;
ambiguous genitalia and male pseudohermaphroditism)
- Cystic fibrosis (CF; disease of lung and pancreas resulting
in thick mucous accumulations and chronic infections)
- Duchenne muscular dystrophy/Becker muscular dystrophy (DMD;
severe to mild muscle wasting, deterioration, weakness)
- Dystonia (DYT; muscle rigidity, repetitive twisting
movements)
-
Emanuel Syndrome (severe mental retardation, abnormal development of the
head, heart and kidney problems)
- Fanconi anemia, group C (FA; anemia, leukemia, skeletal
deformities)
- Factor V-Leiden (FVL; blood-clotting disorder)
- Fragile X syndrome (FRAX; leading cause of inherited
mental retardation)
-
Galactosemia (GALT; metabolic disorder
affects ability to metabolize galactose)
- Hemophilia A and B (HEMA and HEMB; bleeding disorders)
- Hereditary Hemochromatosis (HFE; excess iron storage
disorder)
- Huntington's disease (HD; usually midlife onset; progressive,
lethal, degenerative neurological disease)
-
Marfan Syndrome (FBN1; connective tissue
disorder; tissues of ligaments, blood vessel walls, cartilage, heart valves
and
other structures abnormally
weak)
-
Mucopolysaccharidosis (MPS; deficiency
of enzymes needed to break down long chain sugars
called glycosaminoglycans;
corneal clouding, joint stiffness, heart disease,
mental retardation)
- Myotonic dystrophy (MD; progressive muscle weakness;
most common form of adult muscular dystrophy)
- Neurofibromatosis type 1 (NF1; multiple benign nervous
system tumors that can be disfiguring; cancers)
- Phenylketonuria (PKU; progressive mental retardation
due to missing enzyme; correctable by diet)
-
Polycystic Kidney Disease (PKD1, PKD2; cysts
in the kidneys and other organs)
- Adult Polycystic Kidney Disease (APKD; kidney failure
and liver disease)
- Prader Willi/Angelman syndromes (PW/A; decreased motor
skills, cognitive impairment, early death)
- Sickle cell disease (SS; blood cell disorder; chronic
pain and infections)
- Spinocerebellar ataxia, type 1 (SCA1; involuntary muscle
movements, reflex disorders, explosive speech)
- Spinal muscular atrophy (SMA; severe, usually lethal
progressive muscle-wasting disorder in children)
-
Tay-Sachs Disease (TS; fatal neurological disease of
early childhood; seizures, paralysis)
- Thalassemias (THAL; anemias - reduced red blood cell
levels)
-
Timothy Syndrome (CACNA1C; characterized
by severe cardiac arrhythmia, webbing of the fingers and toes called syndactyly,
autism)
Is genetic testing regulated?
Currently in the United States, no regulations are in place for evaluating
the accuracy and reliability of genetic testing. Most genetic tests developed
by laboratories are categorized as services, which the Food and Drug Administration
(FDA) does not regulate. Only a few states have established some regulatory
guidelines. This lack of government oversight is particularly troublesome in
light of the fact that a handful of companies have started marketing test kits
directly to the public. Some of these companies make dubious claims about how
the kits not only test for disease but also serve as tools for customizing medicine,
vitamins, and foods to each individual's genetic makeup. Another fear is that
individuals who purchase such kits will not seek out genetic counseling to help
them interpret results and make the best possible decisions regarding their
personal welfare. More information on these questionable test kits is available
from Dubious
Genetic Testing, an online report provided by Quackwatch.
For a brief overview of the current regulatory environment for genetic testing,
see the Oversight
of Genetic Testing, a Genetics Brief from the National Conference of State
Legislatures.
Does insurance cover genetic testing?
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. Insured persons would need to decide whether they would want
the insurance company to have this information. States have a patchwork of genetic-information
nondiscrimination laws, none of them comprehensive. Existing state laws differ
in coverage, protections afforded, and enforcement schemes. The National Conference
of State Legislatures provides a listing
of current legislation regarding genetic information and health insurance. The
recent marketing of genetic test kits directly to consumers, may lead to an
increase in demand for insurance coverage. See the Genetics
and Health Insurance (PDF) policy brief from the National Conference of
State Legislatures for more information.
Testing Recommendations
More Information
Educational Modules
- GeneTests Web Site
- Understanding
Gene Testing - A tutorial that illustrates what genes are, explains
how mutations occur and are identified within genes, and discusses the
benefits and limitations of gene testing for cancer and other disorders.
From the National Cancer Institute.
- Genetic
Testing of Newborn Infants - An activity for considering government
policies to guide a program for genetic screening of newborns. From
the Genetic Science Learning Center.
- Understanding
Gene Testing - A basic introduction to genes and genetic testing
from the U.S. Department of Health and Human Services.
Ethical, Legal, and Social Issues
Related Policy and Legislation
Other Resources
Send the url of this page to a friend
|