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Gene screening involves analysing a person's DNA,
usually obtained from a blood sample.
Sometimes a single mutation can cause a person to have
a disease. However, most genetic diseases are
caused by a combination of genetic and environmental
factors, which is why genetic information is only half
the story.
Today there are several different types of genetic
tests including:
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Carrier identification or screening is a genetic test
taken by people who don't have a particular disease, but might
carry the gene for it. Couples considering having children,
whose families have a history of a recessive genetic disorder,
often take the test.
Pre-implantation genetic diagnosis is a genetic test
carried out on embryos that have been fertilised in the lab
using routine IVF procedures. Embryos are tested for the presence
of a specific gene, and only embryos without the gene are
implanted into the mother's womb. This is not legal in all
countries.
Prenatal diagnosis is the genetic testing of a foetus.
This might be done where there is a risk of having a baby
with genes associated with mental or physical deterioration.
Newborn screening is frequently done as a preventive
health measure. This type of screening has clear benefits
to the newborn in cases where treatment is available.
Testing for late-onset disorders which may occur later
in life - including adult diseases such as cancer and heart
disease. These diseases are complex and have both genetic
and environmental causes.
Tests for late onset disorders can have different functions,
depending on the disease:
a) They can predict unequivocally that a person will
get a particular disease in the future. This is true
for some diseases caused by single genes, such as
Huntington's disease.
b) They can be susceptibility tests and can
estimate the likelihood that someone will develop
a particular disease in the future. This would include
tests for Alzheimer's disease and some cancers.
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c) They can confirm diagnosis in a patient with symptoms.
A final type of genetic testing is:
Forensic / Identity testing (DNA fingerprinting).
This type of test is often used to identify genetic information
and discover if it belongs to a specific individual. It can
be used in solving crimes and paternity cases.
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