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Genetic screening,
the systematic search for persons with a particular genotype in
a defined population, serves as an important adjunct of modern
preventive medicine. Such screening has the potential to lessen
the devastating impact of genetic disease. 
The usual purpose is to identify persons whose genotype places
them or their offspring at risk for a genetic disease. A more
recent and perhaps more controversial use is the identification
of persons who have genetically determined susceptibilities to
specific environmental agents (e.g., to the fumes produced in
a given industrial process).
There
are two classes of genetic screening:
- Presymptomatic
Screening
- The detection of persons whose own health is threatened.
- Carrier
Screening - The detection of those healthy individuals whose
genes threaten the health of their future offspring.
One kind
of presymptomatic screening, newborn screening, focuses primarily
on the early diagnosis of some of the inborn genetic errors. Requirements
for this type of genetic screening are that it be economical,
logistically possible, and reliable for the diagnosis of disease
early enough to initiate a therapy that will prevent permanent
and irreversible damage, even death. These requirements have been
met for a variety of inborn errors whose presence can be detected
from a drop of the neonate's blood. The blood sample is applied
to a filter paper, which when dried can be sent to a central laboratory
equipped to monitor a large number of specimens rapidly and economically
for these diseases. Since these are screening tests, with a certain
number of false-positive results, all newborns with a positive
test should then be checked by the most definitive diagnostic
test available.
Problems
with this form of screening involve informing parents about the
tests, preferably before the baby is born, and assuring that adequate
genetic counselling and help in treatment is available if the
baby is affected. One controversial issue is whether these tests
should be mandated by government. Those few parents who refuse
to permit mandatory screening and whose offspring later suffer
damage that could have been prevented might be considered guilty
of child abuse.
Another form
of presymptomatic screening involves the screening of selected
populations for genetic susceptibility to environmental hazards.
The screening of persons whose genotype makes them especially
vulnerable to environmental hazards raises ethical and legal issues
of disclosure, which may affect personal and social welfare. Consider,
for example, factory workers who are screened for a genetic defect
in the production of the enzyme alpha-1-antitrypsin. Affected
workers are susceptible to a form of chronic lung disease (emphysema)
when exposed to certain atmospheric pollutants produced in their
workplace. Public disclosure of this genetic defect might conceivably
result in affected employees losing their jobs, their health insurance,
or both, thus relieving the employer of the responsibility of
cleaning up the workers' environment. On the other hand, personal
knowledge of genetic susceptibility to a serious lung or heart
disease might induce an individual to make beneficial changes
in his life-style and could be an important form of preventive
medicine. Another form of genetic screening seeks to detect those
healthy individuals whose genes pose a threat to the health of
future offspring.
On a societal
level, this consists of screening subpopulations of people in
whom a mutant, disease-producing gene is common. Such populations
include Jews of eastern European origin, in whom the carrier state
for Tay-Sachs
disease is common; those whose origins can be traced to
the lands bordering the Mediterranean Sea, in whom the gene for
thalassemia,
or Cooley's anemia, is common; and blacks of African descent,
in whom the gene for sickle-cell
anemia is prevalent. The effectiveness of these programs
has been vastly increased by the availability in all three of
the intrauterine diagnosis of an affected fetus. Screening of
the susceptible population for Tay-Sachs has significantly lowered
the number of newborns affected by this lethal disease in the
United States.
Gina
Kolata
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