What is genetic screening? Genetic screening is the testing of cells to check for certain kinds of genes, or for potentially damaging changes to those genes. It may be defined as a systematic search for persons with a particular genotype in a defined population. Genetic screening serves as an important adjunct of modern preventive medicine. The usual approach is to identify persons whose genotype places them or their offspring at risk for genetic diseases. Such screening has the potential to lessen the devastating impact of genetic diseases. Genetic screening may be undertaken for research purposes unrelated to disease or the improvement of health. The National Academy of Sciences recommends that genetic screening is an appropriate form of medical care only when certain conditions are met. These include: (1) evidence of substantial public benefit and acceptance, (2) the benefits outweigh the costs; (3) appropriate public education can be carried out; (4) informed consent is feasible; (5) the means are available to evaluate the effectiveness and success of each step in the process (Blank, 1982). Some screening is aimed at the general population, while others are targeted at selective high-risk population; screening can also be conducted at various stages of life.
There are three principal types of genetic screening. (1) Newborn screening identifies serious genetic disease at birth, permitting prompt treatment to prevent mental and physical retardation. (2) Fetal screening and prenatal diagnosis identify genetic disease in the fetus permitting selective termination of pregnancy and the opportunity to have children free of defects detectable in uterus. (3) Carrier screening identifies individuals heterozygous for a gene for a serious recessive disease who may be at risk for having affected offspring.
(1) Newborn screening:
Newborn screening has focused on the detection of inborn errors of metabolism, which is an inherited biochemical defect, classically a deficiency of an intracellular enzyme. Phenylketonuria (PKU) is the first condition for which newborn screening was widely accepted. PKU may be due to phenylalanine hydroxylase deficiency or due to the deficiency of dihydropteridine reductase. High concentration of phenylaanine in the blood of a newborn may have multiple genetic and developmental causes. In general, before a newborn is discharged from the hospital, a sample of its blood is spotted onto filter paper and mailed to a regional laboratory equipped to monitor a large number of specimens rapidly and economically for these diseases. Newborn screening for PKU is a major triumph of genetic screening. Other inborn metabolic errors frequently screened for at birth are galactosemia, branch-chain ketonuria, homocystinuria, and hypothyroidism. Like PKU, these inborn errors may cause severe mental retardation or death which may be preventable by prompt treatment.
(2) Fetal screening and prenatal diagnosis:
Prenatal diagnosis of genetic disorders represents one of the most important practical advances in medical genetics in recent years. In most cases, the fetal screening is applied for a maternal age of 35 or greater because of the increased risk for an offspring with a chromosomal anormaly. The most common of these is Down's syndrome. The screening is usually done by amniocentesis or chorionic villus sampling to obtain cells from the fetus at the 14 to 20 weeks of pregnancy, which are cultured 12 to 18 days and examined for the extra chromosome that causes Down's syndrome. Fetal screening in cases of advanced maternal age has been widely adopted.
(3) Carrier screening:
Carrier screening is the identification
of heterozygotes for an autosomal recessive or X-linked recessive
disease. This form of screening seeks to detect those healthy
individuals whose genes pose a threat to the health of future
offspring. This screening is more controversial than others.
Several considerations should be done for carrier screening.
(a) The disease in question should be serious. (b) The test to
be performed on the population at risk should be simple, relatively
inexpensive, and sensitive. (c) The individual identified as positive
should have some options. (d) The costs avoided should exceed
the costs incurred. It has been demonstrated that many genetic
diseases such as Tray-Sachs, sickle cell anemia, cystic fibrosis,
and thalassemia are found more frequently in particular groups
than the population as a whole. 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. Tay-Sachs
disease is the first disorder for which large-scale carrier screening
was done in the USA. It is serious disease, being characterized
by developmental delay, blindness, seizures, and paralyses; it
is usually fatal by age 3, and no specific treatment is available.
This disease occurs predominantly in the Ashkenazi Jewish population.
Screening of the susceptible population for Tay-Sachs has significantly
decreased the number of newborns affected by this lethal disease
in USA.
The ultimate goal of genetic screening programs is the prevention of genetic disease. Certainly, only few peoples are callous enough to ignore the human benefits of preventing the birth of a grossly abnormal being. However, it is controversial way to prevent the birth of affected persons through use of prenatal diagnosis followed by therapeutic abortion of fetuses diagnosed as genetically defective. Therefore, this part discusses the public policy debates from three points, (1) whether genetic screening should be legally mandated or voluntary, (2) costs and benefits of genetic screening, and (3) whether genetic screening should be a public or private matter.
(1) Should genetic screening be legally mandated or voluntary?
One of the recurring issues in all aspects of genetic screening is if any such screening should to be mandated for reasons of public health and concern for future generations, or remain a private responsibility. Two types of mandatory screening have been established. The first is aimed at detection of affected individuals so that treatment can be offered; the best example is PKU screening. The second type is designed to identify carriers of recessive deleterious genes and inform them of the risk of bearing children with genetic diseases if their spouse is also so identified. The most obvious example of this second type is mandatory screening for sickle cell anemia. Mandatory screening of the first type is much less controversial than compulsory screening for a carrier.
In addition to the issues related to the mechanics of screening, broader ethical and legal dilemmas are reflected in any attempts to intervene in the procreation process. There is much disagreement over both the necessity and right of society to intervene in procreation. Because many couples choose to terminate a pregnancy when the fetus is found to be carrying a severe genetic disorder, prenatal diagnosis has become entangled in the ethical debate that surrounds elective abortion. A more related question is what right does society have to make abortion compulsory in the case of a Down's syndrome fetus? The individual rights and moral discretion of the parents in the case of the Down's fetus may be directly in conflict with the utilitarian demands of society. Lappe (1972) contends that society has no right to intervene in childbearing decisions except in very rare cases. Procreation should be the choice of the parents, because it is they that bear the burden of deleterious genes, not society. Some people believe that an affluent society should be able to absorb the costs. Parents should have the right to bear defective children, even if the social costs of this freedom are high. Because the carrier screening contains implications for influencing reproductive decisions, it is effective only if the carrier refrains from having children or make use of prenatal diagnosis followed by selective abortion. Certainly, each of these steps is controversial, and ethically as well as legally questionable. There appear to be few benefits and many costs to mandatory screening of carriers.
Sonneborn (1973) contends that our society has agreed to improve the quality of life through social and environmental means, and the improvement should be extended to include genetic means as well. Sonneborn holds that people desire not to have defective children and contends that each child has the right to be born free of such defects to the degree this can be achieved. Arguments made for mandatory screening are higher compliance rates, lower unit cost, timely execution, and facilitation of record-keeping of incidence and outcome. However, voluntary screening is more in keeping with the American tradition. Screening conducted with minimal risk to those being screened, which results in treatment, is more easily defended than that for untreatable metabolic disorders. Screening for recessive gene carriers, while offering more informed decisions about marriage and reproduction, at this time should remain voluntary. It recognizes the fact that not all people will benefit equally. For example, those who do not condone termination of pregnancy may not view prenatal diagnosis as a benefit.
Whereas in most states newborn screening is legally mandated, carrier screening is generally voluntary. A National Academy of Sciences Committee has condemned mandatory carrier screening.
(2) Costs and benefits of genetic screening
Despite disagreement over the role of genetic screening and the form it should take, there is much agreement on the need for some action. The facts indicate that one out of every 15 babies is born with a genetic defect of varying severity. Over 15 million Americans in 1982 suffered from one or more of the 2500 known genetic abnormalities. English (1975) estimates that each of the 4000 mongoloids born annually requires about $250,000 worth of care in a lifetime. Peter (1975) states that the cost of caring for a Tay-Sachs baby is estimated to be between $30,000 to $40,000 per year.
The costs of a particular screening procedure may be difficult to estimate and vary as to number screened. According to Guthrie's estimation (1973), to identify one case of PKU costs at a maximum about $40,000 to $50,000. If the PKU does not be identify, the child must be institutionalized for the rest of his life at a cost of at least $250,000. Furthermore, the maximum cost could be reduced somewhat through the use of automated equipment, if regional screening program could be established.
Benefits of screening are much more
difficult to measure; for example, reducing the pain and suffering
of the affected child and the family is a benefit, however, which
is not easily introduced into a cost/benefit equation. The benefits
of genetic screening to society could be measured by (a) increased
productivity of the treated person or in some cases a replacement
person, (b) decreased medical costs, (c) increases in individual
well-being. Conley and Milunsky (1975) compute the value of benefits
for four different genetic disorders by using a model for estimating
social benefits based on two possibilities, (1) abort the defective
fetus and replace with a subsequent child assumed to be normal
(replacement), (2) abort the defective fetus but have no subsequent
child (non-replacement). The higher benefits for the replacement
situation is shown in Table 1. In the non-replacement situation,
social benefits are measured entirely by savings in medical, educational,
and other related costs to society.
Table 1. Benefits in prevention of selected conditions
(3) Should genetic screening be a public or private matter
A quite separate issue is whether
genetic screening should be a public or private
matter. There are five principles about the ethical issues related to genetic screening noted by the President's Commission for the study of Ethical Problems in Medicine and Biomedical and Behavioral Research: confidentiality, autonomy, knowledge, well-being, and equity. These precepts are concerned primarily with protecting the individual from undesirable effects of genetic screening. Some people may perceive genetic screening as an unwarranted invasion of privacy that can stigmatize and emotionally traumatize those who learn that they are carriers of genetic defects, and has the potential of being used to dictate who may or may not reproduce.
Who besides the patient and the physician should have access to the results? Should the physician be free to reveal the test to others? The screening of persons whose genotype is defective raises ethical and legal issues of disclosure which may affect personal and social welfare. Public disclosure of the genetic defect might conceivably result in affected employees losing their jobs, their health insurance, or both. On the other hand, personal knowledge of genetic susceptibility to a serious disease might induce an individual to make beneficial changes in his life-style. Knowing their propensity for a disease, patients may try to buy insurance that insurers will be reluctant to sell; employers may shy away from workers who will become prematurely disabled. This suitation may encourage genetic discrimination. Care must be taken to prevent carriers from suffering a loss of self-esteem; in addition, the identity of carriers should not become public knowledge, as such disclosure may affect employability and social relations. Patients will seek to have testing done privately and results keep secret.
Recently, a study of genetic screening
for cystic fibrosis was conducted with a large-scale population;
the researchers found a surprising fact that more than 125,000
people were informed the screening, only about 1 % volunteered
to take the test. They conclude that people were not interested
in screening for C.F. because they don't understand what the test
means, but if they understood what the tests meant, they would
be more likely to say yes (Coghlan, 1996). Because the public
lacks the background in biology and genetics, genetic screening
is easily misunderstood. Therefore, education must be central
to any efforts at screening, especially when dealing with high-risk
groups.
Genetic screening is both beneficial and protentially harmful, depending on how it is applied. Because of the knowledge of gene, human beings could recognize some relationships between diseases and genes, therefore, genetic screening might be a good method to detect earily the inborn diseases. For example Huntington's disease does not usually start to have an effect until a person is 35 to 40 years old, and offsprings of a person with this disease have a 50 % chance of developing the disease. Before the development of genetic screening, there was no way to know if the person was affected until disease onset.
For newborn screening, from my personal opinion, I agree that the newborn screening should be mandated, because we could offer special care and adequate treatments. So, if parents refuse to permit mandatory newborn screening and whose child later suffers damage that could be prevented, the parents might be considered guilty of child abuse. The family and parents could get much benefits as they can be informed early of the real health condition of the children. I do not agree the results of genetic screening to be public. The physician should not have the right to reveal the test results to public unless the screened person agree to do so. The results should be keep secret.
For fetal screening and prenatal diagnosis, I do not think it should be mandatory, because it may directly encourage people to choose an abortion to terminate a pregnancy when they knew previously of the affected suitation. Would a woman terminate a pregnancy if the fetus was found to have a defective gene? If not, why would such a person need to be tested for carrier status for gene disorder? Unless we could cure the fetus in uterus, it can be screened after birth. The fetus also is a life, and it has the right to be born and live. Even the prenatal diagnosis could be done voluntarily, the counsellor should diagnose the disease accurately and describe its consequences clearly so that parents can act upon the information in a manner appropriate to their suitation.
For carrier screening, I think it
should be tested voluntarily and privately. This type of screening
is the major controversy for the public. We must be aware about
the limitations of screening capabilities. Genetic screening
can identify the risk of many monogenic disorders by study of
the prospective parents, and can identify chromosomal disorders
and monogenic disorders from study of the fetus. But these screening
can not readily identify multifactorial genic disorders, including
most cases of mental retardation and congenital malformation.
On the other hands, even genetic screening could help human beings
diagnose early diseases, a truly effective therapy is not available
for most genic diseases yet.
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