Page 42 - Genetics_From_Genes_to_Genomes_6th_FULL_Part1

34 Chapter 2 Mendel’s Principles of Heredity

GENETICS AND SOCIETY Crowd: © Image Source/Getty Images RF

Developing Guidelines for Genetic Screening
In the early 1970s, the United States launched a national • Should I be screened if a test is available? For most inher-
screening program for carriers of sickle-cell anemia, a recessive ited diseases, no cures presently exist. The psychological
genetic disease that afflicts roughly 1 in 600 African-Americans. burden of anticipating a fatal late-onset disease for which
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The disease is caused by a particular allele, called Hbβ , of the there is no treatment could be devastating, and therefore
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β-globin gene; the dominant normal allele is Hbβ . The protein some people might decide not to be tested. Others may
determined by the β-globin gene is one component of the object to testing for religious reasons, or because of
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oxygen-carrying hemoglobin molecule. Hbβ Hbβ homozy- confidentiality concerns.
gotes have sickle-shaped red blood cells; these patients suffer • If a screening program is established, who should be
a decrease in oxygen supply, tire easily, and often develop heart tested? The answer depends on what the test is trying to
failure from stress on the circulatory system. accomplish as well as on its expense. Ultimately, the cost
The national screening program for sickle-cell anemia was of a procedure must be weighed against the usefulness
based on a simple test of hemoglobin mobility: Normal and sick- of the data it provides. In the United States, for example,
ling hemoglobins move at different rates in a gel. People who only one-tenth as many African-Americans as Caucasians
participated in the screening program and found they were carri- are affected by cystic fibrosis, and Asians almost never
ers could use the test results to make informed reproductive de- exhibit the disease. Should all racial groups be tested for
cisions. A healthy man, for example, who learned he was a carrier cystic fibrosis, or only Caucasians?
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(that is, that he was a Hbβ Hbβ heterozygote) would not have to • Should private employers and insurance companies be
worry about having an affected child if his mate was a noncarrier. allowed to test their clients and employees? Some em-
The original sickle-cell screening program, based on de- ployers advocate genetic screening to reduce the inci-
tection of the abnormal hemoglobin protein, was not an un- dence of occupational disease, arguing that they can use
qualified success, largely because of insufficient educational genetic test results to make sure employees are not as-
follow-through. Many who learned they were carriers mistak- signed to environments that might cause them harm.
enly thought they had the disease. Moreover, employers and Critics of this position say that screening violates workers’
insurance companies that obtained access to the information rights, including the right to privacy, increases racial and
denied jobs or health insurance to some heterozygotes for no ethnic discrimination in the workplace, and provides insur-
acceptable reason. Problems of public relations and education ers with an excuse to deny coverage. In 2008, President
thus made a reliable screening test into a source of dissent and George W. Bush signed into law the Genetic Information
alienation. Nondiscrimination Act, which prohibits insurance compa-
Today, at-risk families may be screened for a growing num- nies and employers in the United States from discriminat-
ber of genetic disorders, thanks to the ability to evaluate geno- ing on the basis of information derived from genetic tests.
types directly. The need to establish guidelines for genetic • Finally, how should people be educated about the mean-
screening thus becomes more and more pressing. Several ing of test results? In one small-community screening
related questions reveal the complexity of the issue. program, people identified as carriers of the recessive, life-
threatening blood disorder known as β-thalassemia were
• Why carry out genetic screening at all? The first reason ostracized; as a result, carriers ended up marrying one
for screening is to obtain information that will benefit indi- another, only making medical matters worse. By contrast,
viduals. For example, if you learn at an early age that you in Ferrara, Italy, where 30 new cases of β-thalassemia had
have a genetic predisposition to heart disease, you can been reported every year, extensive screening combined
change your lifestyle to improve your chances of staying with education was so successful that the 1980s passed
healthy. You can also use the results from genetic screen- with only a few new cases of the disease.
ing to make informed reproductive decisions.
• The second reason for genetic screening, which often Given all of these considerations, what kind of guidelines
conflicts with the first, is to benefit groups within society. would you like to see established to ensure that genetic screen-
Insurance companies and employers, for example, would ing reaches the right people at the right time, and that informa-
like to know who is at risk for various genetic conditions. tion gained from such screening is used for the right purposes?

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normal allele (CF ) that masks the effects of the recessive children are blood relatives; that is, their mating is consan-
abnormal one. An estimated 12 million Americans are carri- guineous (as indicated by the double line). In Fig. 2.24a, the
ers of a recessive CF allele. Table 2.2 summarizes some of consanguineous mating in generation V is between third
the clues found in pedigrees that can help you decide whether cousins. Of course, children with cystic fibrosis can also
a trait is caused by a dominant or a recessive allele. have unrelated carrier parents, but because relatives share
The second salient feature of the cystic fibrosis pedi- genes, their offspring have a much greater than average
grees is that many of the couples who produce afflicted chance of receiving two copies of a rare allele. Whether or