Firas M Abu-El Samem
Humans, like all other living organisms, have genes. These genes instruct our bodies to make proteins, these proteins are the molecules that determine the shape and function of each cell. Each gene or set of genes encode for the production of a particular protein.What is a gene ?The term " gene "was created by Wilhelm Johanssen, a Danish botanist in 1911. He was discussing units of inheritance that Mendel called factors.T.H. Morgan's studies on fruit fly genetics led to the idea of a gene as the smallest unit of recombination. Aggregated with this idea was another that said the gene was the unit of mutation, and another that the gene is the unit of function (the smallest unit of control over the phenotype ). Modern evidence suggests that recombination can occur between any two nucleotide, which make the unit of recombination only one nucleotide long . Some mutations change only one nucleotide, so the unit of mutation could be only one nucleotide long . The unit of function is the cistron which is about 900-1500 nucleotide long. So we can identify the gene as the length of DNA that codes for one functional product (6).
DNA of the human species carries more or less the same set of DNA with some variations . Variations in the DNA sequence can be neutral, others might have positive or negative influence. Genetic screening is testing of this variation (2).
Human race carries 3000-4000 diseases in it's genes, and it is important to distinguish between inherited diseases and infectious diseases. Inherited diseases are caused by mutated genes which are inherited by an individual from his or her parents (2). The faulty gene will be one of the many healthy thousands of genes we possess in our cells. To pinpoint the location of these faulty genes, scientists search for variations in larger piece of DNA called markers, these subunits lie nearby on the DNA chain, and form the basis of genetic screening.
The principle of genetic screening is based on the binding of a probe to the DNA molecule of the patient or the person to be screened. Complementary DNA nucleotide sequences bind to each other. The probe used is usually single stranded DNA, which binds to the test sample. The DNA sample can be analyzed by a technique called restriction fragment polymorphism (RFLP). In this technique the DNA sample is cut up with a mixture of restriction enzymes which cut the DNA at a specific sequences. A radioactive probe is added to the fragments that can bind to certain sequences in the DNA. The fragments are then separated by gel electrophoresis. The DNA fragments move through the gel at varying rates depending on their molecular weight. The pattern of size distribution is quite individual, and the disease causing or linked fragment can be found . Currently the number of disorders that are screenable is measured in hundreds and is rapidly increasing, genetic diseases that have DNA probes available includes: Cystic fibrosis, Thalassemia, Hemophilia, Huntington's chorea, Sickle cell anemia, and many more (3) . One of the problems in genetic screening is the genetic heterogeneity, that is the disease causing mutation may occur any where in the gene, and there are also many mutations that do not cause disease. It is possible to use different probes to cover different mutations, but it is impossible to be sure of a negative result of a disease (4). Another problem of genetic screening is the differences in the expressivity. One person may express the disease to a different extent or at different age to another and this could be due to multiple gene action or variations in the environmental factors which can affect the expression of a certain gene (4), an example of such differences in expressivity can be found in a disease like Wilms tumour or Glucose -6-phosphate dehydrogenase deficiency (3).
Generally there are two types of genetic screening , screening of children and adults, and screening of unborn children. Genetic screening of children and adults has two purposes: first it can confirm whether the person has a mutated genes of certain disease or characteristics. The second purpose is to test adults to see if their children will be at risk of certain disease. Knowing that one or both parents carries a dominant allele for a genetic disease might affect the decision parents make about having children , some times this kind of genetic screening is used for approval of marriage licenses in some countries, like in Danmark, marriage licenses are refused to persons carrying certain genetic defects (2).
A successful screening program for Thalassemia has been used in Cyprus. This program was performed with cooperation of the local church, so all couples who were getting married have to provide a certificate showing the alleles that they have. If both of them were carriers of the Thalassemia then they would know that they should have prenatal screening. Another successful screening program for Thalassemia was performed in Italy. The carrier screening program has detected 30,500 carriers and 1544 at risk couples by mid 1990, about 90% of possible cases are now prevented by prenatal diagnosis and selective abortion (3).
The second type of genetic screening involving screening of unborn children is called Prenatal screening. The purpose of this kind of screening is to detect genetic disorders during early pregnancy. An example of this type of screening is testing for Down's syndrom when the mother is over 40. Prenatal screening has been used for several decades using different techniques. The older technique used is amniocentesis, where cells from the amniotic fluid are removed and cultured. No harm is done to the fetus as these cells are no longer needed for the growth. The fetal samples can be taken at 12-16 weeks and provide sufficient material for analysis . It is now possible to take sample of the chorionic villi (membranes around the fetus ) at 6-9 weeks and analyze the fetal DNA directly to determine whether it has a specific genetic defects. The chorionic villi sampling ( cvs ) may be combined with a maternal blood sampling to detect diseases like Spina bifida or Down's syndrome. Ultrasound is also routinely used and has the advantage of being non-invasive (3). But we are still unable, economically, ethically, and socially to screen every fetus for many diseases with these techniques. Rather they are currently used to screen fetuses from parents of high risk (3).
Preimplantation screening has been used since 1989. The first study involved embryos that were not implanted after screening. Evidence suggests that embryos are not harmed by this procedure. One ethical objection, once it is confirmed that this procedure is safe, is the interference with nature by discarding of diseased embryos at this early stage. But given the economic factors that often influence health care decisions, such as the high cost of health care for people suffering from severe diseases , this kind of screening may be encouraged by governments. On the other hand, religion has a problem with this kind of screening before the birth of the child, because the fact that carrying a defective gene does not mean that child will express this gene (3).
As a result of the rapid developments in the field of genetic screening, genetic counselors are placed in a powerful position. The role of the counselors is to provide parents with information which allows them to make a good decision concerning the coming child. Unfortunately most parents come to the counselors after the birth of the first affected child to discuss the possibility of having another affected child. The acceptance of the genetic counselors from the public depends in the manner in which the counselors work. People would accept the non-directive counseling, which means that the counselors act as decision facilitators providing people with information and leaving decisions up to the patients autonomy. In many countries the genetic screening services are accompanied with counseling services (3).
Genetic screening could have great value if used properly to help people take preventive measures to avoid suffering from some diseases. The first type of genetic screening used was screening of newborn children for PKU deficiency. This test was made compulsory in USA in 1960's. If the new born is found to have PKU deficiency, they can be put on a special diet, and will not suffer from severe mental retardation (3).
Genetic screening also works out economically, because it is cheaper to treat patients before serious damage is done to them by a genetic disease, than to keep sufferers in institutions. There is screening for genetic susceptibility to environmentally induced diseases like elevated blood cholesterol. If screening shows the person is at risk, advise can be given on how to lower risk.
It has been found that many common cancers such as lung, breast, and colon develop by step- wise accumulation of mutations affecting many genes. The disease include the loss of some suppressor genes which inhibit cell growth. Genetic screening may help predicting a cancer, and can be used to warn people to avoid agents that causes more mutations like smoking (5). Social and Ethical Dilemmas of Genetic Screening :
After the rapid progress in this field during the last decade, several issues of the consequences of the new technology began to appear, which in many cases have a negative effect on those people whose genetic tests reveals that they are under risk of some genetic diseases .
In this issue people need to realize that carrying a gene for susceptibility such as the breast cancer gene BRCA1 , dose not necessarily mean a person will get the disease (5) . If you have a susceptibility gene , you may or may not get the disease. If you get it, no one can tell when or how severe, and in many cases there may be no preventive treatment or cure, as is currently the case with the breast cancer (1). And this leads to the difficult question, who should be screened and why ? For now, geneticist and physicians generally agree that no one should be tested just because of fear of an illness. Doctors should offer testing only to those people whose family history suggests that they could carry harmful forms of genes. On the other hand, one should consider the psychological and emotional effects on those people whose genetic tests revealed that they are under risk of such genetically inherited diseases. Most people would choose not to know about their genetic make up that might show that they are under risk, simply because they do not want to spend their lives worrying about some thing that is only possibility.
In the future, there will be a dramatic increase in the amount of patients genetic data. Many individuals will be identified as carriers of genetic diseases, and this data can play an important role in the life of the individuals, by affecting the choice of spouse, decisions on whether to have children, and whether to use prenatal screening and selective abortion or therapy (3).
Genetic information can be a great benefit to the individual persons. However, one of the most dangerous aspects of new technology is the danger of the genetic information becoming available to other people who might be involved in making decisions, that affect every aspect of our lives, especially employers and health insurance companies. This might lead to a genetic discrimination, and recent surveys indicated that health insurance coverage has been denied to many people due to their genetic status. There are many benefits to the insurance companies of knowing people's genetic data, the insurance companies costs could be lowered (3).
An important question is whether it is ethical to use abortion for some treatable diseases such as PKU, which when detected as a new born , can be treated with a dietary measures. Other diseases such as albinism are undesirable but many people suffered from it and lived otherwise normal lives (3). People tend to be more worried about genetic screening tests for people with mental diseases , people diagnosed with the XYY syndrom were imprisoned for long time, as they are considered violent. This kind of screening lead to unfair labeling of people leading to a new type of social discrimination (3).
There are many other issues that could be topics of discussion about the right of people to have their genetic data confidential. These tests can be done with a pinprick to collect blood. How can we ensure that they are not done without our knowledge as a part of another medical examination ? Does the employers have the right to make genetic testing mandatory ? Could the banks use this kind of information to deny loans, mortgages and life insurance companies polices?. These and many other aspects show how the knowledge of genetic information could be misused by those who can benefit from using this information (7).
There is another argument that if we let the parents chose characters for their children, such as being free from the most common genetically inherited diseases, then this might have a harmful effect on social attitudes toward other people who failed to meet such characteristics. While genetic screening could help people have children free of the common genetic defects, it would make the life of other people, who did not use the genetic screening and have children who are suffering from a genetic disease more difficult and complicated. This matter could be seen as not an act of fate but the parents fault (3) .
The use of these new techniques raise many ethical issues. Should we screen embryos for genetic diseases ? If so what diseases must we screen for ? Should we allow couples to select the sex of their child. If genetic test can tell if some one will die young , this can change the way they live. So is it ethical to make him aware of the test results ? In spite of these ethical issues and many more, many people believe that most of these problems could be resolved through. implementation of regulations that prevent the misuse of this powerful technology (1).
In response to what I have discussed previously , about the importance of this issue, and the strong debate about the role of this new technology in our lives, it is difficult to say a final word about the need to proceed with this kind of research or to stop, because this issue is complicated and has different scientific, psychological, economical, emotional, ethical, and religious aspects that should be considered before evaluating what is right and what is wrong.
However, according to the aspects that have been discussed about how this genetic screening data could be misused, by those people who might gain benefits on the expense of those whose genetic screening results revealed that they are under risk of some diseases, it is important to ensure that if the application of any new technology leads to negative impacts on the members of the society, then this new technology will be unaccepted by the majority.
I believe that this kind of the studies and applications of this technology should proceed, because most likely it will has a positive effects in finding the solution for many fatal diseases that affect thousands of people every day. It might also rescue lives of millions who are suffering from diseases. I think the future will be the judge to prove the advantages or the disadvantages so we should not be hasty in our judgment about the misuse of such a new technology.