Screening for most genetic risks will eventually be possible through analysis of chromosomal aberrations. But social or religious factors may impede the applications of scientific progress.
DNA technology has revolutionized the laboratory diagnosis of genetic disease. It has also provided new perspectives for the detection of very minute chromosomal aberrations which are invisible under the microscope. In the near future DNA probes for specific parts of each human chromosome will facilitate large-scale prenatal diagnosis in women at risk of giving birth to offspring with a congenital malformation or genetic disease. They will also contribute to the elucidation of the causes of hitherto unexplained mental retardation and physical handicap.
At present some 750 disease genes have been identified. This has widened the scope of the prenatal diagnosis of genetic diseases and the detection of gene-mutation carriers, who are usually healthy themselves but may have an increased risk of producing affected children. DNA technology also offers new perspectives for the development of animal models for human diseases, making it possible to study pathogenesis and work out new therapeutic strategies. The latter will be especially important in the various types of cancer for which specific chromosomal aberrations and gene defects have been identified both in germ cells and somatic cells.
These techniques of diagnosis and carrier identification form the basis for genetic counselling to couples who on the basis of their family history or exposure to possible harmful environmental factors fear the birth of a handicapped child. The choices are often difficult and involve refraining from pregnancy, accepting the risk, adoption, fertilization with donor gametes, or prenatal diagnosis with the option of terminating the pregnancy if the foetus is found to be affected. Follow-up studies in our own centre revealed that 50 per cent of couples at high genetic risk refrain from pregnancy when there is no prenatal test available. If, however, there is such a test, 85 per cent of the couples choose to have progeny because they know they can avoid the birth of a handicapped child. Hence, prenatal diagnosis should not only be considered as a technology leading to abortion but also as an approach that may provide reassurance and stimulate couples, who might not otherwise have dared to do so, to reproduce.
In the wealthy countries clinical genetics services are universally accepted as part of modern health care. The only controversial issue is whether or not a pregnancy should be terminated because of an affected foetus. Abortion remains ethically, religiously unacceptable to a minority. Nearly all countries offering this option have, however, legalized abortion up to twenty-four weeks of pregnancy and a few countries, like the United Kingdom, do not even have a time limit in the case of an affected foetus. The only remaining concern is social pressure on those parents who give birth to an affected child when this could have been avoided. It is clear that freedom of choice should also be guaranteed for people who for moral reasons do not want to use a specific technique. In the Scandinavian and northwestern European countries today 50 to 60 per cent of pregnant women of advanced child-bearing age undergo prenatal diagnosis and the rest do not want it, even if they know of its existence.
Social attitudes to screening carriers of hereditary diseases
In a number of populations a particular genetic mutation is so prevalent that population screening for carriership is justified, provided that a reliable, easy and cheap test is available, and that the population involved has been well informed. Such carrier screening programmes have led to a marked reduction or an eradication of [Beta]-thalassaemia, a hereditary anaemia which is found amongst Mediterranean populations, of sickle-cell anaemia in Cuba, and of the severe neurological Tay-Sachs disease among Jews in North America and Israel. …