Prenatal diagnosis and genetic screening : community and service implications / a report of the Royal College of Physicians.

  • Royal College of Physicians of London.
Date:
1989
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Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Prenatal diagnosis and genetic screening : community and service implications / a report of the Royal College of Physicians. Source: Wellcome Collection.

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    and most affected infants are born apparently sporadically, ie without a family history. The vast majority of abnormal genes carried in human populations are recessive and most people carry at least one such potentially-lethal gene. Limitations of treatment Primary prevention and social and environmental factors 1.12 It is becoming increasingly possible by using biochemical or DNA methods to detect healthy carriers of single-gene defects. The diagnosis of an individual with a dominant or X-linked condition identifies an entire family at high risk; where carrier testing is possible, the relatively small numbers involved make carrier testing for the family very worthwhile. By contrast, for common recessively-inherited disorders the relatively large numbers of carriers and the rarity of a family history of a disorder make population-screening the only realistic way to identify them. At present, in the absence of a family history, sufficiently accurate methods for carrier detection are available only for the haemoglobin disorders and Tay-Sachs disease, but it is probable that new DNA technology will permit carrier testing for cystic fibrosis and other recessively inherited disorders. 1.13 In practice, people who carry inherited diseases require time both to come to terms with their carrier status and to make informed decisions. It is therefore important, whenever possible, to identify carriers before pregnancy. As mentioned earlier, there is an important planning difference between risks that can be identified before pregnancy and those that can be detected only during the course of preg nancy. 1.14 So far, our improved understanding of the molecular basis for single gene defects has proved much more valuable for diagnosis than for treatment. 1.15 Intrauterine treatment of the affected fetus is of limited value, though intrauterine diagnosis may allow more effective treatment of the newborn child. Neonatal diagnosis allows a few well-defined disorders to be treated satisfactorily, and many congenital malformations can be corrected surgically, but the remainder of these disorders result in either death in infancy or prolonged chronic illness with premature death in adolescence or adult life. There seems little prospect of radical change in this general picture. Support services for children with chronic physical and/or mental disability are generally good, and have led to improved survival to adult age. This means that although, for several reasons, the birth-rate of infants with some conditions is falling the cumulative number who survive and require care is increasing. However, provision for disabled adults is inadequate and the quality of life of older patients and their families often deteriorates [3]. 1.16 The objective of primary prevention is to stop non-inherited congenital disorders arising in the first place by identifying and avoiding causative factors. Examples of primary prevention are: • prevention of Rhesus haemolytic disease of the newborn by postnatal injection of Rhesus negative mothers with anti-D immunoglobulin; • immunisation of young girls against rubella infection; • careful control of maternal diabetes in pregnancy; • improved diet to avoid neural tube defects.