Antenatal diagnosis of genetic disease / edited by A.E.H. Emery.

Date:
1973
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Antenatal diagnosis of genetic disease / edited by A.E.H. Emery. Source: Wellcome Collection.

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    implications of antenatal diagnosis 143 disease (Fraser and Motulsky, 1968; Smith, 1970), and similar results apply here. These are summarized in Table 22 showing the effectiveness of different methods. The results represent maximum levels of prevention, for they assume full application of the tests and methods available. After one affected child has been born in a family, other affected children may be prevented retrospectively. Fraser (1972) has derived expressions to estimate the maximum percentage of cases that might be prevented in this way. Depending on the distri¬ bution of family size, this percentage is about 30 to 40 per cent for dominant conditions and about 20 to 30 per cent for X-linked and recessive conditions. The percentage of cases prevented is likely to be much less in practice; if diagnosis is not made early, if counselling is not effective, or if a proportion of cases are due to new mutations. Because the recurrence risks are not very high for most chromosomal abnormalities (apart from translocation carriers nor for multifactorial disorders (conditions due to many genetic and environmental factors), the proportion of cases prevent¬ able will be quite small. Prospective prevention will be effective for mild dominant and X-linked conditions where female relatives may be carriers of the abnormal allele (Smith, 1970). The proportion of cases prevented by screeening specific groups will depend on the nature of the group and the risks. If the group at risk has a common genetic origin, such as the Ashkenazi Jews for Tay-Sachs disease, a high proportion of cases may be prevented. But for a group at risk for some general condition (such as Down's syndrome in mothers over a certain age), the proportion of cases prevented will be small, because the condition will not be confined to the high-risk group. Parental screening and antenatal diagnosis could theoretically prevent all cases of a reces¬ sive condition, for example sickle-cell anaemia, and all cases for X-linked and dominant conditions, except for those due to new mutations. However, parental screening will not be effective in preventing multifactorial or chromosomal disorders. Finally, 'fetal screening' (antenatal diagnosis applied to all pregnancies) could theoretically prevent all cases of any disease, if antenatal tests were available. However, such extreme applications seem very unlikely in practice. Ascertainment for Antenatal Diagnosis For antenatal diagnosis to be applied effectively to prevent genetic disease, there must be some means of finding matings at risk of having affected children, and various methods to do this are now