The Short-Term Reduction in Birth Incidence of Recessive Diseases as a Result of Genetic Counselling after the Birth of an Affected Child

Abstract

The maximum impact of retrospective genetic coun selling (i.e. after the birth of an affected child) is considered in the case of recessive diseases which can be diagnosed at or soon after birth. The calculations are made both for theoretical distributions of sibship size, such as the Poisson and the negative binomial, and for empirically ascertained distributions. It is shown that the reduction in birth incidence of the disease which can be achieved in one generation in this way is modest, and that it will become even smaller with the trend towards greater uniformity in sibship size with a reduced mean number of children, which may be expected because of the generally accepted need for quantitative control of human reproduction. It is pointed out that prospective genetic counselling (i.e. through the detection before procreation of heterozygotes for diseases such as sickle-cell anaemia) affords hope for far more substantial reductions in birth incidence.