Prospects for genetic screening

Abstract

NOT MANY PEOPLE in the 1970s would deny genetics a place in the physician's store of knowledge. A host of diseases is now seen to be the consequence of genetic mutations, both genic and chromosomal; and techniques have been devised to treat some and to provide support for others. Furthermore, in contrast to diseases of nongenetic origin to whose causes the unwitting victim is unpredictably exposed, the probability of genetic disease can be foretold in particular persons with some precision, allowing the genetic counselor to provide families with the wherewithal to make informed reproductive decisions. It is now possible, given the parental genotypes, to make an antenatal diagnosis of an expanding list of disorders, with the option to terminate the pregnancy if the fetus is affected. So favorable an outcome of the efforts of geneticists to invade the medical consciousness should induce some sense of fulfillment, and it does, but there is one important reservation: the lesson has not been extended far enough. The consequences for individuals of Mendel's law of segregation are well known, but it is less well known that the same rules apply to the distributions of genes among collateral relatives and indeed throughout the population at large. The rules governing the distributions of genes in populations, and the forces which establish their frequencies, form the substance of population genetics; and there is evidence that the impact of population genetics on clinical medicine is slight? This is perhaps not surprising, since medical tradition makes paramount the diagnostic analysis and management of patients one by one; the physician takes each patieni as he comes with only casual