Genetic screening aims to reduce the incidence of inherited diseases, which are responsible for about a third of all admissions of children into hospitals and one half of the deaths of children under fifteen. A committee of the National Academy of Sciences defines genetic screening as “a search in an apparently healthy population for those individuals with genotypes that place them or their offspring at high risk of disease.”
Neil Holtzman, a leading pediatrician and epidemiologist at Johns Hopkins University, has written Proceed with Caution to make people aware of powerful new technologies for genetic screening and to warn of their medical, social, legal, and financial implications. The technologies have sprung from scientific advances that are epitomized by a recent visit of mine to one of the new biotechnology companies. They treated me to seminars on their research and showed me all their expensive equipment until I finally asked: “What do you sell?” “We sell genes.” “How do you isolate them?” “We don’t, we make them ourselves.” Even ten years ago this would have been science fiction.
Holtzman introduces the biochemical basis of genetics and the complex interplay of genetic and other factors in health and disease. He describes the ingenious new methods of locating genetic lesions that are responsible for hereditary diseases, and, once located, of detecting their presence in suspected carriers. He fears that commercial pressures will lead to a premature spread of these new technologies, regardless of the tests’ fallibility, the pitfalls in their interpretation, and the emotional and social problems they may raise. Holtzman’s book is a lucid, richly documented, and forcefully argued plea to resist these pressures; it is addressed to physicians, and to administrators and legislators concerned with public health. I shall try to explain the molecular genetics of inherited diseases in plain words, describe some of the suffering caused by them, and discuss some of the evidence for and against screening.
Animal genes are made of long chains of deoxyribonucleic acid, DNA for short. The chains are twisted into a double helix that looks like a spiral staircase, with banisters made of alternate residues of phosphate and the sugar deoxyribose, and steps made of rings of carbon and nitrogen atoms. The rings are of four different kinds, called adenine, thymine, guanine, and cytosine. They provide the letters of the genetic alphabet, abbreviated as A, T, G, and C; their sequence along the DNA chain is the genetic blueprint that determines an organism’s identity. The sequences of the letters in the two intertwining chains are complementary, such that A is paired with T, and G with C. When a cell divides, the two chains separate and each serves as a template for the synthesis of a daughter chain with a sequence of letters complementary to that of the parent. In the process of replication, each of the parent chains forms a new double helix with its daughter chain; this new double helix contains a copy of the genetic information contained in …