What is genetic information for? One way in which genetic information is used is to identify individuals in the sense of picking them out reliably and uniquely. This is the way information is used in so-called genetic finger-printing and in tests of paternity. Another way genetic information is used is in diagnosis. Suppose I have a certain pattern of symptoms which may indicate one disease, but which may indicate something else. Suppose further that the prognoses of the diseases are different, or that the indicated treatments for the two diseases differ, so that it matters that the diagnosis be correct. It may be known that one of the diseases has a genetic basis, while the other does not (or has a different one). Then one could use genetic information in a diagnostic test to rule out one or both diseases. A third use for genetic information is in predictive screening. Does a patient have a gene implicated in a particular disease, such that they are at increased risk of developing that disease (or are certain to do so)? Is a patient a carrier for a gene which means that any children he or she may have with another carrier for the gene are at risk of a certain genetic disease?
When and why is genetic information sought? Genetic information may be sought for identification purposes, as in genetic fingerprinting. In such cases it is taken that each individual's genome is unique to them (with the possible exception of identical twins, triplets and so on). So if human tissues are found at a crime scene, the genetic material they contain can be used to identify who was present at the site if a matching sample can be obtained from an individual or from a database. Genetic information functions in this case as a sort of natural sign. The genetic material points to the identity of a person.1
The second case is the use of genetic information in diagnostic testing. In general that information is only gathered when a person, having fallen ill, defines themselves as a patient and requests diagnosis and treatment. The doctor seeks for diagnostic signs, among which genetic information may be sought as a marker, in order to make a causal judgement. Without other diagnostic signs, the genetic information on its own is unlikely to be reliable.2 In this situation the usual moral and emotional hazards of diagnosis arise—just as they do when a patient passes from unspecified sickness to being a "cancer patient". Ethically, the specifically genetic nature of the cause may not be relevant, except insofar as the patient theorises their condition historically.3
My topic in this paper is the third of the uses of genetic information: its use in screening for conditions in which some identifiable genetic factor plays a causal role. When is information of this kind gathered? There are three main occasions. The first is when a couple are planning to have a baby, and suspect that they may be carrying genetic factors which put the putative child at risk of some disability or disease; this may be because they are themselves sufferers, or because there is a "history" in one or both of their families, or because they already have a child with the condition in question. The second is when the mother is already pregnant, and she (or the father or both) wish, following medical advice, to have the foetus tested for some of the more common or more serious genetic disorders. The third is after the child has been born (at some point in childhood or later), where parents or child want to know whether the child is at risk of expressing a genetic disorder.
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