Advances in human genetics have transformed our understanding of many inherited conditions. These advances have led to major developments in diagnostic methods, improved classification of diseases and the introduction of some new, rational therapies. Some enthusiastic researchers and commentators have made excessive claims about the pace at which developments in genomic science will lead to changes in routine clinical practice. Other voices, especially those of clinicians and activist groups, have adopted a more cautious and sceptical tone. In this chapter we seek to give a modest account of genetic testing based on what has become possible over the last few decades and what may become feasible over the next 5-10 years. In such a contested and sometimes confusing area, it is necessary for us to use

key words in a clear and precise fashion. By ‘genetic testing’, we do not mean simply the application of a laboratory process to a biological sample; this would imply that genetic testing is simply the application of an artefact independent of its ‘interpretative flexibility’ (Pinch and Bijker 1984). In this book we use the phrase ‘genetic testing’ to encompass not only the application of an ‘assay’ (Zimmern and Kroese 2007) – a laboratory technique of analysing, detecting and quantifying a DNA sample – but also the interpretation of the laboratory findings within the clinical context, i.e., via genetic counselling. In this respect, ‘genetic testing’, in the way it is promoted via websites and television documentaries, falls short of our conceptualisation (see Chapter 5). This is in part a value judgement, an ideological commitment to the importance of delivering genetic counselling. It is not that genetic counselling is necessarily required before any laboratory-based genetic investigation is performed; rather, it is essential that those providing a test (including those made available via the internet) offer a unified package of the scientific investigation accompanied by sound interpretation and professional judgement. In the current climate of rational-economic efficiency and direct-to-consumer marketing, there is a danger that genetic testing will be reduced to a mere laboratory result. Attempts to develop a market for genetic tests of susceptibility to common diseases such as diabetes, cancer, coronary artery disease, hypertension and dementia are likely to gloss over the limited clinical applicability or benefits of such testing and to downplay the appropriate role for genetic counselling.