In Chapters 2 and 3 we have discussed the relationship between genes and disease. We have also outlined the approaches that are being used to discover and quantify associations between specific genetic variants and disease risk, and to understand how genetic risk is modulated by environmental and lifestyle factors.

Although our knowledge of the genetic determinants of disease is incomplete, applications of genetics in medical practice are already in existence or are being developed. Within the specialist service of medical genetics in the UK, consultant clinical geneticists and genetic counsellors see individuals and families who are affected by, or at high risk of, conditions that may have a genetic basis. Genetics professionals attempt to assess whether the condition is, for example, a known disease caused by a single-gene lesion or chromosomal abnormality. They may suggest tests to aid diagnosis. In addition, they may give advice about a variety of issues including genetic risk to other family members, and reproductive options. Specialist genetic services, and related services within the healthcare system, are discussed in more detail in Chapter 5.

Many applications of genetics in health care, both actual and potential, rely on technology designed to test for the presence of specific genetic variants. We begin this chapter with a discussion of genetic testing and its uses in the diagnosis of disease and estimation of disease risk. We then move on to consider broader applications of genetics in the two major component areas of health care: disease prevention and disease management.