Molecular genetic risk screening.

Under the impetus of the Human Genome Project, new disease-associated genes are being discovered at a rapid pace. Mutations in many of these genes are present in a high enough proportion of the general population, or of particular ethnic groups, that global or targeted population screening can be contemplated. If performed early enough, identification of these mutations by molecular genetic testing can be used not merely to diagnose disease but to predict risk of future disease, either in the individual being tested or in his or her offspring. In some cases this knowledge can be the rationale for heightened surveillance and/or preventive or therapeutic interventions. Mass screening has already commenced for cystic fibrosis mutations and has been discussed for such diverse diseases as hereditary hemochromatosis, thrombophilias, familial cancer predispositions, and pharmacogenetic risk factors. However, implementation of such programs is often impeded by the complexity of the gene mutations, by incomplete penetrance, and by thorny ethical and social issues. This chapter reviews the basic criteria to be considered before embarking on population genetic risk screening, and examines multiple disease-screening examples representing a variety of modes of inheritance and technical challenges.