Genetic screening for susceptibility to common diseases, such as the common cancers, cardiovascular disease, and diabetes, may soon be technically feasible. Commercial interests should not be allowed to introduce such screening before proper evaluation or without adequate counselling and support. The evaluation of such testing should include psychosocial and medical outcomes and outcomes for those given low risks as well as high risks. These tests may distract attention away from environmental factors contributing to disease, for which social and political measures may be more appropriate than individualised susceptibility screening and lifestyle modification.

The genes responsible for numerous single gene (mendelian) disorders have been identified over the past few years, but the elucidation of the genetic basis of multifactorial disorders has proceeded more slowly. These diseases are thought to arise from the interaction in an individual of multiple genes, “polygenes,” each generally having a minor effect, with the modifying influence of environmental factors. Most of the common degenerative, neoplastic, and psychiatric disorders of Western society are regarded as multifactorial in aetiology, and polygenic in so far as they are inherited.

The process of elucidating the contribution of particular genetic loci to multifactorial disorders is just beginning. One example is insulin dependent diabetes mellitus, in which genetic susceptibility is influenced by one locus within the major histocompatibility complex on chromosome 6p21, which contributes 42% of the familial clustering, and at least four minor loci.1 2

Baird has suggested that the dissection of the genetic factors predisposing to the common, multifactorial disorders will lead to a paradigm shift in health care, allowing people at increased risk of these diseases to be identified.3 This will lead to health benefits because those at high risk will be able, and motivated, to alter their lifestyles appropriately. Baird does, however, see some potential dangers: “if …