In the field of epidemiology, there has been increasing interest in documenting the results of interaction between specific genes or genotypes and well-understood environmental exposures. Gene-environment interactions are situations in which the combination of an environmental factor, such as exposure to cigarette smoking, with a genetic factor, such as a diseasepredisposing mutation, results in a greater risk or severity of the disease in question than either the genetic or environmental factor acting alone. These interactions have been studied in plants and animals for many years. While they have been hypothesized also to occur in humans, they have been documented in humans only fairly recently. In recent years, many examples of gene-environment interaction have been reported in the literature.

There is now increasing acceptance of the idea ...