New directions in pharmacogenetics: Introduction.

General principles were developed for the selection of subjects for pharmacogenetic investigations. Depending on the particular metabolic pathway involved, studies may require that subjects be under carefully controlled, homogeneous environmental conditions. Otherwise, segregation in families of some genetically transmitted traits can be concealed by effects from multiple host factors. Therefore, in some pharmacogenetic studies of pharmacokinetic variations, differences among subjects with respect to critical host factors can profoundly influence the results obtained and conclusions drawn.