Toxicokinetic genetics: an approach to gene-environment and gene-gene interactions in complex metabolic pathways.

We propose an approach to modelling the joint effects of multiple genes involved in metabolic activation and detoxification of environmental exposures. A physiologically based pharmacokinetic (PBPK) model is used, in which the various person-specific metabolic rates are related to measurements of the genotypes and/or phenotypes at the various stages of the relevant pathways. Markov chain Monte Carlo (MCMC) methods are used to fit the model. We illustrate the approach by application to case-control data on colorectal polyps in relation to consumption of well-done red meat and tobacco smoking via pathways involving heterocyclic amines (regulated by the genes CYP1A2, NAT1 and NAT2) and polycyclic aromatic hydrocarbons (regulated by the genes CYP1A1, EPHX1 (also called mEH) and GSTM3). In this chapter, we focus on the biochemical basis for our conceptual models, deferring detailed mathematical description of the models and simulation results to a separate paper.