Expression data from monozygotic twins discordant for nicotine metabolism

The Nicotine Metabolic Ratio (NMR), the ratio of two stable metabolites of nicotine, cotinine and trans-3’hydroxycotinin, is a determinant of the number of cigarettes smoked per day (CPD), of smoking topography, responsiveness to treatment via transdermal nicotine for smoking cessation, and carcinogen activation and level. The predominant gene involved in nicotine metabolism is CYP2A6, a highly polymorphic locus located in a cluster of P450 cytochrome protein loci on chr19q13. A recent study comprehensively modeling CYP2A6 genetic variation at seven polymorphisms and a related Nicotine Metabolic Ratio, the cotinine: cotinine+nicotine ratio, explains 72% of NMRC/C+N variation. These results suggest that additional genes may be contributing to nicotine and cotinine metabolism directly or via interaction with CYP2A6 or other genes. To identify additional genes that may influence the NMR, we conducted a genome-wide gene expression analysis of lymphoblastoid cell line (LCL) gene expression in a sample of monozygotic twins discordant for the NMR. Eight individuals (four monozygotic twin pairs), each with three replicates for a total of 24 samples