Effect of UGT1A4, UGT2B7, UGT2B15, UGT2B17 and ABC1B polymorphisms on lamotrigine metabolism in Danish patients

Objective To evaluate the impact of genetic polymorphisms of UGT enzymes (UGT1A4, UGT2B7, UGT2B15 and UGT 2B17) and the transporter protein ABCB1 on Lamotrigine (LTG) metabolism. Methods Single nucleotide polymorphisms UGT1A4*2 (P24T, c.70C>A), UGT1A4*3 (L48V c.142T>G), UGT2B7*2 (H802Y, c.802C>T), UGT2B15*2 (Y85D, c.253G>T), UGT2B17 deletion and transporters ABC 1236C> T and 3435C> T were determined in 337 Caucasian patients with epilepsy treated with LTG in Denmark. The prospectively collected data included LTG dosage, LTG plasma concentration, 2-N-GLU concentration, sex, smoking habits, concomitant medicine, oral contraceptives (OC). Results The non-smokers with LTG monotherapy and LTG polytherapy with other non-interacting drugs NIAEDs (n = 199) were analyzed separately in univariant analyses. LTG ratios (LTG plasma concentration/ (LTG dose/weight)) in patients carrying wild type UGT1A4*2 C-allele were 22% lower than in heterozygous C-carriers (p = 0.013). Patients with UGT2B7*2 polymorphism TT genotype had 1.2-fold higher LTG ratios (p = 0.0078) and 0.78-fold lower GLU/LTG ratio (p = 0.0275) than patients homozygous for the C allele. The similar significant findings were also seen comparing homozygotes (TT) with heterozygotes patients (CT). Individuals homozygous for the UGT2B15*2 T allele displayed 18% lower LTG ratio concentrations than individuals homozygous for the G allele (p = 0.014),while significant difference in GLU/LTG ratio was only seen comparing wild type with homozygous patients (GG versus TT, p = 0.031). A copy number variation gene deletion polymorphism of UGT2B17 showed that individuals devoid of the gene (del/del) exhibited 1.3-fold higher LTG ratio (p = 0.015). For ABCB1c.1236 C>T and ABC1B1c.3435 C>T no associations with LTG and GLU ratios were found.Sex specific differences in enzyme activity (most prominent effect in women) on LTG metabolism were found for UGT2B15, UGT2B17, UGT1A4 and UGT2B7 polymorphisms.Multiple regression analysis confirmed the significant effect of OC, VPA and UGT1A4 * 2 and UGT2B7 * 2 on LTG metabolism. Conclusion Our study confirms the previous findings that genetic variations in UGT2B7 and UGT1A4 genes are associated with serum LTG concentrations.Furthermore, our results indicate that it is possible that different UGT genotypes may exert larger impact on LTG metabolism in women than in men.