Genetic variants of d4T drug transporters and dNTP pool regulators, and their association with response to d4T-ART

Abstract

Background: Stavudine (d4T) use is associated with the development of sensory neuropathy (SN), several mechanisms may underlie d4T-induced toxicity, including: (1) Inter-patient genetic variability in the genes modulating the deoxynucleotide triphosphate (dNTP) pool sizes. (2) Variation in intracellular ARV drug concentrations due to genetic variation in drug transporters. In our study we examined the genetic variation in four stavudine transporter genes and seven genes regulating the deoxythymidine triphosphate (dTTP) synthesis and their associations with d4T-induced SN or CD4+ T cell count or mtDNA copy number. Methods: We examined a cohort of HIV-positive South African (SA) adults exposed to d4T, including 143 cases with SN and 120 controls without SN. 26 single nucleotide polymorphisms (SNPs) from the literature were chosen, prioritised on being tagSNPs with minor allele frequency >5% in Kenyan Luhya (a proxy population for the SA Black population); SNP functional effects and suitability for multiplex analysis on the genotyping platform. Genotyping was performed using Sequenom mass spectrometry. A qPCR assay was used to measure the mtDNA copy number. Association of sensory neuropathy, CD4+ T cell count and mtDNA copy number with genetic variants was evaluated using PLINK. Results: All 26 SNPs were in Hardy-Weinberg equilibrium (HWE) in both the cases and controls. SNP rs8187758 of the SLC28A1 transporter gene and a 3-SNP haplotype ABCG2 were significantly associated with CD4+ T cell count after correction for multiple testing (p = 0.043 and p=0.042 respectively), but were not significant in multivariate testing. No SNP remained significantly associated with SN or mtDNA copy number, after correction for multiple testing. Conclusion: Variation in genes encoding molecular transporters of d4T may influence CD4+ T cell counts after ART. This study presents a positive step towards achieving personalized medicine in SA.