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CYP2C9 Promoter Variable Number Tandem Repeat Polymorphism in a Dominican Population: Exploring Differences with Genetic Ancestry

Abstract:

A variable number tandem repeat polymorphism has been described in the CYP2C9 promoter (pVNTR) with three types of fragments: short (pVNTR-S), medium (pVNTR-M), and long (pVNTR-L). The pVNTR-S allele appears in strong linkage disequilibrium (LD) with the non-functional CYP2C9*3 allele in populations of European ancestry, but independently of this, it also appears to reduce the level of CYP2C9 expression in human liver by up to 34%. Objectives: This study, in a Dominican population with varying amounts of Western European, African, and Native American ancestry, aims primarily to determine the frequency of CYP2C9 pVNTR, and the degree of LD of pVNTR-S with CYP2C9*3. Secondarily, it explores if the frequency of the pVNTR-S allele is over- or under-represented in those with a greater component of African ancestry. Methods: A total of 193 healthy volunteers from the Dominican Republic participated in the study. The promoter region of CYP2C9 was amplified and analyzed by capillary electrophoresis. Analyses of CYP2C9 genotypes (*2, *3, *5, *6, and *8) and genetic ancestry, estimated in 176 Dominican individuals by genotyping 90 ancestry informative markers, were previously performed in this population. Results: The frequencies of CYP2C9 pVNTR-L, M, and S variants are 0.065, 0.896, and 0.039, respectively. LD between pVNTR-S and CYP2C9*3 was found (D’ = 0.756, r<sup>2</sup> = 0.702) to be weaker than in European populations. Conclusions: Populations with a greater African ancestry component appear to present a lower-than-expected frequency of pVNTR-S, as well as a lower tendency for this and CYP2C9*3 alleles to be inherited together, as is common in Europeans. The present exploratory results warrant further research in vivo about the effects of pVNTR-S in predicting CYP2C9 activity. Its inclusion in CYP2C9 testing panels for personalized drug therapy could be relevant in populations such as the Dominican, where the LD between pVNTR-S and CYP2C9*3 is low.