Analysis of the TSER and G>C variants in the TYMS gene: a high frequency of low expression genotypes predicted in the Mexican population.

BACKGROUND: In the TYMS gene promoter, there is a repeat polymorphism (TSER) that affects the expression level of the thymidylate synthetase (TS) enzyme involved in the response to some anticancer drugs. The G>C transversion located in the TSER*3R allele decreases the expression level of the TS enzyme avoiding the upstream stimulatory factor (USF-1) binding site. Despite the biomedical impact of the SNP G>C, only TSER has been reported in most worldwide populations. Thus, we studied both TSER and SNP G>C variants in the Mexican population. SUBJECTS AND METHODS: A population sample (n = 156) was genotyped for the TSER and G>C variants by PCR and PCR-RFLPs, respectively, followed by PAGE and silver staining. RESULTS: For TSER, the most frequent allele was 2 R (52.56%), as well as the genotype 2 R/3R (42.3%). Comparison with Latin American, European, and American (USA) populations suggest a heterogeneous worldwide distribution (FST-value = 0.01564; p-value = 0.0000). When the G>C variant was included (2RG, 3RG, and 3RC), a high frequency of low expression genotypes was observed: 2RG/2RG, 2RG/3RC, and 3RC/3RC (84.6%). CONCLUSION: The high frequency of genotypes associated with low TS enzyme expression justifies obtaining the TYMS gene variant profile in Mexican patient's candidates to pharmaceutical treatments like 5'-Fluoracil, methotrexate, and pemetrex.

Prevalence of protective haplotypes of the SLCO1B1 gene for statin transport in Mexican populations.

Aim: To evaluate the genetic distribution of the rs4149056 and rs2306283 variants in the SLCO1B1 gene in Mexican Mestizo (admixed) and Native American groups. Materials & methods: We recruited 360 volunteers who were qPCR-genotyped with TaqMan probes. Results: Allele and genotype frequencies are reported. Among the expected rs4149056-rs2306283 haplotypes, T-A (42.35-58.47%) was the most prevalent which relates to the normal activity of the OATP1B1 transporter. This was followed by the T-G haplotype associated with further statin transport and cholesterol reduction (32.49-43.76%). Conclusion: Based on these SLCO1B1 gene variants, we confirmed that a minimum fraction of the Mexican study populations would be at risk from decreasing simvastatin transport and the development of statin-induced myopathy.

Lay abstract The clinical response to statins, mainly atorvastatin and simvastatin, can be modified by interindividual variability including variations in the SLCO1B1 gene. This gene, that encodes the statin transporter OATP1B1, helps to regulate the cholesterol levels in the blood and is responsible for the presence of adverse drug reactions related to the statin consumption, such as muscular sickness. This study analyzes the distribution of the SLCO1B1 gene variants rs4149056 and rs2306283 in geographically dispersed samples of the two main populations in Mexico: two Mestizo (admixed) populations and three Native American groups. We found that the genetic combinations of T­A and T­G for the two SLCO1B1 gene variants ­ associated with normal or efficient activity of the transporter OATP1B ­ were predominant in all of the study population. Therefore, the SLCO1B1 gene variability suggests that a majority of the Mexican population will respond favorably to simvastatin and have a low risk of developing associated muscular complications.