Studying the genetic structure of a population from a specific geographic region: ...
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Author(s): |
Mariana Saragiotto da Silva
Total Authors: 1
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Document type: | Doctoral Thesis |
Press: | Campinas, SP. |
Institution: | Universidade Estadual de Campinas (UNICAMP). Faculdade de Ciências Médicas |
Defense date: | 2010-07-28 |
Examining board members: |
Íscia Teresinha Lopes Cendes;
Carlos Alberto Mantovani Guerreiro;
Mônica Barbosa de Melo;
Veriano Alexandre Junior;
Marino Muxfeldt Bianchin
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Advisor: | Íscia Teresinha Lopes Cendes; Fernando Cendes |
Abstract | |
Mesial temporal lobe epilepsy (MTLE) is the most frequent syndrome of focal epilepsy and it is often associated with mesial temporal sclerosis (MTS). MTLE has great clinical importance because it is associated with a significant proportion of patients who do not respond to treatment with antiepileptic drugs (AEDs). Several genetic and environmental factors have been attributed to failure in response to AEDs in these patients. Among the genetic causes, it is believed that allelic variations in drug-transporter and metabolizing genes may be responsible for inefficient performance and metabolism of drugs, leading to failure in drug response. Thus, the main objective of this study is to verify whether polymorphisms in candidate genes may be related to drug refractory MTLE. To accomplished this objective we selected single nucleotide polymorphisms (SNPs) in two functional categories of candidates genes: i) drug-transporter genes: 43 SNPS in three selected genes, ABCB1, ABCC2, and RLIP76 (RALBP1) and ii) drug-metabolizing genes belonging to the cytochrome P450 system: 95 SNPs in nine genes, CYP1B1, CYP3A4, CYP3A5, CYP2C9, CYP2C19, CYP2E1, CYP1A1, CYP1A2, CYP2D6. Were genotyped two groups of unrelated patients with MTLE, 78 patients who responded to treatment with antiepileptic drugs (AED-responsive) and 164 pharmacoresistants patients (AED-pharmacoresistant), classified according to previously determined clinical criteria. Moreover, to ensure that both groups could be comparable in terms of genetic structure, all patients were genotyped for 119 additional SNPs not related to the candidate genes. Using the AMOVA and Fst calculation we showed that there is no population structure in both groups (AED-responsive and AED-farmacoresistentes); therefore, they can be compared in association studies. After calculation of gene frequencies of the 141 SNPs selected and genotyped in candidate genes, 75 SNPs were eliminated because there were not in Hardy-Weinberg equilibrium (p <0.05) and showed minor allele frequency (MAF) lower than 5%. In the group of transporter genes our results showed an association with a synonymous SNP rs3740066 (Ile1324Ile), present in exon 28 of ABCC2 gene, where the C allele is more frequent in the group of refractory patients. In addition, further experiments showed that expression of the ABCC2 gene in the hippocampus of farmacoresistentes patients is increased when compared to the hippocampus of individuals without MTLE, from autopsy. For drug metabolizing CYP450 genes, association was found with intronic SNPs present at genes CYP1A2 (rs2551188-TT) and CYP1B1 (rs12904742GG), as well as with 2 additional SNPs at gene CYP2C9 gene: rs2153628AA and rs4086116CT. All variants mentioned above are more frequent in pharmacoresistant patients. In addition, we found association for allelic variants at CYP2C9: rs4086116T, CYP1A2: rs12904742G and CYP2C9: rs1934963C, likewise, the alleles described are more frequent in pharmacoresistant patients. There is a statistically significant difference regarding the presence of hippocampal atrophy between the groups, being more frequent in group farmacoresistentes (p = 0.0000068). The stepwise regression analysis shows that the presence of hippocampal atrophy contributes with 9% of the total variability influencing pharmacoresistance in these MTLE patients. When analyzing the combined effect of the genetic factors which were found to be associated with pharmacoresistance in this study we conclude that their overall contribution to pharmacoresistance was 12%. Therefore, we can conclude that the remaining 79% of variability influencing pharmacoresistance in our group of patients with MTLE can be attributed to other factors not yet identified. Finally, our results show strong evidence indicating that pharmacoresistance in patients with MTLE is polygenic and multifactorial, since it shows clear genetic and environmental influences. (AU) |