Browsing by Subject "pharmacogenetics"

Pharmacogenetics is the study of variations in DNA sequence as related to drug response, i.e. pharmacokinetics, drug efficacy and adverse effects. The literature review of the thesis covers pharmacogenetics of analgesics. The most studied genetic variations affecting the analgesics response are the 118A>G variant of µ-opioid receptor gene (OPRM1) and several variations in the genes coding for cytochrome (CYP) P450 enzymes. Also variations in the COMT gene and the ABCB1 gene coding for P-glycoprotein have been shown to modify the response to analgesics. Genetic polymorphism of CYP2D6, CYP3A4 and CYP3A5 enzymes was studied in the experimental part of the thesis. The aim of the study was to determine if the allele and haplotype frequencies of the CYP2D6, CYP3A4 and CYP3A5 gene variations are different between Finnish breast cancer patients and healthy volunteers. The results will be further used to explore whether the genetic polymorphism of these metabolic enzymes affects the response to a certain drug substance. The study population consisted of 996 Finnish breast cancer patients. Common genetic variants affecting the enzymatic activity of CYP2D6, CYP3A4 and CYP3A5 were studied. In addition to gene copy number, ten single nucleotide polymorphisms (SNP) of the CYP2D6 gene were genotyped. For CYP3A4 gene, genotyping was done for intron 6 SNP rs35599367 shown to decrease CYP3A4 gene expression. CYP3A5 SNP 6986A>G leading to splicing defect and premature STOP codon was also genotyped. Genotyping and copy number determination was done using PCR-based TaqMan® 5'-nuclease method. CYP2D6 haplotype analysis and phenotype predictions were derived based on genotype data. According to CYP2D6 enzyme activity individuals are commonly classified as poor metabolizers (PM), intermediate metabolizers (IM), extensive metabolizers (EM) or ultra-rapid metabolizers (UM). The frequencies of CYP2D6 phenotypic classes in our study population were the following: PM, 2.8%; IM 2.0 %; EM 87.7% and UM 7.6%. The haplotype and phenotype frequencies determined for breast cancer patients coincide with the values observed earlier for Finnish healthy volunteers. In our study population, the minor allele frequency (MAF) of the CYP3A4 rs35599367 SNP was 2.7% and the MAF of the CYP3A5 6986G>A SNP 7.6%. The MAF of CYP3A5 6986G>A SNP found in our study is in line with the previous findings for Finnish healthy volunteers. There are no previous publications on the frequency of CYP3A4 rs35599367 SNP in Finnish population. In conclusion, no differences were detected in the frequency of the studied CYP2D6 and CYP3A5 genetic variations between Finnish breast cancer patients and healthy volunteers. Frequency of CYP3A4 rs35599367 SNP in Finnish healthy volunteers should be determined in order to compare it with our findings in the population comprising of breast cancer patients. The results of this study can be further used to explore the effects of CYP2D6, CYP3A4 and CYP3A5 genetic polymorphism on drug response.

Most xenobiotics are biotransformed by phase I enzymes to a more hydrophilic form in order to get excreted out from the body. In most cases xenobiotics are in lipophilic form when entering body. The most important group in phase I enzymes is cytochrome P450 (CYP) superfamily. Of CYP enzymes probably the most studied is CYP2D6, which is responsible for metabolism of 20-25% of drugs currently on market. Many CYP2D6 substrates belong to therapeutically important drug groups, such as antiarrhytmics, antidepressants, beta-blockers, or neuroleptics. CYP2D6 gene, which encodes the enzyme, exhibits large interindividual variability, which has an effect on the metabolic activity of the enzyme. The frequencies of these genetic variances differ globally on wide scale between and inside populations. Through genotyping it is possible to predict the CYP2D6 metabolic rate, which can be divided into four classes: ultra-rapid metabolizers (UM), extensive metabolizers (EM), intermediate metabolizers (IM), and poor metabolizers (PM). The purpose of our study was to examine the frequencies of CYP2D6 genotypes in Finnish population in detail and compare the results to previous studies. Our study population consisted of 857 healthy volunteers whose DNA was extracted. From DNA sample we genotyped 10 different CYP2D6 genetic variants and the copy number of the gene using Applied Biosystems TaqMan genotyping and copy number assays. This study was the largest CYP2D6 genotype frequency study in Finnish population so far. The results supported the findings of a similar study in a Finnish population of smaller scale. Large majority of study subjects were EMs (87.3%) and the second largest group was Ums (7.2%). IMs and PMs were in clear minority (3.0% and 2.5%, respectively). The expected frequencies for UMs (1-2%) are much lower and for PMs higher (~8%) in other North European populations than in Finns. Accordingly, CYP2D6 genetic profile of Finnish population differs from its neighbours, which may be important for the dose requirements, efficacy, and safety for drugs metabolized by CYP2D6.