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June 1, 2005
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A pharmacogenomic approach to therapy requires systematic knowledge of the regulatory regions of the genes, as well as basic understanding of transcriptional regulatory mechanisms of genes. Using the apolipoprotein (apo) A-I/CIII gene cluster as a model system, we have identified by in vitro and in vivo studies the regulatory elements and the factors which control its transcription. Studies in transgenic mice established that the hepatocyte nuclear factor (HNF-4) binding site of the apoCIII enhancer, which controls transcription of both genes, is required for the intestinal expression of apoA-I and apoCIII genes, and enhances synergistically their hepatic transcription in vivo . The three Sp1 sites of the enhancer are also required for the intestinal expression of apoA-I and apoCIII genes in vivo, and for the enhancement of the hepatic transcription. The regulation of the apoE/apoCI/apoCIV/apoCII cluster is also cited. It is expected that identification of the regulatory regions of genes will be soon accelerated by the sequencing of several mammalian genomes. The functional analyses of the regulatory domains of genes involved in lipid homeostasis, combined with cross-species sequence comparisons in the near future, may identify natural regulatory gene polymorphisms in the general population that will permit rational pharmacogenomic approaches for treatment of dyslipidemias.
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June 1, 2005
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We present some current definitions related to functional and structural proteomics and the human proteome, and we review the following aspects of proteome analysis: Classical 2-D map analysis (isoelectric focusing (IEF) followed by SDS-PAGE); Quantitative proteomics (isotope-coded affinity tag (ICAT), fluorescent stains) and their use in e.g., tumor analysis and identification of new target proteins for drug development; Electrophoretic pre-fractionation (how to see the hidden proteome!); Multidimensional separations, such as: (a) coupled size-exclusion and reverse-phase (RP)-HPLC; (b) coupled ion-exchange and RP-HPLC; (c) coupled RPHPLC and RP-HPLC at 25/60 °C; (d) coupled RP-HPLC and capillary electrophoresis (CE); (e) metal affinity chromatography coupled with CE; Protein chips. Some general conclusions are drawn on proteome analysis and we end this review by trying to decode the glass ball of the aruspex and answer the question: “ Quo vadis, proteome ”?
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June 1, 2005
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In the last few years, a very active line of research took place after the first identification of SCN5A mutations associated with an inherited form of cardiac arrhythmias and sudden death, the LQT3 variant of the long QT syndrome. Subsequently, two allelic diseases additional to LQT3 were shown to be due to mutations in the same gene, the Brugada syndrome (BrS) and the Lev-Lenegre syndrome (progressive cardiac conduction defect). Genotype-phenotype correlation and in vitro expression studies provide evidence that structure-function relationships of the SCN5A protein are much more complex than initially anticipated. The biophysical characterization of the sodium channel defects associated with different phenotypes and the genotype-phenotype correlation studies brought to the attention of the scientific community a plethora of mechanisms by which even a single amino acid substitution may remarkably affect cardiac excitability. Finally, the evidence of patients harboring an SCN5A mutation and overlapping clinical presentations creates a need for a revision of the traditional classification of the above mentioned diseases. It is now appropriate to consider the “sodium channel syndrome” as a unique clinical entity that may manifest itself with a spectrum of possible phenotypes.
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June 1, 2005
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Thanks to its typical expression, haemophilia can be identified in writings from the second century AD. Haemophilia B, an X-linked recessive bleeding disorder due to factor IX (FIX) deficiency, has an incidence of about 1:30000 live male births. The factor 9 ( F9 ) gene was mapped in 1984 on Xq27.1. Haemophilia is diagnosed from prothrombin time, activated partial thromboplastin time, and FIX levels. Carrier females are usually asymptomatic and must be identified only with molecular analysis. Linkage analysis of F9 polymorphisms is rapid and inexpensive but limited by non-informative families, recombinant events, and the high incidence of germline mutations; thus, various procedures have been used for the direct scan of F9 mutations. We set up a novel denaturing high performance liquid chromatographic procedure to scan the F9 gene. This rapid, reproducible procedure detected F9 mutations in 100% of a preliminary cohort of 18 haemophilia B patients. Parallel to the development of more efficient diagnostic tools, the life expectancy and reproductive fitness of haemophilic patients have greatly improved and will continue to improve thanks to the use of less immunogenic recombinant FIX. Hopefully, new approaches based on gene therapy now being evaluated in clinical trials will revolutionise haemophilia B treatment.
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June 1, 2005
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Over the past five years, denaturing high-performance liquid chromatography (DHPLC) has emerged as one of the most versatile technologies for the analysis of genetic variations. With the benefit of novel polymer chemistries used for separation, the accuracy, sensitivity, and the throughput of DHPLC for DNA and RNA analysis have greatly improved. DHPLC has been adopted in many laboratories for the screening of mutations and single-nucleotide polymorphisms (SNPs). The ability of DHPLC to detect known and unknown mutations simultaneously has put this technology at the forefront of genetic analysis for a wide variety of diseases. In addition, the high sensitivity of DHPLC combined with the accuracy of the heteroduplex analysis has allowed the development of applications beyond the scope of traditional sequencing or genotyping, e.g., the early detection of cancer. This article reviews the methods, which made DHPLC a widely used tool for diagnosis in molecular genetics and pharmacogenetics. The article provides an overview of current applications in these fields and points to novel applications in areas like epigenetics and the analysis of heteroplasmic mitochondrial DNA, in which DHPLC is becoming the leading technology.
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June 1, 2005
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Molecular diagnostics is being revolutionized by the completion of the human genome project and by the development of highly advanced technologies for DNA testing. One of the most important challenges is the introduction of high throughput systems such as DNA chips into diagnostic laboratories. DNA microchips are small devices permitting rapid analysis of genetic information, exploiting miniaturization of all components and automation of operational procedures. The most important biochip applications include gene expression and genetic variation identification and both may improve human molecular diagnostics. Here we review several approaches developed to allow rapid detection of many single nucleotide polymorphisms and mutations in large population samples. Among these, the use of microelectronics seems to best fit with the needs of molecular diagnostics.
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Molecular beacons are single-stranded, fluorophore-labeled nucleic acid probes that are capable of generating a fluorescent signal in the presence of target, but are dark in the absence of target. Molecular beacons allow multiplex detection of PCR products in real time in a homogeneous assay format. Real time detection is inherently quantitative and affords a greater dynamic range than end-point detection methods. Reactions in a homogeneous assay format are sealed before amplification takes place, providing improved contamination control. A single cycler/reader instrument, coupled with automated sample preparation, results in higher throughput and greater ease of use. A multiplex qualitative assay that detects Chlamydia trachomatis and Neisseria gonorrhoeae , along with an internal control, has been developed. High specificity is achieved through careful selection of primers, probes and assay conditions. Quantitative HIV, HCV, and HBV viral load assays, with sensitivities of 50 copies/ml, 20 IU/ml, and 50 copies/ml, respectively, are achievable. The viral load assays are designed to quantitate all subtype and genotype specimens equivalently. A molecular beacon assay has been designed to detect a single nucleotide polymorphism in the β 2 adrenergic receptor gene.
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June 1, 2005
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In recent years there has been an increased interest in using biosensors for the recognition and monitoring of molecule interactions. DNA sensors and gene chips are particularly relevant for directly applying the information gathered from the genome projects. In this work electrochemical techniques are used to develop methodologies to detect DNA polymorphisms in human genes using cytochrome P450 3A4 ( CYP3A4 ) as a model gene. CYP3A4 * 1B oligonucleotides were immobilized on the surface of a gold electrode and hybridized with fully complementary oligonucleotide sequences as well as with mismatched sequences corresponding to the CYP3A4 * 1A reference sequence. The methodology developed is based on double-stranded DNA's ability to transport charge along nucleotide stacking. The perturbation of the double helix pi-stack introduced by a mismatched nucleotide reduces electron flow and can be detected by measuring the attenuation of the charge transfer. The methodology developed could identify CYP3A4 * 1A homozygotes by the 5 μC charge attenuation observed when compared with DNA samples containing at least one CYP3A4 * 1B allele.
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June 1, 2005
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For several years it has been possible to routinely detect numerous mutations in the human genome by different methods. The most common technique is a standard PCR, but real time fluorescence PCR is increasingly being used. The purpose of this paper is to compare these two different techniques from the point of view of reliability, time consumption, and cost. More than 600 DNA samples of prevalence studies and from cancer patients were used to determine mutations in the genes of coagulation factor V Leiden, prothrombin, and methylenetetrahydrofolate reductase using standard PCR. A subset of 132 samples from the same pool was also tested by LightCycler PCR for the same coagulation gene mutations. Originally LightCycler techniques were applied for quantitative PCR by real time fluorescence measuring. Adding a melting curve analysis allows mutation detection. The results were perfectly concordant. The cost for the reagents is nearly the same for both methods but the time consumption for standard PCR is much higher than for the LightCycler method, resulting in higher laboratory personnel costs.
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Purified water is a reagent used in a variety of molecular biology experiments, for sample and media preparation, in mobile phases of liquid chromatography techniques, and in rinsing steps. The combination of several technologies in water purification systems allows delivering high-purity water adapted to each application and technique. Through a series of examples, the importance of water quality on biotechnology experiments, such as single nucleotide polymorphism (SNP) analysis by denaturating HPLC, RNA preparation and PCR, is presented. Results obtained on DNA mutation and single nucleotide polymorphism analysis using the denaturating HPLC (DHPLC) technique highlight the benefits of organic removal by UV photooxidation process. Comparative gel electrophoresis data show that ultrafiltration is as efficient as diethylpyrocarbonate (DEPC) treatment for suppressing RNase activity in water. Gel electrophoresis and densitometry measurement also point out the benefits of ultrafiltration to carry out reverse transcriptase-polymerase chain reaction quantitatively.
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We undertook genetic and biochemical assays in patients with arterial (n = 146) and venous (n = 199) thromboembolism and survivors of pulmonary embolism (n = 58) to study causation and gene-life style interactions. In the clinical material from North Western Russia, factor V Leiden was found to be a risk factor in venous thrombosis (OR = 3.6), while the methylenetetrahydrofolate reductase (MTHFR) C677T mutation was a significant variable in both venous (p = 0.03) and arterial thrombosis (p = 0.004). Homocysteine levels were determined (n = 84) and hyperhomocysteinemia correlated with the T allele of the MTHFR gene, and with smoking and coffee consumption. Vitamin supplementation reduced homocysteine levels dependent on MTHFR genotype (36% TT, 25% CT, 22% CC). In pulmonary embolism patients, frequency of the − 455G/A β- fibrinogen dimorphism was studied. Carriers of this allele were significantly underrepresented (p < 0.02) among pulmonary embolism survivors (34.5%) compared to controls (56.7%). Additionally, − 455AA homozygotes were found in 11.7% controls but only 1.7% of pulmonary embolism patients (p = 0.006). In venous and arterial thrombosis cases, MTHFR and homocysteine data led to effective dietary supplementation with a reduced risk of disease progression. Results from the pulmonary embolism study may indicate that screening tests for the − 455G/A β- fibrinogen genetic variation could be of prognostic value, and may point the way for novel anticoagulation strategies.
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June 1, 2005
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Tumour necrosis factor alpha (TNF-α), acting as a modulator of gene expression in adipocytes, has been linked to the development of insulin resistance and obesity. The aim of this study was to investigate whether the A/G variation at position −308 in the TNFα promoter influences the body weight, insulin resistance, and postprandial lipaemia in Polish Caucasians. One hundred twenty one subjects, 38 men and 83 women, representing 40 obese families, were genotyped by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). TNF-1 (GG) and TNF-2 (GA and AA) allele carriers were compared with respect to body mass index, fat/lean body mass composition, waist-to-hip ratio, as well as fasting lipids, glucose, leptin, and insulin fasting, and during the oral glucose tolerance test (4 points within 2 hours) and oral lipid tolerance test (OLTT; 5 points within 8 hours). The insulin sensitivity indices HOMA-IR (homeostasis model assessment of insulin resistance), ISI-COMP (whole body insulin sensitivity index), ISI-HOMA (hepatic insulin sensitivity), and DELTA (early secretory response to an oral glucose load) were calculated. We detected 64 GG, 56 GA, and 1 AA genotypes. Significant increases of insulin resistance parameters in obese female TNF-2 allele carriers were observed (significantly increased HOMA-IR and decreased ISI-HOMA, ISI-composite). The male TNF-2 carriers were characterised by significantly increased levels of triglyceride and free fatty acids during OLTT as well as fasting glucose. The A/G variation at position −308 in the promoter region of the TNF-α gene could be an important genetic factor predisposing to insulin resistance in obese women and increased levels of glucose, triglyceride, and free fatty acids in men.
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Since the inflammatory cytokine tumor necrosis factorα (TNF-α) may play a major role in the pathophysiology of acute coronary syndromes, 299 consecutive male patients hospitalized for coronary artery disease ( i.e., lumen lost ≥50%) were genotyped for the functional −308G/A TNF-α polymorphism using restriction fragment length polymorphism method, in order to evaluate its potential association with the risk of unstable angina and/or myocardial infarction. A higher frequency of carriers of the A allele was observed in patients with unstable angina (n = 58) when compared to control patients with stable angina (n = 95) (39.66% vs . 23.16% respectively, p = 0.029, odds ratio = 2.2) but not in patients with myocardial infarction (n = 146) (23.97% vs . 23.16%, p = NS). Furthermore, we evidenced an interaction of the polymorphism studied with body mass index in patients with unstable angina. Thus, when stratified analysis was performed, results in patients with a body mass index ≤ 27 showed a more striking association between A allele carriage frequency and unstable angina (p = 0.012, odds ratio = 3.0). These results suggest the crucial role of TNF-α in the mechanisms responsible for unstable angina in accordance with the concept of vulnerable plaque. On the other hand, mechanisms controlling myocardial infarction appear more complex and heterogeneous.
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June 1, 2005
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The newly recognised apolipoprotein (apo) AV gene ( APOAV ) has been linked to fasting plasma triglyceride (TG) concentrations with some polymorphisms associated with elevated fasting TGs. Since fasting plasma TGs are mainly determined by the hepatic production of TG-rich particles (very low density lipoprotein; VLDL), and fasting TGs are the major determinants of postprandial lipaemia, we have evaluated the effects of an APOAV polymorphism on postprandial triglyceridaemia, which is largely determined by the intestinal production and clearance of chylomicrons. For this purpose, diurnal capillary triglyceridaemia (reflecting postprandial lipaemia) was determined in a cohort of 88 healthy volunteers (48 males and 40 females) in relation with a −1131T>C variant in the promoter of APOAV. Thirteen of these subjects (7 males and 6 females) were carriers of the −1131C allele, which has been associated with higher fasting plasma TG levels. The carriers had higher fasting capillary TG concentrations, although plasma TGs were not significantly different from non-carriers in this cohort. Surprisingly, total diurnal triglyceridaemia calculated as the area under the capillary TG curve was similar in carriers compared to non-carriers but after correction for fasting capillary TG levels, incremental diurnal triglyceridaemia was significantly lower in carriers (1.74 (5.27) mmol/h/l) than in non-carriers (4.91 (4.90) mmol/h/l; p = 0.036). The same trends were found for both males and females when analysed separately. Since dietary intake, which is a major determinant of incremental diurnal triglyceridaemia, did not differ between the two groups, we believe that these differences are at least partly explained by the APOAV . In summary, the APOAV assessed by means of the −1131T>C variant seemed to have a paradoxical effect on postprandial lipaemia when compared to fasting TG levels.
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June 1, 2005
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The objective of the present study was to analyse the potential synergistic influence of the insertion/deletion polymorphism of the angiotensin-converting enzyme gene ( I/D ACE) and the A1166C polymorphism of the angiotensin-II type 1 receptor gene polymorphisms (A1166C AT1R) on the left ventricular size and performance. Three hundred sixty and one consecutive, Caucasian patients with angiographically confirmed coronary artery disease (CAD) were enrolled into the study. Left ventricular diameter, mass and function were evaluated by echocardiography. Screening for the I/D ACE and A1166C AT1R genotypes was performed by polymerase chain reaction of genomic DNA, followed by restriction enzyme digestion and agarose gel electrophoresis. The I/D ACE and A1166C AT1R genotypes separately were not significantly associated with the left ventricular size and function parameters in CAD patients. However, trends towards decreased left ventricular ejection fraction (LVEF) as well as increased left ventricular end-diastolic diameter (LVEDD) and left ventricular mass index (LVMI) were observed when patients with genotype DD + CC/AC and DD + CC were compared to patients homozygous only in one locus ( DD or CC) . Significant increase in LVEDD and LVMI was observed only in patients with a history of anterior myocardial infarction with combined genotype DD + CC/AC or DD + CC . This study does not support the role of the ACE I/D and AT1R A1166C polymorphisms in the determination of the left ventricular size and performance in patients with significant coronary atherosclerosis. However, it indicates that the influence of polymorphisms may be present in specific patient populations.
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June 1, 2005
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Coronary heart disease (CHD) is a complex genetic disease involving gene-environment interaction. Many association studies between single nucleotide polymorphisms (SNPs) of candidate genes and CHD have been reported. We have applied a new method to analyze such relationships using support vector machines (SVMs), which is one of the methods for artificial neuronal network. We assumed that common haplotype implicit in genotypes will differ between cases and controls, and that this will allow SVM-derived patterns to be classifiable according to subject genotypes. Fourteen SNPs of ten candidate genes in 86 CHD patients and 119 controls were investigated. Genotypes were transformed to a numerical vector by giving scores based on difference between the genotypes of each subject and the reference genotypes, which represent the healthy normal population. Overall classification accuracy by SVMs was 64.4% with a receiver operating characteristic (ROC) area of 0.639. By conventional analysis using the χ 2 test, the association between CHD and the SNP of the scavenger receptor B1 gene was most significant in terms of allele frequencies in cases vs . controls (p = 0.0001). In conclusion, we suggest that the application of SVMs for association studies of SNPs in candidate genes shows considerable promise and that further work could be usefully performed upon the estimation of CHD susceptibility in individuals of high risk.
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June 1, 2005
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This study describes the factors of variation of the enzymes related to the PON1-192 phenotype assessment, i.e., basal paraoxonase, salt-stimulated paraoxonase and arylesterase activities, and compares the PON1-192 phenotype to the PON1 -192 genotype assessments in supposedly healthy subjects issued from the Stanislas cohort study. The studied population included 918 subjects, i.e., 221 families including 441 adults and 477 children aged 4 to 58 years. Potential determinants such as age, gender, body mass index, alcohol and tobacco consumption, and oral contraceptive intake have been studied. The PON ratio (salt-stimulated paraoxonase/arylesterase) was trimodally distributed and the cut-off values used to differentiate the two homozygous (AA and BB phenotypes) from the heterozygous (AB phenotype) subjects were 3.0 and 7.0 in this study. In males, basal paraoxonase and salt-stimulated paraoxonase activities were not affected by alcohol consumption and current smoking, but basal paraoxonase activity was decreased by 15% by current smoking and was increased by 15% by oral contraceptive intake in females as was the salt-stimulated paraoxonase activity. The level of discordance between phenotype and genotype assessments was 7.2% (66/918). Most of the discrepancies were observed between the BB and AB phenotypes (4.25%).
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Modifications in lipoprotein lipase levels lead to elevated triglycerides and reduced high density lipoprotein (HDL), both of which are risk factors for coronary artery disease (CAD). Hence, we examined the influence of the −93T/G, D9N, N291S, and S447X polymorphisms in the lipoprotein lipase ( LPL ) gene on CAD risk and lipid levels in Croatian patients with and without angiographically confirmed CAD. The N291S polymorphism was significantly associated with CAD (OR = 0.36; 95% CI = 0.13, 0.99; p = 0.048). This association was only moderately affected by adjusting for various lipids (OR = 0.36; 95% CI = 0.12, 1.08; p = 0.068). HDL 2 -cholesterol and apolipoprotein A-I levels were significantly higher in non-carriers of the −93T/G and D9N polymorphisms in the CAD group (p = 0.017 and 0.028, respectively). The N291S genetic variant did not show any significant difference between carriers and non-carriers in either group studied for any of the lipids. Lower triglyceride and higher HDL 2 -cholesterol levels in the control group were associated with carriers of the S447X mutation (p = 0.043 and 0.056, respectively). LPL gene polymorphisms might be involved in predisposition to CAD and determination of lipid profiles.
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June 1, 2005
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Background: Methylenetetrahydrofolate reductase 677 (MTHFR 677) polymorphism may provoke hyperhomocysteinemia when folate status is low. The influence of MTHFR 677 mutation on homocysteine (HCY) levels in relation to vitamin B 12 and folate status was investigated in the current study. Subjects and methods: 113 vegetarians, 123 omnivorous Germans, and 117 omnivorous Syrians were recruited. MTHFR 677 genotype, HCY, methylmalonic acid (MMA), total serum vitamin B 12 , serum folate, and vitamin B 6 were determined using conventional methods. Results: Omnivorous Germans displayed the lowest HCY levels compared with vegetarians and Syrians (median 8.0, 10.4, and 11.3 μmol/l, respectively). The highest serum folate and the highest MMA levels were found in vegetarians (median folate = 30.0; MMA = 355 nmol/l). Among vegetarians and Syrians, TT subjects had higher HCY levels than other genotypes which were, however, no longer significant in the highest folate tertiles. When the data were pooled, the odds ratio (OR, 95% CI) for HCY > 12 μmol/l was 3.81 (1.55–9.34) in TT compared with CC subjects. The OR increased to 28.85 (4.63–179.62) in TT subjects who had folate in the lowest tertile, and to 21.84 (4.81–99.1) in TT subjects who had MMA in the highest MMA tertile. Conclusion: MTHFR 677 TT individuals are more liable to hyperhomocysteinemia under vitamin B 12 deficiency than the other two genotypes. In such a case, relative folate shortage may progressively increase HCY levels. TT individuals may have increased folate and vitamin B 12 requirements compared to the other CC and CT genotypes.
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In a narrow meaning, responders to a therapy are all those who will react as expected following the administration of this therapy. However, a wider definition is worth considering: all those for whom the administration of the therapy will be beneficial. Innovative therapies are increasingly expensive and hazardous, and limiting prescriptions to responders is both economically and ethically compulsory. The theoretical basis for such an approach exists. The process of defining the profile of responders consists of identifying the characteristics of the patients that interact with the size of the effect and integrating them quantitatively in a predictive model. The effect model, which is the relation between the risks of the event with and without the treatment, can be used for the prediction. It can integrate interactions of the efficacy with risk factors and/or genes. The data to be used to achieve both the identification of the interactions and the building of the predictive model are those from the studied population, the set of patients enrolled in clinical trials. Hence, the process of defining the therapy is an extrapolation from the studied population. To carry out the extrapolation process one can use various available techniques, of which none fully fits the purpose. No method is currently both fully adequate and validated. Finally, the predictive models, which we need to identify responders, do not exist in practice. Fortunately, new research approaches have been developed recently.
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June 1, 2005
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The number of polymorphisms identified in genes encoding drug metabolising enzymes, drug transporters, and receptors is rapidly increasing. In many cases, these genetic factors have a major impact on the pharmacokinetics and pharmacodynamics of a particular drug and thereby influence the sensitivity to such drug in an individual patient with a certain genotype. The highest impact is seen for drugs with a narrow therapeutic index, with important examples emerging from treatment with antidepressants, oral anticoagulants, and cytostatics, which are metabolised by the polymorphic enzymes cytochrome P450 2D6 (CYP2D6), cytochrome P450 2C9 (CYP2C9), and thiopurine- S -methyltransferase (TPMT), respectively. In order to apply the increasing amount of pharmacogenetic knowledge to clinical practise, specific dosage recommendations based on genotypes will have to be developed to guide the clinician, and these recommendations will have to be evaluated in prospective clinical studies. Such development will lead to a patient-tailored drug therapy which hopefully would be more efficient and will result in fewer adverse drug reactions.
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June 1, 2005
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Cholesterol-lowering therapy is the central approach in the primary and secondary prevention of cardiovascular disease, the leading cause of death in industrialized countries. 3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) are currently the most potent and widely used cholesterol-lowering drugs. Large-scale clinical trials unequivocally demonstrated the efficacy of statin treatment in reducing the risk of cardiovascular events. In general, HMG-CoA reductase inhibitors are well tolerated, although in a minority of patients severe adverse effects like myopathy or rhabdomyolysis may develop. The incidence of this potentially life-threatening side effects increases with co-adminstration of drugs that are metabolized via the same pharmacokinetic pathways or at high-dose statin therapy. The recent focus on the pleiotropic effects of statins that are more frequently observed at higher doses and the conclusion drawn from the large statin trials that low-density lipoprotein (LDL)-cholesterol is “the lower the better”, may need careful consideration in individuals at risk of adverse drug reactions. On the other hand, not all patients respond to statin therapy with a reduction in coronary heart disease (CHD) risk. It is therefore of interest to develop diagnostic test systems, which would allow to identify patients at increased risk of adverse drug reactions or patients with a lack of therapeutic effect. Beside exogenous factors, genetic variability determines the response of an individual to drug therapy and the analysis of genetic variants affecting pharmacokinetic or pharmacodynamic aspects of drug therapy is the subject of pharmacogenomics. This review summarizes current knowledge of the pharmacology and the pharmacogenomics of statin therapy.
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June 1, 2005
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The variability in drug response originates partly from genetics, with possible consequences for drug efficacy, adverse effects, and toxicity. Until now, pharmacogenetics mainly indicated the best known source of variability, that is, the variability caused by drug metabolism. However, simultaneous progress in the knowledge of biochemical targets of drugs and of the human genome, together with the development of new technologies, revealed many new sources of human genetic variation, e.g., in receptors or transporters. Drugs are metabolized by various polymorphic phase I enzymes, including cytochromes P450 (CYP). Among them, the most relevant for the metabolism of cardiovascular drugs are CYP3A4, CYP2C9 or CYP2C19, and CYP2D6. The role of phase II enzymes is limited with regard to cardiovascular drugs biotransformation, but some polymorphisms (glutathion-S-transferase; GSH-T) are linked to cardiovascular risk. Phase III proteins or transporters, especially from the ABC family, must also be considered, as their polymorphisms affect cholesterol and other sterols transport. Among pharmacological targets, some proteins were identified as involved in interindividual variations in the response to cardiovascular drugs. Some examples are apolipoprotein E, angiotensin-converting enzyme, and the β-adrenergic receptor. From the risk concept emphasizing impaired metabolism and adverse effects, we now moved to an approach, which is a personalized, genotype-dependent adaptation of therapy.
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June 1, 2005
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Glutathione S -transferase (GST) and arylamine N -acetyltransferase 2 (NAT2) metabolise many environmental and chemotherapeutic agents, which influence susceptibility to disease. Polymorphisms in these enzymes result in different host phenotypes and contribute to different disease profiles or responses to toxic or chemotherapeutic agents, depending on their frequency in different populations. GST and NAT2 polymorphisms were investigated in different population groups, including African populations, and a range of allelic frequencies have been observed. The GSTM1 null genotype frequency, reported in this paper in two South African ethnic groups, is the lowest reported (0.19–0.21). In contrast, these same groups have a high GSTT1 null frequency (0.41–0.54), which is considerably higher than in African-Americans, or other Africans. The GSTT1 null frequency is comparable to the Chinese, a population with a very high oesophageal cancer incidence, similar to that in the African group. The frequency of the GSTPi Val 105 variant in the South African Xhosas was also high (0.53), differing significantly from the low frequency in other Africans. These variants could therefore be associated with high cancer susceptibility. In addition, the high proportion of NAT2 “fast” alleles may partially explain the high tuberculosis prevalence in South Africans, due to reduced isoniazid efficacy in the presence of rapid acetylation.
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Single nucleotide polymorphisms were examined in the cytochrome 450 3A4 ( CYP3A4 ) and N -acetyltransferase 2 ( NAT2 ) genes, which code for major mediators of the metabolism of a wide variety of therapeutic drugs, as well as xenobiotics. We determined, in a population from Guinea-Bissau, the frequencies of CYP3A4 and NAT2 variants expected to be prevalent among Africans, due to the high frequency previously observed in African Americans. The observed frequencies were 72% for CYP3A4*1B and 19.2% for the NAT2 191 G>A variant. The high frequency found for these potentially function-altering polymorphisms suggests the possibility of impaired metabolism through CYP3A4 and NAT2 in this population. Strikingly, the frequency observed for the NAT2 191 G>A single nucleotide polymorphism (SNP), associated with the slow acetylator phenotype, was significantly higher than found in other African populations, suggesting the existence of a west to east gradient across Sub-Saharan Africa. The prevalence of these variants may be relevant with regard to therapeutic efficacy in African populations for it may potentially affect drug clearance and consequently, increase the incidence of side effects and drug-drug interactions.
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