Peroxisome proliferator-activated receptor γ polymorphisms affect systemic inflammation and survival in end-stage renal disease patients starting renal replacement therapy

The Effect of PPARγ rs1801282 Variant on Mortality Risk Among Asians With Chronic Kidney Disease: A Cohort Study and Meta-Analysis

Background: Chronic kidney disease (CKD) is a public health issue, and an independent risk factor for cardiovascular disease. The peroxisome proliferator-activated receptor gamma (PPARG) plays an important role in the cardiovascular system. Previous studies have examined one important exon polymorphism, Pro12Ala, in PPARG with respect to mortality of CKD patients, but the results were inconsistent and current evidence is insufficient to support a strong conclusion. This study aimed to examine the correlation between Pro12Ala gene polymorphism and mortality among Asians with CKD by trial sequential analysis (TSA).

Methods: The research was divided into observational research and meta-analysis. For the cohort study, 767 subjects from dialysis centers in Taipei were selected as samples, and tracked from December 2015 to February 2017. For the meta-analysis, relevant literature from “PubMed” and “Embase” databases (until December 2016), was searched and TSA was used to verify the results. In order to achieve the best evidence hierarchies, our retrospective cohort study was added to the meta-analysis and the TSA.

Results: The combined sample size for Asian was 1,685 after adding our cohort study, and there was no significant correlation between PPARG Pro12Ala and mortality by the allele model (RR: 0.85, 95% CI: 0.39–1.83, I² = 79.3%). Under the parameter setting with the RR value of 1.5, TSA estimation presented that the cumulative sample size entered into the futility area, and it confirmed the conclusion in this study.

Conclusion: We found that PPARG Pro12Ala gene polymorphism was not related to mortality in CKD Asians patients, and validated our conclusion using TSA after adding our sample.

Role of peroxisome proliferator-activated receptors in stroke prevention and therapy-The best is yet to come?

Role of peroxisome proliferator-activated receptors (PPARs) in the pathophysiology of stroke and protective effects of PPAR ligands have been widely investigated in the last 20 years. Activation of all three PPAR isoforms, but especially PPAR-γ, was documented to limit postischemic injury in the numerous in vivo, as well as in in vitro studies. PPARs have been demonstrated to act on multiple mechanisms and were shown to activate multiple protective pathways related to inflammation, apoptosis, BBB protection, neurogenesis, and oxidative stress. The aim of this review was to summarize two decades of PPAR research in stroke with emphasis on in vivo animal studies. We focus on each PPAR receptor separately and detail their implication in stroke. This review also discusses recent clinical efforts in the field and the epidemiological data with regard to role of PPAR polymorphisms in susceptibility to stroke, and tries to draw conclusions and describe future perspectives.

PPARG Pro12Ala Polymorphism with CKD in Asians: A Meta-Analysis Combined with a Case-Control Study-A Key for Reaching Null Association

BACKGROUND

So far, numerous meta-analyses have been published regarding the correlation between peroxisome proliferator-activated receptor gamma (PPARG) proline 12 alanine (Pro12Ala) gene polymorphism and chronic kidney disease (CKD); however, the results appear to be contradictory. Hence, this study is formulated with the objective of using existing meta-analysis data together with our research population to study the correlation between PPARG Pro12Ala gene polymorphism and CKD and evaluate whether an accurate result can be obtained.

METHODS

First, literature related to CKD and PPARG Pro12Ala available on the PubMed and EMBASE databases up to December 2016 was gathered from 20 publications. Then, the gathered results were combined with our case-control study of 1693 enrolled subjects and a trial sequential analysis (TSA) was performed to verify existing evidence and determine whether a firm conclusion can be drawn.

RESULTS

The TSA results showed that the cumulative sample size for the Asian sample was 6078 and was sufficient to support a definite result. The results of this study confirmed that there is no obvious correlation between PPARG Pro12Ala and CKD for Asians (OR = 0.82 (95% CI = 0.66-1.02), I² = 63.1%), but this was not confirmed for Caucasians. Furthermore, the case-control sample in our study was shown to be the key for reaching this conclusion.

CONCLUSIONS

The meta-analysis results of this study suggest no significant correlation between PPARG Pro12Ala gene polymorphism and CKD for Asians after adding our samples, but not for Caucasian.

PPARG2 Pro12Ala and TNFα -308G>A Polymorphisms Are Not Associated with Heart Failure Development in Patients with Ischemic Heart Disease after Coronary Artery Bypass Grafting

TNFα and PPARγ are important modulators of metabolism, inflammation, and atherosclerosis. Coronary artery disease is the leading cause of heart failure (HF). The aim of the study was to assess whether polymorphisms of the TNFα (-308G>A) and PPARG2 (Pro12Ala) genes are associated with the risk of developing HF by patients with ischemic heart disease. Methods. 122 patients without HF (aged 63 ± 8.8 years, 85% males) with confirmed coronary artery disease qualified for coronary bypass grafting were enrolled in the study. After the procedure, they were screened for cardiac parameters. Those with elevated NT-proBNP or diminished left ventricular ejection fraction during follow-up were assigned to the HF group (n=78), and the remaining ones to the non-HF group (n=44). The TNFα -308G>A and PPARG2 Pro12Ala polymorphisms were detected using the TaqMan method. Results. The distributions of TNFα -308G>A and PPARG2 Pro12Ala did not differ between the HF and non-HF groups (-308G>A: 16% vs. 11.4% of alleles; Pro12Ala: 23.9% vs. 20.5% of alleles, respectively). IL-6 concentration in the plasma of TNFα A-allele carriers at months 1 and 12 after CABG was higher in the HF group compared to the non-HF group (1 month after CABG: 5.3 ± 3.4 vs. 3.1 ± 2.9, p<0.05; 12 months after CABG: 4.2 ± 3,9 vs. 1.4 ± 1.2, p<0.01, respectively). Both polymorphisms were not related to changes in the plasma TNFα concentration or other parameters related to HF. Conclusions. Our study did not reveal any correlation between the PPARG2 Pro12Ala and TNFα -308G>A polymorphisms and development of HF in patients with ischemic heart disease after coronary bypass grafting.

Association between PPARs Gene Functional Polymorphisms and Ischemic Stroke in Chinese Uyghur Population

PPARγ and PPARα belong to a receptor family of ligand-activated transcription factors involved in the regulation of inflammation, cellular glucose uptake, protection against atherosclerosis and endothelial cell function. Through these effects, they might be involved with the ischemic stroke (IS). We recruited 100 IS patients diagnosed by CTs or/and magnetic resonance imaging (MRI) and 100 normal healthy controls from Chinese Uyghur Population to assess the nature of the functional polymorphisms of PPARs and any links with IS in this unique population which has 60% European ancestry and 40% East Asian ancestry. We found that the Ala allele of the PPARγ Pro12Ala polymorphism was more common in controls than IS subjects (P = 0.008, corrected for multiple testing) in the Uyghur Population. Pro/Ala carriage may be associated with a decreased risk of IS in Uyghurs (OR 0.542, 95% CI 0.346-0.850). Additionally, the 162Val allele frequency at the DNA-binding region of PPARα was extremely rare in Chinese Uguhur IS patients and controls. Our population and ethnic-based study demonstrates that the 162Val allele frequency was extremely low in the Chinese Uyghur Population different from Some European and African populations and the PPARγ 12 Pro/Ala resulting in an amino acid exchange in N-terminal sequence may be an independent protective factor for IS in the Chinese Uyghur Population.

Diabetes mellitus, superoxide dismutase and peroxisome proliferator activated receptor gamma polymorphisms modify the outcome of end-stage renal disease patients of Han Chinese origin

AIM

Increased oxidative stress significantly modifies the outcome of patients with diabetes mellitus (DM) and end-stage renal disease (ESRD), and is counteracted by antioxidative capacity. We aimed to investigate whether antioxidant single nucleotide polymorphisms (SNPs) influence the outcome of ESRD individuals and the influences exerted by DM, which has not been tested before.

METHODS

We prospectively enrolled multi-centre ESRD patients of Han Chinese origin between 2002 and 2003, recording their antioxidant (superoxide dismutase [SOD2], glutathione peroxidase [GPX1]) and peroxisome proliferator activated receptor-γ (PPAR-γ) genotyping results, and stratified based on DM. They were followed up until 2008, with risk factors for mortality analyzed by Cox proportional hazard regression.

RESULTS

We discovered that diabetic ESRD carriers of CC genotype of SOD2 exon 2 had an increased risk of mortality compared to non-diabetic ones with other genotypes (hazard ratio [HR] 4.04, P = 0.04), while GPX1 SNPs had no influence. Interactions between SOD2 and PPAR-γ SNPs regarding the mortality influence were also detected (for SOD2 CC genotype x PPAR-γ exon 6 CT genotype, HR 3.19, P = 0.008), suggesting the importance of considering a combination panel of SNPs on patient survival.

CONCLUSION

This might be the largest study focusing on the relationship between antioxidant SNPs and the outcomes of diabetic ESRD patients of Han Chinese origin. More studies are needed to validate our findings.

The PPARγ2 P12A polymorphism is not associated with all-cause mortality in patients with type 2 diabetes mellitus

The high mortality risk of patients with type 2 diabetes mellitus may well be explained by the several comorbidities and/or complications. Also the intrinsic genetic component predisposing to diabetes might have a role in shaping the risk of diabetes-related mortality. Among type 2 diabetes mellitus SNPs, rs1801282 is of particular interest because (i) it is harbored by peroxisome proliferator-activated receptor-γ2 (PPARγ2), which is the target for thiazolidinediones which are used as antidiabetic drugs, decreasing all-cause mortality in type 2 diabetes mellitus, and (ii) it is associated with insulin resistance and related traits, risk factors for overall mortality in type 2 diabetes mellitus. We investigated the role of PPARγ2 P12A, according to a dominant model (PA + AA vs. PP individuals) on incident all-cause mortality in three cohorts of type 2 diabetes mellitus, comprising a total of 1672 patients (462 deaths) and then performed a meta-analysis of ours and all available published data. In the three cohorts pooled and analyzed together, no association between PPARγ2 P12A and all-cause mortality was observed (HR 1.02, 95 % CI 0.79-1.33). Similar results were observed after adjusting for age, sex, smoking habits, and BMI (HR 1.09, 95 % CI 0.83-1.43). In a meta-analysis of ours and all studies previously published (n = 3241 individuals; 666 events), no association was observed between PPARγ2 P12A and all-cause mortality (HR 1.07, 95 % CI 0.85-1.33). Results from our individual samples as well as from our meta-analysis suggest that the PPARγ2 P12A does not significantly affect all-cause mortality in patients with type 2 diabetes mellitus.

Sequence variants of peroxisome proliferator-activated receptor-gamma gene and the clinical courses of patients with end-stage renal disease

Background. PPAR-γ single nucleotide polymorphisms (SNPs) reportedly play an important role in determining metabolic risk among diverse population. Whether PPAR-γ SNPs affect the clinical courses in ESRD patients is unknown. Methods. From a multicenter cohort, we identified 698 patients with prevalent ESRD between 2002 and 2003, and other 782 healthy subjects as control. Two PPAR-γ SNPs, Pro12Ala (rs1801282) and C161T (rs3856806), were genotyped and their association with ESRD was examined. Both groups were prospectively followed until 2007, and the predictability of genotypes for the long-term survival of ESRD patients was analyzed. Results. After multivariable-adjusted regression, GG genotype of Pro12Ala was significantly more likely to associate with ESRD (P < 0.001) among patients with non-diabetes-related ESRD. Cox's proportional hazard regression showed that both Pro12Ala and C161T polymorphisms were significant predictors of mortality in ESRD patients with DM (Pro12Ala: GG versus other genotypes, hazard ratio [HR] <0.01; P < 0.001; for C161T, CC versus TT genotypes, HR 2.86; P < 0.001; CT versus TT genotypes, HR 1.93; P < 0.001). Conclusion. This is the first and largest study to evaluate PPAR-γ SNPs in ESRD patients. Further mechanistic study is needed to elucidate the role of PPAR-γ among ESRD patients.

Pro12Ala polymorphism of the PPARγ2 gene interacts with a mediterranean diet to prevent telomere shortening in the PREDIMED-NAVARRA randomized trial

BACKGROUND

The gene variant Pro/Ala (rs1801282) in the PPARγ2 has been associated with lower cardiovascular risk and greater benefit from lifestyle interventions. This polymorphism also seems to be associated with longer lifespan, but no information on telomere length (TL) is available. Our aim was to study the association between the Ala allele and changes in TL in high cardiovascular risk subjects and the potential interaction with a Mediterranean dietary pattern.

METHODS AND RESULTS

A total of 521 subjects (55-80 years) participating in the Prevención con Dieta Mediterránea randomized trial were genotyped. Changes in TL, measured by quantitative real-time polymerase chain reaction (PCR), were assessed over 5 years of a nutritional intervention, which promoted adherence to the Mediterranean diet (MeDiet). Interestingly, Ala carriers showed lower telomere shortening after 5 years compared with the Pro/Pro genotype (P=0.031). This association was modulated by MeDiet because those Ala carriers who reported better conformity to the MeDiet exhibited increased TL (P<0.001). Moreover, a reduction in carbohydrate intake (≤9.5 g/d) resulted in increased TL among Ala carriers. Notably, an apparent gene-diet interaction was found through the observed changes in the MUFA+PUFA/carbohydrates ratio: as this ratio increased, TL lengthening was detected to a greater extent in the Ala carriers compared with the Pro/Pro subjects (P for interaction <0.001).

CONCLUSIONS

The Pro12Ala polymorphism is associated with TL homeostasis after 5 years follow-up in subjects at high cardiovascular risk. In addition, a higher adherence to the MeDiet pattern strengthens the prevention of telomere shortening among Ala carriers.

CLINICAL TRIAL REGISTRATION

www.controlled-trials.com; Unique Identifier: ISRCTN35739639.

Variants of the human PPARG locus and the susceptibility to chronic periodontitis

Apart from its regulatory function in lipid and glucose metabolism, peroxisome proliferator-activated receptor (PPAR)γ has impact on the regulation of inflammation and bone metabolism. The aim of the study was to investigate the association of five polymorphisms (rs10865710, rs2067819, rs3892175, rs1801282, rs3856806) within the PPARG gene with chronic periodontitis. The study population comprised 402 periodontitis patients and 793 healthy individuals. Genotyping of the PPARG gene polymorphisms was performed by PCR and melting curve analysis. Comparison of frequency distribution of genotypes between individuals with periodontal disease and healthy controls for the polymorphism rs3856806 showed a P-value of 0.04 but failed to reach significance after correction for multiple testing ( P < 0.01). Two single nucleotide polymorphisms (SNPs) (rs10865710 and rs3892175) were found to be in strong linkage disequilibrium to rs2067819 (D’ > 0.90). A 3-site analysis (rs2067819-rs1801282-rs3856860) revealed five haplotypes with a frequency of ≥1% among cases and controls. Following adjustment for age, gender and smoking, none of the haplotypes was significantly different between periodontitis and healthy controls after Bonferroni correction. This study could not show a significant association between PPARG gene variants and chronic periodontitis.

Continuous reduction of plasma paraoxonase activity with increasing dialysis vintage in hemodialysis patients

Plasma paraoxonase (PON) is an enzyme that hydrolyzes organic phosphate and aromatic carboxylic acid esters. Reduced activity is associated with early events of atherogenesis. The relevance of PON phenotypes is not well characterized in hemodialysis patients. In a cross-sectional study we measured PON activity in 377 hemodialysis patients photometrically using the substrates 4-nitrophenylacetate and phenylacetate. The PON ratio was calculated from 4-nitrophenylacetate-derived activity divided by phenylacetate-derived activity. Frequency distribution of the PON ratio showed three different PON phenotypes. 74% of hemodialysis patients showed PON phenotype 1, 21% PON phenotype 2, and 5% PON phenotype 3. Compared to hemodialysis patients with PON 1, patients with PON 2 or 3 showed higher conversion rates for 4-nitrophenylacetate. We observed a significant reduction of PON ratio with increasing dialysis vintage (P<0.001 by ANOVA and post test for linear trend). In patients on hemodialysis treatment for less than 12 months, the PON ratio was 1.16 ± 0.08 (n=64). In patients on hemodialysis treatment for more than 60 months the PON ratio was 1.00 ± 0.04 (n=130; P=0.05). This reduction of PON activity was due to reduced 4-nitrophenylacetate-derived PON activity with increasing dialysis vintage. In conclusion, plasma PON ratio significantly declines with increasing dialysis vintage.

Inflammation and cachexia in chronic kidney disease

Chronic inflammation is associated with cachexia and increased mortality risk in patients with chronic kidney disease (CKD) and end-stage renal disease (ESRD). Inflammation suppresses appetite and causes the loss of protein stores. In CKD patients, increased serum levels of pro-inflammatory cytokines may be caused by reduced renal function, volume overload, oxidative or carbonyl stress, decreased levels of antioxidants, increased susceptibility to infection in uremia, and the presence of comorbid conditions. Cachexia is brought about by the synergistic combination of a dramatic decrease in appetite and an increase in the catabolism of fat and lean body mass. Pro-inflammatory cytokines act on the central nervous system to alter appetite and energy metabolism and to provide a signal-through the nuclear factor-kappaB and ATP-ubiquitin-dependent proteolytic pathways-that causes muscle wasting. Further research into the molecular pathways leading to inflammation and cachexia may lead to novel therapeutic therapies for this devastating and potentially fatal complication of chronic disease.

Identification of a novel allele of peroxisome proliferator-activated receptor gamma (PPARG) and its association with resistance to Aeromonas salmonicida in Atlantic salmon (Salmo salar)

Bacterial and viral diseases are major problems in Atlantic salmon aquaculture, but may be challenged through selection of brood stock with enhanced survival to diseases. Today's selection strategy is based on controlled challenge tests using siblings of the breeding candidates, and is thus indirect. Direct trait records on breeding candidates can potentially be provided through identification of genetic variation linked to the susceptibility to the disease. Peroxisome proliferator-activated receptor gamma (PPARG) is a lipid-sensing transcription factor primarily known for inducing fat-accumulation in adipocytes, but also in lipid-accumulating macrophages, in mammalian species. Here we report a novel allele of PPARG, pparg-2, in Atlantic salmon. pparg-2 has an insertion of sixty nucleotides that encodes two additional copies of the almost perfect decapeptide motif, (F/C/Y)NHSPDR(S/N)HS, compared to the previously described pparg-1. pparg-1 contains six copies of this repeat unit whereas eight copies are present in the novel pparg-2 allele. pparg-2 mRNA was detectable in kidney and spleen of random Atlantic salmon samples. Here, we studied the effect of pparg-1 and pparg-2 on survival upon challenge to a highly virulent bacterium, Aeromonas salmonicida, causing furunculosis, and the virus causing infectious salmon anaemia (ISA), respectively, in a Norwegian aquaculture population of Atlantic salmon. ppar alleles were found to be significantly associated with survival upon challenge to A. salmonicida, but not to ISA. pparg-2 was the better allele in terms of survival in the challenge test for furunculosis, survival rates being 0.32, 0.40 and 0.42 for animals with the pparg-1,-1, pparg-1, -2 and pparg-2, -2 genotypes, respectively. We conclude that pparg-2 is in linkage disequilibrium (LD) with, or identical to, a locus contributing to different susceptibility to furunculosis in Atlantic salmon. PPARG was mapped to linkage group eight (LG8) but could only be positioned on the male linkage map since all the informative parents in the mapping families were males. This is the first report showing an association between pparg alleles and an enhanced immune response in fish.

A functional polymorphism of the NFKB1 gene increases the risk for alcoholic liver cirrhosis in patients with alcohol dependence

BACKGROUND

The genetic basis for the predisposition to alcoholic liver cirrhosis (ALC) remains unknown. Increasing evidence supports a role for the nuclear factor (NF)-kappaB, the NF-kappaB inhibitor alpha (NFKBIA), and the peroxisome proliferator-activated receptor (PPAR)-gamma in the pathogenesis of alcoholic liver disease, raising the possibility that common polymorphisms in genes encoding these molecules may confer susceptibility to ALC. The objective of this study was to analyze the relationship between common polymorphisms in NFKB1, NFKBIA, and PPARG2 genes and the presence of ALC.

METHODS

A total of 258 male alcoholics (161 without liver disease and 97 with ALC) and 101 healthy controls were genotyped for the -94ins/delATTG NFKB1, 3'-UTR+126G>A NFKBIA, and 34C>G PPARG2 polymorphisms. The association of these genetic variants with ALC was tested in alcoholic patients with alcohol abuse and alcohol dependence. A logistic regression analysis was further performed to analyze the model of inheritance.

RESULTS

We found an association between the presence of the deletion allele in NFKB1 polymorphism and ALC in patients with alcohol dependence. We found no association between NFKBIA and PPARG2 polymorphisms and the presence of ALC.

CONCLUSIONS

The deletion allele of the -94ins/del NFKB1 polymorphism could be associated with a higher risk of developing ALC through an increase in inflammation, as supported by previous data.

Inflammation in chronic kidney disease: role in the progression of renal and cardiovascular disease

Inflammation is the response of the vasculature or tissues to various stimuli. An acute and chronic pro-inflammatory state exists in patients with chronic kidney disease (CKD), contributing substantially to morbidity and mortality. There are many mediators of inflammation in adults with CKD and end-stage kidney disease (ESKD), including hypoalbuminemia/malnutrition, atherosclerosis, advanced oxidation protein products, the peroxisome proliferators-activated receptor, leptin, the thiobarbituric acid reactive system, asymmetric dimethyl arginine, iron, fetuin-A, and cytokines. Inflammation contributes to the progression of CKD by inducing the release of cytokines and the increased production and activity of adhesion molecules, which together contribute to T cell adhesion and migration into the interstitium, subsequently attracting pro-fibrotic factors. Inflammation in CKD also causes mortality from cardiovascular disease by contributing to the development of vascular calcifications and endothelial dysfunction. Similar to the situation in adults, cardiovascular disease in pediatric CKD is linked to inflammation: abnormal left ventricular wall geometry is positively associated with markers of inflammation. This review focuses on traditional and novel mediators of inflammation in CKD and ESKD, and the deleterious effect inflammation has on the progression of renal and cardiovascular disease.

Role of PPARgamma in renoprotection in Type 2 diabetes: molecular mechanisms and therapeutic potential

DN (diabetic nephropathy) is a chronic disease characterized by proteinuria, glomerular hypertrophy, decreased glomerular filtration and renal fibrosis with loss of renal function. DN is the leading cause of ESRD (end-stage renal disease), accounting for millions of deaths worldwide. TZDs (thiazolidinediones) are synthetic ligands of PPARgamma (peroxisome-proliferator-activated receptor gamma), which is involved in many important physiological processes, including adipose differentiation, lipid and glucose metabolism, energy homoeostasis, cell proliferation, inflammation, reproduction and renoprotection. A large body of research over the past decade has revealed that, in addition to their insulin-sensitizing effects, TZDs play an important role in delaying and preventing the progression of chronic kidney disease in Type 2 diabetes. Although PPARgamma activation by TZDs is in general considered beneficial for the amelioration of diabetic renal complications in Type 2 diabetes, the underlying mechanism(s) remains only partially characterized. In this review, we summarize and discuss recent findings regarding the renoprotective effects of PPARgamma in Type 2 diabetes and the potential underlying mechanisms.

Genetics and reverse epidemiology among patients on chronic hemodialysis

A reversal in the association between traditional and nontraditional risk factors and clinical outcomes is often encountered in patients with chronic illness, including among those with advanced chronic kidney disease (CKD) on maintenance hemodialysis (MHD). The effects of the malnutrition-inflammation complex syndrome (MICS) may play a significant role in the reversal of this risk factor-outcomes association. the MICS, this syndrome complex is not universal in its prevalence among MHD patients. The significant inter- and intra-individual differences in the prevalence of inflammation, oxidative stress, and malnutrition, indicates the influence of genetic factors in this variability. In recent years, enormous advancement in the field of molecular genetics, genomics and bioinformatics, have revolutionized studies of the genetic epidemiology of several diseases. However, genetic association studies are at a preliminary stage in the population with advanced CKD (Table 1). Preliminary studies of the impact of polyphisms in inflammation and oxidative stress-related genes and genes affecting body composition and metabolism suggest that genetic variation may indeed affect the phenotype of the MHD population. Further, some of these gene polymorphisms may also contribute to a reversal of the association between traditional risk factors, such as BMI, blood pressure, and cholesterol and clinical outcomes in this vulnerable patient population. Genetic studies in patients with advanced CKD pose enormous challenges, including recruitment of sufficient numbers of patients to achieve adequate statistical power, resolution of immense genotypic and phenotypic heterogeneity, and gene-environment and gene-gene interactions. However, well-designed adequately powered studies with carefully defined phenotypes may potentially allow definition of risk profiles characterized by combinations of relevant Single nucleotide polymorphisms in the setting of given environmental factors. Accurate risk stratification that takes into account genetic information would allow more informed targeting of pharmacologic intervention and better refined clinical trial methodologies.

Place of genotyping and phenotyping in understanding and potentially modifying outcomes in peritoneal dialysis patients

With the landmark publication of the human genome sequence and its subsequent division into haplotype blocks, the characterization of genetic variations is becoming a feasible approach to study both the pathophysiology and risk factors of complex traits. A number of strategies are available today for identifying candidate genes or polymorphisms associated with pertinent phenotypes. For Mendelian diseases with high penetrance owing to mutations in a single gene, such as polycystic kidney disease, linkage studies have been very successful in mapping the disease loci owing to the availability of families with multiple affected members. In contrast to monogenic conditions, complex diseases such as end-stage renal disease (ESRD) and complex traits such as individual variations in membrane transport and complications during the course of peritoneal dialysis (PD) therapy have a number of competing determinants and inhibitors, both genetic and environmental. Current results reflect this complexity, with few studies showing a large effect of any single risk factor on survival or outcome on PD. However, these studies have so far been small (less than 500 patients) and have not utilized bioinformatics or novel technologies (e.g., multiplex genotyping equipment). In the following review, we outline current approaches for using genetic data in clinical studies as well as highlight some of the most promising results in ESRD patients, particularly those on PD.

PPARG locus haplotype variation and exacerbations in asthma

The peroxisome proliferator-activated receptor gamma (PPARgamma) regulates inflammation and may play a role in asthma. Using mouthwash-derived DNA and clinical interviews and measurements, we investigated the association of previously characterized single-nucleotide polymorphisms in the PPARG gene (Pro12Ala, C1431T, and C-681G) with asthma exacerbations in patients aged 3-22 years (n=569). The common homozygous haplotype combination of the Pro12 and C1431 alleles was associated with increased risk for asthma exacerbations (ProC, odds ratio (OR) 1.87, 95% confidence interval 1.25-2.79; P=0.002). The ProC genotype was associated with increased school absences (OR 1.82, 95% confidence interval 1.21-2.76; P=0.004) and hospital admissions (OR 2.32, 95% confidence interval 1.18-4.58; P=0.015) over the preceding 6 months. The population-attributable risk of this genotype was 33%. Common genetic variation at the PPARG locus may play an important role in modulating the long-term control of asthma in children and young adults.

New insights on inflammation in chronic kidney disease–genetic and non-genetic factors

Cardiovascular disease (CVD) remains the major cause of morbidity and mortality in chronic kidney disease (CKD). As traditional risk factors cannot alone explain the unacceptable high prevalence and incidence of CVD in this population, inflammation (which is interrelated to insulin resistance, oxidative stress, wasting and endothelial dysfunction) has been suggested to be a significant contributor. Indeed, several different inflammatory biomarkers, such as high sensitivity C-reactive protein (CRP) has been shown to independently predict mortality in CKD patients. The causes of the highly prevalent state of inflammation in CKD are multiple and include factors such as volume overload, co-morbidity, intercurrent clinical events, the dialysis procedure per se as well as genetic factors. Indeed, multiple cytokine DNA polymorphisms may affect the inflammatory state, the clinical phenotype as well as outcome in this patient population.