Gene polymorphism association studies in dialysis: vascular access

Association of Genetic Polymorphisms of Renin-Angiotensin-Aldosterone System-Related Genes with Arterio-Venous Fistula Malfunction in Hemodialysis Patients

Hemodialysis (HD) is the most commonly-used renal replacement therapy for patients with end-stage renal disease worldwide. Arterio-venous fistula (AVF) is the vascular access of choice for HD patients with lowest risk of infection and thrombosis. In addition to environmental factors, genetic factors may also contribute to malfunction of AVF. Previous studies have demonstrated the effect of genotype polymorphisms of angiotensin converting enzyme on vascular access malfunction. We conducted a multicenter, cross-sectional study to evaluate the association between genetic polymorphisms of renin-angiotensin-aldosterone system and AVF malfunction. Totally, 577 patients were enrolled. Their mean age was 60 years old and 53% were male. HD patients with AVF malfunction had longer duration of HD (92.5 ± 68.1 vs. 61.2 ± 51.9 months, p < 0.001), lower prevalence of hypertension (44.8% vs. 55.3%, p = 0.025), right-sided (31.8% vs. 18.4%, p = 0.002) and upper arm AVF (26.6% vs. 9.7%, p < 0.001), and higher mean dynamic venous pressure (DVP) (147.8 ± 28.3 vs. 139.8 ± 30.0, p = 0.021). In subgroup analysis of different genders, location of AVF and DVP remained significant clinical risk factors of AVF malfunction in univariate and multivariate binary logistic regression in female HD patients. Among male HD patients, univariate binary logistic regression analysis revealed that right-side AVF and upper arm location are two important clinical risk factors. In addition, two single nucleotide polymorphisms (SNPs), rs275653 (Odds ratio 1.90, p = 0.038) and rs1492099 (Odds ratio 2.29, p = 0.017) of angiotensin II receptor 1 (AGTR1), were associated with increased risk of AVF malfunction. After adjustment for age and other clinical factors, minor allele-containing genotype polymorphisms (AA and CA) of rs1492099 still remained to be a significant risk factor of AVF malfunction (Odds ratio 3.63, p = 0.005). In conclusion, we demonstrated that rs1492099, a SNP of AGTR1 gene, could be a potential genetic risk factor of AVF malfunction in male HD patients.

Single nucleotide variants in the protein C pathway and mortality in dialysis patients

BACKGROUND

The protein C pathway plays an important role in the maintenance of endothelial barrier function and in the inflammatory and coagulant processes that are characteristic of patients on dialysis. We investigated whether common single nucleotide variants (SNV) in genes encoding protein C pathway components were associated with all-cause 5 years mortality risk in dialysis patients.

METHODS

Single nucleotides variants in the factor V gene (F5 rs6025; factor V Leiden), the thrombomodulin gene (THBD rs1042580), the protein C gene (PROC rs1799808 and 1799809) and the endothelial protein C receptor gene (PROCR rs867186, rs2069951, and rs2069952) were genotyped in 1070 dialysis patients from the NEtherlands COoperative Study on the Adequacy of Dialysis (NECOSAD) cohort) and in 1243 dialysis patients from the German 4D cohort.

RESULTS

Factor V Leiden was associated with a 1.5-fold (95% CI 1.1-1.9) increased 5-year all-cause mortality risk and carriers of the AG/GG genotypes of the PROC rs1799809 had a 1.2-fold (95% CI 1.0-1.4) increased 5-year all-cause mortality risk. The other SNVs in THBD, PROC, and PROCR were not associated with 5-years mortality.

CONCLUSION

Our study suggests that factor V Leiden and PROC rs1799809 contributes to an increased mortality risk in dialysis patients.

Haemostasis in chronic kidney disease

The coagulation system has gained much interest again as new anticoagulatory substances have been introduced into clinical practice. Especially patients with renal failure are likely candidates for such a therapy as they often experience significant comorbidity including cardiovascular diseases that require anticoagulation. Patients with renal failure on new anticoagulants have experienced excessive bleeding which can be related to a changed pharmacokinetic profile of the compounds. However, the coagulation system itself, even without any interference with coagulation modifying drugs, is already profoundly changed during renal failure. Coagulation disorders with either episodes of severe bleeding or thrombosis represent an important cause for the morbidity and mortality of such patients. The underlying reasons for these coagulation disorders involve the changed interaction of different components of the coagulation system such as the coagulation cascade, the platelets and the vessel wall in the metabolic conditions of renal failure. Recent work provides evidence that new factors such as microparticles (MPs) can influence the coagulation system in patients with renal insufficiency through their potent procoagulatory effects. Interestingly, MPs may also contain microRNAs thus inhibiting the function of platelets, resulting in bleeding episodes. This review comprises the findings on the complex pathophysiology of coagulation disorders including new factors such as MPs and microRNAs in patients with renal insufficiency.

Association of TNF-α -308 G > A and ACE I/D gene polymorphisms in hemodialysis patients with arteriovenous fistula thrombosis

PURPOSE

Tumor necrosis factor-α (TNF - α) -308 G > A promoter polymorphism seems to be associated with adverse clinical outcome in hemodialysis patients (HD). Angiotensin-converting enzyme (ACE) gene may be the causative factor contributing to the deterioration of renal functions. The aim of this study was to investigate the relationship between vascular access failure and the genetic polymorphisms of ACE and TNF-α gene.

METHODS

We enrolled and genotyped 47 HD patients with arteriovenous fistula (AVF) thrombosis, 51 HD patients without AVF thrombosis, and 40 healthy controls. The genotypes of these polymorphisms were determined by polymerase chain reaction and restriction fragment length polymorphism.

RESULTS

The genotype distribution of TNF-α -308 G > A in patients with thrombosis was significantly different from the patients without thrombosis (p = 0.008). There was no significant difference between the two groups in terms of ACE I/D polymorphism (p = 0.213).

CONCLUSION

Our results propose that TNF-α -308 G > A genotype may be a potential genetic marker on HD patients with AVF thrombosis.

Candidate gene analysis of arteriovenous fistula failure in hemodialysis patients

BACKGROUND AND OBJECTIVES

Arteriovenous fistula (AVF) failure remains an important cause of morbidity in hemodialysis patients. The exact underlying mechanisms responsible for AVF failure are unknown but processes like proliferation, inflammation, vascular remodeling, and thrombosis are thought to be involved. The current objective was to investigate the association between AVF failure and single nucleotide polymorphisms (SNPs) in genes related to these pathophysiologic processes in a large population of incident hemodialysis patients.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

A total of 479 incident hemodialysis patients were included between January 1997 and April 2004. Follow-up lasted 2 years or until AVF failure, defined as surgery, percutaneous endovascular intervention, or abandonment of the vascular access. Forty-three SNPs in 26 genes, related to proliferation, inflammation, endothelial function, vascular remodeling, coagulation, and calcium/phosphate metabolism, were genotyped. Relations were analyzed using Cox regression analysis.

RESULTS

In total, 207 (43.2%) patients developed AVF failure. After adjustment, two SNPs were significantly associated with an increased risk of AVF failure. The hazard ratio (95% confidence interval) of LRP1 rs1466535 was 1.75 (1.15 to 2.66) and patients with factor V Leiden had a hazard ratio of 2.54 (1.41 to 4.56) to develop AVF failure. The other SNPs were not associated with AVF failure.

CONCLUSIONS

In this large cohort of hemodialysis patients, only 2 of the 43 candidate SNPs were associated with an increased risk of AVF failure. Whether other factors, like local hemodynamic circumstances, are more important or other SNPs play a role in AVF failure remains to be elucidated.

Complications of arteriovenous fistulae: beyond venous stenosis

Vascular access is the lifeline of hemodialysis patients. Currently, arteriovenous fistulae and grafts are considered permanent options for vascular access, and they share common access problems. The successful creation of a permanent vascular access depends on patient characteristics, vessel parameters, and possibly genetic factors. Utilization of a dialysis access at least 3 times a week leads to significant wear and tear of the access. The buttonhole technique is associated with a higher incidence of infection, and evidence regarding various perceived advantages remain contradictory. Infiltration and aneurysm formation of an access are common, and the literature on its impact on vascular access outcomes is limited. A patient who undergoes hemodialysis often requires multiple accesses during his or her lifetime, and the maintenance of a persistent vascular access may require creative solutions. Intensified research is crucial to comprehending the pathophysiology and treatment options for some of the common problems of vascular accesses.

Association of factor V gene polymorphism with arteriovenous graft failure

BACKGROUND

Dialysis grafts fail due to recurrent stenosis and thrombosis. Vasoactive and prothrombotic substances affecting intimal hyperplasia or thrombosis may modify graft outcomes.

STUDY DESIGN

Genetic polymorphisms association study of patients enrolled in a multicenter randomized clinical trial.

SETTING & PARTICIPANTS

354 Dialysis Access Consortium (DAC) Study patients receiving a new graft with DNA samples obtained. Participants were randomly assigned to treatment with aspirin plus dipyridamole versus placebo.

PREDICTOR

DNA sequence polymorphisms for the following candidate genes and their interaction with the study intervention: methylenetetrahydrofolate reductase (MTHFR), heme oxygenase 1 (HO-1), factor V (F5), transforming growth factor β1 (TGFβ1), klotho, nitric oxide synthase (NOS), and angiotensin-converting enzyme (ACE).

OUTCOME

Graft failure (>50% stenosis, angioplasty, thrombosis, surgical intervention, or permanent loss of function).

RESULTS

During a median patient follow-up of 34.3 months, 304 grafts failed. After adjusting for clinical factors (patient age, sex, access location, diabetes, cardiovascular disease, baseline aspirin use, body mass index, timing of graft placement, and study treatment) and genetic ancestral background, single-nucleotide polymorphism rs6019 of the factor V gene was associated significantly with graft failure in a dominant model (HR of 1.70 [95% CI, 1.32-2.19; P < 0.001] for G/C and G/G genotypes vs C/C genotypes). There was no significant association between graft failure and polymorphisms of MTHFR, HO-1, TGFβ1, klotho, NOS, or ACE.

LIMITATIONS

Small sample size.

CONCLUSION

The rs6019 genotype of Factor V is associated with increased risk of graft failure. Anticoagulation may reduce graft failure in patients with the G/C or G/G genotypes.

Genetic causation of neointimal hyperplasia in hemodialysis vascular access dysfunction

The major cause of hemodialysis vascular access failure is venous stenosis resulting from neointimal hyperplasia. Genetic factors have been shown to be associated with cardiovascular disease and peripheral vascular disease (PVD) in the general population. Genetic factors may also play an important role in vascular access stenosis and development of neointimal hyperplasia by affecting pathways that lead to inflammation, endothelial function, oxidative stress, and vascular smooth muscle proliferation. This review will discuss the role of genetics in understanding neointimal hyperplasia development in hemodialysis vascular access dysfunction and other disease processes with similar neointimal hyperplasia development such as coronary artery disease and PVD.

Role of thrombophilia in vascular access thrombosis among chronic hemodialysis patients in Tunisia

Vascular access thrombosis represents a serious and common problem in hemodialysis patients. Therefore, identification of relevant thrombotic risk factors could lead to an improved antithrombotic therapy. This case control study was performed to evaluate the relationship between some thrombophilias and vascular access thrombosis in hemodialysis patients. Seventy-eight patients undergoing dialysis (between May 2007 and September 2009) were selected as subjects. This sample was divided into two groups; a case group of 28 patients who had sustained one or more thrombotic events that resulted in vascular access failure and a control group of 50 patients, who had never had a thrombotic occlusion of a functioning permanent dialysis access. Antithrombin, protein C and protein S levels were measured. Also, both groups were tested for the factor V Leiden mutation, the prothrombin G20210A mutation, the methylene tetrahydrofolate reductase C677T and A1298C mutations. Among genetic mutations of factor V Leiden, prothrombin G20210A and methylene tetrahydrofolate reductase genes, the C677T methylene tetrahydrofolate reductase mutation was the only significant genetic cause of vascular access thrombosis (P=0.005). Our data demonstrated a significantly increased risk of vascular access thrombosis in carriers of the C677T methylene tetrahydrofolate reductase mutation.

Role of thrombotic risk factors in end-stage renal disease

INTRODUCTION

Genetic polymorphisms that are found among factors of the coagulation cascade are factor V leiden mutation (FVL), prothrombin (PT), and methylenetetrahydrofolate reductase (MTHFR), reported for thrombotic complications. We have investigated the associations of these gene polymorphisms in patients with end-stage renal disease (ESRD).

METHODS

We genotyped 258 patients for FV G1691A, PT G20210A, and MTHFR (C677T, A1298C) gene by using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis and were compared with 569 healthy controls. Serum folate, total homocysteine (tHcys), and vitamin B(12) were measured in both patients with ESRD and controls.

RESULTS

No homozygous individuals for the mutant AA genotype of FVL G1691A were observed in this study. The frequency of the heterozygous genotypes was (11.2%), which was nearly 3 times higher than that observed in controls (3.2%), with a odds ratio of 3.87 (P = .0001, 95% CI = 2.11-7.11). PT G20210A mutation was missing in both patients and the controls. At MTHFR locus, TT genotype of C677T was present in 9.6% among ESRD, while CC genotype of A1298C was present in 11.7% of the ESRD. In control group, it was significantly low that is, 4.2% and 3.2%, respectively (P = .0034; OR = 2.44, 95% CI = 1.36-4.36 and P < .0001; OR = 4.03; 95% CI = 2.2-7.37). The combined analysis of the 2 genotypes showed further increased risk in ESRD ~15 folds. Further, the carrier of TT and CC genotypes of C677T and A1298C had significantly higher total homocysteine (tHcys) level than those with CC and AA genotypes (P < .001).

CONCLUSION

The carrier of FVL, TT genotype of C677T, and CC genotype of A1298C polymorphisms may act as risk factors for ESRD.

Polymorphism in the promoter region of the klotho gene (G-395A) is associated with early dysfunction in vascular access in hemodialysis patients

BACKGROUND/AIMS

Vascular access dysfunction is an important cause of morbidity and mortality in hemodialysis (HD) patients. Recent studies have shown that a klotho gene mutation is related to endothelial dysfunction, thrombosis, and arteriosclerosis, which are regarded as causes of vascular access dysfunction. We investigated the relationship between the klotho G-395A polymorphism and early dysfunction in vascular access in HD patients.

METHODS

Patients who underwent vascular access operations between 1999 and 2002 were enrolled (n=126). Genotyping was performed by allelic discrimination using a 5'-nuclease polymerase chain reaction assay. Clinical data that could be relevant to access dysfunction were obtained from medical records. Early dysfunction of vascular access was defined as the need for any angioplastic or surgical intervention to correct or replace a poorly or nonfunctioning vascular access within 1 year and at least 8 weeks after initial access placement.

RESULTS

Of the 126 patients, the genotype frequency of G-395A was 72.2% for GG (n=91), 24.6% for GA (n=31), and 3.2% for AA (n=4), and the frequency of minor allele was 0.155. Clinical data were similar between the two groups, divided according to the status of the A allele. Early dysfunction occurred in 34 (27.0%) of patients, but it occurred at a significantly higher rate in A allele carriers (45.7%, 16/35) than in noncarriers (19.8%, 18/91; p=0.003).

CONCLUSIONS

Our results suggest that the klotho G-395A polymorphism could be a risk factor for early dysfunction of vascular access in HD patients.