Methylenetetrahydrofolate reductase gene polymorphism as a risk factor for diabetic nephropathy: a meta-analysis

Polymorphism in the HaeIII single nucleotide polymorphism of the SLC2A1 gene and cardiovascular disease in the early type 2 diabetes mellitus

INTRODUCTION

SLC2A1 polymorphism may play a role in the smooth muscle cell proliferation and extracellular matrix synthesis in vessels. However, the role of SLC2A1 polymorphism on diabetic cardiovascular disease (CVD) have not yet been identified. In this study, we aimed to investigate the association between SLC2A1 HaeIII polymorphism and CVD in Korean patients with type 2 diabetes mellitus (T2DM) according to disease duration.

METHODS

A total of 846 patients with T2DM who visited the Chungbuk National University Hospital were investigated. The HaeIII polymorphism of SLC2A1 gene was determined by real time polymerase chain reaction method. Genotyping results were presented GG, AG, or AA. Subgroup analysis was performed according to duration of T2DM (⩽10, 11-20, >20 years).

RESULTS

The AA genotype was significantly associated with higher prevalence of CVD in patients with DM duration less than 10 years (26.3% vs 9.2%, p = 0.014). There was no significant association between SLC2A1 HaeIII polymorphism and other diabetic complications including, retinopathy, nephropathy, neuropathy, cerebrovascular disease, and peripheral artery disease.

CONCLUSIONS

The SLC2A1 HaeIII polymorphism was associated with CVD in Korean patients with T2DM with short disease duration.

Association between end-stage diabetic nephropathy and MTHFR (C677T and A1298C) gene polymorphisms

AIM

Methylenetetrahydrofolate reductase (MTHFR) is a regulatory enzyme of homocysteine metabolism. The C677T and A1298C polymorphism of the MTHFR gene has been reported to be associated with elevated plasma homocysteine in patients with Diabetic nephropathy. This study aimed to investigate the influence of the C677T and A1298C polymorphisms on the progression chronic kidney disease in diabetic nephropathy of south Indian population.

METHODS

We genotyped 145 DN cases and 100 controls for the C677T and A1298C polymorphisms using PCR-RFLP based protocols, and all diabetic nephropathy cases divided into two groups based on CKD stages: 60 DN cases were early stage (CKD1 to CKD3) and 85 DN cases were advanced stage (CKD4 and CKD5). Association χ² and univariate analysis were performed.

RESULTS

The C677T (OR = 4.2; 95% CI = 2.31-7.64 and P = 0.001) and A1298C (OR = 2.8; 95% CI = 1.05-7.57 and P = 0.033) polymorphism was shown that the significant association between the cases and control. Furthermore, the MTHFR gene polymorphism C677T (OR = 2.48; 95% CI = 1.25-4.9 and P = 0.008) was observed that the significant contribution of the progression of CKD in DN.

CONCLUSION

These findings suggest that the C677T and A1298C polymorphism of MTHFR gene was associated with diabetic nephropathy in a south Indian population. Furthermore, the present study provides evidence that the C677T polymorphism was associated with CKD progression in DN.

Interaction of MTHFR C677T polymorphism with smoking in susceptibility to diabetic nephropathy in Chinese men with type 2 diabetes

We investigated the interaction of MTHFR C677T polymorphism (rs1801133) with smoking in susceptibility to diabetic nephropathy (DN) in Chinese men with type 2 diabetes mellitus (T2DM). We studied 655 Chinese men with T2DM, who were divided into two groups (321 with DN and 334 without DN). The genotype of MTHFR C677T polymorphism was detected by real-time polymerase chain reaction. MTHFR TT genotype carried a higher risk of DN compared with the CC genotype (OR = 2.05; P = 0.002). The T allele showed marked association with DN development in patients who smoked, using additive, recessive, and dominant models (OR = 1.60, 1.83, and 1.88, respectively; P = 0.006, 0.002, and 0.04, respectively), which was not observed in the nonsmoking group. Patients with TT and CT genotypes, who smoked had a higher risk of DN compared with the control group (non-smoking with CC genotype; OR = 3.73 and 2.28, respectively; P < 0.001 and P = 0.004, respectively), whereas the other groups were not observed. In conclusion, the T allele of rs1801133 may be a risk factor for DN in Chinese men with T2DM, and synergy appears to exist between the MTHFR rs1801133 and smoking in susceptibility to DN.

The contribution of genetic variants of SLC2A1 gene in T2DM and T2DM-nephropathy: association study and meta-analysis

An association study was conducted to investigate the relation between 14 variants of glucose transporter 1 gene (SLC2A1) and the risk of type 2 diabetes (T2DM) leading to nephropathy. We also performed a meta-analysis of 11 studies investigating association between diabetic nephropathy (DN) and SLC2A1 variants. The cohort included 197 cases (T2DM with nephropathy), 155 diseased controls (T2DM without nephropathy) and 246 healthy controls. The association of variants with disease progression was tested using generalized odds ratio (ORG). The risk of type 2 diabetes leading to nephropathy was estimated by the OR of additive and co-dominant models. The mode of inheritance was assessed using the degree of dominance index (h-index). We synthesized results of 11 studies examining association between 5 SLC2A1 variants and DN. ORG was used to assess the association between variants and DN using random effects models. Significant results were derived for co-dominant model of rs12407920 [OR = 2.01 (1.17-3.45)], rs841847 [OR = 1.73 (1.17-2.56)] and rs841853 [OR = 1.74 (1.18-2.55)] and for additive model of rs3729548 [OR = 0.52 (0.29-0.90)]. The mode of inheritance for rs12407920, rs841847 and rs841853 was 'dominance of each minor allele' and for rs3729548 'non-dominance'. Frequency of one haplotype (C-G-G-A-T-C-C-T-G-T-C-C-A-G) differed significantly between cases and healthy controls [p = .014]. Regarding meta-analysis, rs841853 contributed to an increased risk of DN [(ORG = 1.43 (1.09-1.88); ORG = 1.58 (1.01-2.48)] between diseased controls versus cases and healthy controls versus cases, respectively. Further studies confirm the association of rs12407920, rs841847, rs841853, as well as rs3729548 and the risk of T2DM leading to nephropathy.

Association between MTHFR C677T polymorphism and diabetic nephropathy in the Chinese population: An updated meta-analysis and review

To clarify the effects of MTHFR C677T polymorphism on the risk of diabetic nephropathy (DN) in the Chinese population, an updated meta-analysis was performed. Related studies were identified from PubMed, Springer Link, Ovid and Chinese Databases up to 24 February 2015. A total of 15 studies including 1227 DN cases, 586 healthy controls and 1277 diabetes mellitus (DM) controls were involved in this meta-analysis. Overall, a significantly elevated risk of DN was associated with all variants of MTHFR C677T when compared with the healthy group (T vs C, odds ratio (OR) = 2.22, 95% confidence interval (CI) = 1.88-2.61; TT vs CC, OR = 4.22, 95% CI = 3.02-5.90; TT + CT vs CC, OR = 2.62, 95% CI = 2.07-3.31; TT vs CC + CT, OR = 2.81, 95% CI = 2.08-3.81) or DM (T vs C, OR = 1.78, 95% CI = 1.59-2.00; TT vs CC, OR = 2.95, 95% CI = 2.33-3.73; TT + CT vs CC, OR = 1.93, 95% CI = 1.63-2.29; TT vs CC + CT, OR = 2.31, 95% CI = 1.87-2.84). In subgroup analyses stratified by ethnicity and geographic areas, it revealed the significant results in Chinese Han, in North and South China. The risk conferred by MTHFR C677T polymorphism is higher in North China than in South China. This meta-analysis showed that the MTHFR C677T variants may influence DN risk in Chinese, and further studies with gene-gene and gene-environment interactions are required for definite conclusions.

Association between the RAGE gene -374T/A, -429T/C polymorphisms and diabetic nephropathy: a meta-analysis

AIM

The investigations into the association between the receptor for advanced glycation end products (RAGE) gene -374T/A, -429T/C polymorphisms and diabetic nephropathy (DN) in several case-control studies have rendered conflicting results. To shed light on these inconclusive findings, a meta-analysis of all the eligible studies relating these two polymorphisms to the risk of DN was conducted.

METHODS

The databases were searched for relevant articles up to July 2014. A pooled estimate of the genetic association, the heterogeneity between studies, and the publication bias were investigated.

RESULTS

Eight studies with 1725 cases and 1857 controls were enrolled in -374T/A polymorphism analysis. The main analysis indicated no association for the allele contrast, the recessive model and the dominant model. Subgroup analyses in Caucasians and in type 2 diabetes also showed no association between -374T/A polymorphism and DN. Five studies with 1019 cases and 792 controls were enrolled in -429T/C polymorphism analysis. The main analysis revealed heterogeneity and no association for the allele contrast and the dominant model. However, the recessive model for -429C allele diminished the heterogeneity and showed a marginal association overall [fixed-effects OR = 2.83 (1.33-6.00) and random effects OR = 2.50 (1.00-6.24), respectively].

CONCLUSIONS

Our meta-analysis indicated that the RAGE gene -429CC genotype might be a risk factor for DN in patients with type 2 diabetes.

Methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism: epidemiology, metabolism and the associated diseases

The Methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism is associated with various diseases (vascular, cancers, neurology, diabetes, psoriasis, etc) with the epidemiology of the polymorphism of the C677T that varies dependent on the geography and ethnicity. The 5,10-Methylenetetrahydrofolate reductase (MTHFR) locus is mapped on chromosome 1 at the end of the short arm (1p36.6). This enzyme is important for the folate metabolism which is an integral process for cell metabolism in the DNA, RNA and protein methylation. The mutation of the MTHFR gene which causes the C677T polymorphism is located at exon 4 which results in the conversion of valine to alanine at codon 222, a common polymorphism that reduces the activity of this enzyme. The homozygous mutated subjects have higher homocysteine levels while the heterozygous mutated subjects have mildly raised homocysteine levels compared with the normal, non-mutated controls. Hyperhomocysteinemia is an emerging risk factor for various cardiovascular diseases and with the increasing significance of this polymorphism in view of the morbidity and mortality impact on the patients, further prevention strategies and nutritional recommendations with the supplementation of vitamin B12 and folic acid which reduces plasma homocysteine level would be necessary as part of future health education. This literature review therefore focuses on the recent evidence-based reports on the associations of the MTHFR C677T polymorphism and the various diseases globally.

Methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism and susceptibility to diabetic nephropathy in Chinese type 2 diabetic patients: a meta-analysis

The association between methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism and diabetic nephropathy (DN) or diabetes mellitus (DM) risk has been widely reported, but the results are still debatable. To investigate the role of MTHFR C677T polymorphism on DM or DN, 13 separate studies in the Chinese population on the relation between MTHFR C677T polymorphism and DM or DN were analyzed by a meta-analysis. Five genetic models were used to estimate the association between MTHFR C677T polymorphism and the risk of DM or DN. Overall, our meta-analysis for DN versus healthy controls produced significant results for all genetic contrasts except for the co-dominant model (allele contrast: OR = 2.24, 95%CI: 1.88-2.65, p < 0.00001, Pheterogeneity = 0.49). However, the meta-analysis for DM versus healthy controls produced non-significant results for all contrasts (allele contrast: OR = 1.12, 95%CI: 0.92-1.35, p = 0.25, Pheterogeneity = 0.07). In addition, the meta-analysis for DM versus DN produced significant results for all contrasts (allele contrast: OR = 1.88, 95%CI: 1.65-2.15, p < 0.00001, Pheterogeneity = 0.83). The current meta-analysis suggested that MTHFR C677T polymorphism might influence DN risk, but not for DM in the Chinese population.

MTHFR 677T variant contributes to diabetic nephropathy risk in Caucasian individuals with type 2 diabetes: a meta-analysis

OBJECTIVE

Previous studies regarding the association between 5,10-methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism and diabetic nephropathy (DN) risk in Caucasian individuals with type 2 diabetes reported conflicting results. To derive a more precise estimation of this association, a meta-analysis was performed.

MATERIALS/METHODS

Odds ratios (ORs) with corresponding 95% confidence intervals (95% CIs) were pooled to assess the association between MTHFR C677T polymorphism and DN risk. Finally, 10 case-control studies with a total of 1590 DN cases and 1555 type 2 diabetic controls without DN were included.

RESULTS

Overall, there was an association between MTHFR C677T polymorphism and increased risk of DN under four comparison models (OR T vs. C=1.50, 95% CI 1.07-2.02, P=0.02; OR TT vs. CC=2.09, 95% CI 1.07-4.08, P=0.03; OR TT vs. TC+CC=1.70, 95% CI 1.10-2.63, P=0.017; OR TC+TT vs. CC=1.85, 95% CI 1.19-2.88, P=0.006). Sensitivity analysis suggested exclusion of any single study did not materially alter the overall pooled ORs above.

CONCLUSIONS

This meta-analysis supports that there is an association between MTHFR C677T polymorphism and DN risk, and MTHFR 677T variant contributes to increased risk of DN in Caucasian individuals with type 2 diabetes.

An updated meta-analysis of methylenetetrahydrofolate reductase gene 677C/T polymorphism with diabetic nephropathy and diabetic retinopathy

Studies investigating the association of methylenetetrahydrofolate reductase (MTHFR) gene 677C/T polymorphism with diabetic nephropathy and diabetic retinopathy have so far reported inconclusive results. We therefore aim to address this inconclusiveness by conducting a meta-analysis. Random-effects model was applied irrespective of between-study heterogeneity. Data and study quality were assessed in duplicate. A total of 7807 and 1599 subjects from 21 and 8 studies were analyzed for diabetic nephropathy and diabetic retinopathy, respectively. Carriers of 677TT genotype were 1.71 (95% confidence interval [95% CI]: 1.02-2.88; P=0.042) and 2.89 (95% CI: 1.51-5.53; P=0.001) times more likely to develop diabetic nephropathy separately relative to diabetic patients without nephropathy and nondiabetic controls. Likewise, this association was preserved for diabetic patients with retinopathy referring to those without (odds ratio [OR]=1.86; 95% CI: 1.21-2.86; P=0.004). Subgroup analyses showed that ethnicity was a possible confounder, especially in West Asians and Africans, and so were gender and duration of diabetes mellitus in diabetic nephropathy studies. Probability of publication bias was low across all comparisons as reflected by the funnel plot and corresponding test. Taken together, our results demonstrate that MTHFR gene 677TT genotype might confer a moderately augmented risk for diabetic nephropathy and diabetic retinopathy.

Variants of the MTHFR gene and susceptibility to acute lymphoblastic leukemia in children: a synthesis of genetic association studies

BACKGROUND

Acute lymphoblastic leukemia (ALL) is a complex disease with genetic background. The genetic association studies (GAS) that investigated the association between ALL and the MTHFR C677T and A1298C gene variants have produced contradictory or inconclusive results.

MATERIALS AND METHODS

In order to decrease the uncertainty of estimated genetic risk effects, a meticulous meta-analysis of published GAS related the variants in the MTFHR gene with susceptibility to ALL was conducted. The risk effects were estimated based on the odds ratio (OR) of the allele contrast and the generalized odds ratio (OR(G)). Cumulative and recursive cumulative meta-analyses were also performed.

RESULTS

The analysis showed marginal significant association for the C677T variant, overall [OR=0.91 (0.82-1.00) and OR(G)=0.89 (0.79-1.01)], and in Whites [OR=0.88 (0.77-0.99) and OR(G)=0.85 (0.73-0.99)]. The A1298C variant produced non-significant results. For both variants, the cumulative meta-analysis did not show a trend of association as evidence accumulates and the recursive cumulative meta-analysis indicated lack of sufficient evidence for denying or claiming an association.

CONCLUSION

The current evidence is not sufficient to draw definite conclusions regarding the association of MTHFR variants and development of ALL.

Interaction of MTHFR 1298C with ACE D allele augments the risk of diabetic nephropathy in Western Iran

The aim of the current study was to examine the influence of interaction between polymorphisms of methylenetetrahydrofolate reductase (MTHFR) C677T and A1298C with angiotensin converting enzyme insertion/deletion (ACE I/D) polymorphism on the risk of diabetic nephropathy (DN). In a case control study using polymerase chain reaction (PCR)- and PCR-restriction fragment length polymorphism (RFLP), the presence of three polymorphisms in 140 patients with type 2 diabetes mellitus (T2DM) with nephropathy including patients with micro- and macro-albuminuria and 72 patients with normoalbuminuria from Western Iran were investigated. In the presence of both MTHFR 677 T and ACE D alleles, there was a trend toward increased risk of DN 2.68-fold (p=0.054). The possession of both MTHFR 677 T and ACE D alleles increased the risk of macro-albuminuria four times (p=0.035). The concomitant presence of both MTHFR 1298 C and ACE D alleles increased the risk of macro-albuminuria 7.8-fold (p=0.012). In addition, the risk of progression from micro- to macro-albuminuria in the presence of both alleles tended to be increased (4.1-fold, p=0.09). Our study for the first time demonstrated a synergistic effect between ACE I/D with either MTHFR C677T or A1298C polymorphism on the increased risk of DN among patients with T2DM. We found that MTHFR 1298 C strongly interacts with the ACE D allele and augments the risk of DN in our population.

Association between genetic polymorphism of the angiotensin-converting enzyme and diabetic nephropathy: a meta-analysis comprising 26,580 subjects

Introduction: The effect of angiotensin-converting enzyme ( ACE) insertion/deletion (I/D) polymorphism on risk of diabetic nephropathy (DN) is still conflicting. The present meta-analysis was performed to evaluate the overall risk of this polymorphism associated with DN in different groups.

Materials and methods: A predefined search was performed on 14,108 DN cases and 12,472 controls from 63 published studies by searching electronic databases and reference lists of relevant articles.

Results: In this meta-analysis, we found a significant association between the ACE I/D polymorphism and the risk of DN for all genetic models (ID versus II: odds ratio [OR] = 1.12, 95% confidence interval [CI] 1.02–1.24; DD versus II: OR = 1.27, 95% CI 1.13–1.44; allele contrast: OR = 1.15, 95% CI 1.08–1.23; dominant model: OR = 1.18, 95% CI 1.07–1.31; and recessive model: OR = 1.18, 95% CI 1.08–1.30, respectively). In stratified analysis by ethnicity and DM type, we further found that the Asian group with type 2 diabetes mellitus (T2DM) showed a significant association for all genetic models (ID versus II: OR = 1.25, 95% CI 1.07–1.47; DD versus II: OR = 1.57, 95% CI 1.24–1.98; allele contrast: OR = 1.30, 95% CI 1.15–1.46; dominant model: OR = 1.37, 95% CI 1.10–1.69; and recessive model: OR = 1.34, 95% CI 1.15–1.56, respectively).

Conclusions: Our study suggested that the ACE I/D polymorphism may contribute to DN development, especially in the Asian group with T2DM.

Association between the MTHFR gene and Alzheimer's disease: a meta-analysis

BACKGROUND

The association between methylenetetrahydrofolate reductase (MTHFR) gene (rs1801133) 677C/T polymorphism and Alzheimer's disease (AD) is controversial. The objective of the study was to investigate the possible association between MTHFR 677C/T polymorphism and AD.

METHOD

We performed a meta-analysis pooling data from all relevant studies including 3,299 cases and 4,363 controls. We applied a random-effects or fixed-effects model to combine odds ratio (OR) and 95% confidence intervals (95% CI).

RESULTS

This meta-analysis demonstrated that the MTHFR T allele or dominant model for T allele (CT + TT) had an increased risk for AD in combined populations (OR, 95% CI: 1.13, 1.05-1.21; 1.18, 1.07-1.31, respectively), and a significant association was found in allele contrast, recessive, and dominant model in Asian populations, but not in Caucasian populations.

CONCLUSION

The MTHFR C677T polymorphism is associated with AD in Asian populations, but not in Caucasians.

Interaction of eNOS polymorphism with MTHFR variants increase the risk of diabetic nephropathy and its progression in type 2 diabetes mellitus patients

The present study has investigated the role of endothelial nitric oxide (eNOS) G894T polymorphism and its interaction with methylenetetrahydrofolate reductase (MTHFR) C677T and A1298C variants on the predisposition to diabetic nephropathy and its progression. Using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method the eNOS G894T and MTHFR polymorphisms were detected in 72 microalbuminuric, 68 macroalbuminuric, and 72 normoalbuinuric type 2 diabetes mellitus (T2DM) patients from Western Iran. The presence of GT and GT + TT genotypes of eNOS were associated with insignificantly 1.86- and 1.68-fold increased risk of macroalbuminuria, respectively and 1.21- and 1.13-fold increased risk of microalbuminuria, respectively. However, the concomitant presence of eNOST and MTHFR 1298C alleles were significantly increased the risk of macroalbuminuria (6.6-fold, P < 0.001) and progression from micro- to macro-albuminuria (3.85 times, P = 0.011). Also, the presence of both alleles of eNOST and MTHFR 677T were significantly associated with increased risk of macroalbuminuria (4.8-fold, P = 0.005). The presence of GT + TT genotypes of eNOS was significantly associated with increased risk of coronary artery disease in micro- and macro-albuminuric patients compared to normoalbuminuric patients. The concomitant presence of three mutant alleles significantly increased the risk of macroalbuminuria and progression from micro- to macro-albuminuria 38.5- and 10.5-fold, respectively. Our study indicated that eNOS T allele interacts with MTHFR variants, especially MTHFR A1298C to increase the risk of macroalbuminuria and progression from micro-to macro-albuminuria. Also, Interaction between three alleles of eNOST, MTHFR 677T, and 1298C highly increased the risk of macroalbuminuria and progression of diabetic nephropathy in T2DM patients.

Synergistic effects of the MTHFR C677T and A1298C polymorphisms on the increased risk of micro- and macro-albuminuria and progression of diabetic nephropathy among Iranians with type 2 diabetes mellitus

OBJECTIVES

To find whether polymorphisms of methylenetetrahydrofolate reductase (MTHFR) C677T and A1298C are risk factors for diabetic nephropathy (DN) among type 2 diabetes mellitus (T2DM) patients from Western Iran.

DESIGN AND METHODS

The MTHFR polymorphisms were detected in 72 microalbuminuric, 68 macroalbuminuric and 72 normoalbuinuric T2DM patients by PCR-RFLP.

RESULTS

The possession of both MTHFR 677T and 1298C alleles increase the risk of microalbuminuria to 4.3-fold (p=0.007) in T2DM patients. The presence of either MTHFR 677T, 1298C allele is sufficient to increase the risk of macroalbuminuria in T2DM patients by 4.1 and 5.5 times (p=0.027, and p=0.006, respectively). The concomitant presence of both 677T and 1298C alleles act in synergy to increase the risk of macroalbuminuria by 20.4-fold (p<0.001) and progression of DN from microalbuminuria to macroalbuminuria (OR=4.73, p=0.01).

CONCLUSION

Both MTHFR 677T and 1298C alleles increased the susceptibility to the onset and progression of DN in Iranians with T2DM.

Genetic variants of homocysteine/folate metabolism pathway and risk of inflammatory bowel disease: a synopsis and meta-analysis of genetic association studies

A synopsis and meta-analysis of studies that investigated the association between genetic variants involved in the homocysteine/folate metabolism pathway and risk of inflammatory bowel disease (IBD) were conducted. Four variants (MTHFR C6TTT, MTHFR A1298C, MTR A2756G and MTRR A66G) showed significant associations in individual studies. In meta-analyses, only the variant MTR A2756G indicated an association with the risk of IBD for the allele contrast and the dominant model (odds ratio (OR) 1.48 (1.12-1.97) and OR 1.55 (1.12-2.15), respectively). The effect sizes for Crohn's disease and ulcerative colitis were similar to IBD. Cumulative meta-analysis for C677T indicated a downward trend of association as information accumulates.

Unravelling the genetic basis of renal diseases; from single gene to multifactorial disorders

Chronic kidney disease is common with up to 5% of the adult population reported to have an estimated glomerular filtration rate of < 60 ml/min/1.73 m(2). A large number of pathogenic mutations have been identified that are responsible for 'single gene' renal disorders, such as autosomal dominant polycystic kidney disease and X-linked Alport syndrome. These single gene disorders account for < 15% of the burden of end-stage renal disease that requires dialysis or kidney transplantation. It has proved more difficult to identify the genetic susceptibility underlying common, complex, multifactorial kidney conditions, such as diabetic nephropathy and hypertensive nephrosclerosis. This review describes success to date and explores strategies currently employed in defining the genetic basis for a number of renal disorders. The complementary use of linkage studies, candidate gene and genome-wide association analyses are described and a collation of renal genetic resources highlighted.

Endothelial nitric oxide synthase gene polymorphisms and diabetic nephropathy: a HuGE review and meta-analysis

Candidate-gene association studies that examined the association between polymorphisms of endothelial nitric oxide synthase (NOS3) gene (G894T, 4b/a, and T786C) and diabetic nephropathy or diabetes leading to severe nephropathy produced inconclusive results. Thus, a meta-analysis of all candidate-gene association studies with endothelial nitric oxide synthase genotyping (7401 cases and 8046 controls) was conducted. Other study designs, such as family-based association studies and genome-wide linkage and association studies were also reviewed for supportive evidence of implication of endothelial nitric oxide synthase gene in diabetic nephropathy. The meta-analysis showed that G894T is significantly associated with diabetic nephropathy and diabetes leading to severe nephropathy in type 2 diabetics and in East Asians, respectively. Concerning the 4b/a polymorphism and its relationship to diabetes leading to severe nephropathy, a significant association was shown for East Asians. Heterogeneity between studies was in general high. There was no differential magnitude of effect in large versus small studies. One genome-wide linkage scan provided evidence of linkage nearby the endothelial nitric oxide synthase locus. Studies exploring gene and environment interactions with endothelial nitric oxide synthase polymorphisms may help understand better the genetics of diabetic nephropathy.

A field synopsis and meta-analysis of genetic association studies in peripheral arterial disease: The CUMAGAS-PAD database

In an electronic search of the literature, the authors systematically retrieved all published studies that investigated genetic susceptibility to peripheral arterial disease (PAD). They created a comprehensive database of all eligible studies, collecting detailed genetic and bioinformatics data on each polymorphism. Data from eligible studies were synthesized using meta-analysis techniques. Gene variants were classified into distinct pathophysiologic pathways, and their potential involvement in PAD pathogenesis was determined. Forty-one publications that examined 44 gene polymorphisms were included. For 37 polymorphisms, the variant form had a functional effect. Twenty-three polymorphisms in 22 potential PAD candidate genes (F2, FGB, MTHFR, ITGB3, ACE, AGT, IL6, CCL2, ICAM1, SELE, MMP9, PPARG, MMP1, ADD1, P2RY12, LIPC, PLA2G7, SCARB1, MMP3, MTTP, LPA, CHRNA3) showed a significant association in individual studies. Eighty-eight percent of the studies had statistical power of less than 50%, and in 15 studies the genotype distribution in the control group did not conform to Hardy-Weinberg equilibrium. Data on 12 polymorphisms (F5 1691 G/A, MTHFR 677C/T, F2 20210 G/A, ITGB3 1565 T/C, ACE I/D, AGT 704C/T, AGT -6G/A, AGT 733C/T, IL6 -174 G/C, MMP9 -1562C/T, ICAM1 1462A/G, CHRNA3 831C/T) were synthesized, and a positive association was found for 3 (IL6 -174 G/C, ICAM1 1462A/G, CHRNA3 831C/T).

Genetics of diabetic nephropathy

Genetic susceptibility has been proposed as an important factor for the development and progression of diabetic nephropathy, and research efforts have been invested worldwide to identify the susceptibility gene for diabetic nephropathy. Although, several candidate genes were shown to be associated with the disease, the results were not always consistent; most of the genes conferring susceptibility to diabetic nephropathy remain to be identified. Recent development of the single nucleotide polymorphism (SNP) typing technology and collation of information on linkage disequilibrium in the human genome have facilitated genome-wide association studies (GWASs) for investigating novel disease-susceptibility genes across the entire human genome. GWASs are considered a powerful and promising approach and are expected to be useful for identifying convincing susceptibility genes for several common diseases; however, to date, these studies have not been able to completely cover the entire human genome.

Methylenetetrahydrofolate reductase and methionine synthase reductase gene polymorphisms and protection from microvascular complications in adolescents with type 1 diabetes

Folate status has been associated with endothelial dysfunction in adolescents with type 1 diabetes, and elevated total plasma homoocyst(e)ine (tHcy) is a risk for vascular disease in the non-diabetic population. Polymorphisms in genes involved in folate and homocysteine metabolism are implicated in vascular disease. We aimed to determine whether polymorphisms in the methylenetetrahydrofolate reductase (MTHFR) and methionine synthase reductase (MTRR) genes are risk factors for early microvascular disease in a large group of adolescents with type 1 diabetes. Four hundred and eighty adolescents were screened annually for retinopathy and microalbuminuria for a median of 4 yr. Molecular analysis for the polymorphisms 677C-->T, 1298A-->C in MTHFR, and 66A-->G in MTRR was performed. The MTRR 66GG genotype reduced the risk for elevated albumin excretion rate (AER) (OR 0.47, CI 0.25, 0.88, p = 0.018) and showed a trend to reduced risk for microalbuminuria (OR 0.27, CI 0.06-1.21, p = 0.09). Survival without elevated AER was increased with the MTRR 66GG genotype (12.4 vs. 9.7 yr, p = 0.04) and with the MTHFR 1298CC genotype (15.2 vs. 10.2 yr, p = 0.007). Conversely, survival without retinopathy was reduced with the MTHFR 677TT and MTRR 66GG combined genotype (6.2 vs. 10.2 yr, p = 0.015). The MTRR 66GG and MTHFR 1298 CC genotypes may confer protection against early nephropathy, possibly because they are associated with lower tHcy. The MTHFR 677 TT was only related to earlier onset retinopathy in combination with MTRR 66GG.