The association between two common mutations C677T and A1298C in human methylenetetrahydrofolate reductase gene and the risk for diabetic nephropathy in type II diabetic patients

The MTHFR C677T/A1298C polymorphism is associated with increased risk of microangiopathy in type 2 diabetes mellitus: A systematic review and meta-analysis

Extensive case-control association studies have been conducted over the past few decades to investigate the relationship between MTHFR polymorphism and type 2 diabetes mellitus (T2DM) microangiopathy. However, the strength of the evidence and clinical significance are unclear. Consequently, a meta-analysis was performed to examine the correlations between two prevalent MTHFR single nucleotide polymorphisms, MTHFR C677T and A1298C, and T2DM microangiopathy. Randomized controlled trials were systematically searched in PubMed, Cochrane, Embase, Web of Science, CNKI, VIP database, China Biology Medicine, and Wanfang until August 2023. A total of 42 studies were included. Random-effect models were utilized to estimate odds ratios (ORs) with 95% confidence intervals (CIs) to assess the association between MTHFR polymorphisms and T2DM microangiopathy susceptibility. T2DM microangiopathy was significantly associated with the MTHFR C677T polymorphism in the overall population (T vs C, OR = 1.43, 95% CI = 1.25-1.64; TT + CT vs CC: OR = 1.56, 95% CI = 1.30-1.88; TT vs CT + CC: OR = 1.66, 95% CI = 1.38-1.99; TT vs CC: OR = 2.03, 95% CI = 1.58-2.60). Additionally, the dominant model revealed that the MTHFR A1298C polymorphism was associated with T2DM microangiopathy (OR = 1.27, 95% CI: 1.09-1.47). This meta-analysis revealed that MTHFR may be involved in the pathogenesis of T2DM microangiopathy, providing a reference for early diagnosis and treatment of T2DM.

The Association of Methylenetetrahydrofolate Reductase (MTHFR) A1298C Gene Polymorphism with Susceptibility to Diabetic Nephropathy: A Meta-Analysis

This meta-analysis was conducted to investigate the association between MTHFR A1298C polymorphism and susceptibility to diabetic nephropathy. PubMed, Embase, Web of Science, Cochrane Library, China national knowledge infrastructure (CNKI) and China Wanfang database were searched for studies on the association between MTHFR A1298C single nucleotide polymorphism and susceptibility to diabetic nephropathy until May 2022. Data were analyzed by Stata 15.0 software. Odds ratio (OR) was used as the effect size. A total of 7 articles were identified, including 1287 cases in the diabetic nephropathy group and 1431 cases in the control group. The pooled OR of allele C at MTHFR A1298C was 1.28 (95% CI: 1.02-1.59, p=0.03) compared with allele A. The pooled OR values of dominant, and heterozygous genetic models were 1.45 (95% CI: 1.13-1.86), and 1.42 (95% CI: 1.19-1.70), respectively, and the differences were all statistically significant. There was no statistical significance in the recessive (OR=1.06, 95% CI: 0.62-1.82), and homozygous gene inheritance models (OR=1.29, 95% CI: 0.72-2.31). In conclusion, MTHFR A1298C polymorphism is associated with susceptibility to diabetic nephropathy. Allele C, genotype CC+AC, and AC at MTHFR A1298C locus can increase the risk of diabetic nephropathy.

MTHFR C667T polymorphism and diabetic nephropathy susceptibility in patients with type 2 diabetes mellitus: An updated meta-analysis

Background

Numerous studies indicated that there exists a relationship between methylenetetrahydrofolate reductase (MTHFR) C667T polymorphism and diabetic nephropathy (DN) susceptibility; nonetheless, available proof reported from individual studies has not been consistent, so we performed an updated meta-analysis to evaluate the relationship between MTHFR C667T variant and DN.

Materials and methods

Relevant studies published before February 2022 were searched from the electronic databases PubMed, Embase, Scopus, Chinese Biology Medicine and the Chinese National Knowledge Infrastructure. The strength of the association was examined by odds ratio (OR) with 95% confidence interval (CI).

Results

The findings illustrated that there was a significant relationship between the polymorphism of C677T and DN compared with that to DM controls in allele (OR = 1.59, 95% CI = 1.39–1.82), dominant (OR = 1.76, 95% CI = 1.47–2.11) and recessive (OR = 1.85, 95% CI = 1.56–2.20) models in all populations. Moreover, as compared with the healthy controls, a significant relationship between C677T and DN was found in three genetic comparison models (allele: OR = 1.81, 95% CI = 1.43–2.29; dominant: OR = 2.09, 95% CI = 1.54–2.85; recessive: OR = 2.02, 95% CI = 1.51–2.70). Furthermore, stratifying data by race, diabetes duration and whether in Hardy–Weinberg equilibrium revealed substantially augmented vulnerability to DN in all subgroups.

Conclusion

The current meta-analysis highlighted conclusive results for the robust association between C677T polymorphisms and DN susceptibility.

Associations between Serum Betaine, Methyl-Metabolizing Genetic Polymorphisms and Risk of Incident Type 2 Diabetes: A Prospective Cohort Study in Community-Dwelling Chinese Adults

Previous studies have explored associations between betaine and diabetes, but few have considered the effects of genes on them. We aimed to examine associations between serum betaine, methyl-metabolizing genetic polymorphisms and the risk of type 2 diabetes in Chinese adults. This prospective study comprised 1565 subjects aged 40–75 without type 2 diabetes at baseline. Serum betaine was measured by high-performance liquid chromatography tandem mass spectrometry. Genotyping of methyl-metabolizing genes was detected by Illumina ASA-750K arrays. Cox proportional hazards model was used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs). During a median of 8.9 years of follow-up, 213 participants developed type 2 diabetes. Compared with participants in the lowest quartile of serum betaine, those in the highest quartile had lower risk of type 2 diabetes, adjusted HRs (95%CIs) was 0.46 (0.31, 0.69). For methylenetetrahydrofolate reductase (MTHFR) G1793A (rs2274976) and MTHFR A1298C (rs1801131), participants carrying 1793GA + AA and 1298AC + CC had lower risk of type 2 diabetes. Interactions of serum betaine and genotype of MTHFR G1793A and MTHFR A1298C could be found influencing type 2 diabetes risk. Our findings indicate that higher serum betaine, mutations of MTHFR G1793A and A1298C, as well as the joint effects of them, are associated with lower risk of type 2 diabetes.

Methylenetetrahydrofolate reductase C677T gene polymorphism and the association with dyslipidemia in type 2 diabetic Palestinian patients

BACKGROUND

Dyslipidemia in diabetes is common and characterized by hypertriglyceridemia with decreased levels of high-density lipoprotein. The objective of this study was to assess the prevalence of MTHFR C677T polymorphism in Palestinian T2DM patients and to investigate the association between this polymorphism and lipid profile in diabetic patients with and without dyslipidemia.

METHODS

A total of 208 T2DM patients including 98 with dyslipidemia and 110 without dyslipidemia were enrolled in this study. The MTHFR C677T genotyping was conducted by PCR-RFLP followed by agarose gel electrophoresis.

RESULTS

There were no significant differences in either the genotype distribution or allele frequency in T2DM patients with or without dyslipidemia (37.8% CC, 54% CT, 8.2% TT vs. 48.2% CC, 41.8% CT, 11% TT; p = 0.209). However, among the dyslipidemic group, the TT carriers have a higher HDL level (46.8 ± 17.8) compared to (CC+CT) carriers (34.68 + 11.9) (p = 0.01). In the group without dyslipidemia, there was a significant elevation in diastolic blood pressure (DBP) among the CC carriers (83.6 ± 10.6) compared to those who carried at least one mutant allele (CT+TT) (78.1 ± 11.1) (p = 0.009).

CONCLUSIONS

The study shows that in our Palestinian population the MTHFR 677TT genotype lowers DBP significantly in patients without dyslipidemia and is related to increased level of HDL in diabetic dyslipidemia patients.

Methylenetetrahydrofolate reductase genetic polymorphism and the risk of diabetic nephropathy in type 2 diabetic patients

BACKGROUND

As indicated by numerous studies, there exists a relationship between the polymorphism of methylenetetrahydrofolate reductase (MTHFR) and susceptibility to diabetic nephropathy (DN) in various populations; nonetheless, the findings remain inconsistent. Therefore, we carried out a meta-analysis to determine the relationship between the MTHFR gene polymorphism and DN susceptibility.

MATERIALS AND METHOD

Related studies were identified from PubMed, Cochrane Library, EMBASE, and the China National Knowledge Infrastructure database (time period: from building the library to October 2019). The strength of the association was examined using odds ratios (ORs) with 95% confidence intervals (95% CIs).

RESULTS

The findings illustrated that the C677T gene polymorphism was significantly associated with an enhanced susceptibility to DN compared to that with diabetes mellitus in allelic (OR = 1.64, 95% CI = 1.34-2.00, P < .001), dominant (OR = 1.85, 95% CI = 1.40-2.46, P < .001), codominant (heterozygote: OR = 1.67, 95% CI = 1.27-2.21, P < .001; homozygote: OR = 2.55, 95% CI = 1.82-3.57, P < .001), and recessive (OR = 1.89, 95% CI = 1.50-2.38, P < .001) models of the overall population. Moreover, as compared with the healthy controls, a significantly augmented susceptibility to DN was found in all 5 genetic comparison models (allelic: OR = 2.06, 95% CI = 1.58-2.67, P < .001; dominant: OR = 2.52, 95% CI = 1.73-3.69, P < .001; codominant: OR = 3.78, 95% CI = 2.50-5.70, P < .001; recessive: OR = 2.41, 95% CI = 1.96-2.97, P < .001). Furthermore, stratifying data by ethnicity revealed substantially augmented vulnerability to DN in not only Caucasian but also Asian populations.

CONCLUSION

The present study suggests that the C677T polymorphism was associated with an augmented susceptibility to DN.

Association of MTHFR C677T polymorphism and type 2 diabetes mellitus (T2DM) susceptibility

Introduction

Methylenetetrahydrofolate reductase (MTHFR) is essential in mediating folate metabolism, and thus plays an important role in diabetes and diabetic complications. MTHFR C677T (rs1801133 C>T) polymorphism has been proposed to be linked with type 2 diabetes mellitus (T2DM) susceptibility. However, the conclusions are inconsistent. Therefore, we rechecked their linkage aiming to obtain a more reliable estimation by performing an updated meta‐analysis.

Methods

We searched electronic databases PubMed, EMBASE, CNKI, and Wanfang to obtain studies updated to October 2019.

Results

After carefully screening, we finally incorporated 68 studies with 10,812 cases and 8,745 controls. The genotype frequency of C677T polymorphism was analyzed pooled to generate odds ratios (ORs) and 95% confidence intervals (CIs). Pooled results presented that MTHFR C677T polymorphism was significantly associated with T2DM under homozygous (OR = 1.64, 95% CI = 1.39–1.94), heterozygous (OR = 1.38, 95% CI = 1.20–1.59), recessive (OR = 1.41, 95% CI = 1.23–1.61), dominant (OR = 1.47, 95% CI = 1.27–1.70), and allele (OR = 1.37, 95% CI = 1.23–1.52) genetic models. Stratified analysis demonstrated that C677T genotype was associated with T2DM in Asian populations, but not Caucasian and African populations.

Conclusion

Our results indicated that MTHFR C677T polymorphism confers to T2DM, especially in Asian populations. Much more large‐scale case–control studies are needed to strengthen such conclusion in the future.

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.

Assessment of coding region variants in Kuwaiti population: implications for medical genetics and population genomics

Consanguineous populations of the Arabian Peninsula have been underrepresented in global efforts that catalogue human exome variability. We sequenced 291 whole exomes of unrelated, healthy native Arab individuals from Kuwait to a median coverage of 45X and characterised 170,508 single-nucleotide variants (SNVs), of which 21.7% were ‘personal’. Up to 12% of the SNVs were novel and 36% were population-specific. Half of the SNVs were rare and 54% were missense variants. The study complemented the Greater Middle East Variome by way of reporting many additional Arabian exome variants. The study corroborated Kuwaiti population genetic substructures previously derived using genome-wide genotype data and illustrated the genetic relatedness among Kuwaiti population subgroups, Middle Eastern, European and Ashkenazi Jewish populations. The study mapped 112 rare and frequent functional variants relating to pharmacogenomics and disorders (recessive and common) to the phenotypic characteristics of Arab population. Comparative allele frequency data and carrier distributions of known Arab mutations for 23 disorders seen among Arabs, of putative OMIM-listed causal mutations for 12 disorders observed among Arabs but not yet characterized for genetic basis in Arabs, and of 17 additional putative mutations for disorders characterized for genetic basis in Arab populations are presented for testing in future Arab studies.

A NOS3 polymorphism determines endothelial response to folate in children with type 1 diabetes or obesity

OBJECTIVE

To determine the effect of polymorphisms in NOS3 and folate pathway enzymes on vascular function and folate status and endothelial response to folate in children with diabetes or obesity.

STUDY DESIGN

A total of 244 subjects (age 13.8 ± 2.8 years, 125 males) were studied for NOS3 and/or folate pathway polymorphisms using polymerase chain reaction/restriction fragment length polymorphism, including at baseline: 139 with type 1 diabetes; 58 with obesity; and 47 controls. The effect of NOS3 genotype on endothelial response to folate (5 mg) was assessed in 85 subjects with diabetes and 28 obese subjects who received active treatment during intervention trials. Vascular function (flow-mediated dilatation [FMD] and glyceryl trinitrate-mediated dilatation), clinical, and biochemical measurements were assessed at baseline and 8 weeks in folate intervention studies.

RESULTS

Folate pathway enzyme and NOS3 polymorphisms did not significantly affect baseline vascular function. The polymorphism in intron 4 of endothelial nitric oxide synthase altered endothelial response to folate significantly: in subjects with diabetes FMD improved by 6.4 ± 5% (insertion carriers) vs 2.3 ± 6.6% (deletion carriers), P = .01; in obese subjects FMD improved by 1.8 ± 5.4% (insertion carriers) and deteriorated by -3.2 ± 7.2% (deletion carriers), P = .05. More subjects carrying the insertion normalized FMD after folate supplementation (insertion 64% vs deletion 28%, χ(2) = 10.14, P = .001).

CONCLUSIONS

A NOS3 polymorphism predicts endothelial response to folate in children with diabetes or obesity, with implications for vascular risk and folate intervention studies.

Association of interleukin-6 -174 G>C promoter polymorphism with increased risk of type 2 diabetes mellitus patients with diabetic nephropathy in Turkey

OBJECTIVE

Diabetic nephropathy (DN) is a serious complication of diabetes mellitus. We aimed to evaluate the interleukin (IL)-6 gene polymorphisms in type 2 DN and control subjects.

MATERIALS AND METHODS

The patients selected from the Department of Endocrinology and Metabolism Diseases included 43 type 2 diabetes mellitus patients without DN and 43 type 2 diabetes mellitus patients with DN and 340 healthy normal controls. All subjects underwent venous blood drawing for complete hormonal assays, lipid profile, glucose, and insulin and Il-6 gene polymorphism genetic analysis.

RESULTS

IL-6 -174 G>C genotype distribution was different between the control group and the type 2 diabetes mellitus patients (p=0.004). The higher frequency of the polymorphic G allele was also similar for the group with type 2 diabetes mellitus as for the control group. The frequency of the polymorphic G allele was 83.9% in diabetic patients with nephropathy versus 70.9% in those without nephropathy (p=0.039).

CONCLUSION

We suggest that the -174 G>C polymorphism of the IL-6 gene is an independent risk factor for DN in Turkish type 2 diabetes mellitus patients.

Genetic predisposition for development of nephropathy in type 2 diabetes mellitus

The aim of the study was to explore the association of the angiotensin-converting enzyme (ACE) gene I/D polymorphism and the methylenetetrahydrofolate reductase (MTHFR) gene C677T polymorphism with development of diabetic nephropathy in type 2 diabetes mellitus. Three groups were recruited during 2007-2011: 232 normal controls, 185 type 2 diabetics without nephropathy, and 407 type 2 diabetics with nephropathy. The ACE I/D and MTHFR C677T polymorphisms were examined using PCR and PCR-RFLP methods. We found no significant association of the ACE I/D polymorphism with diabetic nephropathy in genotype, allele, dominant, and recessive models. We observed a significant association of MTHFR C677T with development of diabetic nephropathy in type 2 diabetics. The MTHFR C677T polymorphism plays a significant role in predisposition of renal insufficiency in diabetic patients.

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.

Is C677T polymorphism in methylenetetrahydrofolate reductase gene a risk factor for diabetic nephropathy or diabetes mellitus in a Chinese population?

BACKGROUND AND AIMS

To date, case-control studies on the association between C677T polymorphism in methylenetetrahydrofolate reductase (MTHFR) gene and diabetes mellitus (DM) or diabetic nephropathy (DN) in different populations have provided inconclusive results. To clarify the effect of the C677T polymorphism on the risk of both DM and DN in a Chinese population, a meta-analysis was performed.

METHODS

A comprehensive literature search was conducted to collect data from all case-control observational studies that investigated association of C677T polymorphism in MTHFR gene with DM or DN in a Chinese population.

RESULTS

Overall, 12 studies in a Chinese population published up to 2011 were combined, and the heterogeneity among them varied from none to moderate. The 677T allele showed significant association with DN (OR = 1.97, 95% CI [1.71, 2.28], p <0.00001), but no relationship with DM (OR = 1.03, 95% CI [0.89, 1.18], p = 0.70) compared with the 677C allele in a Chinese population. Similarly, evidence of significant association with DN was detected in the additive model, the recessive model and the dominant model for allele T (additive model: OR = 3.26, 95% CI [2.46, 4.31], p <0.00001; recessive model: OR = 2.32, 95% CI [1.81, 2.97], p <0.00001; dominant model: OR = 2.35, 95% CI [1.89, 2.91], p <0.00001); however, no relationship with DM was found (additive model: OR = 1.01, 95% CI [0.76, 1.35], p = 0.94; recessive model: OR = 0.98, 95% CI [0.76, 1.26], p = 0.87; dominant model: OR = 1.23, 95% CI [0.91, 1.65], p = 0.18). There were no sources of bias in the selected studies, and the sensitivity analysis (exclusion of studies not in Hardy-Weinberg equilibrium) suggested stability of this meta-analysis.

CONCLUSIONS

C677T polymorphism in MTHFR gene may be a risk factor for DN, but not for DM, in a Chinese population.

Interleukin-10 (-1082G/A) gene polymorphism in patients with type 2 diabetes with and without nephropathy

OBJECTIVE

Interleukin (IL)-10 is a major anti-inflammatory cytokine that plays a crucial role in the regulation of the immune system. IL-10 has met the criteria for an anti-inflammatory and an immunosuppressive cytokine, its activity may be important for clinical outcome of diabetic nephropathy (DN). We aimed at evaluating the relation between the genotypic and allelic frequencies of the IL-10 (-1082G/A) polymorphisms, and their association with the risk to develop DN in the Turkish population.

RESEARCH DESIGN AND METHODS

The (IL)-10 (-1082G/A) genotypes were retrospectively determined in 43 patients with nephropathy and 48 without nephropathy and a control group of 112 healthy individuals. The polymorphisms were analyzed by polymerase chain reaction restriction fragment length polymorphism.

RESULTS

This genotype distribution was different between control subjects and patients with type 2 diabetes in which 24.2% were AA, 75.8% were GA, and 0% were GG (p<0.001). The frequency of the mutant G allele was 36.1% in patients with diabetes nephropathy versus 39.6% in those without nephropathy (p>0.05). The genotype frequencies were AA, 27.9%; GA, 72.1%; and GG, 0% in patients with diabetes with nephropathy versus AA, 20.8%; GA, 79.2%; and GG, 0% in those without nephropathy (p>0.05).

CONCLUSIONS

The polymorphisms of IL-10 (-1082G/A) genes were significantly associated with the occurrence of patients with type 2 diabetes. The IL-10 (-1082G/A) genotype and allele frequencies were not different between patients with diabetes with nephropathy and those without nephropathy. Therefore, we conclude that the IL-10 (-1082G/A) gene polymorphism is not associated with the development of DN in Turkish patients with type 2 diabetes.

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.

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.

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.

Methyltetrahydrofolate reductase C677T gene mutation and hyperhomocysteinemia as a novel risk factor for diabetic nephropathy

Hyperhomocysteinemia is a well-defined risk factor for endothelial dysfunction and atherosclerosis. A point mutation (677 C-T) of MTHFR gene results in a significant increase at plasma homocysteine levels. In this study we aimed to evaluate the effects of MTHFR gene mutation and consequent hyperhomocysteinemia on the development of diabetic microvascular complications in comparison with the other defined risk factors. Diabetic patients without a history of macrovascular complication or overt nephropathy enrolled into the study. The presence of MTHFR 677 C-T point mutation was evaluated by Real-Time PCR technique by using a LightCycler. MTHFR heterozygous mutation was present in 24 patients over 52. Patients with diabetes were divided into two groups according to the presence of MTHFR gene mutation. Both groups were well matched regarding age and diabetes duration. Metabolic parameters, plasma homocysteine, microalbuminuria, folic acid, and vitamin B12 levels were also studied. Presence of neuropathy and retinopathy were evaluated by specific tests. Duration of diabetes, BMI, systolic and diastolic blood pressure, plasma CRP, HbA1c, and lipid levels were not different between the two groups. Plasma homocysteine (12.89 +/- 1.74 and 8.98 +/- 1.91 micromol/l; P < 0.0001) and microalbuminuria levels (73.40 +/- 98.15 and 29.53 +/- 5.08 mg/day; P = 0.021) were significantly higher in the group with MTHFR gene mutation while creatinine clearance levels (101.1 +/- 42.6 and 136.21 +/- 51.50 ml/min; P = 0.008) were significantly lower. Sixteen over 22 (73%) of the patients with diabetic nephropathy had MTHFR gene mutation, while this was only 27% (8 over 30) in normoalbuminuric patients (P = 0.017). There was a significant correlation of plasma homocysteine level with microalbuminuria (r = 0.54; P = 0.031) in the patients with diabetic nephropathy who had C677T polymorphism. We did not find any specific association of MTHFR gene mutation and hyperhomocysteinemia with retinopathy or neuropathy.

MTHFR (Ala 222 Val) polymorphism and AMI in patients with type II diabetes mellitus

The prevalent Ala222Val single nucleotide polymorphism of the MTHFR gene has been shown to be associated with type II diabetes. The objective of the present study was to find out whether there is genetic predisposition for development of acute myocardial infarction in type II diabetes mellitus among South Indian Tamil population. PCR-based restriction enzyme analysis was performed in DNA isolated from 120 acute myocardial infarction patients with diabetes mellitus and 100 non diabetic healthy individuals with no documented cardiovascular diseases. The results indicate that the MTHFR 677TT genotype is absent in both case and controls. The MTHFR 677CT genotype was observed among 32 (26.7 %) cases and 20 (20%) controls and the MTHFR 677CC genotype among 88 (73.3%) cases and 80 (80%) controls. The allelic frequencies were in accordance to Hardy Weinberg equilibrium. There was no statistical difference in genotype distribution between cases and controls. In conclusion, we suggest that the analysis of MTHFR genotyping for C677T polymorphism alone need not be considered to find out whether there is genetic predisposition for development of acute myocardial infarction in type II diabetes mellitus among South Indian Tamil population.

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.

The relationship of the methylenetetrahydrofolate reductase C677T gene polymorphism in Turkish type 2 diabetic patients with and without nephropathy

BACKGROUND

Poor glycaemic control, hypertension and duration of diabetes are risk factors for the development of diabetic nephropathy, but there may be genetic factors. Recently, a common C to T mutation at nucleotide position 677 of the MTHFR gene (MTHFR677C > T) has been reported to be correlated with hyperhomocysteinemia and the severity of coronary artery disease as macroangiopathy. We aim to investigate Turkish type 2 diabetic patients with/without diabetic nephropathy and healthy group and examine the contribution of the MTHFR gene polymorphism to the development of diabetic nephropathy.

METHODS

DNA was extracted from peripheral leukocytes of the subjects. Genotyping of the MTHFR C677T polymorphism for all individuals was performed by melting curve analysis of the generated amplicons after real-time online PCR.

RESULTS

This genotype distribution did not differ between control subjects and type 2 diabetic patients in which 6.8% were TT, 43.7% were CT and 49.5% were CC (chi2 = 0.201, p > 0.05). The frequency of the mutant T allele was 23.4% in diabetic patients with nephropathy versus 33.0% in those without nephropathy. The genotype frequencies were TT, 2.1%; CT, 46.6%; CC, 55.3% in diabetic patients with nephropathy versus TT, 10.7%; CT, 44.6%; CC, 44.6% in those without nephropathy.

CONCLUSIONS

The MTHFR genotype and allele frequencies were not different between diabetic patients with and without nephropathy (chi2 = 3, 386, p > 0.005; chi2 = 2.320, p > 0.005, respectively). Therefore, we conclude that the MTHFR gene polymorphism is not associated with the development of diabetic nephropathy in Turkish type 2 diabetic patients.

MTHFR A1298C polymorphism is associated with cardiovascular risk in end stage renal disease in North Indians

The methylenetetrahydrofolate reductase (MTHFR) C677T gene polymorphism has been shown to be associated with cardiovascular disease and in patients with end-stage renal disease (ESRD). However, the relationship between MTHFR polymorphisms and cardiovascular disease (CVD) in patients on hemodialysis has not been examined. The aim of this study was to assess the association of polymorphisms of MTHFR gene with homocysteine (Hcy) and intimal medial thickness (IMT) in patients on hemodialysis. We performed case-control study involving107 patients with ESRD and 103 healthy controls. Plasma Hcy was measured in all the subjects and these subjects were genotyped for three MTHFR polymorphisms (C677T, A1298C, and G1793A). We observed significantly higher Hcy levels in patients as compared to controls. The frequency of MTHFR 1298CC genotype was significantly higher in ESRD patients than in controls (21.4% vs. 2.9%); the frequency of the MTHFR C677T genotypes did not differ between groups (26.1% vs. 17.4%). Compound heterozygous MTHFR 677CT/1298AC genotypes showed maximum association with the risk of ESRD (OR: 12.8; 5%CI: 1.64-10.01, P < 0.05). Concurrent occurrence of MTHFR 677CC wild genotype with either 1298CC or 1793GA significantly increased the risk of disease (OR: 7.20; 95%CI: 2.06-2.51, P < 0.001 and OR: 7.60; 95%CI: 1.68-34.35; P < 0.05, respectively). MTHFR 1298CC genotype was associated with higher Hcy levels. IMT was also significantly higher in patients with the 1298CC genotype (P < 0.05). Thus, A1298C polymorphism of MTHFR gene appears to be associated with the severity of carotid atherosclerosis and co-occurrence of MTHFR polymorphisms may be a risk factor for CVD in patients on hemodialysis.

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

Investigations into the association between diabetic nephropathy (DN) and MTHFR C677T gene polymorphism in several case-control studies has yielded contradictory results. To shed light on these inconclusive findings, a meta-analysis of all available studies relating the C677T polymorphism to the risk of developing DN was conducted. The PubMed database was searched, and case-control studies investigating the association between MTHFR C677T gene polymorphism and DN were included in the meta-analysis. The meta-analysis included 15 studies, of which 8 involved Caucasians and 5 East Asians; 11 studies involved subjects with type 2 diabetes and 4 with type 1 diabetes. The main analysis (all studies) revealed significant heterogeneity between the studies (P(Q)<0.01) and a marginal association between the 677T allele and the risk of developing DN; the random effects (RE) pooled odds ratio (OR) was 1.30 (1.03-1.64). However, the sensitivity analysis (exclusion of studies not in Hardy-Weinberg equilibrium) produced non-significant results. The recessive model derived significant results in main analysis [fixed effects (FE) OR=1.32 (1.10-1.58), P(Q)=0.27], and in type 2 diabetes [FE OR=1.30 (1.06-1.60), P(Q)=0.38]. The additive model produced significant association in main analysis [RE OR=1.65 (1.13-2.42), P(Q)<0.01] in Caucasians [FE OR=1.48 (1.11-1.98), P(Q)=0.17] and in type 2 diabetes [RE OR=1.65 (1.03-2.67), P(Q)<0.01]. However, sensitivity analysis diminished the significant results in type 2 diabetes. There is no differential magnitude of effect in large versus small studies. In conclusion, although there is some evidence of association between MTHFR C677T gene polymorphism and DN, the above findings reinforce the need for further and more rigorous association studies.

MTHFR C677T and A1298C gene polymorphisms and hyperhomocysteinemia as risk factors of diabetic nephropathy in type 2 diabetes patients

Point mutations in methylenetetrahydrofolate reductase (MTHFR) and hyperhomocysteinemia were implicated in the pathogenesis of diabetic nephropathy (DN) in many ethnic groups. This study addressed the association of C677T and A1298C single nucleotide polymorphisms (SNPs) of MTHFR gene with DN in Tunisian type 2 diabetes (T2DM) patients. Study subjects comprised 93 DN patients, 267 patients with normoalbuminuria, and 400 control subjects. C677T and A1298C genotypes were determined by PCR-RFLP analysis, and homocysteine levels were measured by ELISA. A1298C and C677T were highly prevalent among T2DM patients, with allele frequencies of 0.26 and 0.36, respectively. Higher mutant 677T allele and 677C/T and 677T/T genotypes of C677T SNP, but not A1298C SNP, together with 677C/1298A, 677C/1298C, and 677T/1298A haplotypes were seen in DN patients compared to normoalbuminuric patients, (p<0.001). Plasma homocysteine was positively associated with MTHFR 677T/T genotype among the three groups, and was significantly elevated in double heterozygous DN patients but not in normoalbuminuric patients or controls. Logistic regression analysis with DN as dependent variable showed that homocysteine (OR, 1.153) and MTHFR 677T/T (OR, 9.799) were the only variables associated with DN, after adjusting for possible confounding variables. C677T, but not A1298C, SNP, is a risk factor for DN, presumably acting by elevating homocysteine levels.

Plasma total homocysteine levels in children with type 1 diabetes: relationship with vitamin status, methylene tetrahydrofolate reductase genotype, disease parameters and coronary risk factors

The objectives of this study were: to determine plasma total homocysteine tHcy levels and the prevalence of hyperhomocysteinemia in children with type 1 diabetes, to determine correlates of plasma tHcy levels with nutritional factor such as serum folic acid and vitamin B12 levels, genetic factors as methylenetetrahydrofolate reductase MTHFR gene polymorphism (C677T and A1298C), to attempt to identify possible dependencies between tHcy and the degree of metabolic control, the duration of the disease and presence of complications, and also to determine the relationship between other coronary risk factors. Plasma tHcy levels and other related parameters performed in 32 children with type 1 diabetes and 23 age-sex matched healthy children. Median tHcy level was higher in the patient group (11.38, 3.28 to 66.01 micromol/l) than the control group (8.78, 1.06 to 13.66 mol/l) (p < 0.05). A 28.1 per cent (n = 9) of the diabetic patients had hyperhomocysteinemia, four case with mild and five case with moderate. Plasma tHcy levels were positively correlated with disease duration and C-reactive protein CRP levels and negatively correlated with disease onset age. The hyperhomocysteinemic group had higher CRP levels, longer disease duration and early onset of disease than non-hyperhomocysteinemic group (p < 0.05 in both), respectively. The hyperhomocysteinemic group had significantly higher CRP, total cholesterol, triglyceride, apolipoprotein B, systolic blood pressure, blood urea nitrogen and creatinine levels and lower folate, apolipoprotein A1 levels and glomerular filtration rate values than the control group. Plasma tHcy levels were higher in diabetic children with poor metabolic control. Because of hyperhomocysteinemia is common in diabetic children and plasma tHcy levels correlated with early onset of the disease and disease duration, we recommend the usage of plasma tHcy levels as a risk indicator parameter with other coronary risk factor for detecting and preventing cardiovascular disease in diabetic children.

The relationship between C677T methylenetetrahydrofolate reductase gene polymorphism and retinopathy in type 2 diabetes: a meta-analysis

The association between retinopathy in type 2 diabetes [diabetic retinopathy (DR)] and the C677T polymorphism in the methylenetetrahydrofolate reductase (MTHFR) gene has been investigated in several case-control studies. These studies rendered contradictory results, some indicating that the polymorphism is associated with the risk of developing DR whereas others concluded there is no association. To shed light on these inconclusive findings, a meta-analysis of all available studies relating the C677T polymorphism to the risk of developing DR was conducted. Four out of five identified studies included populations of East Asian descent, and only one involved samples from European descent (Caucasians). Overall, the meta-analysis suggested large heterogeneity between studies (p = 0.08, I(2) = 52%) and marginal association between C677T transition and the risk of developing DR: random effects odds ratio (OR) = 1.39 [95% CI (1.05, 1.83)]. The sensitivity analysis [exclusion of one East Asian study with the controls not in Hardy-Weinberg equilibrium (HWE)] showed no heterogeneity (p = 0.25, I(2) = 27%) and no significant association: fixed effects OR = 1.22 [95% CI (0.99, 1.51)] and random effects OR = 1.24 [95% CI (0.96, 1.60)]. The sub-group analysis for the East Asian population produced a significant association: fixed effects OR = 1.48 [95% CI (1.20, 1.83)] and random effects OR = 1.52 [95% CI (1.14, 2.03)]. However, sensitivity analysis in East Asians revealed that the association is marginal: fixed effects OR = 1.33 [95% CI (1.04, 1.70)] and random effects OR = 1.36 [95% CI (1.01, 1.83)]. There is a source of bias in the selected studies: the largest studies failed to show association while the smallest study claimed an association. The above findings reinforce the need for larger and more rigourous studies in this area.

Methotrexate related adverse effects in patients with rheumatoid arthritis are associated with the A1298C polymorphism of the MTHFR gene

BACKGROUND

There is an association between C677T polymorphism of the methylenetetrahydrofolate reductase (MTHFR) gene and methotrexate related toxicity.

OBJECTIVE

To examine the relations between the recently described A1298C polymorphism of the MTHFR gene, plasma homocysteine, methotrexate toxicity, and disease activity in patients with rheumatoid arthritis.

DESIGN

A cross sectional study on 93 methotrexate treated patients with rheumatoid arthritis, comprising a clinical interview and physical examination to determine disease activity and methotrexate related adverse reactions. Genotype analysis of the MTHFR gene was carried out and fasting plasma homocysteine and serum folate concentrations were measured. The data were analysed using univariate analysis. Allele and genotype distributions were compared with those of a healthy control group.

RESULTS

The frequency of the 1298CC genotype (24.7%) in the rheumatoid study group was greater than expected in the general population (12.8%, p<0.001). This genotype was associated with a significantly low rate of methotrexate related side effects. The odds ratio for side effects in patients with wild type 1298AA genotype v 1298CC genotype was 5.24 (95% confidence interval, 1.38 to 20). No correlation of disease activity variables or plasma homocysteine with MTHFR A1298C and C677T polymorphisms was observed.

CONCLUSIONS

1298CC polymorphism was more common in methotrexate treated rheumatoid patients than expected in the population, and was associated with a reduction in methotrexate related adverse effects. The A1298C polymorphism of the MTHFR gene may indicate a need to adjust the dose of methotrexate given to patients with rheumatoid arthritis.

Microsatellite DNA polymorphism of human adrenomedullin gene in type 2 diabetic patients with renal failure

BACKGROUND

Adrenomedullin (AM) is a hypotensive peptide widely produced in the cardiovascular organs and tissues such as the heart, kidney, and the vascular cells. We have previously cloned and sequenced the genomic DNA encoding human AM gene, and determined that the gene is located in the short arm of chromosome 11. The 3'-end of the gene is flanked by the microsatellite marker of cytosine adenine (CA) repeats. In this study, we investigated the association between DNA variations in AM gene and the predisposition to develop nephropathy in type 2 diabetes mellitus.

METHODS

Genomic DNA was obtained from the peripheral leukocytes of 233 normal healthy subjects (NH), 139 type 2 diabetic patients on hemodialysis (DM-HD), 106 control patients with type 2 diabetes without nephropathy (DM-C) and 318 hemodialysis patients due to chronic glomerulonephritis (CGN-HD). The genomic DNA was subject to polymerase chain reaction (PCR) using a fluorescence-labeled primer, and the number of CA repeats were determined by polyacrylamide gel electrophoresis (PAGE).

RESULTS

In our Japanese subjects, there existed four types of alleles with different CA-repeat number; 11, 13, 14, and 19. The frequencies of these alleles were 11: 27.7%, 13: 32.8%, 14: 35.6%, and 19: 3.9% in NH. These allele frequencies were not significantly different in DM-C and CGN-HD. However, DM-HD showed significantly different distribution of allele frequency from other groups (chi 2 = 18.9, P = 0.026). Namely, the frequency of 19-repeat allele in DM-HD was higher (9.0%) than NH, DM-C, and CGN-HD (P = 0.005, 0.041, and 0.004, respectively).

CONCLUSION

The microsatellite DNA polymorphism of AM gene may be associated with the genetic predisposition to develop nephropathy in Japanese patients with type 2 diabetes mellitus.

High-dose vitamin therapy stimulates variant enzymes with decreased coenzyme binding affinity (increased K(m)): relevance to genetic disease and polymorphisms

As many as one-third of mutations in a gene result in the corresponding enzyme having an increased Michaelis constant, or K(m), (decreased binding affinity) for a coenzyme, resulting in a lower rate of reaction. About 50 human genetic dis-eases due to defective enzymes can be remedied or ameliorated by the administration of high doses of the vitamin component of the corresponding coenzyme, which at least partially restores enzymatic activity. Several single-nucleotide polymorphisms, in which the variant amino acid reduces coenzyme binding and thus enzymatic activity, are likely to be remediable by raising cellular concentrations of the cofactor through high-dose vitamin therapy. Some examples include the alanine-to-valine substitution at codon 222 (Ala222-->Val) [DNA: C-to-T substitution at nucleo-tide 677 (677C-->T)] in methylenetetrahydrofolate reductase (NADPH) and the cofactor FAD (in relation to cardiovascular disease, migraines, and rages), the Pro187-->Ser (DNA: 609C-->T) mutation in NAD(P):quinone oxidoreductase 1 [NAD(P)H dehy-drogenase (quinone)] and FAD (in relation to cancer), the Ala44-->Gly (DNA: 131C-->G) mutation in glucose-6-phosphate 1-dehydrogenase and NADP (in relation to favism and hemolytic anemia), and the Glu487-->Lys mutation (present in one-half of Asians) in aldehyde dehydrogenase (NAD + ) and NAD (in relation to alcohol intolerance, Alzheimer disease, and cancer).

Biological and clinical implications of the MTHFR C677T polymorphism

The enzyme methylenetetrahydrofolate reductase (MTHFR) directs folate species either to DNA synthesis or to homocysteine (Hcy) remethylation. The common MTHFR C677T polymorphism affects the activity of the enzyme and hence folate distribution. Under conditions of impaired folate status, the homozygous TT genotype has been regarded as harmful because it is associated with a high concentration of plasma total Hcy, increased risk of neural tube defects and colorectal neoplasias, and can also predispose individuals to adverse effects from drugs with antifolate effects. The MTHFR C677T polymorphism shows no consistent correlation with cardiovascular risk and longevity but, in combination with positive folate balance, the TT genotype is associated with decreased risk of colorectal neoplasias. Because of the high prevalence of this polymorphism in most populations, the TT variant might represent an ancestral genetic adaptation to living constraints (tissue injury or unbalanced vitamin intake) that has become a determinant of disease profiles in modern times.