C677T methylene-tetrahydrofolate reductase mutation in type 2 diabetic patients with and without hyperhomocysteinaemia

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.

Hyperhomocysteinemia and elevated ox-LDL in Tunisian type 2 diabetic patients: Role of genetic and dietary factors

INTRODUCTION

Total plasma homocysteine (tHcy) is an emerging risk factor for the development of atherosclerosis. However, its relationship with diabetes is still unclear.

OBJECTIVES

We evaluated the association between tHcy levels and methylenetetrahydrofolate reductase (MTHFR) 677C-->T genotype in a type 2 diabetes mellitus (DM) population and their relationship with oxidized LDL (ox-LDL) according to dietary habits and vascular complications.

DESIGN AND METHODS

Eighty-six DM patients were compared to 120 healthy volunteers.

RESULTS

Associated higher tHcy levels and significantly higher ox-LDL levels (p<0.001) were found in DM patients compared to healthy subjects. Homozygosity for the T allele of MTHFR was more frequent in diabetics than in healthy subjects (12.8% vs. 7.2%) and it was associated with higher tHcy levels. Moreover, this elevated level was associated with significantly higher ox-LDL levels in DM patients with hypertension (p<0.05). Improving folate and vitamin C intakes could have beneficial effects on lowering the tHcy and ox-LDL levels.

CONCLUSIONS

The interplay of genetic and dietary factors modulates the effect of homocysteine on cardiovascular risk factors.

The MTHFR CT polymorphism confers a high risk for stroke in both homozygous and heterozygous T allele carriers with Type 2 diabetes

OBJECTIVE

Individuals with Type 2 diabetes are at increased risk of stroke. Plasma homocysteine (tHcy) is an independent risk factor for cardiovascular (CV) disease. The methylene-tetrahydrofolate reductase (MTHFR) gene polymorphism (thermolabile variant C(677)T) is associated with CV risk, partly as a result of increased Hcy, especially in homozygous subjects.

AIM

To relate the occurrence of the MTHFR polymorphism with stroke prevalence by examining allelic frequency and genotype distribution in 165 subjects with Type 2 diabetes studied for the presence of thermolabile C(677)T MTHFR mutation.

RESULTS

Mean age was 67.7 years, and tHcy 18.2 micromol/l. T allele frequency was 38.5%. MTHFR genotypes were: normal (CC) 40%; heterozygous (CT) 43%; homozygous (TT) 17%. Serum levels of folic acid and B12 vitamin were within normal limits. Stroke prevalence was 14%. Sixty-four per cent of stroke-free subjects had the normal C allele vs. 46% in stroke subjects. The frequencies of genotypes (CC-CT-TT) were (%): 44-41-15 in stroke-free vs. 17-57-26 in stroke patients. Coronary (CAD) and peripheral artery disease (PAD) were common in all groups, with no differences according to genotypes. Stroke prevalence was markedly higher in genotypes CT and TT (18 and 21%) compared with CC (6%). Mean tHcy levels were higher in TT subjects.

CONCLUSION

The allelic frequency of C(677)T MTHFR mutation in Type 2 diabetes subjects with stroke is markedly different from that of subjects without stroke. Genotypic characteristics suggest that C(677)T MTHFR mutation confers a higher risk for stroke to both homozygous and heterozygous T allele carriers that cannot be ascribed solely to raised tHcy and/or lower folate status in CT subjects, nor to phenotypic expression of conventional risk factors for stroke. The impact of the MTHFR polymorphism on stroke may result from T allele-linked deleterious effects, or C allele-linked protection. Confirmatory studies are warranted, as this cohort was not randomly selected, and a type 1 error cannot be ruled out.

Homocysteine levels are associated with MTHFR A1298C polymorphism in Indian population

An elevated level of homocysteine is an independent risk factor for cardiovascular diseases and is associated with other complex disorders. Homocysteine levels can be elevated due to dietary and/or genetic factors. A majority of Indian population have a low level of vitamin B12 (presumably due to vegetarian diet)--a critical nutritional factor, deficiency of which results in hyperhomocysteinemia. Hence, polymorphisms in the genes responsible for homocysteine metabolism can be perceived to have a greater impact in relation to hyperhomocysteinemia in Indian population. For this reason, the effects of diet and/or methylenetetrahydrofolate reductase (MTHFR) polymorphism were assessed in 200 individuals having varying homocysteine levels. Homocysteine levels were significantly elevated in individuals adhering to a vegetarian diet (P = 0.019) or having MTHFR A1298C polymorphism (P = 0.006). The minor allele frequency (MAF) of MTHFR C677T and A1298C was 0.15 and 0.44 respectively in this cohort. Since the MAF of these polymorphisms differed considerably from Caucasian and other Asian populations, frequencies of these polymorphisms were also determined in more than 400 individuals from different ethnic populations, selected from the entire country based on their geographical location and linguistic lineage, and was found to be similar to that of our cohort. The fact that MTHFR A1298C polymorphism is significantly associated with homocysteine levels, and that the CC genotype is present at a higher frequency in the Indian population, makes it extremely relevant in terms of its potential impact on hyperhomocysteinemia.

Homocysteine, vitamin B 12 and folate in Alzheimer's and vascular dementias: The paradoxical effect of the superimposed type II diabetes mellitus condition

BACKGROUND

Increased concentration of plasmatic homocysteine (tHcy) and decreased vitamin B 12 (B12) and folate (FOL) are associated with Alzheimer's (AD) and vascular (VaD) dementias, with type II diabetes mellitus (DM), and reported as risk factors of these diseases.

METHODS

The sample (n=122; males=60; mean age=73+/-7 years) comprised AD and VaD patients without DM, with a concomitant DM (AD+DM, VaD+DM), DM alone and controls (CTR), resulting in 6 groups. tHcy, B12 and FOL were determined in duplicate.

RESULTS

The one-way ANOVA yielded significant differences between groups for all variables: tHcy p<10(-12); B12 p<10(-3); FOL p<10(-4). Significance for comparisons between groups was set at alpha=0.05, using the Bonferroni's statistic. The comparisons: DM vs. CTR, AD+DM vs. AD, VaD+DM vs. VaD, and DM demented vs. DM non-demented resulted significant for all variables, except for B12 in 2 comparisons.

CONCLUSIONS

In demented and control subjects, tHcy and FOL exhibit extreme differences, not so marked between DM and controls. Demented patients with concomitant diabetes are closer to controls than their non-diabetic counterparts. Diabetes affects tHcy and FOL values, which are changed with opposite sign to non-demented. These results suggests a paradoxical phenomenon when diabetes is superimposed to dementias.

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.