Iranian Journal of

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Background: Due to homeostatic and regulatory potentials of nitric oxide (NO) in vascular physiology, regulatory systems that determine NO bio-synthesis and bioavailability have been the subject of extensive research in molecular medicine. In the field of vascular system pathophysiology, endothelial nitric oxide synthase (eNOS) which is the major producer and regulator of NO in vascular tissues has received the most attention. Impairment of NO bioavailability (NO quenching) is a common feature in poorly controlled diabetics due to increased catabolism and decreased production of NO. Such impairment in severe forms could end to vasodilation breakdown in peripheral tissues (mainly in skeletal muscles) and defective regional blood flow, that in turn disturb insulin-dependent glucose uptake ensuing insulin resistance state.
Methods: The phenotypic impact of an eNOS gene polymorphism at position 786*C/T (that its functionality has been revealed already) on genetic propensity to diabetic retinopathy is evaluated in a British-Caucasian population with type 1 diabetes (T1DM).
Results: In contrast to genotypes, there was a significant difference in distribution of allele frequencies between T1DM patients (n= 249) and healthy controls (n= 104) (p= 0/036), that may imply eNOS and/or NO involvement in development of T1DM. Most notably a significant difference also was evident in allele frequency between retinopaths (n= 134) and healthy controls (p= 0/02). No significant difference was detected when the genotype/allele frequencies were compared between retinopaths (n= 134) and non-retinopaths diabetics (n= 115) (p=NS).
Conclusion: Our data is compatible with previous studies which demonstrated that allele C of eNOS 786*C/T polymorphism is associated with increased HbA1c levels. By emphasizing the phenotypic and prognostic value of the abovementioned polymorphism, our data calls for further investigations to find out whether this polymorphism can be employed as a genetic marker in clinical medicine to recognize high-risk diabetics at the time of diabetes onset/diagnosis.

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Background: Type 1 diabetes (T1DM) is an organ specific auto-immune disease, which is resulted by selective destruction of  islet cells. Insulitis as the initial event prior to T1DM development is featured mainly by lymphocytic infiltration, that may recede frequently leading to healthy state (benign insulitis). Among the issues that govern which of these outcome lie ahead in insulitis are the genetic background of the host and also the immunological circumstances in  islets' micro-environment.
Methods: As a "case-control association study" the impact of a polymorphism within TNF- gene at position -308*G/A on genetic susceptibility to T1DM is analyzed in a British-Caucasian population (248 cases and 118 healthy controls).
Results: The distribution of genotype/allele frequencies between patients and controls did not reflect significant differences (p= NS).
Conclusion: Since the crucial role of TNF- in development of T1DM is well established, our data may confer that the examined polymorphic marker does not have functional effects on TNF- gene expression, influencing the local or systemic level of this pro-inflammatory cytokine. However, in addition to addressing the uncertainties in "genotype-phenoype" correlations in complex diseases (i.e. T1DM), the negative results of our study also may instead draw attention to the potential impacts of post-transcriptional regulatory mechanisms relative to gene structural-based regulatory systems.

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Background: Despite substantial progress in the clinical management of diabetes, diabetic nephropathy (DN) still occurs recurrently, implicating diabetes as the major underlying condition leading to the end stage renal disease. One of the main reasons is the influential role of genetic or inherited backgrounds of diabetics that are almost overlooked in daily practice. Owing to be orchestrated by the genetic makeup, cellular and molecular responses are different to similar metabolic disturbances. This in turn defines susceptibility/resistance state of the host to chronic diabetic complications, including DN. Separate analysis of every single gene that may be involved in genetics of a multi-factorial disease (such as DN) is the only available way to dissect the genetic basis of the disease and overcome its complexity. Among different genes accountable for DN, Transforming Growth Factor (TGF)-1 has an exceptional place. TGF-1 has profound impact on cell growth and proliferation, and in particular the regulation of extra cellular matrix deposition, branding it as a "pro-fibrotic" and "hypertrophic" mediator.
Methods: By employing ARMS-PCR technique, the genetic susceptibility to DN was studied in 248 patients with T1DM (86 DN+, 162 DN−) and 113 healthy controls, all from British Caucasian origin. The analysis of two functional TGF-1 gene variations, which change codons 10 (+869*C/T) and 25 (+915*G/C) was carried out.
Results: There were some differences in alleles/genotypes distribution, but no significant association was apparent in patients as a whole or DN+/DN− subgroups and controls (P=NS). Conclusion: The negative result of this study may be false. As DN is a mortal disability, some fraction of risky genotypes associated with DN may previously be excluded by death. Such under-representation of the risky-genotypes (selective survivor effect) can be avoided by carrying out a prospective study. However, if the non-association result is true, it may question the functionality and reliability of the examined polymorphisms at least in the context of diabetes. Moreover, it does not underestimate the role of TGF-1 at the level of gene/protein themselves in development of DN.

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Background: Vascular factors in conjunction with metabolic issues are involved in both etiopathogenesis of diabetic neuropathy (DNU), and more remarkably in "repair" phase, when the net balance between neuroregenerative/degenerative reactions is dictated to some extent by these factors. The ischemic nature of DNU indicates the importance of re-establishment of blood vessels. VEGF, a growth factor which, in addition to its hemodynamic effects, possesses an "angiogenic" capacity has been the subject of extensive investigations in DNU, especially, interventional therapies. The impacts of racial and inherited backgrounds in the development of DNU suggest that the genetic issues partially govern the outcome of diabetic late complications, including DNU. By conducting a candidate gene case-control association study, present study explores the possibility if the inter-individual variations of VEGF gene structure by any means encode the genetic susceptibility/resistance in the course of DNU.
Methods: The distribution of VEGF gene polymorphisms frequencies were analyzed at positions –7*C/T, -1001*G/C, -1154*G/A and –2578*C/A and were evaluated by ARMS-PCR in 248 type 1 diabetic subjects (81 DNU+, 167 DNU−) and 113 healthy controls, all from "British-Caucasian" origin.
Results: When the frequency of the polymorphic alleles/genotypes between patients and controls, and also between two subgroups within patients' group with each other (DNU+ vs. DNU−) or with healthy controls were compared, only in one situation a significant difference was evident. The distribution of a VEGF gene polymorphism at promoter region (–7*C/T) at allelic (but not at genotypic) level was notably different between diabetics, with and without neuropathy, while the minor allele (T) conferred a protective effect (P=0.03 OR = 1.75).
Conclusion: The present study may imply a prognostic value for VEGF gene polymorphism at promoter region (–7*C/T) in DNU. However, it requires further studies to appreciate better the phenotypic impact of this polymorphism in this chronic complication of diabetes. A catalog of candidate genes polymorphisms that functionally reflect a protection/predisposition to DNU can provide the genotypic profile that can be useful to reasonably predict the overall behavior of diabetic subjects to the metabolic derangements relative to development of DNU, which in turn may require adoption of relevant preventive and therapeutic measures.

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Background: VEGF is newly discovered growth factor that has diverse biologic properties. The bottom-line of these activities is conduction and orchestration of a series of reactions that are taking place at microvasculature of different tissues/organs. Among the growth factors, cytokines and other mediators that reflect meaningful alteration in their local/systemic level, VEGF is the distinct player which can explain by its own all hemodynamic and architectural manifestations present in diabetic retinopathy (DR). The present study was conducted to pursue the role of a candidate gene structure variation, VEGF gene polymorphisms, in genetic susceptibility/resistance to development of DR through a cross sectional case-control study.
Methods: The frequency of four SNPs in VEGF gene at positions –7*C/T, –1001*G/C, –1154*G/A and –2578*C/A has been traced among 248 type 1 diabetic subjects (135 DR+, 113 DR−) along with 95 healthy controls. The populations had "British-Caucasian" background and ARMS-PCR technique was employed for DNA genotyping.
Results: Comparing the polymorphic variants' frequency at both allelic and genotypic levels among different groups/subgroups, significant difference was noticeable for –7*C/T polymorphism between diabetic patients with vs. without DR, while T allele conferred protective effect (p=0.002 OR=1.98).
Conclusion: Contemplating that up-regulation/over-expression of VEGF (local/systemic) as a common pre-requisite for DR development, our hypothesis was that whether the VEGF gene structural variations is correlated with the magnitude of VEGF expression in response to different stimuli present in diabetic context, namely hypoxia and hyperglycemia. Our data indicate that among the examined polymorphisms of VEGF gene, only SNP at position –7*C/T harbored significant difference between DR+ vs. DR− cases, proposing phenotypic impact for that SNP illustrating by evolvement/impediment of DR. However, reminding the insubstantial role of genetic issues in development of DR relative to DN or DNU, replicating current hypothesis by providing larger sample size and also employing more polymorphic markers could shed more light on the subject of present study.

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Background: Single nucleotide polymorphisms of Adiponectin gene have been associated with BMI, insulin sensitivity and type 2 diabetes, reportedly. In present study we performed a genetic association study for Adiponectin gene at position +45*T/G in type 2 diabetes and normal subjects of Tehran population.

Methods: Diabetic patients were selected from diabetes clinic and normal healthy control subjects aged between 25-64 years selected from zone 17 of Tehran. Adiponectin gene polymorphism was analyzed using PCR-RFLP method in normal healthy controls (N=70), obese diabetic patients (N=80) and non-obese diabetic patients (N=72).

Results: Frequency of TT genotype was 62.5% in non-obese diabetic patients and 78% in control group, that was statistically significant (TT vs TG+GG: P=0.02, OR=2.2, CI:0.98-5.00). There was also a significant difference for allele T and G frequencies when we compared between non-obese diabetic patients and controls group. The frequency of allele G was increased in non-obese diabetic (20.1%) patients compared to controls (12%) (P: 0.04 OR: 1.8 CI: 0.9-3.7).

Conclusion: This study showed TG and GG alleles of Adiponectin gene polymorphism at position +45*T/G are risk factors for development of diabetes mellitus while this effect is independent from BMI and obesity.

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Background: IFN-g is one of the most essential and fundamental player in initiation and development of T1DM. This mediator belongs to T Helper-1(Th1) class of cytokines and exerts stimulation and differentiation of naïve T cells towards Th1 cells and meanwhile inhibits differentiation and proliferation of Th2 cells. These effects are highly important in induction and progression of cell-mediated immune responses that is aberrantly operative in development of T1DM. Due to such outstanding role, numerous studies including genetic manipulation have focused on the role of this pro-inflammatory cytokine in T1DM.

 Methods: In a genetic association study the influence of IFN-g gene variation in position +874*T/A on development of T1DM was analysed in 248 British Caucasian T1DM patients in comparison with 119 healthy matched controls. ARMS-PCR procedure was designed for detection of the variants at allele/genotype level. 

Results: No significant association between IFN-g gene polymorphism and T1DM was apparent (P≥ 0.05). The distribution of these polymorphic variants was in Hardy-Weinberg equilibrium.

Conclusion: While some studies have shown an association between the examined polymorphism of IFN-g and T1DM, our data do not support that. According to present study the selected polymorphic marker (+874*T/A) is not among the polymorphisms that governs in part genetic susceptibility to T1DM. That irreproducibility or controversial results is a common observation in genetic studies of complex traits such as T1DM, reflecting a fragile correlation between genotype and phenotype. This study also underlines the importance of replication of association studies to confirm the previous results/interpretations.

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Background: The alteration of IGF-I systemic level in diabetes is typically characterized by depletion of free IGF-I plasma level and its decreased bioavailability. With regard to protective and advantageous effects of IGF-I on tissue healing and cellular regeneration such depletion could facilitate or accelerate tissue damages and complications.  By contrast, the local concentration of IGF-I is reportedly increased in particular tissues during some occasions, which has also clinical implications as IGF-I could function in an autocrine and paracrine manner.

The present study was conducted to assess that whether the differential outcome of diabetic subjects relative to diabetic retinopathy (DR) is linked to some extent to the structural variations of IGF-I gene.

Methods: Two polymorphisms of the IGF-I gene at positions -383*C/T and -1089*C/T were employed for genotyping analysis by ARMS-PCR assay and the data of genotype/allele distribution was compared between two subgroups of 248 British Caucasian type 1 diabetic subjects, 135 cases with DR and 113 controls (DR^-).

Results: The distribution of these polymorphisms did not associate significantly with presence or absence of DR (P≥ 0.05).

Conclusion: Since the involvement of IGF-I in development of DR is fairly rational, our results firstly may reflect some reservations about the functionality of the employed polymorphic markers and secondly may indicate that all regulators of IGF-I functionality or its local concentration level including IGFBPs and IGFRs should be taken into account, so their genes could be the subject of new study to accomplish current investigation.