Diabetic microvascular complications are not associated with two polymorphisms in the GLUT-1 and PC-1 genes regulating glucose metabolism in Caucasian type 1 diabetic patients

The pivotal role of glucose transporter 1 in diabetic kidney disease

Diabetes mellitus (DM) is a significant public health problem. Diabetic kidney disease (DKD) is the most common complication of DM, and its incidence has been increasing with the increasing prevalence of DM. Given the association between DKD and mortality in patients with DM, DKD is a significant burden on public health resources. Despite its significance in DM progression, the pathogenesis of DKD remains unclear. Aberrant glucose uptake by cells is an important pathophysiological mechanism underlying DKD renal injury. Glucose is transported across the bilayer cell membrane by a glucose transporter (GLUT) located on the cell membrane. Multiple GLUT proteins have been identified in the kidney, and GLUT1 is one of the most abundantly expressed isoforms. GLUT1 is a crucial regulator of intracellular glucose metabolism and plays a key pathological role in the phenotypic changes in DKD mesangial cells. In an attempt to understand the pathogenesis of DKD better, we here present a review of studies on the role of GLUT1 in the development and progression of DKD.

Predictors of future microalbuminuria in children and adolescents with type 1 diabetes mellitus in Egypt

Introduction

The present study was designed to assess the validity and efficacy of urinary markers (NAG, RBP, transferrin, α1-microglobulin, and plasma homocysteine) as early predictors of microalbuminuria in diabetic nephropathy in children and adolescents with type-1 diabetes, and its relation with haemoglobin glycated (HbA_1c), serum lipid profile, and blood pressure.

Material and methods

This study is a follow-up study to the 2002 study by Salem et al. The present study included 35 type 1 diabetes mellitus (T1DM) children and adolescents recruited from regular attendees of the specialised Diabetology Clinic, Children’s hospital, Ain Shams University, with previously measured urinary N-acetyl-β-glucosaminidase (13) or homocysteine (11) or transferrin (28) or α1-microglobulin (27) or retinol binding protein (13) as an early predictor of diabetic nephropathy in T1DM. Thirty-five patients with type 1 diabetes mellitus were enrolled, and 24 patients were normoalbuminuric at baseline. The patients were tested for markers other than urinary microalbumin, to predict diabetic nephropathy and early renal impairment in children and adolescents with type 1 diabetes mellitus.

Results

Regarding the metabolic control between the studied groups, we found that there is significant difference in HbA_1c between the microalbuminuric patients and the normoalbuminuric patients. According to the number of positive markers of diabetic nephropathy, the only parameter that was higher in patients with more than one elevated marker was mean systolic blood pressure. Although mean diabetic blood pressure was higher, it was not statistically significant. Regarding to the predictability of urinary markers, urinary N-acetyl-β-glucosaminidase is the most predictable marker with high sensitivity and specificity. The least sensitivity noticed was urinary RBP and the least specificity noticed was urinary α1-microglobulin.

Conclusions

Regarding the predictability of urinary markers, urinary NAG is the most predictable marker with both high sensitivity and specificity, with a sensitivity of 60%, specificity 75%, positive predictive value 60%, negative predictive value 75%, and a diagnostic accuracy of 0.58%. Urinary RBP is another marker with low sensitivity but high specificity. Urinary α1-microglobulin is a valid marker with high sensitivity but low specificity. Contrary to previous markers, plasma homocysteine has high specificity but low sensitivity.

Ion channels and transporters in diabetic kidney disease

Type 1 and 2 diabetes mellitus are major medical epidemics affecting millions of patients worldwide. Diabetes mellitus is the leading cause of diabetic kidney disease (DKD), which is the most common cause of end-stage renal disease (ESRD). DKD is associated with significant changes in renal hemodynamics and electrolyte transport. Alterations in renal ion transport triggered by pathophysiological conditions in diabetes can exacerbate hypertension, accelerate renal injury, and are integral to the development of DKD. Renal ion transporters and electrolyte homeostasis play a fundamental role in functional changes and injury to the kidney during DKD. With the large number of ion transporters involved in DKD, understanding the roles of individual transporters as well as the complex cascades through which they interact is essential in the development of effective treatments for patients suffering from this disease. This chapter aims to gather current knowledge of the major renal ion transporters with altered expression and activity under diabetic conditions, and provide a comprehensive overview of their interactions and collective functions in DKD.

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 the ENPP1 K121Q polymorphism and risk of diabetic kidney disease: a systematic review and meta-analysis

The potential association between the K121Q (A/C, rs1044498) polymorphism in the ectonucleotide pyrophosphatase/phosphodiesterase (ENPP1) gene and risk of diabetic kidney disease (DKD) has been investigated. Nevertheless, the effect of this variant on DKD risk is still under debate, and conflicting results have been reported. To this date, no meta-analysis has evaluated the association of the K121Q polymorphism with DKD. This paper describes the first meta-analysis conducted to evaluate whether the ENPP1K121Q polymorphism is associated with DKD. A literature search was conducted to identify all case-control or cross-sectional studies that evaluated associations between the ENPP1K121Q polymorphism and DKD. Pooled odds ratios (OR) and 95% confidence intervals (95% CI) were calculated for allele contrast, additive, dominant and recessive inheritance models. Seven studies were eligible for inclusion in the meta-analysis, providing data on 3571 type 1 or type 2 diabetic patients (1606 cases with DKD and 1965 diabetic controls without this complication). No significant heterogeneity was observed among the studies included in the meta-analysis when assuming different inheritance models (I² < 50% or P > 0.10 for the entire sample and after stratification by ethnicity). Meta-analysis results revealed significant associations between the K121Q polymorphism and risk of DKD in Asians and Europeans when assuming the different inheritance models analyzed. The most powerful association was observed for the additive model (OR = 1.74, 95% CI 1.27-2.38 for the total sample). In conclusion, the present meta-analysis detected a significant association between the ENPP1K121Q polymorphism and increased susceptibility of DKD in European and Asian populations.

Association of genetic variants with diabetic nephropathy

Diabetic nephropathy accounts for the most serious microvascular complication of diabetes mellitus. It is suggested that the prevalence of diabetic nephropathy will continue to increase in future posing a major challenge to the healthcare system resulting in increased morbidity and mortality. It occurs as a result of interaction between both genetic and environmental factors in individuals with both type 1 and type 2 diabetes. Genetic susceptibility has been proposed as an important factor for the development and progression of diabetic nephropathy, and various research efforts are being executed worldwide to identify the susceptibility gene for diabetic nephropathy. Numerous single nucleotide polymorphisms have been found in various genes giving rise to various gene variants which have been found to play a major role in genetic susceptibility to diabetic nephropathy. The risk of developing diabetic nephropathy is increased several times by inheriting risk alleles at susceptibility loci of various genes like ACE, IL, TNF-α, COL4A1, eNOS, SOD2, APOE, GLUT, etc. The identification of these genetic variants at a biomarker level could thus, allow the detection of those individuals at high risk for diabetic nephropathy which could thus help in the treatment, diagnosis and early prevention of the disease. The present review discusses about the various gene variants found till date to be associated with diabetic nephropathy.

Investigation of SLC2A1 26177A/G gene polymorphism via high resolution melting curve analysis in Malaysian patients with diabetic retinopathy

PURPOSE

In this study, we aimed to investigate the possible association between SLC2A1 26177A/G polymorphism and diabetic retinopathy (DR) in Malaysian patients with type 2 diabetes.

METHODS

Genomic DNA was extracted from 211 Malaysian type 2 diabetic patients (100 without retinopathy [DNR], 111 with retinopathy) and 165 healthy controls. A high resolution melting assay developed in this study was used to detect SLC2A1 26177A/G polymorphism followed by statistical analysis.

RESULTS

A statistically significant difference in 26177G minor allele frequency between healthy controls (19.7 %) and total patient group (26.1 %) (p<0.05, Odd ratio = 1.437, 95% Confidence interval = 1.015-2.035) as well as between healthy controls (19.7 %) and DNR patients (27.5%) (p<0.05, Odd ratio = 1.546, 95% Confidence interval = 1.024-2.336) was shown in this study. However, when compared between DR and DNR patients, there was no significant difference (p>0.05).

CONCLUSIONS

This is the first study which shows that SLC2A1 26177G allele is associated with type 2 diabetes in Malaysian population but not with DR.

Relationship between five GLUT1 gene single nucleotide polymorphisms and diabetic nephropathy: a systematic review and meta-analysis

So far, case-control studies on the association between glucose transporter 1 (GLUT1) gene single nucleotide polymorphisms (SNPs) and diabetic nephropathy (DN) have generated considerable controversy. To clarify the linkage of GLUT1 SNPs on the risk of DN, a systematic review and meta-analysis was performed. A comprehensive literature search of electronic databases was conducted to obtain relative studies. Nine case-control studies were included. Significant differences were found between XbaI SNP (rs841853) and increased risk of DN in all genetic models. Subgroup analyses for Caucasians population and DN from both type 1 and type 2 diabetes also revealed positive results. For Enh2-1 SNP (rs841847), Enh2-2 SNP (rs841848) and HaeIII SNP (rs1385129), obvious linkages were demonstrated in recessive model. However, analysis for the association between HpyCH4V SNP (rs710218) and the susceptibility of DN showed no significance. Likewise, negative outcome was also found in the assessment for the influence of XbaI or Enh2-2 SNP on the pathogenesis progress of DN. The evidence currently available shows that XbaI, Enh2 and HaeIII SNPs, but not HpyCH4V SNP, in GLUT1 gene may be genetic susceptibility to DN. However, data does not support the association between either XbaI or Enh2-2 SNP and the severity of DN.

Genetic variation of glucose transporter-1 (GLUT1) and albuminuria in 10,278 European Americans and African Americans: a case-control study in the Atherosclerosis Risk in Communities (ARIC) study

Background

Evidence suggests glucose transporter-1(GLUT1) genetic variation affects diabetic nephropathy and albuminuria. Our aim was to evaluate associations with albuminuria of six GLUT1 single nucleotide polymorphisms(SNPs), particularly XbaI and the previously associated Enhancer-2(Enh2) SNP.

Methods

A two-stage case-control study was nested in a prospective cohort study of 2156 African Americans and 8122 European Americans with urinary albumin-to-creatinine ratio(ACR). Cases comprised albuminuria(N = 825; ≥ 30 μg/mg) and macroalbuminuria(N = 173; ≥ 300 μg/mg). ACR < 30 μg/mg classified controls(n = 9453). Logistic regression and odds ratios(OR) assessed associations. The evaluation phase(stage 1, n = 2938) tested associations of albuminuria(n = 305) with six GLUT1 SNPs: rs841839, rs3768043, rs2297977, Enh2(rs841847) XbaI(rs841853), and rs841858. Enh2 was examined separately in the replication phase(stage 2, n = 7340) and the total combined sample (n = 10,278), with all analyses stratified by race and type 2 diabetes.

Results

In European Americans, after adjusting for diabetes and other GLUT1 SNPs in stage 1, Enh2 risk genotype(TT) was more common in albuminuric cases(OR = 3.37, P = 0.090) whereas XbaI (OR = 0.94, p = 0.931) and remaining SNPs were not. In stage 1, the Enh2 association with albuminuria was significant among diabetic European Americans(OR = 2.36, P = 0.025). In African Americans, Enh2 homozygosity was rare(0.3%); XbaI was common(18.0% AA) and not associated with albuminuria. In stage 2(n = 7,340), Enh2 risk genotype had increased but non-significant OR among diabetic European Americans(OR = 1.66, P = 0.192) and not non-diabetics(OR = 0.99, p = 0.953), not replicating stage 1. Combining stages 1 and 2, Enh2 was associated with albuminuria(OR 2.14 [1.20-3.80], P = 0.009) and macroalbuminuria(OR 2.69, [1.02-7.09], P = 0.045) in diabetic European Americans. The Enh2 association with macroalbuminuria among non-diabetic European Americans with fasting insulin(OR = 1.84, P = 0.210) was stronger at the highest insulin quartile(OR = 4.08, P = 0.040).

Conclusions

As demonstrated with type 1 diabetic nephropathy, the GLUT1 Enh2 risk genotype, instead of XbaI, may be associated with type 2 diabetic albuminuria among European Americans, though an association is not conclusive. The association among diabetic European Americans found in stage 1 was not replicated in stage 2; however, this risk association was evident after combining all diabetic European Americans from both stages. Additionally, our results suggest this association may extend to non-diabetics with high insulin concentrations. Rarity of the Enh2 risk genotype among African Americans precludes any definitive conclusions, although data suggest a risk-enhancing role.

The association of 18F-deoxyglucose (FDG) uptake of PET with polymorphisms in the glucose transporter gene (SLC2A1) and hypoxia-related genes (HIF1A, VEGFA, APEX1) in non-small cell lung cancer. SLC2A1 polymorphisms and FDG-PET in NSCLC patients

BACKGROUND

Positron emission tomography imaging of lung cancers with 2-[fluorine-18]-fluoro-2-deoxy-D-glucose is a non-invasive diagnostic, and prognostic tool that measures tumor metabolism. We have analyzed the effect of solute carrier family 2 (facilitated glucose transporter), member 1 polymorphisms on 2-[fluorine-18]-fluoro-2-deoxy-D-glucose-uptake with a combination of polymorphisms of hypoxia-inducible factor 1 alpha, apurinic/apyimidinic endonuclease, and vascular endothelial growth factor A in a hypoxia-related pathway.

METHODS

We investigated the association between solute carrier family 2 (facilitated glucose transporter), member 1 -2841A>T, hypoxia-inducible factor 1 alpha Pro582Ser, Ala588Thr, apurinic/apyimidinic endonuclease Asp148Glu, or vascular endothelial growth factor A +936C>T and 2-[fluorine-18]-fluoro-2-deoxy-D-glucose-uptake among 154 patients with non-small-cell lung cancer.

RESULTS

The solute carrier family 2 (facilitated glucose transporter), member 1 -2841A>T polymorphism was significantly associated with 2-[fluorine-18]-fluoro-2-deoxy-D-glucose-uptake in combination with the apurinic/apyimidinic endonuclease Asp148Glu (T>G) polymorphism in the squamous cell type of non-small-cell lung cancer. The solute carrier family 2 (facilitated glucose transporter), member 1 TT genotype had a higher maximum standardized uptake values than the AA + AT genotype when the apurinic/apyimidinic endonuclease genotype was TT (mean maximum standardized uptake values, 12.47 +/- 1.33 versus 8.46 +/- 2.90, respectively; P = 0.028). The mean maximum standardized uptake values were not statistically different with respect to vascular endothelial growth factor A and hypoxia-inducible factor 1 alpha polymorphisms.

CONCLUSION

A glucose transporter gene polymorphism was shown to be statistically associated with glucose-uptake when the apurinic/apyimidinic endonuclease genotype is TT in patients with the squamous cell type of non-small-cell lung cancer. Our findings suggest that a newly developed tracer for positron emission tomography could be affected by genetic polymorphisms.

Risk genotypes and haplotypes of the GLUT1 gene for type 2 diabetic nephropathy in the Tunisian population

OBJECTIVE

Diabetic nephropathy (DN) is a long-term complication of both type 1 and type 2 diabetes. Genetic studies on DN have been of little help so far, since several genetic association studies have shown conflicting results. Here we report the findings of a case-control study on five SNPs in the glucose transporter 1 (GLUT1) gene. The study investigated the association of five GLUT1 genotypes and haplotypes with DN.

RESEARCH DESIGN AND METHODS

All subjects, 126 DN (cases) and 273 type 2 diabetes (controls), were genotyped using the polymerase chain reaction restriction fragment length polymorphism.

RESULTS

The TT and the AA genotypes of the Haell and Enh2 SNP1, increased the risk of DN. The study also identified CGT as the highest risk haplotype (4.4-fold) followed by CAT with an increased risk of DN of 2.6-fold.

CONCLUSIONS

The GLUT1 gene confers susceptibility to DN in type 2 diabetes patients in the Tunisian population.

Glucose transporter polymorphisms are associated with clear-cell renal carcinoma

Clear-cell renal cell carcinoma (CCRCC) is identified by abundant glycogen-rich cytoplasm, due to the aberrant influx and storage of glucose. The objective was to investigate the frequency of polymorphisms of the facilitative glucose transporter (GLUT1). GLUT1 is a downstream target of Hypoxia-inducible factor (HIF-1alpha), a mediator of hypoxia-controlled angiogenesis. In this study, we examine the allelic frequency of polymorphisms in the promoter and the second intron of the GLUT1 gene. Genomic DNA was extracted from normal tissue of 92 patients undergoing nephrectomy for CCRCC, and 99 normal cord blood DNA samples were used to provide control frequencies. The regions of DNA encompassing the polymorphisms were amplified and digested with appropriate endonuclases. The products were separated and viewed by gel electrophoresis. There was a highly significant decrease in the A-2841 genotype (P=0.0004) in the promoter region of those patients with CCRCC compared to the control population. There was also a significant decrease in the T+22999 allele in the intron 2 of those patents with CCRCC (P=0.004) compared to the same control population. This study suggests that GLUT1 is one of a number of genes that may increase susceptibility to developing CCRCC.

Assessment of 115 candidate genes for diabetic nephropathy by transmission/disequilibrium test

Several lines of evidence, including familial aggregation, suggest that allelic variation contributes to risk of diabetic nephropathy. To assess the evidence for specific susceptibility genes, we used the transmission/disequilibrium test (TDT) to analyze 115 candidate genes for linkage and association with diabetic nephropathy. A comprehensive survey of this sort has not been undertaken before. Single nucleotide polymorphisms and simple tandem repeat polymorphisms located within 10 kb of the candidate genes were genotyped in a total of 72 type 1 diabetic families of European descent. All families had at least one offspring with diabetes and end-stage renal disease or proteinuria. As a consequence of the large number of statistical tests and modest P values, findings for some genes may be false-positives. Furthermore, the small sample size resulted in limited power, so the effects of some tested genes may not be detectable, even if they contribute to susceptibility. Nevertheless, nominally significant TDT results (P < 0.05) were obtained with polymorphisms in 20 genes, including 12 that have not been studied previously: aquaporin 1; B-cell leukemia/lymphoma 2 (bcl-2) proto-oncogene; catalase; glutathione peroxidase 1; IGF1; laminin alpha 4; laminin, gamma 1; SMAD, mothers against DPP homolog 3; transforming growth factor, beta receptor II; transforming growth factor, beta receptor III; tissue inhibitor of metalloproteinase 3; and upstream transcription factor 1. In addition, our results provide modest support for a number of candidate genes previously studied by others.

Glucose transporters in diabetic nephropathy

Changes in glucose transporter expression in glomerular cells occur early in diabetes. These changes, especially the GLUT1 increase in mesangial cells, appear to play a pathogenic role in the development of ECM expansion and perhaps other features of diabetic nephropathy. In addition, it appears that at least some diabetic patients may be predisposed to nephropathy because of polymorphisms in their GLUT1 genes. GLUT1 overexpression leads to increased glucose metabolic flux which in turn triggers the polyol pathway and activation of PKC alpha and B1. Activation of these PKC isoforms can lead directly to AP-1 induced increases in fibronectin expression and ECM accumulation. Other, more novel effects of GLUT1 on cellular hypertrophy and injury could also promote changes of diabetic nephropathy. Strategies to prevent GLUT1 overexpression could ameliorate or prevent the progression of diabetic nephropathy.

A novel polymorphism in the 5' flanking region of the glucose transporter (GLUT1) gene is strongly associated with diabetic nephropathy in patients with Type 1 diabetes mellitus

Glucose transporter 1 (GLUT1) activity has been implicated in renal hypertrophy and extracellular matrix formation in mesangial cells. Recent studies have suggested that polymorphisms in the GLUT1 gene are associated with susceptibility to diabetic nephropathy (DN) in patients with diabetes mellitus. In this study, a novel polymorphism (A-2841T) in the 5' flanking region of GLUT1 was examined in 288 patients with Type 1 diabetes mellitus (T1DM) and 101 normal controls. The polymorphisms were amplified and the fragment digested with the enzyme HpyCH4V. There was a highly significant increase in the frequency of the TT-2841 genotype in patients with nephropathy (n=131) compared with those with either no microvascular complications after a 20-year duration of diabetes (uncomplicated; n=72; 54.5% vs. 2.7%, chi=79.4, P<.000001). There was no difference between the uncomplicated group and those who only had retinopathy (n=50; 2.7% vs. 4.0%, respectively). The frequency in recently diagnosed patients was 17.1% and only 2.0% in normal controls. In contrast, the AA genotype was found in 13.6% of the nephropaths, 76.3% of uncomplicated, 48.0% of retinopaths, and 65% of normal controls. These results confirm previous reports of an association between the GLUT1 gene and susceptibility to DN but not retinopathy. The localisation of this polymorphism suggests that it may be involved in the expression of the gene.

Association between the GLUT1 gene polymorphism and the risk of diabetic nephropathy: a meta-analysis

The association between diabetic nephropathy (DN) and the XbalphaI polymorphism in the GLUT1 gene has been investigated in several case-control studies. These studies rendered contradictory results: the allele XbalphaI(-) was shown either to be a risk factor or neutral, or even protective for the development of the disease. To shed some light on these inconclusive findings, a meta-analysis of all available studies relating the XbalphaI polymorphism to the risk of developing DN was conducted. Five out of six identified studies included Caucasian populations, and only one involved samples from an Asian population. Overall, the meta-analysis suggested large heterogeneity between studies (P<0.01, I2=68%) and lack of association between allele XbalphaI(-) and the risk of developing DN relative to allele XbalphaI(+): random effects odds ratio (OR)=1.26 [95% CI (0.93, 1.69)]. Excluding one study with the controls not in Hardy-Weinberg equilibrium, the sensitivity analysis revealed that heterogeneity (P=0.28, I2=21%) could be explained, and then, there is an overall association: fixed effects OR=1.34 [95% CI (1.13, 1.60)]. Then, significant ORs were also found on analysis of subgroups: for the Caucasian population, fixed effects OR=1.29 [95% CI (1.08, 1.56)] and for the type 2 diabetic patients fixed effects OR=1.69 [95% CI (1.09, 2.63)]. In type 1 diabetes, there is a moderate heterogeneity (P=0.19, I2=41%) with fixed effects OR=1.29 [95% CI (1.06, 1.56)] and random effects OR=1.32 [95% CI (1.01, 1.71)]. There is a source of bias in the selected studies: large studies failed to show association while small studies claimed an association. Although there is evidence of association between GLUT1 and DN, the above findings reinforce the need for further and more rigorous association studies.

PC-1 amino acid variant Q121 is associated with a lower glomerular filtration rate in type 2 diabetic patients with abnormal albumin excretion rates

OBJECTIVE

To study the relationships between the PC-1 K121Q variant and diabetic nephropathy (DN) in patients with type 2 diabetes.

RESEARCH DESIGN AND METHODS

A total of 125 patients with type 2 diabetes and abnormal albumin excretion rate (AER) (range 20-5416 microg/min) were followed up for 4 years with repeated measurements of glomerular filtration rate (GFR). Genomic DNA was extracted from all patients, and the PC-1 K121Q polymorphism was determined by the PCR AvaII restriction enzyme. A subset of 64 patients underwent a percutaneous kidney biopsy at baseline, and glomerular structure was analyzed by electron microscopic morphometric analysis. At baseline, age (56 +/- 8 vs. 59 +/- 7 years), BMI (28.3 +/- 4.3 vs. 28.6 +/- 3.7 kg/m(2)), known duration of type 2 diabetes (11.1 +/- 7 vs. 11.9 +/- 8 years), and HbA(1c) (8.6 +/- 1.8 vs. 8.4 +/- 1.7%) were similar in K121K (KK, n = 87, 73 men/14 women) and XQ (35 K121Q + 3 Q121Q, n = 38, 27 men/11 women) patients. Baseline GFR was 96 +/- 28 ml. min(-1). 1.73 m(-2) and was related (P = 0.01-0.001) to age, known diabetes duration, and systolic blood pressure.

RESULTS

XQ patients had lower GFR (P < 0.05) than KK patients (88 +/- 30 vs. 100 +/- 26 ml. min(-1). 1.73 m(-2)); this difference persisted also after factoring in age and known diabetes duration. The rate of progression of DN was similar in KK and XQ patients: %deltaGFR was 4.1/year (median, range: 22.9-30.6) vs. 4.2/year (9.8-26.7). Morphometric parameters of diabetic glomerulopathy were similar in the two genotype groups.

CONCLUSIONS

Among patients with type 2 diabetes with abnormal AER, those carrying the Q PC-1 genotype have more severe DN but not a faster GFR decline than KK patients, thus suggesting faster DN development since diabetes diagnosis in XQ patients.

Physiological and pathophysiological functions of the ecto-nucleotide pyrophosphatase/phosphodiesterase family

The ecto-nucleotide pyrophosphatase/phosphodiesterase (E-NPP) multigene family contains five members. NPP1-3 are type II transmembrane metalloenzymes characterized by a similar modular structure composed of a short intracellular domain, a single transmembrane domain and an extracellular domain containing a conserved catalytic site. The short intracellular domain of NPP1 has a basolateral membrane-targeting signal while NPP3 is targeted to the apical surface of polarized cells. NPP4-5 detected by database searches have a predicted type I membrane orientation but have not yet been functionally characterized. E-NPPs have been detected in almost all tissues often confined to specific substructures or cell types. In some cell types, NPP1 expression is constitutive or can be induced by TGF-beta and glucocorticoids, but the signal transduction pathways that control expression are poorly documented. NPP1-3 have a broad substrate specificity which may reflect their role in a host of physiological and biochemical processes including bone mineralization, calcification of ligaments and joint capsules, modulation of purinergic receptor signalling, nucleotide recycling, and cell motility. Abnormal NPP expression is involved in pathological mineralization, crystal depositions in joints, invasion and metastasis of cancer cells, and type 2 diabetes. In this review we summarize the present knowledge on the structure and the physiological and biochemical functions of E-NPP and their contribution to the pathogenesis of diseases.

Minor effect of GLUT1 polymorphisms on susceptibility to diabetic nephropathy in type 1 diabetes

Elevation of intracellular glucose in mesangial cells as mediated by GLUT1 may be important in initiating cellular mechanisms that cause diabetic nephropathy. To determine whether DNA sequence differences in GLUT1 confer susceptibility to this complication, single-nucleotide polymorphisms (SNPs) in this gene were examined using a large case-control study. SNPs examined included the known XbaI (intron 2) and HaeIII SNPs (exon 2). Four novel SNPs located in three putative enhancers were also investigated. Homozygosity for the XbaI(-) allele was associated with diabetic nephropathy (odds ratio 1.83 [95% CI 1.01-3.33]). Furthermore, homozygosity for the A allele for a novel SNP (enhancer-2 SNP 1) located in a putative insulin-responsive enhancer-2 was associated with diabetic nephropathy (2.38 [1.16-4.90]). Patients who were homozygous for risk alleles at both XbaI SNP and enhancer-2 SNP 1 [i.e., homozygosity for XbaI(-)/A haplotype] also had an increased risk of diabetic nephropathy (2.40 [1.13-5.07]). Because enhancer-2 SNP 1 may directly control GLUT1 expression, the strong linkage disequilibrium between the two SNPs likely accounts for XbaI SNP being associated with diabetic nephropathy. In conclusion, our study confirms that SNPs at the GLUT1 locus are associated with susceptibility to diabetic nephropathy in type 1 diabetes. Although these SNPs confer a considerable personal risk for diabetic nephropathy, they account for a limited proportion of cases among type 1 diabetic patients.

ACE and PC-1 gene polymorphisms in normoalbuminuric Type 1 diabetic patients: a 10-year prospective study

The aim of this study was to analyze the role of ACE gene insertion/deletion (I/D) and PC-1 gene K121Q polymorphisms in the changes of glomerular filtration rate (GFR), urinary albumin excretion rate (UAER), and blood pressure (BP) levels in a cohort of normoalbuminuric Type 1 diabetic patients. This is a 10.2+/-2.0-year prospective study of 30 normotensive normoalbuminuric Type 1 diabetic patients. UAER (immunoturbidimetry), GFR ((51)Cr-EDTA single injection technique), GHb (ion exchange chromatography), and BP levels were measured at baseline and at 1.7+/-0.6-year intervals. The presence of ACE gene I/D and PC-1 gene K121Q polymorphisms was determined by polymerase chain reaction (PCR) and restriction enzyme techniques. Three patients developed diabetic nephropathy (DN), all carriers of allele D. The presence of allele D was the only predictor (R(2)=.15, F=4.92, P=.035) of the observed GFR decline (-0.29+/-0.34 ml/min/month, P<.05). UAER increased during the study (log UAER=0.0275+/-0.042 microg/min/month, P=.002) and was associated with baseline UAER levels only (R(2)=.17, F=5.72, P=.024). A significant increase (P<.05) in cases of hypertension and retinopathy were observed in ID/DD (n=19) and not in II patients (n=11). Patients with the KQ/QQ genotype (n=8) presented a significant increase (P=.045) in new cases of retinopathy. In conclusion, the presence of the ACE gene D allele in this sample of normoalbuminuric normotensive Type 1 diabetic patients was associated with a higher proportion of microvascular complications and hypertension.

Polymorphism in ecto-nucleotide pyrophosphatase/phosphodiesterase 1 gene (ENPP1/PC-1) and early development of advanced diabetic nephropathy in type 1 diabetes

A polymorphism in the ecto-nucleotide pyrophosphatase/phosphodiesterase 1 gene (ENPP1) (previously known as PC-1), resulting in an amino acid change from lysine to glutamine at codon 121 (K121Q), is associated with insulin resistance. A small follow-up study of patients with type 1 diabetes and proteinuria found that renal function declines more rapidly in carriers of the Q variant than in noncarriers. To examine this finding further, we conducted a large case-control study and a family-based study. Genomic DNA was obtained from 659 patients: 307 with normal urinary albumin excretion despite diabetes duration of >15 years (control subjects) and 352 with advanced diabetic nephropathy, of whom 200 had persistent proteinuria and 152 had end-stage renal disease (ESRD). Individuals were genotyped for Q and K variants using a previously described protocol. The frequency of Q variant carriers was 21.5% in control subjects, 31.5% in subjects with proteinuria, and 32.2% in subjects with ESRD (P = 0.012). In a stratified analysis according to duration of diabetes, the risk of early-onset ESRD for carriers of the Q variant was 2.3 times that for noncarriers (95% CI, 1.2-4.6). The Q variant was not associated with late-onset ESRD. Similar findings were obtained in a family-based study. We conclude that carriers of the Q variant of ENPP1 are at increased risk for developing ESRD early in the course of type 1 diabetes.