Role of GLUT1 gene in susceptibility to diabetic nephropathy in type 2 diabetes

BACKGROUND: The XbaI polymorphism in the glucose transporter GLUT1 gene has been implicated in the development of diabetic nephropathy in Chinese type 2 diabetes patients. METHODS: To examine whether the XbaI polymorphism is involved in the development of diabetic nephropathy in Caucasian type 2 diabetes patients, a large case control study was performed. The study group of 444 patients with type 2 diabetes consisted of three subgroups: 162 patients with normoalbuminuria (only patients with duration of type 2 diabetes of at least 10 years after diagnosis); 150 with microalbuminuria; and 132 subjects with persistent proteinuria or chronic renal failure (CRF). The polymerase chain reaction (PCR)-based genotyping of the XbaI polymorphism was performed in each subject. RESULTS: The genotype distribution in the subgroups showed an increased frequency of the (+/+) genotype in patients with microalbuminuria (41%; OR 1.40, 95% CI, 0.89 to 2.24) and proteinuria/CRF (47%; OR 1.82, 95% CI, 1.13 to 2.93, P = 0.013) when compared with normoalbuminuria (33%). No difference in the genotype distribution was observed between type 2 diabetes patients and healthy controls. CONCLUSIONS: The results of this study in Caucasian patients with type 2 diabetes indicate that the XbaI(-) allele in the GLUT1 gene protects against the development of diabetic nephropathy. Our results are in contrast to the case control study in Chinese patients with type 2 diabetes in which the presence of the XbaI(-) allele appeared to have a strong association with the development of diabetic nephropathy.     

Genetic susceptibility to type 2 diabetic nephropathy in human and animal models

SUMMARY:   Diabetic nephropathy is the most common cause of end-stage renal disease (ESRD) in Japan, Western Europe, and the United States. Mega studies such as Diabetes Control and Complication Trial (DCCT), Epidemiology of Diabetes Interventions and Complications (EDIC), and the United Kingdom Prospective Diabetes Study (UKPDS) clarified that poor glycemic and blood pressure control are undoubtedly involved in the development of nephropathy. However, these factors are not sufficient to predict which diabetic patients will develop renal disease, because not all patients with poor glycemic and blood pressure control develop renal disease. Since ethnic variations and familial clustering of diabetic nephropathy have been observed, genetic factors might contribute to susceptibility to this disease. Several methods such as (genome wide) association studies, sib-pair analysis, and quantitative trait loci (QTLs) analysis are available to examine polygenic diseases. However, no mutations that could explain the majority of nephropathy cases have been identified so far. The development of most diabetic nephropathy might be explained by the polygenic effect (i.e. many minor gene-gene interactions might be very important in the development of nephropathy). Identification of candidate genes of nephropathy enables targeting of therapy in patients at risk and development of novel therapeutic agents.     

Genetic susceptibility to nephropathy in Pima Indians with type 2 diabetes mellitus

Summary: In Pima Indians, the incidence of end-stage renal disease, nearly all of which is attributable to type 2 diabetes mellitus, is more than 20 times that in the general United States population. Studies in the Pimas indicate that factors other than diabetes per se enhance susceptibility to the development of diabetic nephropathy. Aggregation of renal disease in families, a relationship between parental blood pressure and diabetic nephropathy in the offspring, and an association between higher prediabetic blood pressure and the occurrence of renal disease after the onset of diabetes all point to individual differences in susceptibility. Although clustering of environmental exposures may be responsible for these findings, they may also represent genetic transmission of susceptibility to renal disease. Recently, linkage analyses were performed in 98 diabetic sib-pairs, both affected by diabetic nephropathy. Two adjacent markers on chromosome 7 met the criteria for suggestive linkage with two-point analysis. Positioned between these markers is the gene coding for aldose reductase. Polymorphisms of this locus are associated with diabetic microvascular complications in other populations. Linkage studies provide evidence that familial aggregation of diabetic renal disease reflects, in part, genetic transmission of susceptibility that appears to be independent of the transmission of diabetes.     

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.     

A quantitative trait locus influencing type 2 diabetes susceptibility maps to a region on 5q in an extended French family

Type 2 diabetes is a heterogeneous disorder of glucose metabolism characterized by insulin resistance, beta-cell dysfunction, and increased glucose production by the liver. Given the high degree of genetic heterogeneity, multiple genes with small to moderate effects may influence susceptibility to diabetes. To circumvent this limitation, we searched for quantitative trait loci (QTLs) that explain the variation in susceptibility of type 2 diabetes in a single extended family, as these individuals are likely to share polymorphisms. We collected genotypic and phenotypic data on 152 individuals ascertained through a multimedia campaign in France to find diabetes-prone families for genetic studies. The effects of genes and covariates (age and sex) on diabetes status were estimated using a threshold model and a maximum likelihood variance component approach. We obtained suggestive evidence of linkage (logarithm of odds [LOD] = 2.4) for diabetes status on chromosome 5q. Within the 1-LOD unit support interval, there are two strong candidates: PCSK1 and CAST. Furthermore, we have obtained a replication (LOD = 1.6) for a QTL for type 2 diabetes on chromosome 11 detected by Hanson and colleagues (1998).     

Oxidative stress markers in type 2 diabetes patients with diabetic nephropathy

Background

Epidemiological studies show that 5–40 % of type 2 diabetes (T2DM) patients have diabetic nephropathy, and oxidative stress is one of several underlying mechanisms. We investigated associations between oxidative stress markers and severity of diabetic nephropathy.

Methods

Fifty-nine T2DM patients from the endocrinology outpatient department were included, and their levels of oxidative stress markers were measured. Three groups were determined by their urine albumin-to-creatinine ratio (UACR): group A (UACR < 30 mg/g, n = 22); group B (30 ≤ UACR < 300 mg/g, n = 22); and group C (UACR ≥ 300 mg/g, n = 15).

Results

Vitamin C levels correlated negatively and moderately with serum creatinine (γ = ?0.459, p < 0.001), urine albumin (γ _s = ?0.458, p = 0.001) and UACR (γ _s = ?0.408, p = 0.001), but only weakly with hydroxy-2-deoxyguanosine (8-OHdG) and estimated glomerular filtration rate (eGFR). Vitamin C levels decreased as 8-OHdG, serum creatinine, albumin and UACR increased. T2DM patients with more severe diabetic nephropathy had lower vitamin C levels.

Conclusion

Our results identified several oxidative stress markers that may be clinically important in diabetic nephropathy. Studies with larger sample sizes should be undertaken to confirm these findings.

     

Higher urinary IgM excretion in type 2 diabetic nephropathy compared to type 1 diabetic nephropathy.

BACKGROUND: Proteinuria, due to impairment of the charge- and/or size selectivity of the glomerular capillary wall (GCW) is the earliest clinical evidence of diabetic nephropathy (DN). To study the pathophysiological differences between patients with DN in type 1 diabetes mellitus (type 1 DN) and type 2 diabetes mellitus (type 2 DN), we compared the patterns of urinary proteins of different size and charge in the two entities of diabetic kidney disease. METHODS: Urine concentrations of albumin, IgG2, IgG4 and IgM were assessed in 22 (15 males and 7 females) patients with type 1 DN, and in 20 (18 males and 2 females) patients with type 2 DN. Comparisons with one control group of 13 (12 males and one female) patients with nephrosclerosis due to systemic hypertension and a second control group of 16 (14 males and 2 females) healthy controls were made. RESULTS: The urine excretion of IgG2 and IgM and the ratio of IgG2 to IgG4 (IgG2/IgG4), were significantly higher in type 2 DN compared to type 1 DN (P < 0.01). Patients with type 2 DN and patients with nephrosclerosis had significantly higher urine excretion of IgG and IgM compared to the age-matched healthy subjects (P < 0.001). The IgG2/IgG4 ratio was higher in type 2 DN compared to nephrosclerosis and healthy controls (P < 0.01). CONCLUSION: The increased urine excretion of IgG and IgM that accompanies albuminuria in type 2 DN suggests that the dominant pathophysiological mechanism of proteinuria in type 2 DN might be an alteration of the size selective properties of the glomerular capillary wall, including the occurrence of non-discriminatory "shunt pathways." The charge selective properties of the glomerular capillary wall seem to be intact in type 2 DN, as indicated by the high IgG2/IgG4 ratio. The mechanisms of proteinuria in type 1 DN seem to be merely a consequence of an impaired charge selectivity of the glomerular capillary wall.     

Nephrinuria in diabetic nephropathy of type 1 diabetes

Diabetic nephropathy is the leading cause of end-stage renal disease. Because early diagnosis and treatment may prevent the complication, new tools for an early detection are needed. One of the key components of the glomerular filtration slit spanning between neighboring podocytes is nephrin. Its expression is altered in experimental models of diabetes and also in various human proteinuric diseases, including diabetes. We studied whether type 1 diabetic patients with or without nephropathy exhibit immunoreactive nephrin in the urine, reflecting early damage of the filtration barrier. Diabetic patients with normoalbuminuria (n = 40), with microalbuminuria (n = 41), and with macroalbuminuria (n = 39) and patients previously normoalbuminuric but now testing positive for microalbuminuria (newMicro, n = 39) were screened for nephrinuria with Western blotting using two affinity-purified anti-nephrin antibodies. Nondiabetic healthy subjects (n = 29) were also studied. Nephrinuria was present in 30% of normoalbuminuric, 17% of microalbuminuric, 28% of macroalbuminuric, and 28% of newMicro patients. Of female patients, 35% were nephrinuric compared with only 19% of male patients (P = 0.02). None of the control subjects was nephrinuric. In conclusion, glomerular filtration barrier may be affected in one-third of diabetic patients manifesting as early nephrinuria. Nephrinuria may have prognostic value and become a marker of susceptibility for kidney complications in diabetes.     

Pyridorin in type 2 diabetic nephropathy

Pyridoxamine dihydrochloride (Pyridorin, NephroGenex) inhibits formation of advanced glycation end products and scavenges reactive oxygen species and toxic carbonyls, but whether these actions translate into renoprotective effects is unknown. In this double-blind, randomized, placebo-controlled trial, we randomly assigned 317 patients with proteinuric type 2 diabetic nephropathy to twice-daily placebo; Pyridorin, 150 mg twice daily; or Pyridorin, 300 mg twice daily, for 52 weeks. At baseline, the mean age ± SD was 63.9±9.5 years, and the mean duration of diabetes was 17.6±8.5 years; the mean serum creatinine level was 2.2±0.6 mg/dl, and the mean protein-to-creatinine ratio was 2973±1932 mg/g. Regarding the primary end point, a statistically significant change in serum creatinine from baseline to 52 weeks was not evident in either Pyridorin group compared with placebo. However, analysis of covariance suggested that the magnitude of the treatment effect differed by baseline renal function. Among patients in the lowest tertile of baseline serum creatinine concentration, treatment with Pyridorin associated with a lower average change in serum creatinine concentration at 52 weeks (0.28, 0.07, and 0.14 mg/dl for placebo, Pyridorin 150 mg, and Pyridorin 300 mg, respectively; P=0.05 for either Pyridorin dose versus placebo); there was no evidence of a significant treatment effect in the middle or upper tertiles. In conclusion, this trial failed to detect an effect of Pyridorin on the progression of serum creatinine at 1 year, although it suggests that patients with less renal impairment might benefit.     

Assessing genetic susceptibility to diabetic nephropathy

SUMMARY:   Diabetic nephropathy is a serious complication of diabetes and the leading cause of end-stage renal disease. Studies indicate both environmental and genetic factors contribute to the development and progression of diabetic nephropathy. In particular, epidemiological evidence shows a familial clustering of nephropathy in siblings with diabetes, supporting an important role of genetic susceptibility in the pathogenesis of diabetic nephropathy.
A common approach in genetic research is assessment of candidate gene polymorphisms using case-control analysis; a number of studies have evaluated predictable candidate genes for diabetic nephropathy. In contrast, only a few studies have used a whole genome approach, such as scanning of micro-satellite markers, in the assessment of genetic susceptibility to diabetic nephropathy. A whole genome linkage analysis using families of Pima Indians showed susceptibility loci for diabetic nephropathy on chromosome 3, 7, and 20. Another linkage analysis using discordant sib-pairs of Caucasian families with type 1 diabetes identified a critical area on chromosome 3q. However, these results have been inconclusive and further investigation is required.
Recently, a genome-wide, case-control analysis identifying susceptibility genes for diabetic nephropathy was performed. As a result, a single nucleotide polymorphism in exon 23 of the solute carrier family 12 (sodium-chloride cotransporter) member 3 gene was found to be strongly associated with diabetic nephropathy. Although further assessment of this polymorphism is needed, this strategy offers great promise in the identification of genetic factors predisposing patients to diabetic nephropathy. Identification of genetic susceptibility markers may offer new hope in the diagnosis and treatment of diabetic nephropathy.     

Higher incidence of diabetic nephropathy in type 2 than in type 1 diabetes in early-onset diabetes in Japan

BACKGROUND: Whether the type of diabetes, race, and year and age of diagnosis affect the incidence of diabetic vascular complications is unknown. That both type 1 and type 2 diabetes occur in the young Japanese population prompted us to investigate whether the type of diabetes and the year of diagnosis are related to the incidence of nephropathy. METHODS: Of the 17,256 diabetic patients who visited the outpatient clinic at our diabetes center between 1965 and 1990, 1578 (9.1%) had early-onset diabetes (diagnosed before the age of 30); of these, 620 (39%) had type 1, and 958 (61%) had type 2 diabetes. The incidence of nephropathy was analyzed in the patients according to postpubertal duration and year of diagnosis. RESULTS: The cumulative incidence of nephropathy after 30 years of postpubertal diabetes was significantly higher (P < 0.0001) in type 2 diabetic patients (44.4%, 95% CI, 37.0 to 51.8%) than in type 1 diabetic patients (20.2%, 95% CI, 14.9 to 25.8%). The incidence of nephropathy among type 1 diabetic patients has declined during the past two decades, whereas it has not among type 2 diabetic patients. The rate ratio for type 2 diabetic patients diagnosed between 1980 and 1984 relative to type 1 diabetic patients diagnosed in the same period was 2.74 (95% CI, 1. 17 to 6.41). CONCLUSIONS: The incidence of nephropathy has declined in Japanese patients with type 1 but not in those with type 2 diabetes. In young Japanese patients, because of the higher incidence of nephropathy in type 2 diabetes and the higher prevalence of type 2 than type 1 diabetes, type 2 diabetes is likely the major cause of diabetic nephropathy.     

基质金属蛋白酶在糖尿病肾病作用中的研究

目的 探讨2型糖尿病及糖尿病肾病患者血清基质金属蛋白酶水平的变化及其相关影响因素.方法 选取2型糖尿病患者94例,其中2型糖尿病无蛋白尿组患者37例;微量蛋白尿组(尿白蛋白/肌酐为30 ～ 300 mg/g)27例;显著蛋白尿组患者(尿白蛋白/肌酐＞300mg/g)30例.健康体检者32名作为对照组.所有检测对象于清晨空腹抽肘静脉血,应用酶联免疫吸附法测定血清基质金属蛋白酶2及血浆纤溶酶原激活物抑制物1.结果 (1)微量蛋白尿组患者血清基质金属蛋白酶2水平为(4.3±4.1)μg/L,显著蛋白尿组患者为(4.6±4.1)μg/L,与正常对照组[2.8±0.4)μg/L]比较差异有统计学意义(P＜0.05);(2)微量蛋白尿组患者血浆纤溶酶原激活物抑制物1水平为(69±19)μg/L,显著蛋白尿组患者为(69±18)μg/L,与正常对照组[(52±30)μg/L]比较差异有统计学意义(P＜0.05);(3)相关分析结果表明,血清基质金属蛋白酶2与血浆纤溶酶原激活物抑制物1水平无相关(r =0.077,P=0.468);(4)在2型糖尿病患者中血清基质金属蛋白酶2水平与尿素氮、肌酐水平相关(r分别为0.370及0.468,P分别为0.00、0.000),血浆纤溶酶原激活物抑制物1水平与空腹血糖、甘油三酯、高密度脂蛋白、尿酸呈正相关(r分别为0.196、0.342、-0.167、0.203,P分别为0.004、0.000、0.016、0.003).结论 2型糖尿病合并蛋白尿患者血清基质金属蛋白酶2及血浆纤溶酶原激活物抑制物1水平升高,是2型糖尿病患者合并肾病的危险因素.     

Replication study for the association of 3 SNP loci identified in a genome-wide association study for diabetic nephropathy in European type 1 diabetes with diabetic nephropathy in Japanese patients with type 2 diabetes

Background

A recent genome-wide association study for diabetic nephropathy in European type 1 diabetes identified 3 candidate loci for diabetic nephropathy. In this study, we examined the association of the 3 single nucleotide polymorphism (SNP) loci with susceptibility to diabetic nephropathy in Japanese subjects with type 2 diabetes.

Methods

We genotyped 3 SNPs, rs7583877 in AFF3, rs12437854 in the RGMA-MCTP2 locus and rs7588550 in ERBB4, for 2,300 Japanese patients with type 2 diabetes [initial study, 1,055 nephropathy cases with overt proteinuria or with end-stage renal disease (ESRD) and 1,245 control patients with normoalbuminuria]. The association of these SNPs with diabetic nephropathy was examined by using a logistic regression analysis.

Results

We observed a significant association of rs7588550 in ERBB4 with diabetic nephropathy in the Japanese patients with type 2 diabetes, although the effect direction was not consistent with that in the European study [p = 0.0126, odds ratio (OR) = 0.79, 95 % confidence interval (CI): 0.65–0.95]. We further examined the association of rs7588550 with diabetic nephropathy in an independent Japanese cohort (596 nephropathy cases and 311 controls) and observed the same trend of the association with the initial study. We did not observe any association of the remaining 2 SNP loci with diabetic nephropathy in the present Japanese sample.

Conclusion

The association of SNP loci derived from GWAS in European type 1 diabetes with diabetic nephropathy was not replicated in the Japanese patients with type 2 diabetes, although the ERBB4 locus may have some effect also in Japanese type 2 diabetes.     

血管内皮生长因子基因多态性与糖尿病肾病的相关性研究

目的 探讨血管内皮生长因子(VEGF)-634G／C基因多态性与糖尿病肾病(DN)的关系。方法 运用PCR-限制性多态性片段长度(RFLP)技术检测98例健康对照者和216例2型糖尿病患者[其中DN患者104例，单纯2型糖尿病(DM)患者112例]的基因型，比较各组的基因型和等位基因频率。结果 (1)CC基因型者血清VEGFT水平高于CG及GG型者；(2)DN组CC基因型和C等位基因频率显著高于DM组和正常对照组；(3)与GG型和CG型组相比，CC型组DN的发生率明显上升；(4)Logistic回归分析显示VEGF、VEGF基因多态性、收缩压(SBP)、HbA1c、LDL-C、体重指数(BMI)是DN的危险因素。结论 VEGF-63gG／C多态性与2型DM伴发肾病的发生有关，C等位基因可能是DN的易感基因。     

Quantitative trait loci for fasting glucose in young Europeans replicate previous findings for type 2 diabetes in 2q23-24 and other locations

Long before reaching diagnostic cutoff levels for type 2 diabetes, fasting glucose can be a powerful risk marker for this disease. We conducted a genome-wide search for fasting glucose as a quantitative trait in 412 young European sib-pairs including obese children, with adjustment for sex, age, and BMI. We identified more quantitative trait loci specific to fasting glucose and more significant than would be found by simple chance estimated by permutation tests. The strongest linkage was on chromosome 2q (logarithm of odds [LOD] = 3.00) in a region previously linked to type 2 diabetes as a disease. We also found linkage signals of fasting glucose with 7q (LOD = 2.03), 8q (1.28), 17p (2.12), 17q (1.4), and 11p (1.33). These findings suggest that the quantitative genetics of fasting glucose could contribute to the search for type 2 diabetes genes.