Genetics of diabetes complications

Nanopore Sequencing of RAGE Gene Polymorphisms and Their Association with Type 2 Diabetes

The receptor for advanced glycation end products (RAGE) is a transmembrane protein that interacts with its ligands, advanced glycation end products (AGEs). AGEs are elevated in diabetes and diabetic complications, leading to increased oxidative stress and activation of pro-inflammatory pathways facilitated by AGE-RAGE signaling. Polymorphisms in the RAGE gene can potentially affect AGE-RAGE interaction and its downstream signaling, which plays a crucial role in the progression of diabetes and its complications. In this study, we used nanopore sequencing for genotyping of RAGE polymorphism and identified a maximum number of 33 polymorphisms, including two previously unreported novel mutations in a cohort of healthy, type 2 diabetics without nephropathy and type 2 diabetics with nephropathy in order to identify associations. Two novel RAGE polymorphisms in the intron 8 and 3'UTR region at genomic locations 32181834 and 32181132, respectively, were detected with a low frequency. For four previously reported polymorphisms, cross-validation by PCR-RFLP showed 99.75% concordance with nanopore sequencing. Analysis of genotype distribution and allele frequencies revealed that five single nucleotide polymorphisms, i.e., rs1800625, rs3131300, rs3134940, rs2070600, and rs9391855, were associated with an increased risk for type 2 diabetes.

Neuropathy in paediatric type 1 diabetes mellitus - clinical characterization and analysis of risk factors in the diabetes prospective follow-up registry DPV (Diabetes-Patienten-Verlaufsdokumentation)-registry

OBJECTIVES

Data on the prevalence, clinical features and risk factors associated with paediatric diabetic neuropathy (DN) are scarce.

METHODS

We retrospectively analysed data from the DPV registry, including patients under 20 years of age, treated for type 1 diabetes mellitus (T1D) between 2005 and 2021. Patients with non-diabetic neuropathy were excluded. Data came from centres in Austria, Germany, Luxembourg and Switzerland.

RESULTS

1,121 of the 84,390 patients included had been diagnosed with DN. Univariate analysis showed patients with DN to be older and predominantly female, with a longer duration of T1D, higher insulin dosages per kg and day, lower rates of insulin pump therapy, higher postprandial glucose-, higher HbA_1c-and higher cholesterol levels, and higher diastolic and systolic blood pressure values. There was also a larger proportion of smokers and higher prevalence of diabetic retinopathy. Median duration of diabetes at diagnosis of DN was 8.3 years. Multivariable analysis, adjusted for demographics revealed an increased risk for DN among female patients and those who were older, underweight (BMI-SDS), smoked cigarettes or had a longer duration of T1D or higher levels of HbA_1c and postprandial blood glucose. The presence of retinopathy and higher cholesterol levels were also linked to increased risk while not-using insulin pump therapy was not.

CONCLUSIONS

DN can develop after just a short duration of T1D. Prevention may be achieved by a lowering of HbA_1c-and postprandial glucose levels through improved glycaemic control. This warrants further investigation. The slight female predominance suggests further hormonal and genetic etiological factors.

Intraretinal Microvascular Abnormalities and Venous Beading Have Different Genetic Profiles in Caucasian Patients with Non-Proliferative Diabetic Retinopathy

Diabetic Retinopathy (DR) is a leading cause of preventable visual impairment in the working age population. Despite the increasing prevalence of DR, there remain gaps in our understanding of its pathophysiology. This is a prospective case-control study comparing the genetic profiles of patients with no DR vs. non-proliferative DR (NPDR) focusing on intraretinal microvascular abnormalities (IRMA) and venous beading (VB) in Caucasians. A total of 596 participants were recruited to the study; 199 with moderate/severe NPDR and 397 with diabetes for at least 5 years without DR. Sixty-four patients were excluded due to technical issues. In total, 532 were analysed; 181 and 351 were in the NPDR group and no DR group, respectively. Those with severe IRMA and VB had distinctly different genetic profiles from each other and from the no DR group, which further supports the theory that these two features of DR might have different etiologies. This also suggests that IRMA and VB are independent risk factors for the development of PDR and may have different pathophysiologies. If these findings are confirmed in larger studies, this could pave the way for personalised treatment options for those more at risk of developing different features of NPDR.

Adiponectin/AdiopR1 signaling prevents mitochondrial dysfunction and oxidative injury after traumatic brain injury in a SIRT3 dependent manner

Mitochondrial dysfunction and oxidative injury, which contribute to worsening of neurological deficits and poor clinical outcomes, are hallmarks of secondary brain injury after TBI. Adiponectin (APN), beyond its well-established regulatory effects on metabolism, is also essential for maintaining normal brain functions by binding APN receptors that are ubiquitously expressed in the brain. Currently, the significance of the APN/APN receptor (AdipoR) signaling pathway in secondary injury after TBI and the specific mechanisms have not been conclusively determined. In this study, we found that APN knockout aggravated brain functional deficits, increased brain edema and lesion volume, and exacerbated oxidative stress as well as apoptosis after TBI. These effects were significantly alleviated after APN receptor agonist (AdipoRon) treatment. Moreover, we found that AdipoR1, rather than AdipoR2, mediated the protective effects of APN/AdipoR signaling against oxidative stress and brain injury after TBI. In neuron-specific AdipoR1 knockout mice, mitochondrial damage was more severe after TBI, indicating a potential association between APN/AdipoR1 signaling inactivation and mitochondrial damage. Mechanistically, neuron-specific knockout of SIRT3, the most important deacetylase in the mitochondria, reversed the neuroprotective effects of AdipoRon after TBI. Then, PRDX3, a critical antioxidant enzyme in the mitochondria, was identified as a vital downstream target of the APN/SIRT3 axis to alleviate oxidative injury after TBI. Finally, we revealed that APN/AdipoR1 signaling promotes SIRT3 transcription by activating the AMPK-PGC pathway. In conclusion, APN/AdipoR1 signaling plays a protective role in post-TBI oxidative damage by restoring the SIRT3-mediated mitochondrial homeostasis and antioxidant system.

Matrix Metalloproteinase-2 (MMP-2) and-9 (MMP-9) Gene Variants and Microvascular Complications in Type 2 Diabetes Patients

Vascular complications are the leading cause of increased morbidity and mortality of diabetic patients. It has been postulated that matrix metalloproteinases MMP-2 and MMP-9, zinc-dependent endopeptidases through remodeling of the extracellular matrix, can contribute to the onset and progression of diabetic vascular complications. The aim of our study was to assess whether there is a major difference in single nucleotide polymorphisms in the MMP-2 (at position -1306C˃T) and MMP-9 (at position -1562C˃T) gene in type 2 diabetic patients and healthy controls and to determine whether there is an association of these gene variants with the presence of microvascular complications in diabetic patients. Our study included 102 type 2 diabetes patients and a control group which was comprised of 56 healthy controls. All diabetic patients were screened for microvascular diabetes complications. Genotypes were detected by polymerase chain reactions followed by restriction analyses with specific endonucleases and their frequencies were determined. The MMP-2 variant -1306C>T showed a negative correlation with type 2 diabetes (p=0.028). It was also shown that the presence of the -1306C allele increases the probability of developing type 2 diabetes. This was a 2.2 fold increase and that the -1306 T allele has a protective role in regards to type 2 diabetes. The MMP-2 variant -1306T showed a negative correlation with diabetic polyneuropathy (p=0.017), meaning that allele-1306T has a protective role in regards to diabetic polyneuropathy while the presence of allele -1306C increases the probability of developing diabetic polyneuropathy by 3.4 fold. Our study showed that the MMP-2 gene variant (-1306C) doubles the risk of developing type 2 diabetes, and for the first time an association of this gene variant and the presence of diabetic polyneuropathy was shown.

The roles of long non-coding RNAs in ocular diseases

In recent years, lncRNAs have been shown to regulate gene expression at the epigenetic, transcriptional and translational level, thus exerting various functions in biological and pathological processes involving cell proliferation, apoptosis, cell cycle and immune response. An increasing number of researches have unveiled that lncRNAs are dysregulated in pathogenesis and the development of different ocular diseases, such as glaucoma, cataract, retinal disease and ocular tumors. Also, it has been reported that lncRNAs may exert significant roles in various ocular diseases. Here, we summarized the functions of lncRNAs on relevant ocular diseases and further clarified their mechanisms. Here, several previous studies with detailed information of lncRNAs which have been proved to be the diagnostic or prognostic biomarkers and potential therapeutic targets were included. Also, it is our hope to provide a thorough knowledge of the functions of lncRNAs in eye diseases and the methods by which lncRNAs can influence ocular diseases.

Peripheral and Autonomic Neuropathy Status of Young Patients With Type 1 Diabetes Mellitus at the Time of Transition From Pediatric Care to Adult-Oriented Diabetes Care

INTRODUCTION

The prevalence of neuropathic lesions in young patients with type 1 diabetes mellitus (T1DM) at the time of transition from pediatric care to adult-oriented diabetes care is poorly studied. A comparative study with healthy volunteers to assess the possible neuropathic condition of this special population and to identify the potential early screening needs has not been performed yet. The results may provide important feedback to pediatric diabetes care and a remarkable baseline reference point for further follow up in adult diabetes care.

PATIENTS AND METHODS

Twenty-nine young patients with T1DM [age: 22.4 ± 2.9 years; HbA1c: 8.5 ± 2.1%, diabetes duration: 12.2 ± 5.8 years; (mean ± SD)] and 30 healthy volunteers (age: 21.5 ± 1.6 years; HbA1c: 5.3 ± 0.3%) were involved in the study. Autonomic function was assessed by standard cardiovascular reflex tests. Complex peripheral neuropathic testing was performed by Neurometer^®, Neuropad^®-test, Tiptherm^®, Monofilament^®, and Rydel-Seiffer tuning fork tests.

RESULTS

T1DM patients had significantly higher diastolic blood pressure than controls (80 ± 9 vs. 74 ± 8 mmHg, p < 0.01), but there was no significant difference in systolic blood pressure (127 ± 26 vs. 121 ± 13 mmHg). Cardiovascular reflex tests had not revealed any significant differences between the T1DM patients and controls. No significant differences with Neurometer^®, Neuropad^®-test, and Monofilament^® were detected between the two groups. The vibrational sensing on the radius on both sides was significantly impaired in the T1DM group compared to the controls with Rydel-Seiffer tuning fork test (right: 7.5 ± 1.0 vs. 7.9 ± 0.3; left: 7.5 ± 0.9 vs. 7.9 ± 0.3, p < 0.05). The Tiptherm^®-test also identified a significant impairment in T1DM patients (11 sensing failures vs. 1, p < 0.001). In addition, the neuropathic complaints were significantly more frequently present in the T1DM patient group than in the controls (9 vs. 0, p < 0.01).

CONCLUSION

In this young T1DM population, cardiovascular autonomic neuropathy and cardiac morphological alterations could not be found. However, Rydel-Seiffer tuning fork and Tiptherm^®-tests revealed peripheral sensory neurological impairments in young T1DM patients at the time of their transition to adult diabetes care.

Incidence and risk factors of vascular complications in people with impaired fasting glucose: a national cohort study in Korea

This study aimed to evaluate the risk of vascular complications of impaired fasting glucose (IFG). This population-based study included 425,608 participants from the National Health Screening Cohort in Korea in 2003 and 2004 who were followed-up until 2015. The participants were classified into normal, IFG, and diabetes groups based on fasting plasma glucose levels. Incidence rate (per 1000 person-year) was evaluated for the following vascular complications: cardiovascular (ischemic heart disease, cerebrovascular disease, arterial and capillary disease), renal, and retinal diseases. Hazard ratios (HR) of IFG for diabetes were estimated after adjusting for patient characteristics. Among the 88,330 IFG participants, the incidence of cardiovascular, chronic renal and retinal diseases were 11.52, 0.47, and 1.08 per 1000 person-years, respectively. Furthermore, IFG patients with a family history of diabetes, past history of hypertension, and high body mass index had significantly increased risk of vascular complications [adjusted HR, cardiovascular: 1.39 (95% CI 1.33–1.46); renal: 2.17 (95% CI 1.66–2.83); and retinal: 1.14 (95% CI 0.98–1.32)]. IFG patients have a substantial risk of cardiovascular, chronic renal and retinal diseases. Therefore, early preventative interventions are beneficial, especially for those with high-risk factors, in whom should emphasize on maintaining a healthy lifestyle, early screening and continuous follow-up.

Diabetic neuropathy in children and adolescents with type 1 diabetes mellitus: Diagnosis, pathogenesis, and associated genetic markers

Diabetic neuropathy (DN) is a common long-term complication of type 1 (T1D) and type 2 (T2D) diabetes mellitus, with significant morbidity and mortality. DN is defined as impaired function of the autonomic and/or peripheral nervous system, often subclinical, particularly in children and adolescents with T1D. Nerve conduction studies (NCS) and skin biopsies are considered gold-standard methods in the assessment of DN. Multiple environmental and genetic factors are involved in the pathogenesis of DN. Specifically, the role of metabolic control and glycemic variability is of paramount importance. A number of recently identified genes, including the AKR1B1, VEGF, MTHFR, APOE, and ACE genes, contribute significantly in the pathogenesis of DN. These genes may serve as biomarkers to predict future DN development or treatment response. In addition, they may serve as the basis for the development of new medications or gene therapy. In this review, the diagnostic evaluation, pathogenesis, and associated genetic markers of DN in children and adolescents with T1D are presented and discussed.

MALAT1 as a Diagnostic and Therapeutic Target in Diabetes-Related Complications: A Promising Long-Noncoding RNA

Diabetes mellitus is a global issue with increasing incidence rate worldwide. In an uncontrolled case, it can advance to various organ-related complications leading to an increase in morbidity and mortality. Long non-coding RNA (lncRNA) Metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) appears to be a fairly novel lncRNA that is relevant to diabetes and its role in diabetic-related diseases initiation and progression have long been a subject of attention to many scholars. The expression of MALAT1 is elevated in different diabetic-related diseases. In this review, we demonstrate the various functions of MALAT1 in the different diabetes-related complications including ischemic reperfusion injury, retinopathy, cataract, atherosclerosis, cardiomyopathy, non-alcoholic steatohepatitis, gastroparesis, kidney disease, and gestational diabetes. The emerging evidence showed that the role of MALAT1 in diabetic-related complications is both pro-inflammatory and apoptosis in different cell types. These results concluded that MALAT1 is a potential diagnostic and future targeted therapy for diabetes-associated complications.

ANRIL regulates production of extracellular matrix proteins and vasoactive factors in diabetic complications

noncoding RNAs (lncRNAs) have gained widespread interest due to their prevailing presence in various diseases. lncRNA ANRIL (a. k. a. CDKN2B-AS1) is located on human chromosome 9 (p21.3) and transcribed in opposite direction to the INK4b-ARF-INK4a gene cluster. It has been identified as a highly susceptible region for diseases such as coronary artery diseases and type 2 diabetes. Here, we explored its regulatory role in diabetic nephropathy (DN) and diabetic cardiomyopathy (DCM) in association with epigenetic modifiers p300 and polycomb repressive complex 2 (PRC2) complex. We used an ANRIL-knockout (ANRILKO) mouse model for this study. The wild-type and ANRILKO animals with or without streptozotocin-induced diabetes were monitored for 2 min. At the end of the time point, urine and tissues were collected. The tissues were measured for fibronectin (FN), type IV collagen (Col1α4), and VEGF mRNA and protein expressions. Renal function was determined by the measurement of 24-h urine volume and albumin/creatinine ratio at euthanasia. Renal and cardiac structures were investigated using periodic acid-Schiff stain and/or immunohistochemical analysis. Elevated expressions of extracellular matrix (ECM) proteins were prevented in ANRILKO diabetic animals. Furthermore, ANRILKO had a protective effect on diabetic mouse kidneys, as evidenced by lowering of urine volume and urine albumin levels in comparison with the wild-type diabetic animals. These alterations regulated by ANRIL may be mediated by p300 and enhancer of zeste 2 (EZH2) of the PRC2 complex. Our study concludes that ANRIL regulates functional and structural alterations in the kidneys and hearts in diabetes through controlling the expressions of ECM proteins and VEGF.

Microalbuminuria as a simple predictor of incident diabetes over 8 years in the Korean Genome and Epidemiology Study (KoGES)

Microalbuminuria (MAU) is a common subclinical disease and related with cardiovascular outcome both in diabetic and non-diabetic patients. However, there is rare data about the effect of MAU on the development of diabetes. Thus, we aimed to investigate whether MAU is associated with the development of incident diabetes. A total of 3385 subjects without diabetes (1503 men and 1882 women; mean age, 53 years) who participated in the Ansung–Ansan cohort study from 2001–2002 (baseline) to 2011–2012 (fifth follow-up visit) were followed for a mean of 8 years. The prevalence of MAU at baseline was 10.8% (365 patients), and the incidence of newly developed diabetes during the follow-up period was 15.3% (56 patients) in subjects with MAU. The hazard ratio (HR) for development of diabetes was 1.43 (95% confidence interval (CI) 1.07–1.91, p-value 0.016), independent of traditional risk factors for diabetes including pre-diabetes, age, obesity, and family history. The impact of MAU on diabetes was also significant in the non-pre-diabetic population (HR 2.08, 95% CI 1.07–4.03, p-value 0.031). In conclusion, our results show that incident MAU is associated with future development of diabetes and could be an early marker for diabetes, even in the non-prediabetic population.

Neurodegeneration and Neuroinflammation in Diabetic Retinopathy: Potential Approaches to Delay Neuronal Loss

In spite of the extensive research the complex pathogenesis of diabetic retinopathy (DR) has not been fully elucidated. For many years it has been thought that diabetic retinopathy manifests only with microangiopathic lesions, which are totally responsible for the loss of vision in diabetic patients. In view of the current knowledge on the microangiopathic changes in the fundus of the eye, diabetic retinopathy is perceived as a neurodegenerative disease. Several clinical tools are available to detect neuronal dysfunction at early stages of diabetes. Many functional changes in the retina can be identified before vascular pathology develops, suggesting that they result from a direct effect of diabetes on the neural retina. In the course of diabetes there is a chronic loss of retinal neurons due to increased frequency of apoptosis. The neuronal apoptosis begins very early in the course of diabetes. This observation has led to suggestions that precautions against DR should be implemented immediately after diabetes is diagnosed. Neurodegeneration cannot be reversed; therefore treatments preventing neuronal cell loss in the retina need to be developed to protect diabetic patients. This review is an attempt to summarize what is currently known about the mechanisms of neuronal apoptosis in the context of diabetic retinopathy and vascular degeneration as well as about potential treatments of DR

Genetic components in diabetic retinopathy

Diabetic retinopathy (DR) is a serious complication of diabetes, which is fast reaching epidemic proportions worldwide. While tight glycemic control remains the standard of care for preventing the progression of DR, better insights into DR etiology require understanding its genetic basis, which in turn may assist in the design of novel treatments. During the last decade, genomic medicine is increasingly being applied to common multifactorial diseases such as diabetes and age-related macular degeneration. The contribution of genetics to the initiation and progression of DR has been recognized for some time, but the involvement of specific genes and genetic variants remains elusive. Several investigations are currently underway for identifying DR susceptibility loci through linkage studies, candidate gene approaches, and genome-wide association studies. Advent of next generation sequencing and high throughput genomic technologies, development of novel bioinformatics tools and collaborations among research teams should facilitate such investigations. Here, we review the current state of genetic studies in DR and discuss reported findings in the context of biochemical, cell biological and therapeutic advances. We propose the development of a consortium in India for genetic studies with large cohorts of patients and controls from limited geographical areas to stratify the impact of the environment. Uniform guidelines should be established for clinical phenotyping and data collection. These studies would permit identification of genetic loci for DR susceptibility in the Indian population and should be valuable for better diagnosis and prognosis, and for clinical management of this blinding disease.

ELMO1 protects renal structure and ultrafiltration in kidney development and under diabetic conditions

Engulfment and cell motility 1 (ELMO1) functions as a guanine exchange factor for Rac1 and was recently found to protect endothelial cells from apoptosis. Genome wide association studies suggest that polymorphisms within human elmo1 act as a potential contributing factor for the development of diabetic nephropathy. Yet, the function of ELMO1 with respect to the glomerulus and how this protein contributes to renal pathology was unknown. Thus, this study aimed to identify the role played by ELMO1 in renal development in zebrafish, under hyperglycaemic conditions, and in diabetic nephropathy patients. In zebrafish, hyperglycaemia did not alter renal ELMO1 expression. However, hyperglycaemia leads to pathophysiological and functional alterations within the pronephros, which could be rescued via ELMO1 overexpression. Zebrafish ELMO1 crispants exhibited a renal pathophysiology due to increased apoptosis which could be rescued by the inhibition of apoptosis. In human samples, immunohistochemical staining of ELMO1 in nondiabetic, diabetic and polycystic kidneys localized ELMO1 in glomerular podocytes and in the tubules. However, ELMO1 was not specifically or distinctly regulated under either one of the disease conditions. Collectively, these results highlight ELMO1 as an important factor for glomerular protection and renal cell survival via decreasing apoptosis, especially under diabetic conditions.

Glutathione peroxidase-1 gene (GPX1) variants, oxidative stress and risk of kidney complications in people with type 1 diabetes

BACKGROUND AND AIM

Glutathione peroxidase (GPX) is a class of antioxidant enzymes that catalyze the reduction of hydrogen peroxide to water. GPX1 is the most abundant isoform and is expressed in all kidney cells. Isoprostane and advanced oxidation protein products (AOPP) were identified as markers of oxidative stress in patients with kidney disease. We investigated associations of GPX1 genotypes with kidney complications, and with plasma concentrations of isoprostane and AOPP in type 1 diabetic patients.

METHODS

Four SNPs in the GPX1 gene region were genotyped in SURGENE (n=340; 10-year follow-up); GENEDIAB (n=461) and GENESIS (n=584) cohorts of type 1 diabetic patients. Subsets of GENEDIAB (n=237) and GENESIS (n=466) participants were followed up for 9 and 5years, respectively. Plasma concentrations of isoprostane and AOPP were measured at baseline in GENEDIAB. Hazard ratios (HR) were estimated for incidence of kidney complications.

RESULTS

In SURGENE, 98 renal events (new cases of microalbuminuria or progression to more severe stage of diabetic nephropathy) occurred during follow-up. The minor T-allele of rs3448 was associated with the incidence of renal events (HR 1.81, 95% CI 1.16-2.84, p=0.008). In GENESIS/GENEDIAB pooled study, end stage renal disease (ESRD) occurred during follow-up in 52 individuals. The same variant was associated with the incidence of ESRD (HR 3.34, 95% CI, 1.69-6.98, p=0.0004). The variant was also associated with higher plasma isoprostane concentration in GENEDIAB cohort: 2.02±0.12 (TT+CT) vs 1.75±0.13 (CC) ng/mL (p=0.009), and with higher plasma AOPP in the subset of participants with the baseline history of ESRD (TT+CT 67±6 vs CC 48±6μmol/L, p=0.006).

CONCLUSIONS

The minor T-allele of rs3448 was associated with kidney complications (incidences of microalbuminuria, renal events and ESRD) in patients with type 1 diabetes. The risk allele was associated with higher plasma concentrations of isoprostane and AOPP. Our results are consistent with the implication of GPX1 in the mechanism of renal protection against oxidative stress in type 1 diabetic patients.

Analysis of the Relationship Between ADIPOR1 Variants and the Susceptibility of Chronic Metabolic Diseases in a Northeast Han Chinese Population

Objective: Shared genetic variants in ADIPOR1 have been identified as closely related to coronary artery disease (CAD), type 2 diabetes (T2D), and T2D with CAD susceptibility, suggesting that these variants are strong candidates for the common soil hypothesis. Therefore, it is essential to analyze the relationship between ADIPOR1 variants and the susceptibility to CAD, T2D, and T2D with CAD in other populations.

Materials and Methods: A case–control study was conducted which included three case cohorts [CAD (n = 316), T2D (n = 295), T2D with CAD (n = 302)], and a control cohort (n = 268) from a population in northeast China. Six ADIPOR1 single-nucleotide polymorphisms were genotyped by high-resolution melting and polymerase chain reaction–restriction fragment length polymorphism.

Results: We confirmed that the shared variant, rs3737884*G, in ADIPOR1 is associated with CAD, T2D, and T2D with CAD (p-value range: 6.54E-6–1.82E-5, odds ratio [OR] range: 1.770–1.844) and that rs16850797*C is associated with T2D and T2D with CAD (p-value range: 0.001–0.001, OR range: 1.529–1.571). We also found that a novel shared variant, rs7514221*C, is associated with an increased susceptibility to CAD, T2D, and T2D with CAD (p-value range: 0.002–0.004, OR range: 1.194–2.382) in this population.

Conclusions:ADPOR1 variants, rs3737884*G and rs7514221*C, may be shared risk factors associated with CAD, T2D, and T2D with CAD in a population of northeast China.

Distal Sensorimotor Neuropathy: Improvements in Diagnosis

Neurological complications of diabetes are common, affecting up to 50% of people with diabetes. In these patients, diabetic sensorimotor neuropathy (DSPN) is by far the most frequent complication. Detecting DSPN has traditionally been a clinical exercise that is based on signs and symptoms. However, the appearance of morphometric and neurophysiological techniques along with composite scoring systems and new screening tools has induced a paradigm change in the detection and stratification of DSPN and our understanding of its natural history and etiopathogenesis. These newer techniques have provided further evidence that changes in small nerve fiber structure and function precede large fiber changes in diabetes. Although useful, the challenge for the use of these new techniques will be their sensitivity and specificity when widely adopted and ultimately, their ability to demonstrate improvement when pathogenic mechanisms are corrected. Concurrently, we have also witnessed an emergence of simpler screening tools or methods that are mainly aimed at quicker detection of large fiber neuropathy in the outpatient setting. In this review, we have focused on techniques and tools that receive particular attention in the current literature, their use in research and potential use in the clinical environment.

Polymorphisms of the UCP2 Gene Are Associated with Glomerular Filtration Rate in Type 2 Diabetic Patients and with Decreased UCP2 Gene Expression in Human Kidney

INTRODUCTION

Uncoupling protein 2 (UCP2) reduces production of reactive oxygen species (ROS) by mitochondria. ROS overproduction is one of the major contributors to the pathogenesis of chronic diabetic complications, such as diabetic kidney disease (DKD). Thus, deleterious polymorphisms in the UCP2 gene are candidate risk factors for DKD. In this study, we investigated whether UCP2 -866G/A, Ala55Val and Ins/Del polymorphisms were associated with DKD in patients with type 2 diabetes mellitus (T2DM), and whether they had an effect on UCP2 gene expression in human kidney tissue biopsies.

MATERIALS AND METHODS

In a case-control study, frequencies of the UCP2 -866G/A, Ala55Val and Ins/Del polymorphisms as well as frequencies of the haplotypes constituted by them were analyzed in 287 T2DM patients with DKD and 281 T2DM patients without this complication. In a cross-sectional study, UCP2 gene expression was evaluated in 42 kidney biopsy samples stratified according to the presence of the UCP2 mutated -866A/55Val/Ins haplotype.

RESULTS

In the T2DM group, multivariate logistic regression analysis showed that the -866A/55Val/Ins haplotype was an independent risk factor for DKD (OR = 2.136, 95% CI 1.036-4.404), although neither genotype nor allele frequencies of the individual polymorphisms differed between case and control groups. Interestingly, T2DM patients carrying the mutated haplotype showed decreased estimated glomerular filtration rate (eGFR) when compared to subjects with the reference haplotype (adjusted P= 0.035). In kidney biopsy samples, UCP2 expression was significantly decreased in UCP2 mutated haplotype carriers when compared to kidneys from patients with the reference haplotype (0.32 ± 1.20 vs. 1.85 ± 1.16 n fold change; adjusted P< 0.000001).

DISCUSSION

Data reported here suggest that the UCP2 -866A/55Val/Ins haplotype is associated with an increased risk for DKD and with a lower eGFR in T2DM patients. Furthermore, this mutated haplotype was associated with decreased UCP2 gene expression in human kidneys.

Meta-analysis of association between K469E polymorphism of the ICAM-1 gene and retinopathy in type 2 diabetes

AIM

To collectively evaluate the association of intercellular adhesion molecule-1 (ICAM-1) gene K469E polymorphism (rs5498) with diabetic retinopathy (DR) in patients with type 2 diabetic mellitus (T2DM).

METHODS

Overall review of available literatures relating K469E polymorphism to the risk of DR was conducted on 4 electronic databases. Meta-analysis was performed by Stata 12.0 to calculate pooled odds ratios (ORs). Potential sources of heterogeneity and bias were explored.

RESULTS

Seven studies with genotype frequency data including 1120 cases with DR and 956 diabetic controls free of DR were included. Meta-analysis did not show significant association of K469E polymorphism with DR (P>0.05). A statistically significant association was detected between the K469E polymorphism and proliferative diabetic retinopathy (PDR) in Asians only in dominant model (GG+AG vs AA) with pooled OR of 0.729 (95%CI: 0.564-0.942, P=0.016, P heterogeneity=0.143), however, this association was not detected in recessive model (GA+AA vs GG; OR=1.178, 95%CI: 0.898-1.545, P=0.236, P heterogeneity=0.248) or allelic model (G vs A; OR=0.769, 95% CI: 0.576-1.026, P=0.074, P heterogeneity=0.094). No publication bias was found by Funnel plot, Begg's and Egger's test.

CONCLUSION

This research found no statistically significant association between ICAM-1 gene K469E polymorphism and DR in patients with T2DM, but showed significant association of the K469E polymorphism with PDR in Asian diabetic patients only in dominant model. Further investigation would be required to consolidate the conclusion.

Identifying Common Genetic Risk Factors of Diabetic Neuropathies

Type 2 diabetes mellitus (T2DM) is a global public health problem of epidemic proportions, with 60-70% of affected individuals suffering from associated neurovascular complications that act on multiple organ systems. The most common and clinically significant neuropathies of T2DM include uremic neuropathy, peripheral neuropathy, and cardiac autonomic neuropathy. These conditions seriously impact an individual's quality of life and significantly increase the risk of morbidity and mortality. Although advances in gene sequencing technologies have identified several genetic variants that may regulate the development and progression of T2DM, little is known about whether or not the variants are involved in disease progression and how these genetic variants are associated with diabetic neuropathy specifically. Significant missing heritability data and complex disease etiologies remain to be explained. This article is the first to provide a review of the genetic risk variants implicated in the diabetic neuropathies and to highlight potential commonalities. We thereby aim to contribute to the creation of a genetic-metabolic model that will help to elucidate the cause of diabetic neuropathies, evaluate a patient's risk profile, and ultimately facilitate preventative and targeted treatment for the individual.

Genetics of diabetes complications

Chronic hyperglycemia and duration of diabetes are the major risk factors associated with development of micro- and macrovascular complications of diabetes. Although it is believed that hyperglycemia induces damage to the particular cell subtypes, e.g., mesangial cells in the renal glomerulus, capillary endothelial cells in the retina, and neurons and Schwann cells in peripheral nerves, the exact mechanisms underlying these damaging defects are not yet well understood. Clustering of micro- and macrovascular complications in families of patients with diabetes suggests a strong genetic susceptibility. However, until now only a handful number of genetic variants were reported to be associated with either nephropathy (ACE, ELMO1, FRMD3, and AKR1B1) or retinopathy (VEGF, AKR1B1, and EPO), and only a few studies were carried out for genetic susceptibility to cardiovascular diseases (ADIPOQ, GLUL) in patients with diabetes. It is, therefore, obvious that the accumulation of more data from larger studies and better phenotypically characterized cohorts is needed to facilitate genetic discoveries and unravel novel insights into the pathogenesis of diabetic complications.

Novel insights into metabolic sequelae of obstructive sleep apnoea: a link between hypoxic stress and chronic diabetes complications

An increasing body of evidence suggests that obstructive sleep apnoea (OSA) is independently associated with an increased risk of cardiovascular disease, glucose intolerance, and deteriorations in glycaemic control. Despite the knowledge of a multifactorial pathogenesis of long-term diabetes complications, there is a paucity of information on impact of comorbidities associated with chronic intermittent hypoxemia on development and progression of chronic diabetes complications. This review explores the clinical and scientific overlap of OSA and type 2 diabetes mellitus (T2DM) and its possible impact on the development and progression of diabetes macrovascular and microvascular complications. Multiple prospective observational cohort studies have demonstrated that OSA significantly increases the risk of cardiovascular disease independent of potential confounding risk factors. The current evidence further suggests that OSA with concurrent T2DM is associated with an increased risk of oxidative stress-induced damage of vulnerable endothelial and mesangial cells and peripheral nerves. Further studies are needed to validate the impact of OSA treatment on diabetes micro- and macrovascular complications. Since it is presently still unknown whether OSA treatment may provide a diabetes-modifying intervention that could delay or halt the progression of chronic diabetes complications, the emphasis is on early diagnosis and satisfactory treatment of both OSA and T2DM.

Genetics in diabetic retinopathy: current concepts and new insights

There is emerging evidence which indicates the essential role of genetic factors in the development of diabetic retinopathy (DR). In this regard it should be highlighted that genetic factors account for 25-50% of the risk of developing DR. Therefore, the use of genetic analysis to identify those diabetic patients most prone to developing DR might be useful in designing a more individualized treatment. In this regard, there are three main research strategies: candidate gene studies, linkage studies and Genome-Wide Association Studies (GWAS). In the candidate gene approach, several genes encoding proteins closely related to DR development have been analyzed. The linkage studies analyze shared alleles among family members with DR under the assumption that these predispose to a more aggressive development of DR. Finally, Genome-Wide Association Studies (GWAS) are a new tool involving a massive evaluation of single nucleotide polymorphisms (SNP) in large samples. In this review the available information using these three methodologies is critically analyzed. A genetic approach in order to identify new candidates in the pathogenesis of DR would permit us to design more targeted therapeutic strategies in order to decrease this devastating complication of diabetes. Basic researchers, ophthalmologists, diabetologists and geneticists should work together in order to gain new insights into this issue.

Sex-specific associations of variants in regulatory regions of NADPH oxidase-2 (CYBB) and glutathione peroxidase 4 (GPX4) genes with kidney disease in type 1 diabetes

Oxidative stress is involved in the pathophysiology of diabetic nephropathy. The superoxide-generating nicotinamide adenine dinucleotide phosphate-oxidase 2 (NOX2, encoded by the CYBB gene) and the antioxidant enzyme glutathione peroxidase 4 (GPX4) play opposing roles in the balance of cellular redox status. In the present study, we investigated associations of single nucleotide polymorphisms (SNPs) in the regulatory regions of CYBB and GPX4 with kidney disease in patients with type 1 diabetes. Two functional SNPs, rs6610650 (CYBB promoter region, chromosome X) and rs713041 (GPX4 3'untranslated region, chromosome 19), were genotyped in 451 patients with type 1 diabetes from a Brazilian cohort (diabetic nephropathy: 44.6%) and in 945 French/Belgian patients with type 1 diabetes from Genesis and GENEDIAB cohorts (diabetic nephropathy: 62.3%). The minor A-allele of CYBB rs6610650 was associated with lower estimated glomerular filtration rate (eGFR) in Brazilian women, and with the prevalence of established/advanced nephropathy in French/Belgian women (odds ratio 1.75, 95% CI 1.11-2.78, p = 0.016). The minor T-allele of GPX4 rs713041 was inversely associated with the prevalence of established/advanced nephropathy in Brazilian men (odds ratio 0.30, 95% CI 0.13-0.68, p = 0.004), and associated with higher eGFR in French/Belgian men. In conclusion, these heterogeneous results suggest that neither CYBB nor GPX4 are major genetic determinants of diabetic nephropathy, but nevertheless, they could modulate in a gender-specific manner the risk for renal disease in patients with type 1 diabetes.

Advances in our understanding of diabetic retinopathy

Diabetic retinopathy remains the most common complication of diabetes mellitus and is a leading cause of visual loss in industrialized nations. The clinicopathology of the diabetic retina has been extensively studied, although the precise pathogenesis and cellular and molecular defects that lead to retinal vascular, neural and glial cell dysfunction remain somewhat elusive. This lack of understanding has seriously limited the therapeutic options available for the ophthalmologist and there is a need to identify the definitive pathways that initiate retinal cell damage and drive progression to overt retinopathy. The present review begins by outlining the natural history of diabetic retinopathy, the clinical features and risk factors. Reviewing the histopathological data from clinical specimens and animal models, the recent paradigm that neuroretinal dysfunction may play an important role in the early development of the disease is discussed. The review then focuses on the molecular pathogenesis of diabetic retinopathy with perspective provided on new advances that have furthered our understanding of the key mechanisms underlying early changes in the diabetic retina. Studies have also emerged in the past year suggesting that defective repair of injured retinal vessels by endothelial progenitor cells may contribute to the pathogenesis of diabetic retinopathy. We assess these findings and discuss how they could eventually lead to new therapeutic options for diabetic retinopathy.

Association between PCSK9 and LDLR gene polymorphisms with coronary heart disease: case-control study and meta-analysis

OBJECTIVE

To explore the association of rs11206510 (PCSK9 gene) and rs1122608 (LDLR gene) polymorphisms with coronary heart disease (CHD) in Han Chinese.

METHODS

A total of 813 participants (290 CHD cases, 193 non-CHD controls and 330 healthy controls) were recruited in the case-control study. DNA genotyping was performed on the SEQUENOM® Mass-ARRAY iPLEX® platform. χ(2)-test was used to compare the genotype distribution and allele frequencies. Two meta-analyses were performed to establish the association between the two polymorphisms with CHD.

RESULTS

No significant associations between the two SNPs and the risk of CHD were observed in the present study. The meta-analysis of rs11206510 of PCSK9 gene comprises 11 case-control studies with a total of 69,054 participants. Significant heterogeneity was observed in Caucasian population in subgroup analysis of the association studies of rs11206510 with CHD (P=0.003, I(2)=67.2%). The meta-analysis of LDLR gene rs1122608 polymorphism comprises 7 case-control studies with a total of 20,456 participants and the heterogeneity of seven studies was minimal (P=0.148, I(2)=36.7%).

CONCLUSION

The results of the meta-analyses indicated that both SNPs were associated with CHD in Caucasians (P<0.05) but not in Asians. The results from our case-control study and meta-analyses might be explained by genetic heterogeneity in the susceptibility of CHD and ethnic differences between Asians and Caucasians.

Role of insulin resistance in kidney dysfunction: insights into the mechanism and epidemiological evidence

Several lines of evidence suggest a pathogenic role of insulin resistance on kidney dysfunction. Potential mechanisms are mostly due to the effect of single abnormalities related to insulin resistance and clustering into the metabolic syndrome. Hyperinsulinemia, which is inevitably associated to insulin resistance in non diabetic states, also appears to play a role on kidney function by inducing glomerular hyperfiltration and increased vascular permeability. More recently, adipocytokine which are linked to insulin resistance, low grade inflammation, endothelial dysfunction and vascular damage have been proposed as additional molecules able to modulate kidney function. In addition, recent evidences point also to a role of insulin resistance at the level of the podocyte, an important player in early phases of diabetic kidney damage, thus suggesting a new mechanism through which a reduction of insulin action can affect kidney function. In fact, mouse models not expressing the podocyte insulin receptor develop podocytes apoptosis, effacement of its foot processes along with thickening of the glomerular basement membrane, increased glomerulosclerosis and albuminuria. A great number of epidemiological studies have repeatedly reported the association between insulin resistance and kidney dysfunction in both non diabetic and diabetic subjects. Among these, studies addressing the impact of insulin resistance genes on kidney dysfunction have played the important role to help establish a cause-effect relationship between these two traits. Finally, numerous independent intervention studies have shown that a favourable modulation of insulin resistance has a positive effect also on urinary albumin and total protein excretion. In conclusion, several data of different nature consistently support the role of insulin resistance and related abnormalities on kidney dysfunction. Intervention trials designed to investigate whether treating insulin resistance ameliorates also hard renal end-points are both timely and needed.

Type 2 Diabetes Genetics: Beyond GWAS

The global epidemic of type 2 diabetes mellitus (T2D) is one of the most challenging problems of the 21(st) century leading cause of and the fifth death worldwide. Substantial evidence suggests that T2D is a multifactorial disease with a strong genetic component. Recent genome-wide association studies (GWAS) have successfully identified and replicated nearly 75 susceptibility loci associated with T2D and related metabolic traits, mostly in Europeans, and some in African, and South Asian populations. The GWAS serve as a starting point for future genetic and functional studies since the mechanisms of action by which these associated loci influence disease is still unclear and it is difficult to predict potential implication of these findings in clinical settings. Despite extensive replication, no study has unequivocally demonstrated their clinical role in the disease management beyond progression to T2D from impaired glucose tolerance. However, these studies are revealing new molecular pathways underlying diabetes etiology, gene-environment interactions, epigenetic modifications, and gene function. This review highlights evolving progress made in the rapidly moving field of T2D genetics that is starting to unravel the pathophysiology of a complex phenotype and has potential to show clinical relevance in the near future.

Chemotactic cytokine receptor 5 gene polymorphism: relevance to microvascular complications in type 2 diabetes

We investigated the involvement of chemotactic cytokine receptor 5 (CCR5) gene polymorphism in microvascular complications of T2DM. All subjects were genotyped with the 59029 SNP in the CCR5 gene. The genotype/allele frequencies did not differ between T2DM patients and controls. Genotype distribution was compared in patients with and without complications (nephropathy, retinopathy and neuropathy). The frequency of A allele was significantly higher in patients with complications (OR for A allele 3.07, 95% CI 2.49-3.77). The A allele carriage was associated with diabetic nephropathy (OR 6.17, 95% CI 3.28-11.6). An association was observed between 59029 polymorphism and age at T2DM onset. The A allele was more frequent in early onset than in late onset patients. For AA homozygotes OR was 2.38 (1.19-4.76) and 2.26 (1.12-4.58) in complicated and uncomplicated subgroups, respectively. These results suggest that CCR5 gene polymorphism is associated with diabetic nephropathy in T2DM.

Peri-conception hyperglycaemia and nephropathy are associated with risk of congenital anomaly in women with pre-existing diabetes: a population-based cohort study

AIMS: The aim of this study was to quantify the risk of major congenital anomaly, and to assess the influence of peri-conception HbA(1c) and other clinical and socio-demographic factors on the risk of congenital anomaly occurrence in offspring of women with type 1 and type 2 diabetes diagnosed before pregnancy. METHODS: This was a population-based cohort study using linked data from registers of congenital anomaly and diabetes in pregnancy. A total of 401,149 singleton pregnancies (1,677 in women with diabetes) between 1996 and 2008 resulting in live birth, fetal death at ≥20 weeks' gestation or termination of pregnancy for fetal anomaly were included. RESULTS: The rate of non-chromosomal major congenital anomaly in women with diabetes was 71.6 per 1,000 pregnancies (95% CI 59.6, 84.9), a relative risk of 3.8 (95% CI 3.2, 4.5) compared with women without diabetes. There was a three- to sixfold increased risk across all common anomaly groups. In a multivariate analysis, peri-conception glycaemic control (adjusted OR [aOR] 1.3 [95% CI 1.2, 1.4] per 1% [11 mmol/mol] linear increase in HbA(1c) above 6.3% [45 mmol/mol]) and pre-existing nephropathy (aOR 2.5 [95% CI 1.1, 5.3]) were significant independent predictors of congenital anomaly. Associations with gestation at booking (aOR 1.1 [95% CI 1.0, 1.1]) and parity (aOR 1.6 [95% CI 1.0, 2. 5]) were not significant. Unadjusted risk was higher for women from deprived areas or who did not take folate. Type and duration of diabetes, ethnicity, age, BMI, preconception care, smoking and fetal sex were not associated with congenital anomaly risk. CONCLUSIONS: Peri-conception glycaemia is the most important modifiable risk factor for congenital anomaly in women with diabetes. The association with nephropathy merits further study.

Endoplasmic reticulum stress-related factors protect against diabetic retinopathy

The endoplasmic reticulum (ER) is a principal mediator of signal transduction in the cell, and disruption of its normal function (a mechanism known as ER stress) has been associated with the pathogenesis of several diseases. ER stress has been demonstrated to contribute to onset and progression of diabetic retinopathy (DR) by induction of multiple inflammatory signaling pathways. Recent studies have begun to describe the gene expression profile of ER stress-related genes in DR; moreover, genes that play a protective role against DR have been identified. P58^IPK was determined to be able to reduce retinal vascular leakage under high glucose conditions, thus protecting retinal cells. It has also been found by our lab that ER-associated protein degradation factors exhibit significantly different expression patterns in rat retinas under sustained high glucose conditions. Future research based upon these collective genomic findings will contribute to our overall understanding of DR pathogenesis as well as identify potential therapeutic targets.

ADIPOQ and adiponectin: the common ground of hyperglycemia and coronary artery disease?

Plasma adiponectin and the coding gene for adiponectin, ADIPOQ, are thought to explain part of the interaction between obesity, insulin resistance, type 2 diabetes (T2DM) and coronary artery disease (CAD). Here, we illustrate the role that adiponectin and ADIPOQ variants might play in the modulation of CAD, especially in the occurrence of hyperglycemia. Recent evidence suggests that total and high molecular weight (HMW) adiponectin levels are apparent markers of better cardiovascular prognosis in patients with low risk of CAD. However, in subjects with established or high risk of CAD, these levels are associated with poorer prognosis. We also provide recent evidences relating to the genetic control of total and HMW adiponectin levels, especially evidence regarding ADIPOQ. Accumulated data suggest that both adiponectin levels and polymorphisms in the ADIPOQ gene are linked to the risk of CAD in patients with hyperglycemia, and that these associations seem to be independent from each other, even if adiponectin levels are partly dependent on ADIPOQ.

Association between genetics of diabetes, coronary artery disease, and macrovascular complications: exploring a common ground hypothesis

Type 2 diabetes and coronary artery disease (CAD) are conditions that cause a substantial public health burden. Since both conditions often coexist in the same individual, it has been hypothesized that they have a common effector. Insulin and hyperglycemia are assumed to play critical roles in this scenario. In recent years, many genetic risk factors for both diabetes and CAD have been discovered, mainly through genome-wide association studies. Genetic aspects of diabetes, diabetic macrovascular complications, and CAD are assumed to have intersections leading to the common effector hypothesis. However, only a few genetic risk factors could be identified that modulate the risk for both conditions. Polymorphisms in TCF7L2 and near the CDKN2A/B genes seem to be of great importance in this regard since they appear to modulate both conditions, and they are not necessarily related to insulinism, or hyperglycemia, for CAD development. Other issues related to this hypothesis, such as the problems of phenotype heterogeneity, are also of interest. Recent studies have contributed to a better understanding of the complex genetics of diabetic macrovascular complications. Much effort is still needed to clarify the associations in the genetics of diabetes, and cardiovascular disease. At present, there is little genetic evidence to support a common effector hypothesis, other than insulin or hyperglycemia, for the association between these conditions.

Oxidative stress and diabetic kidney disease

The number of people with diabetic kidney disease continues to increase worldwide despite current treatments. Of the pathophysiologic mechanisms that have been identified in the development and progression of diabetic nephropathy, oxidative stress (more accurately described as increased levels of reactive oxygen species; ROS) is of major importance. The increase in ROS is due to both increased production and to decreased and/or inadequate antioxidant function. To date, human clinical trials with antioxidants have not been shown to be effective. This is likely due, at least in part, to the lack of specificity of current agents. Recent research has determined both major sources of high glucose-induced cellular ROS production as well as high glucose-induced changes in antioxidant function. Treatments targeted at one or more of the specific diabetes-induced alterations in the regulation of ROS levels will likely lead to effective treatments that prevent the development and progression of diabetic kidney disease.