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275 result(s) for "Bowden, Donald W."
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Diabetic Microvascular Disease: An Endocrine Society Scientific Statement
Both type 1 and type 2 diabetes adversely affect the microvasculature in multiple organs. Our understanding of the genesis of this injury and of potential interventions to prevent, limit, or reverse injury/dysfunction is continuously evolving. This statement reviews biochemical/cellular pathways involved in facilitating and abrogating microvascular injury. The statement summarizes the types of injury/dysfunction that occur in the three classical diabetes microvascular target tissues, the eye, the kidney, and the peripheral nervous system; the statement also reviews information on the effects of diabetes and insulin resistance on the microvasculature of skin, brain, adipose tissue, and cardiac and skeletal muscle. Despite extensive and intensive research, it is disappointing that microvascular complications of diabetes continue to compromise the quantity and quality of life for patients with diabetes. Hopefully, by understanding and building on current research findings, we will discover new approaches for prevention and treatment that will be effective for future generations.This scientific statement reviews and discusses the microvascular complications of diabetes on an organ-by-organ basis.
Metabolomic signatures of cognitive function in a type 2 Diabetes-Enriched cohort
To understand the relationship between type 2 diabetes (T2D) and risk for developing cognitive impairment, this study is the first to examine association between metabolites measured at mid-life and cognitive performance assessed later in life (8–10 years) in a T2D-enriched cohort. The discovery set included metabolomics from European Americans (EAs; n  = 137) and African Americans (AAs; n  = 134) from the Diabetes Heart Study (DHS) and the African American-DHS (AA-DHS). The cognitive testing battery included measures of executive function, memory, attention, language, and global cognition. Ancestry-specific linear regression analyses were performed and a false discovery rate (FDR)-corrected p-value was used to assess significance. Overall, fewer significant metabolites were associated with cognitive performance in AAs ( n  = 19) as compared to EAs ( n  = 118) suggesting racial differences. There was a positive association between sphingomyelins and cognitive performance, consistent with prior reports. Novel findings implicated partially characterized metabolites linked to oxidative breakdown of bilirubin to multiple cognitive domains suggesting further exploration of this class of metabolites towards improving pathophysiologic understanding and early intervention. Cross-ancestry replication identified four metabolites that generalized to both populations. Replication was performed among additional study participants, i.e. 421 EAs and 167 AAs, followed by a formal meta-analysis. Replication bolstered the association of multiple metabolites with cognitive function. Among these, cortisol was associated in AAs suggesting a link between stress and risk for reduced cognitive function. Further work is needed to provide insight into the pathophysiologic mechanisms and highlight metabolites for inclusion in risk stratification models of cognitive performance.
MYH9 is a major-effect risk gene for focal segmental glomerulosclerosis
Cheryl Winkler and colleagues use admixture mapping to identify risk variants in MYH9 associated with focal segmental glomerulosclerosis and end-stage renal disease in African Americans. The risk variants are more common in populations with West African ancestry and contribute to the excess burden of end-stage kidney diseases in these populations. A similar finding is reported in an accompanying paper by Linda Kao and colleagues. The increased burden of chronic kidney and end-stage kidney diseases (ESKD) in populations of African ancestry has been largely unexplained. To identify genetic variants predisposing to idiopathic and HIV-1–associated focal segmental glomerulosclerosis (FSGS), we carried out an admixture-mapping linkage-disequilibrium genome scan on 190 African American individuals with FSGS and 222 controls. We identified a chromosome 22 region with a genome-wide logarithm of the odds (lod) score of 9.2 and a peak lod of 12.4 centered on MYH9 , a functional candidate gene expressed in kidney podocytes. Multiple MYH9 SNPs and haplotypes were recessively associated with FSGS, most strongly a haplotype spanning exons 14 through 23 (OR = 5.0, 95% CI = 3.5–7.1; P = 4 × 10 −23 , n = 852). This association extended to hypertensive ESKD (OR = 2.2, 95% CI = 1.5–3.4; n = 433), but not type 2 diabetic ESKD ( n = 476). Genetic variation at the MYH9 locus substantially explains the increased burden of FSGS and hypertensive ESKD among African Americans.
Evaluation of Candidate Nephropathy Susceptibility Genes in a Genome-Wide Association Study of African American Diabetic Kidney Disease
Type 2 diabetes (T2D)-associated end-stage kidney disease (ESKD) is a complex disorder resulting from the combined influence of genetic and environmental factors. This study contains a comprehensive genetic analysis of putative nephropathy loci in 965 African American (AA) cases with T2D-ESKD and 1029 AA population-based controls extending prior findings. Analysis was based on 4,341 directly genotyped and imputed single nucleotide polymorphisms (SNPs) in 22 nephropathy candidate genes. After admixture adjustment and correction for multiple comparisons, 37 SNPs across eight loci were significantly associated (1.6E-05
An integrated germline and somatic genomic model for coronary artery disease
Multiple germline and somatic genomic factors are associated with risk of coronary artery disease, but there is no single measure of risk that integrates all information from a DNA sample. To address this gap, we develop an integrated genomic model that includes six germline and somatic genetic drivers for coronary artery disease, including polygenic risk score, genetically-proxied proteomic/metabolomic risk scores, and clonal hematopoiesis of indeterminate potential. We evaluated its predictive power in the UK Biobank (N = 391,536), and validate it using data from the TOPMed program (N = 34,177). The 10-year coronary artery disease risk based on the integrated genomic model profile ranges from 1.1% to 15.5% in the UK Biobank and from 3.8% to 33.0% in TOPMed, with a more pronounced gradient in males than females. The integrated genomic model captures the cumulative effect of multiple genetic drivers, identifying individuals at high risk for coronary artery disease despite lacking any single high-risk genetic factor, as well as individuals at low risk despite carrying known high-risk factors. In middle age, the integrated genomic model augments the performance of the Pooled Cohort Equations, a clinical risk calculator for coronary artery disease. While the integrated genomic model yields only modest incremental predictive value over polygenic risk score at the population level, it identifies approximately 13% of high-risk individuals not detected by polygenic risk score alone. Coronary artery disease has several genetic risk factors. Here, the authors develop a model that combines germline and somatic genetic drivers to predict coronary artery disease risk, identifying high-risk individuals not detected by polygenic risk scores alone.
Genome-wide association study of vitamin D concentrations and bone mineral density in the African American-Diabetes Heart Study
Relative to European Americans, African Americans have lower 25-hydroxyvitamin D (25OHD) and vitamin D binding protein (VDBP) concentrations, higher 1,25-dihydroxyvitamin D (1,25(OH) 2 D 3 ) concentrations and bone mineral density (BMD), and paradoxically reduced burdens of calcified atherosclerotic plaque (subclinical atherosclerosis). To identify genetic factors contributing to vitamin D and BMD measures, association analysis of >14M variants was conducted in a maximum of 697 African American-Diabetes Heart Study participants with type 2 diabetes (T2D). The most significant association signals were detected for VDBP on chromosome 4; variants rs7041 (β = 0.44, SE = 0.019, P = 9.4x10 -86 ) and rs4588 (β = 0.17, SE = 0.021, P = 3.5x10 -08 ) in the group-specific component (vitamin D binding protein) gene ( GC ). These variants were found to be independently associated. In addition, rs7041 was also associated with bioavailable vitamin D (BAVD; β = 0.16, SE = 0.02, P = 3.3x10 -19 ). Six rare variants were significantly associated with 25OHD, including a non-synonymous variant in HSPG2 (rs116788687; β = -1.07, SE = 0.17, P = 2.2x10 -10 ) and an intronic variant in TNIK (rs143555701; β = -1.01, SE = 0.18, P = 9.0x10 -10 ), both biologically related to bone development. Variants associated with 25OHD failed to replicate in African Americans from the Insulin Resistance Atherosclerosis Family Study (IRASFS). Evaluation of vitamin D metabolism and bone mineral density phenotypes in an African American population enriched for T2D could provide insight into ethnic specific differences in vitamin D metabolism and bone mineral density.
Identification of genetic effects underlying type 2 diabetes in South Asian and European populations
South Asians are at high risk of developing type 2 diabetes (T2D). We carried out a genome-wide association meta-analysis with South Asian T2D cases ( n  = 16,677) and controls ( n  = 33,856), followed by combined analyses with Europeans (n eff  = 231,420). We identify 21 novel genetic loci for significant association with T2D ( P  = 4.7 × 10 −8 to 5.2 × 10 −12 ), to the best of our knowledge at the point of analysis. The loci are enriched for regulatory features, including DNA methylation and gene expression in relevant tissues, and highlight CHMP4B , PDHB , LRIG1 and other genes linked to adiposity and glucose metabolism. A polygenic risk score based on South Asian-derived summary statistics shows ~4-fold higher risk for T2D between the top and bottom quartile. Our results provide further insights into the genetic mechanisms underlying T2D, and highlight the opportunities for discovery from joint analysis of data from across ancestral populations. Marie Loh, Weihua Zhang et al. use a genome-wide association study meta-analysis to examine variants associated with Type 2 diabetes (T2D) in South Asian and European ancestry cohorts. Their results provide further insights into the genetic mechanisms underlying T2D across ancestral populations.
Genome-wide association study identifies novel loci for type 2 diabetes-attributed end-stage kidney disease in African Americans
Background End-stage kidney disease (ESKD) is a significant public health concern disproportionately affecting African Americans (AAs). Type 2 diabetes (T2D) is the leading cause of ESKD in the USA, and efforts to uncover genetic susceptibility to diabetic kidney disease (DKD) have had limited success. A prior genome-wide association study (GWAS) in AAs with T2D-ESKD was expanded with additional AA cases and controls and genotypes imputed to the higher density 1000 Genomes reference panel. The discovery analysis included 3432 T2D-ESKD cases and 6977 non-diabetic non-nephropathy controls ( N  = 10,409), followed by a discrimination analysis in 2756 T2D non-nephropathy controls to exclude T2D-associated variants. Results Six independent variants located in or near RND3/RBM43 , SLITRK3 , ENPP7 , GNG7 , and APOL1 achieved genome-wide significant association ( P  < 5 × 10 −8 ) with T2D-ESKD. Following extension analyses in 1910 non-diabetic ESKD cases and 908 non-diabetic non-nephropathy controls, a meta-analysis of 5342 AA all-cause ESKD cases and 6977 AA non-diabetic non-nephropathy controls revealed an additional novel all-cause ESKD locus at EFNB2 (rs77113398; P  = 9.84 × 10 –9 ; OR = 1.94). Exclusion of APOL1 renal-risk genotype carriers identified two additional genome-wide significant T2D-ESKD-associated loci at GRAMD3 and MGAT4C . A second variant at GNG7 (rs373971520; P  = 2.17 × 10 –8 , OR = 1.46) remained associated with all-cause ESKD in the APOL1 -negative analysis. Conclusions Findings provide further evidence for genetic factors associated with advanced kidney disease in AAs with T2D.
Hepatic Steatosis and Subclinical Cardiovascular Disease in a Cohort Enriched for Type 2 Diabetes: The Diabetes Heart Study
To explore mechanisms whereby hepatic steatosis may be associated with cardiovascular risk, we investigated cross-sectional relationships between hepatic steatosis, regional fat accumulation, inflammatory biomarkers, and subclinical measures of atherosclerosis in the Diabetes Heart Study. The Diabetes Heart Study is a family study of sibling pairs concordant for type 2 diabetes. A subset of 623 randomly selected participants was evaluated for hepatic steatosis, defined as a liver:spleen attenuation ratio of <1.0 by computed tomography. We quantified visceral fat, subcutaneous fat, coronary, aortic, and carotid artery calcium by computed tomography; and carotid atherosclerosis by ultrasound. Associations between the liver:spleen attenuation ratio and these factors were expressed as Spearman correlations. After adjustment for age, race, gender, body mass index, and diabetes status, the liver:spleen attenuation ratio correlated with visceral fat (r =-0.22, P < 0.0001) and subcutaneous fat (r =-0.13, P= 0.031). Hepatic steatosis was associated with lower high-density lipoprotein (r = 0.21, P < 0.0001), higher triglycerides (r =-0.25, P < 0.0001), higher C-reactive protein (r =-0.095, P= 0.004), and lower serum adiponectin (r = 0.34, P < 0.0001). There were no significant associations between the liver:spleen attenuation ratio and coronary, aortic, or carotid calcium, or carotid intimal thickness. This suggests that hepatic steatosis is less likely a direct mediator of cardiovascular disease and may best be described as an epiphenomenon. The strong correlations between pro-atherogenic biomarkers, visceral fat, and elements of the metabolic syndrome suggest that hepatic steatosis reflects more than general adiposity, but represents a systemic, inflammatory, pro-atherogenic adipose state.
Informed Conditioning on Clinical Covariates Increases Power in Case-Control Association Studies
Genetic case-control association studies often include data on clinical covariates, such as body mass index (BMI), smoking status, or age, that may modify the underlying genetic risk of case or control samples. For example, in type 2 diabetes, odds ratios for established variants estimated from low-BMI cases are larger than those estimated from high-BMI cases. An unanswered question is how to use this information to maximize statistical power in case-control studies that ascertain individuals on the basis of phenotype (case-control ascertainment) or phenotype and clinical covariates (case-control-covariate ascertainment). While current approaches improve power in studies with random ascertainment, they often lose power under case-control ascertainment and fail to capture available power increases under case-control-covariate ascertainment. We show that an informed conditioning approach, based on the liability threshold model with parameters informed by external epidemiological information, fully accounts for disease prevalence and non-random ascertainment of phenotype as well as covariates and provides a substantial increase in power while maintaining a properly controlled false-positive rate. Our method outperforms standard case-control association tests with or without covariates, tests of gene x covariate interaction, and previously proposed tests for dealing with covariates in ascertained data, with especially large improvements in the case of case-control-covariate ascertainment. We investigate empirical case-control studies of type 2 diabetes, prostate cancer, lung cancer, breast cancer, rheumatoid arthritis, age-related macular degeneration, and end-stage kidney disease over a total of 89,726 samples. In these datasets, informed conditioning outperforms logistic regression for 115 of the 157 known associated variants investigated (P-value = 1 × 10(-9)). The improvement varied across diseases with a 16% median increase in χ(2) test statistics and a commensurate increase in power. This suggests that applying our method to existing and future association studies of these diseases may identify novel disease loci.