Search

To identify genetic variants associated with diabetic retinopathy (DR), we performed a large multiethnic genome-wide association study. Discovery included eight European cohorts (n = 3,246) and seven African American cohorts (n = 2,611). We meta-analyzed across cohorts using inverse-variance weighting, with and without liability threshold modeling of glycemic control and duration of diabetes. Variants with a P value

The Diabetes Heart Study, initiated in 1997, includes examination and follow-up of 1221 European Americans, 85% with type 2 diabetes (T2D). Baseline examination included extensive medical history, laboratory measures, and CT-imaging for coronary artery calcium (CAC). Through 2016, 451 participants had died. CVD-attributable deaths occurred over an age range of 39-93 years. In high-risk participants with T2D and CAC>1000, 52% died after mean 14.9 year follow-up; however, many are still alive. 64% of surviving T2D participants lived with diabetes for >20 years and 16.4% (31 male, 46 female) >30 years. Among deceased individuals, the average duration of diabetes was 20.8 years. Comparing long-term T2D-survivors to deceased, difference in CAC, a powerful predictor of mortality, was not significant (P=0.85) with mean CAC in survivors (male=4730, female=1147) and deceased (male=4085, female=1220). Conventional clinical measures did not differ significantly (glucose, HbA1c, BP; P>0.05) or were modestly different (cholesterol P=0.033; LDL P=0.035). There was a difference in the use of statins at baseline: 53% in survivors, 41% in deceased (P=0.05) and C-reactive protein (P=0.04). The strongest individual trait difference was in duration of T2D at baseline (P Disclosure D.W. Bowden: None. J. Xu: None. B.I. Freedman: Consultant; Self; AstraZeneca, Ionis Pharmaceuticals, Inc. N. Palmer: None. F. Hsu: None. Funding National Institutes of Health

To identify genetic variants associated with diabetic retinopathy (DR), we performed a large multiethnic genome-wide association study. Discovery included eight European cohorts (n = 3,246) and seven African American cohorts (n = 2,611). We meta-analyzed across cohorts using inverse-variance weighting, with and without liability threshold modeling of glycemic control and duration of diabetes. Variants with a P value

Type 2 diabetes (T2D) disproportionally affects African Americans (AfA) but, to date, genetic variants identified from genome-wide association studies (GWAS) are primarily from European and Asian populations. We examined the single nucleotide polymorphism (SNP) and locus transferability of 40 reported T2D loci in six AfA GWAS consisting of 2,806 T2D case subjects with or without end-stage renal disease and 4,265 control subjects from the Candidate Gene Association Resource Plus Study. Our results revealed that seven index SNPs at the TCF7L2, KLF14, KCNQ1, ADCY5, CDKAL1, JAZF1, and GCKR loci were significantly associated with T2D (P < 0.05). The strongest association was observed at TCF7L2 rs7903146 (odds ratio [OR] 1.30; P = 6.86 × 10−8). Locus-wide analysis demonstrated significant associations (Pemp < 0.05) at regional best SNPs in the TCF7L2, KLF14, and HMGA2 loci as well as suggestive signals in KCNQ1 after correction for the effective number of SNPs at each locus. Of these loci, the regional best SNPs were in differential linkage disequilibrium (LD) with the index and adjacent SNPs. Our findings suggest that some loci discovered in prior reports affect T2D susceptibility in AfA with similar effect sizes. The reduced and differential LD pattern in AfA compared with European and Asian populations may facilitate fine mapping of causal variants at loci shared across populations.

OBJECTIVE Variation in the transcription factor 7-like 2 (TCF7L2) locus is associated with type 2 diabetes across multiple ethnicities. The aim of this study was to elucidate which variant in TCF7L2 confers diabetes susceptibility in African Americans. RESEARCH DESIGN AND METHODS Through the evaluation of tagging single nucleotide polymorphisms (SNPs), type 2 diabetes susceptibility was limited to a 4.3-kb interval, which contains the YRI (African) linkage disequilibrium (LD) block containing rs7903146. To better define the relationship between type 2 diabetes risk and genetic variation we resequenced this 4.3-kb region in 96 African American DNAs. Thirty-three novel and 13 known SNPs were identified: 20 with minor allele frequencies (MAF) >0.05 and 12 with MAF >0.10. These polymorphisms and the previously identified DG10S478 microsatellite were evaluated in African American type 2 diabetic cases (n = 1,033) and controls (n = 1,106). RESULTS Variants identified from direct sequencing and databases were genotyped or imputed. Fifteen SNPs showed association with type 2 diabetes (P < 0.05) with rs7903146 being the most significant (P = 6.32 × 10−6). Results of imputation, haplotype, and conditional analysis of SNPs were consistent with rs7903146 being the trait-defining SNP. Analysis of the DG10S478 microsatellite, which is outside the 4.3-kb LD block, revealed consistent association of risk allele 8 with type 2 diabetes (odds ratio [OR] = 1.33; P = 0.022) as reported in European populations; however, allele 16 (MAF = 0.016 cases and 0.032 controls) was strongly associated with reduced risk (OR = 0.39; P = 5.02 × 10−5) in contrast with previous studies. CONCLUSIONS In African Americans, these observations suggest that rs7903146 is the trait-defining polymorphism associated with type 2 diabetes risk. Collectively, these results support ethnic differences in type 2 diabetes associations.

OBJECTIVE—Polymorphisms in the adiponectin gene (ADIPOQ) have been associated with type 2 diabetes and diabetic nephropathy in type 1 diabetes, in mostly European-derived populations. RESEARCH DESIGN AND METHODS—A comprehensive association analysis of 24 single-nucleotide polymorphisms (SNPs) in the adiponectin gene was performed for type 2 diabetes and diabetic nephropathy in African Americans. RESULTS—The minor allele (A) in a single SNP in intron 1 (rs182052) was associated with diabetic nephropathy (P = 0.0015, odds ratio [OR] 1.37, CI 1.13–1.67, dominant model) in an African American sample of 851 case subjects with diabetic nephropathy and 871 nondiabetic control subjects in analyses incorporating adjustment for varying levels of racial admixture. This association remained significant after adjustment of the data for BMI, age, and sex (P = 0.0013–0.0004). We further tested this SNP for association with longstanding type 2 diabetes without nephropathy (n = 317), and evidence of association was also significant (P = 0.0054, OR 1.46, CI 1.12–1.91, dominant model) when compared with the same set of 871 nondiabetic control subjects. Combining the type 2 diabetes and diabetic nephropathy samples into a single group of case subjects (n = 1,168) resulted in the most significant evidence of association (P = 0.0003, OR 1.40, CI 1.17–1.67, dominant model). Association tests between age at onset of type 2 diabetes and the rs182052 genotypes also revealed significant association between the presence of the minor allele (A/A or A/G) and earlier onset of type 2 diabetes. CONCLUSIONS—The SNP rs182052 in intron 1 of the adiponectin gene is associated with type 2 diabetes in African Americans.

OBJECTIVEThe vascular ectonucleotidase ENTPD1 protects against renal injury and modulates glucose homeostasis in mouse models. We sought to determine whether human variation in ENTPD1 influences predisposition to diabetes or diabetic nephropathy.RESEARCH DESIGN AND METHODSWe analyzed ENTPD1 single nucleotide polymorphisms (SNPs) in 363 African American control subjects, 380 subjects with type 2 diabetes and end-stage renal disease (DM-ESRD), and 326 subjects with ESRD unrelated to diabetes (non–DM-ESRD). Using human cell lines, we correlated disease-associated ENTPD1 haplotypes with ENTPD1 gene expression. Finally, we studied consequences of ENTPD1 deletion in a mouse model of type 2 diabetes (db/db).RESULTSA common ENTPD1 two-SNP haplotype was associated with increased risk for DM-ESRD (P = 0.0027), and an uncommon four-SNP haplotype was associated with protection against DM-ESRD (P = 0.004). These haplotypes correlated with ENTPD1 gene expression levels in human cell lines in vitro. Subjects with high ENTPD1-expressing haplotypes were enriched in the DM-ESRD group. By crossing ENTPD1-null mice with db mice, we show that ENTPD1 deletion has prominent effects on metabolic syndrome traits. Specifically, deletion of ENTPD1 lowered glucose levels in control (db/−) mice with one functional leptin receptor and dramatically lowered weights in db/db mice with no functional leptin receptors. Similar effects were seen in aged ENTPD1-null mice with normal leptin receptors.CONCLUSIONSENTPD1 polymorphisms appear to influence susceptibility to type 2 diabetes and/or diabetic nephropathy in African Americans. Studies in human cell lines and in vivo mouse data support a potential role for ENTPD1 genetic variation in susceptibility to type 2 diabetes.

OBJECTIVE—Variants in the ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1) gene have shown positive associations with diabetes and related phenotypes, including insulin resistance, metabolic syndrome, and type 1 diabetic nephropathy. Additionally, evidence for linkage for type 2 diabetes in African Americans was observed at 6q24-27, with the proximal edge of the peak encompassing the ENPP1 gene. Our objective was to comprehensively evaluate variants in ENPP1 for association with type 2 diabetic end-stage renal disease (ESRD). RESEARCH DESIGN AND METHODS—Forty-nine single nucleotide polymorphisms (SNPs) located in the coding and flanking regions of ENPP1 were genotyped in 577 African-American individuals with type 2 diabetic ESRD and 596 African-American control subjects. Haplotypic association and genotypic association for the dominant, additive, and recessive models were tested by calculating a χ2 statistic and corresponding P value. RESULTS—Nine SNPs showed nominal evidence for association (P < 0.05) with type 2 diabetic ESRD in one or more genotypic model. The most significant associations were observed with rs7754586 (P = 0.003 dominant model, P = 0.0005 additive, and P = 0.007 recessive), located in the 3′ untranslated region, and an intron 24 SNP (rs1974201: P = 0.004 dominant, P = 0.0005 additive, and P = 0.005 recessive). However, the extensively studied K121Q variant (rs1044498) did not reveal evidence for association with type 2 diabetic ESRD in this African-American population. CONCLUSIONS—This study was the first to comprehensively evaluate variants of the ENPP1 gene for association in an African-American population with type 2 diabetes and ESRD and suggests that variants in the distal region of the ENPP1 gene may contribute to diabetes or diabetic nephropathy susceptibility in African Americans.

OBJECTIVE— Several whole-genome association studies have reported identification of type 2 diabetes susceptibility genes in various European-derived study populations. Little investigation of these loci has been reported in other ethnic groups, specifically African Americans. Striking differences exist between these populations, suggesting they may not share identical genetic risk factors. Our objective was to examine the influence of type 2 diabetes genes identified in whole-genome association studies in a large African American case-control population. RESEARCH DESIGN AND METHODS— Single nucleotide polymorphisms (SNPs) in 12 loci (e.g., TCF7L2, IDE/KIF11/HHEX, SLC30A8, CDKAL1, PKN2, IGF2BP2, FLJ39370, and EXT2/ALX4) associated with type 2 diabetes in European-derived populations were genotyped in 993 African American type 2 diabetic and 1,054 African American control subjects. Additionally, 68 ancestry-informative markers were genotyped to account for the impact of admixture on association results. RESULTS— Little evidence of association was observed between SNPs, with the exception of those in TCF7L2, and type 2 diabetes in African Americans. One TCF7L2 SNP (rs7903146) showed compelling evidence of association with type 2 diabetes (admixture-adjusted additive P [Pa] = 1.59 × 10−6). Only the intragenic SNP on 11p12 (rs9300039, dominant P [Pd] = 0.029) was also associated with type 2 diabetes after admixture adjustments. Interestingly, four of the SNPs are monomorphic in the Yoruba population of the HAPMAP project, with only the risk allele from the populations of European descent present. CONCLUSIONS— Results suggest that these variants do not significantly contribute to interindividual susceptibility to type 2 diabetes in African Americans. Consequently, genes contributing to type 2 diabetes in African Americans may, in part, be different from those in European-derived study populations. High frequency of risk alleles in several of these genes may, however, contribute to the increased prevalence of type 2 diabetes in African Americans.

The Family Investigation of Nephropathy and Diabetes (FIND) was initiated to map genes underlying susceptibility to diabetic nephropathy. A total of 11 centers participated under a single collection protocol to recruit large numbers of diabetic sibling pairs concordant and discordant for diabetic nephropathy. We report the findings from the first-phase genetic analyses in 1,227 participants from 378 pedigrees of European-American, African-American, Mexican-American, and American Indian descent recruited from eight centers. Model-free linkage analyses, using a dichotomous definition for diabetic nephropathy in 397 sibling pairs, as well as the quantitative trait urinary albumin-to-creatinine ratio (ACR), were performed using the Haseman-Elston linkage test on 404 microsatellite markers. The strongest evidence of linkage to the diabetic nephropathy trait was on chromosomes 7q21.3, 10p15.3, 14q23.1, and 18q22.3. In ACR (883 diabetic sibling pairs), the strongest linkage signals were on chromosomes 2q14.1, 7q21.1, and 15q26.3. These results confirm regions of linkage to diabetic nephropathy on chromosomes 7q, 10p, and 18q from prior reports, making it important that genes underlying these peaks be evaluated for their contribution to nephropathy susceptibility. Large family collections consisting of multiple members with diabetes and advanced nephropathy are likely to accelerate the identification of genes causing diabetic nephropathy, a life-threatening complication of diabetes.

Recent studies have demonstrated the importance of sex effects on the underlying genetic architecture of insulin-related traits. To explore sex-specific genetic effects on fasting insulin, we tested for genotype-by-sex interaction and conducted linkage analysis of fasting insulin in Hypertension Genetic Epidemiology Network families. Hypertensive siblings and their first-degree relatives were recruited from five field centers. We performed a genome scan for quantitative trait loci influencing fasting insulin among 1,505 European Americans and 1,616 African Americans without diabetes. Sex-stratified linear regression models, adjusted for race, center, and age, were explored. The Mammalian Genotyping Service typed 391 microsatellite markers, spaced roughly 9 cM. Variance component linkage analysis was performed in SOLAR using ethnic-specific marker allele frequencies and multipoint IBDs calculated in MERLIN. We detected a quantitative trait locus influencing fasting insulin in female subjects (logarithm of odds [LOD] = 3.4) on chromosome 2 at 95 cM (between GATA69E12 and GATA71G04) but not in male subjects (LOD = 0.0, P for interaction = 0.007). This sex-specific signal at 2p13.2 was detected in both European-American (LOD = 2.1) and African-American (LOD = 1.2) female subjects. Our findings overlap with several other linkage reports of insulin-related traits and demonstrate the importance of considering complex context-dependent interactions in the search for insulin-related genes.

African Americans have twice the prevalence of type 2 diabetes as Caucasians and much greater genetic diversity. We identified an inframe insertion of a proline in the insulin promoter factor 1 (IPF1) gene (InsCCG243), which was relatively common (minor allele frequency ∼0.08) in African Americans and showed a trend to association with type 2 diabetes in preliminary studies. An earlier French study identified InsCCG243 as a cause of autosomal dominant diabetes. To determine the role of this variant in African Americans, we examined an additional population from North Carolina (n = 368) and a subset of African-American participants from the Atherosclerosis Risk in Communities (ARIC) study (n = 1,741). We also looked for segregation in 66 African-American families and for a role in insulin secretion in 112 nondiabetic subjects. InsCCG243 did not increase the risk of type 2 diabetes (P = 0.16 in North Carolina; P = 0.97 in the ARIC study) and did not segregate with type 2 diabetes in families. However, we found suggestive evidence for reduced insulin response to glucose (P = 0.05). Neither indirect measures of β-cell mass nor β-cell compensation were altered (P > 0.1). InsCCG243 does not act in a dominant, highly penetrant fashion in African Americans and is not a significant risk factor for type 2 diabetes in this population.

Cardiovascular disease (CVD) is a major contributor to morbidity and mortality in type 2 diabetes, but the relationship between CVD and type 2 diabetes is not well understood. The Diabetes Heart Study is a study of type 2 diabetes–enriched families extensively phenotyped for measures of CVD, type 2 diabetes, and metabolic syndrome. A total of 977 Caucasian subjects from 358 pedigrees (575 type 2 diabetic relative pairs) with at least two individuals with type 2 diabetes and, where possible, unaffected siblings were included in a genome scan. Qualitative traits evaluated in this analysis are with or without the presence of coronary calcified plaque (CCP) and with or without carotid calcified plaque (CarCP) measured by electrocardiogram–gated helical computed tomography. In addition, prevalent CVD was measured using two definitions: CVD1, based on self-reported history of clinical CVD (393 subjects), and CVD2, defined as CVD1 and/or CCP >400 (606 subjects). These discrete traits (type 2 diabetes, metabolic syndrome, CVD1, CVD2, CCP, and CarCP) frequently coincide in the same individuals with concordance ranging from 42.9 to 99%. Multipoint nonparametric linkage analysis revealed evidence for coincident mapping of each trait (type 2 diabetes, metabolic syndrome, CVD1, CVD2, CCP, and CarCP) to three different genomic regions: a broad region on chromosome 3 (70–160 cM; logarithm of odds [LOD] scores ranging between 1.15 and 2.71), chromosome 4q31 (peak LOD 146 cM; LOD scores ranging between 0.90 and 2.41), and on chromosome 14p (peak LOD 23 cM; LOD scores ranging between 1.43 and 2.31). Ordered subset analysis (OSA) suggests that the linked chromosome 3 region consists of at least two separate loci on 3p and 3q. In addition, OSA based on lipid measures and other traits identify family subsets with significantly stronger evidence of linkage (e.g., CVD2 on chromosome 3 at 87 cM subsetting on low HDL with an initial LOD of 2.19 is maximized to an LOD of 7.04 in a subset of 25% of the families and CVD2 on chromosome 14 at 22 cM subsetting on high triglycerides with an initial LOD of 1.99 maximized to an LOD of 4.90 in 44% of the families). When subjects are defined as affected by the presence of each trait (type 2 diabetes, metabolic syndrome, CVD1, and CCP), significant evidence for linkage to the 3p locus is observed with a peak LOD of 4.13 at 87 cM. While the correlated nature of the traits makes it unclear whether these loci represent distinct type 2 diabetes, metabolic syndrome, or CVD loci or single loci with pleiotropic effects, the coincident linkage suggests that identification of the underlying genes may help clarify the relationship of diabetes, metabolic syndrome, and CVD.

Individuals with type 2 diabetes are at increased risk of cardiovascular disease (CVD) mortality and display increased levels of subclinical CVD. Genetic variation in PTPN1, a diabetes susceptibility gene, was investigated for a role in diabetic atherosclerosis. The PTPN1 gene encodes protein tyrosine phosphatase-1B, which is ubiquitously expressed and plays a role in the regulation of several signaling pathways. Subclinical atherosclerosis was assessed in 590 Caucasian participants with type 2 diabetes in the Diabetes Heart Study using B-mode ultrasound measurement of carotid intima-media thickness (IMT) and computed tomography measurement of carotid calcified plaque (CarCP) and coronary calcified plaque (CorCP). Twenty-three single nucleotide polymorphisms (SNPs) in PTPN1 were genotyped and assessed for association with IMT, CarCP, and CorCP. A total of 12 SNPs within a block of linkage disequilibrium encompassing the coding sequence of PTPN1 were significantly associated with CorCP (P values from

Genome-wide linkage scans were carried out using a multipoint variance components method in white and black families of the NHLBI Hypertension Genetic Epidemiology Network (HyperGEN) study to identify quantitative trait loci (QTLs) for pancreatic β-cell function and insulin sensitivity estimated through the newly released nonlinear computer version of homeostasis model assessment 2. Participants fasting 3.6) evidence supporting linkages was detected on chromosome 8q24 at D8S1179 (135 cM, LOD score 4.2, empirical P = 0.002) and at D8S1128 (140 cM, LOD score 3.7, empirical P = 0.003). In addition, two regions supported linkage for insulin sensitivity index in the obese black families on chromosome 7q11 at D7S3046 (79 cM, LOD score 3.0, empirical P = 0.018) and on chromosome 6q26 at D6S1277 (173 cM, LOD score 3.0, empirical P = 0.018). Reducing clinical heterogeneity using obesity data and improved estimates of β-cell function and insulin sensitivity may have permitted identification of a QTL on chromosome 8q24 for β-cell function in the presence of estimated insulin resistance and a QTL on chromosome 7q11 for insulin sensitivity. These regions replicate previous reports for type 2 diabetes–associated traits.

Genome-wide linkage analyses were performed using a multipoint variance components method in eight study groups from four multicenter networks (whites and blacks in GenNet; whites, blacks, and Mexican Americans in GENOA; whites and blacks in HyperGEN; and Asians in SAPPHIRe) that comprise the National Heart, Lung, and Blood Institute Family Blood Pressure Program (FBPP), in order to identify quantitative trait loci (QTLs) influencing fasting glucose, insulin, and homeostasis model assessment of insulin resistance (HOMA-IR). These study populations were enriched with subjects who had elevated blood pressure. Participants fasting

Type 2 diabetes susceptibility is determined by multiple genetic and environmental factors. Genome-wide linkage scans have localized common regions, possibly harboring susceptibility genes on chromosomes 1, 2, 12, and 20. Variability in linkage findings underscores the probable genetic heterogeneity of type 2 diabetes. Thus, we conducted a genome scan of diabetes status using maximum likelihood methods that model affection status by a liability threshold model. Hypertensive sibships and their offspring and/or parents in the Hypertension Genetic Epidemiology Network study were recruited from five field centers. The diabetes phenotype was derived using the World Health Organization criteria and adjusted for race/study center, age, age2, sex, and with and without percent body fat. In total, 567 diabetic participants were identified in 437 families. Variance component linkage analysis was performed among 1,545 Caucasians and 1,608 African Americans using race-specific marker allele frequencies. We detected a quantitative trait loci (QTLs) influencing diabetes variance (logarithm of odds = 3.4) on chromosome 22, which overlaps a positive type 2 diabetes finding among Canadian Oji-Cree Indians. We also observed suggestive evidence for linkage on chromosomes 1, 2, 5, 8, 14, 17, and 19. The identification and replication of type 2 diabetes QTLs will bring us closer to the detection of functional genes that influence diabetes susceptibility.

African Americans are at increased risk of type 2 diabetes and many diabetes complications. We have carried out a genome-wide scan for African American type 2 diabetes using 638 affected sibling pairs (ASPs) from 247 families ascertained through impaired renal function to identify type 2 diabetes loci in this high-risk population. Of the 638 ASPs, 210 were concordant for diabetes with impaired renal function. A total of 390 markers, at an average spacing of 9 cM, were genotyped by the Center for Inherited Disease Research (CIDR) as part of the International Type 2 Diabetes Linkage Analysis Consortium. Nonparametric linkage (NPL) analyses conducted using the exponential model implemented in Genehunter Plus provided suggestive evidence for linkage at 6q24-q27 (163.5 cM, logarithm of odds [LOD] 2.26). Multilocus NPL regression analysis identified the 6q locus (D6S1035, LOD 2.67) and two additional regions: 7p (LOD 1.06) and 18q (LOD 0.87) as important in this model. NPL regression-based interaction analyses and ordered subset analyses (OSAs) supported the presence of a locus at chromosome 7p (29–34 cM) in the pedigrees with the earliest mean age of diagnosis of type 2 diabetes (P = 0.009 for interaction, ΔP = 0.0034 for OSA) and lower mean BMI (P = 0.009 for interaction, ΔP = 0.070 for OSA). These results provide evidence that genes predisposing African-American individuals to type 2 diabetes are located in the 6q and 7p regions of the genome.

The potential contribution of maturity-onset diabetes of the young (MODY) genes to NIDDM susceptibility in African-American and Caucasian NIDDM-affected sibling pairs with a history of adult-onset diabetic nephropathy has been evaluated. Evidence for linkage to NIDDM was found with polymorphic loci that map to the long arms of human chromosomes 20 and 12 in regions containing the MODY1 and MODY3 genes. Nonparametric analysis of chromosome 20 inheritance data collected with the MODYl-linked marker D20S197 provides evidence forlinkage to NIDDM with a P value of 0.005 in Caucasian sib pairs using affected sibpair (ASP) analyses. Nonparametric analysis of chromosome 12 inheritance data collected with the MODY3-linked markers D12S349 and D12S86 provides evidence for linkage to NIDDM with P values of 0.04 and 0.006, respectively, in Caucasian sib pairs using similar analyses. No evidence for linkage of MODY1 and MODY3 markers to NIDDM in African-American sib pairs was observed. In addition, no evidence for linkage to MODY2 (glucokinase-associated MODY) was observed with either study population. Results of multipoint maximum logarithm of odds (LOD) score analysis were consistent with the ASP results. A maximum LOD score of 1.48 was calculated for linkage to MODYl-linked loci and 1.45 to MODY3-linked loci in Caucasian sib pairs. Tabulation of allele sharing in affected sib pairs with D20S197 and D12S349 suggests that affected sibling pairs may inherit susceptibility genes simultaneously from chromosome 20 and chromosome 12. The results suggest that genes contributing to NIDDM in the general Caucasian population are located in the regions containing the MODY1 and MODY3 genes.

Type 2 diabetes (T2D) disproportionally affects African Americans (AfA) but, to date, genetic variants identified from genome-wide association studies (GWAS) are primarily from European and Asian populations. We examined the single nucleotide polymorphism (SNP) and locus transferability of 40 reported T2D loci in six AfA GWAS consisting of 2,806 T2D case subjects with or without end-stage renal disease and 4,265 control subjects from the Candidate Gene Association Resource Plus Study. Our results revealed that seven index SNPs at the TCF7L2, KLF14, KCNQ1, ADCY5, CDKAL1, JAZF1, and GCKR loci were significantly associated with T2D (P < 0.05). The strongest association was observed at TCF7L2 rs7903146 (odds ratio [OR] 1.30; P = 6.86 × 10−8). Locus-wide analysis demonstrated significant associations (Pemp < 0.05) at regional best SNPs in the TCF7L2, KLF14, and HMGA2 loci as well as suggestive signals in KCNQ1 after correction for the effective number of SNPs at each locus. Of these loci, the regional best SNPs were in differential linkage disequilibrium (LD) with the index and adjacent SNPs. Our findings suggest that some loci discovered in prior reports affect T2D susceptibility in AfA with similar effect sizes. The reduced and differential LD pattern in AfA compared with European and Asian populations may facilitate fine mapping of causal variants at loci shared across populations.

Diabetic nephropathy, the most common cause of end-stage renal disease, aggregates in families and specific ethnic groups. Deconstructing diabetic nephropathy into intermediate, quantitative phenotypes may increase feasibility of detecting susceptibility loci by genetic screens. Glomerular filtration rate (GFR), which characterizes diabetic nephropathy, was employed as a quantitative trait in a preliminary whole-genome scan.Estimated GFR (eGFR) was calculated for 882 diabetic sibpairs (mean age 57 years) of African-American (25.6% of total), American Indian (8.6%), European-American (14.2%), and Mexican-American (51.6%) descent enrolled in the initial phase of the Family Investigation of Nephropathy and Diabetes (FIND). A whole-genome scan was performed using 404 microsatellite markers (average spacing 9 cM) and model-free linkage analysis.For all ethnicities combined, strong evidence for linkage was observed on chromosomes 1q43 (P = 3.6 x 10(-3)), 7q36.1 (P = 2.1 x 10(-4)), 8q13.3 (P = 4.6 x 10(-4)), and 18q23.3 (P = 2.7 x 10(-3)). Mexican-American families, who comprised the major ethnic subpopulation in FIND, contributed to linkage on chromosomes 1q43, 2p13.3, 7q36.1, 8q13.3, and 18q23.3, whereas African-American and American-Indian families displayed linkage peaks on chromosomes 11p15.1 and 15q22.3, respectively.We have demonstrated multiple chromosomal regions linked to eGFR in a multi-ethnic collection of families ascertained by a proband with diabetic nephropathy. Identification of genetic variants within these loci that are responsible for the linkage signals could lead to predictive tests or novel therapies for subsets of patients at risk for diabetic nephropathy.

OBJECTIVE—Recently, variants in the TCF7L2 gene have been reported to be associated with type 2 diabetes across multiple Europid populations, but only one small sample of African-American type 2 diabetic patients has been examined. Our objective was to investigate the importance of TCF7L2 in a larger African-American case-control population. RESEARCH DESIGN AND METHODS—We investigated single nucleotide polymorphisms (SNPs) in six known type 2 diabetes genes in 577 African-American case subjects with type 2 diabetes enriched for nephropathy and 596 African-American control subjects. Additionally, we genotyped 70 ancestry-informative markers (AIMs) to apply adjustments for differences in ancestral proportions. RESULTS—The most significant associations were observed with TCF7L2 intron 3 SNPs rs7903146 (additive P = 4.10 × 10−6, odds ratio [OR] 1.51; admixture-adjusted Pa = 3.77 × 10−6) and rs7901695 (P = 0.001, OR 1.30; Pa = 0.003). The 2-SNP haplotype containing these SNPs was also associated with type 2 diabetes (P = 3 × 10−5). Modest associations were also seen with TCF7L2 intron 4 SNPs rs7895340, rs11196205, and rs12255372 (0.01 < P < 0.05; 0.03 < Pa < 0.08), as well as with ATP-sensitive inwardly rectifying potassium channel subunit Kir6.2 (KCNJ11) and hepatocyte nuclear factor 4-α (HNF4A) SNPs (0.01 < P < 0.05; 0.01 < Pa < 0.41). No significant associations were detected with genotyped calpain 10 (CAPN10), peroxisome proliferator–activated receptor γ (PPARG), and transcription factor 1 (TCF1) SNPs. CONCLUSIONS—This study indicates that variants in the TCF7L2 gene significantly contribute to diabetes susceptibility in African-American populations.

The Family Investigation of Nephropathy and Diabetes (FIND) was initiated to map genes underlying susceptibility to diabetic nephropathy. A total of 11 centers participated under a single collection protocol to recruit large numbers of diabetic sibling pairs concordant and discordant for diabetic nephropathy. We report the findings from the first-phase genetic analyses in 1,227 participants from 378 pedigrees of European-American, African-American, Mexican-American, and American Indian descent recruited from eight centers. Model-free linkage analyses, using a dichotomous definition for diabetic nephropathy in 397 sibling pairs, as well as the quantitative trait urinary albumin-to-creatinine ratio (ACR), were performed using the Haseman-Elston linkage test on 404 microsatellite markers. The strongest evidence of linkage to the diabetic nephropathy trait was on chromosomes 7q21.3, 10p15.3, 14q23.1, and 18q22.3. In ACR (883 diabetic sibling pairs), the strongest linkage signals were on chromosomes 2q14.1, 7q21.1, and 15q26.3. These results confirm regions of linkage to diabetic nephropathy on chromosomes 7q, 10p, and 18q from prior reports, making it important that genes underlying these peaks be evaluated for their contribution to nephropathy susceptibility. Large family collections consisting of multiple members with diabetes and advanced nephropathy are likely to accelerate the identification of genes causing diabetic nephropathy, a life-threatening complication of diabetes.

The estrogen receptor-α gene (ESR1) was selected as a positional candidate under a type 2 diabetes linkage peak at 6q24-27. A total of 42 ESR1 single nucleotide polymorphisms (SNPs) were genotyped in 380 African-American type 2 diabetic case subjects with end-stage renal disease (ESRD) and 276 African-American control subjects. A total of 22 ancestry informative markers were also genotyped, and the program Admixmap was used to adjust allelic and haplotypic association tests for individual estimates of admixture. The most significant association with type 2 diabetes–ESRD was with rs1033182 in intron 2 (P = 0.013, admixture-adjusted Pa = 0.021). Genotyping 17 SNPs across a region of ESR1 intron 1–intron 2 in an expanded population of 851 case and 635 control subjects supported association with rs1033182 (P = 0.004, Pa = 0.027) and with an independent six-SNP haplotype of high linkage disequilibrium spanning 6.4 kb (P < 0.0001, Pa < 0.0001). The same 17 ESR1 SNPs were genotyped in 300 European-American type 2 diabetes–ESRD case subjects and 310 European-American control subjects. Two intron 2 SNPs, rs2431260 (P = 0.015) and rs1709183 (P = 0.019), and a four-SNP haplotype containing these SNPs (P = 0.033) were associated with type 2 diabetes and/or ESRD. Results suggest that intron 1 and intron 2 of the ESR1 gene may contain functionally important regions related to type 2 diabetes or ESRD risk.

Recent studies have demonstrated the importance of sex effects on the underlying genetic architecture of insulin-related traits. To explore sex-specific genetic effects on fasting insulin, we tested for genotype-by-sex interaction and conducted linkage analysis of fasting insulin in Hypertension Genetic Epidemiology Network families. Hypertensive siblings and their first-degree relatives were recruited from five field centers. We performed a genome scan for quantitative trait loci influencing fasting insulin among 1,505 European Americans and 1,616 African Americans without diabetes. Sex-stratified linear regression models, adjusted for race, center, and age, were explored. The Mammalian Genotyping Service typed 391 microsatellite markers, spaced roughly 9 cM. Variance component linkage analysis was performed in SOLAR using ethnic-specific marker allele frequencies and multipoint IBDs calculated in MERLIN. We detected a quantitative trait locus influencing fasting insulin in female subjects (logarithm of odds [LOD] = 3.4) on chromosome 2 at 95 cM (between GATA69E12 and GATA71G04) but not in male subjects (LOD = 0.0, P for interaction = 0.007). This sex-specific signal at 2p13.2 was detected in both European-American (LOD = 2.1) and African-American (LOD = 1.2) female subjects. Our findings overlap with several other linkage reports of insulin-related traits and demonstrate the importance of considering complex context-dependent interactions in the search for insulin-related genes.

Genome-wide linkage scans were carried out using a multipoint variance components method in white and black families of the NHLBI Hypertension Genetic Epidemiology Network (HyperGEN) study to identify quantitative trait loci (QTLs) for pancreatic beta-cell function and insulin sensitivity estimated through the newly released nonlinear computer version of homeostasis model assessment 2. Participants fasting8 h, with diagnosed type 2 diabetes, or taking blood glucose or blood lipid-lowering medications were excluded. Both phenotypes were adjusted separately by race and sex for the effects of age, BMI, and field center before linkage scans using 370 microsatellite markers were performed. A total of 685 white families (1,180 sibpairs) and 773 black families (775 sibpairs) were evaluated as well as subsets including 267 obese white families (757 sibpairs) and 427 obese black families (599 sibpairs) identified through tree-linkage analyses using interacting covariates of age, sex, and BMI. For beta-cell function in the obese white families, significant (logarithm of odds [LOD] score3.6) evidence supporting linkages was detected on chromosome 8q24 at D8S1179 (135 cM, LOD score 4.2, empirical P = 0.002) and at D8S1128 (140 cM, LOD score 3.7, empirical P = 0.003). In addition, two regions supported linkage for insulin sensitivity index in the obese black families on chromosome 7q11 at D7S3046 (79 cM, LOD score 3.0, empirical P = 0.018) and on chromosome 6q26 at D6S1277 (173 cM, LOD score 3.0, empirical P = 0.018). Reducing clinical heterogeneity using obesity data and improved estimates of beta-cell function and insulin sensitivity may have permitted identification of a QTL on chromosome 8q24 for beta-cell function in the presence of estimated insulin resistance and a QTL on chromosome 7q11 for insulin sensitivity. These regions replicate previous reports for type 2 diabetes-associated traits.

Hepatocyte nuclear factor 4α (HNF4A), the gene for the maturity-onset diabetes of the young type 1 monogenic form of type 2 diabetes, is within the type 2 diabetes–linked region on chromosome 20q12-q13.1 and, consequently, is a positional candidate gene for type 2 diabetes in the general population. Previous studies have identified only a few rare coding mutations. However, recent studies suggest that single nucleotide polymorphisms (SNPs) located near the P2 (β-cell) promoter of HNF4A are associated with diabetes susceptibility. In this study, we evaluated 23 SNPs spanning 111 kb including the HNF4A gene for association with type 2 diabetes in a collection of Caucasian type 2 diabetic patients with end-stage renal disease (n = 300) and control subjects (n = 310). None of the individual SNPs were associated with type 2 diabetes in this collection of case subjects (P values ranging from 0.06 to 0.99). However, haplotype analysis identifies significant differences between haplotype frequencies in type 2 diabetic case and control subjects (P = 0.013 to P < 0.001), with two uncommon “risk” haplotypes (2.4 and 2.2% of chromosomes) and two uncommon “protective” haplotypes (7.1 and 5.0% of chromosomes) accounting for the evidence of association. Our results suggest that type 2 diabetes linked to 20q12–13 is a heterogeneous disease in which different populations may have different type 2 diabetes susceptibility loci.

Genome-wide linkage analyses were performed using a multipoint variance components method in eight study groups from four multicenter networks (whites and blacks in GenNet; whites, blacks, and Mexican Americans in GENOA; whites and blacks in HyperGEN; and Asians in SAPPHIRe) that comprise the National Heart, Lung, and Blood Institute Family Blood Pressure Program (FBPP), in order to identify quantitative trait loci (QTLs) influencing fasting glucose, insulin, and homeostasis model assessment of insulin resistance (HOMA-IR). These study populations were enriched with subjects who had elevated blood pressure. Participants fasting8 h, those with a history of type 2 diabetes, or those on antidiabetic medications were excluded from the current investigation. These three phenotypes were suitably transformed to approximate normal distributions. Each phenotype was adjusted for the effects of age, BMI, and field center separately by sex within each of the eight network ethnicity groups before genetic analysis. A total of 8,664 subjects comprising 5,923 sibpairs from 4,043 families with 365 markers were available for conducting a meta-analysis using a modified Fisher's method of combining the P values from each of the eight scans. Evidence of linkages was found on chromosome 7q36 at 163 cM, with a logarithm of odds (LOD) score of 3.21 for HOMA-IR, and on chromosome 19q13 at 88 cM, with a LOD score of 3.33 for fasting glucose. We also found suggestive linkages (LOD score/=2.2) on chromosome 7q36 at 163 cM, with LOD scores of 2.31 for fasting glucose and 2.26 for fasting insulin (versus the LOD score of 3.21 for HOMA-IR at this locus). In conclusion, QTLs were identified on chromosomes 7q36 and 19q13 for fasting glucose, insulin, and insulin resistance in large and multiple-ethnicity populations in the FBPP with good replications across several other independent studies for relevant traits. Follow-up dense mapping and association studies are warranted.

Type 2 diabetes susceptibility is determined by multiple genetic and environmental factors. Genome-wide linkage scans have localized common regions, possibly harboring susceptibility genes on chromosomes 1, 2, 12, and 20. Variability in linkage findings underscores the probable genetic heterogeneity of type 2 diabetes. Thus, we conducted a genome scan of diabetes status using maximum likelihood methods that model affection status by a liability threshold model. Hypertensive sibships and their offspring and/or parents in the Hypertension Genetic Epidemiology Network study were recruited from five field centers. The diabetes phenotype was derived using the World Health Organization criteria and adjusted for race/study center, age, age2, sex, and with and without percent body fat. In total, 567 diabetic participants were identified in 437 families. Variance component linkage analysis was performed among 1,545 Caucasians and 1,608 African Americans using race-specific marker allele frequencies. We detected a quantitative trait loci (QTLs) influencing diabetes variance (logarithm of odds = 3.4) on chromosome 22, which overlaps a positive type 2 diabetes finding among Canadian Oji-Cree Indians. We also observed suggestive evidence for linkage on chromosomes 1, 2, 5, 8, 14, 17, and 19. The identification and replication of type 2 diabetes QTLs will bring us closer to the detection of functional genes that influence diabetes susceptibility.

The PTPN1 gene codes for protein tyrosine phosphatase 1B (PTP1B) (EC 3.1.3.48), which negatively regulates insulin signaling by dephosphorylating the phosphotyrosine residues of the insulin receptor kinase activation segment. PTPN1 is located in 20q13, a genomic region linked to type 2 diabetes in multiple genetic studies. Surveys of the gene have previously identified only a few uncommon coding single nucleotide polymorphisms (SNPs). We have carried out a detailed association analysis of 23 noncoding SNPs spanning the 161-kb genomic region, which includes the PTPN1 gene. These SNPs have been assessed for association with type 2 diabetes in two independently ascertained collections of Caucasian subjects with type 2 diabetes and two control groups. Association is observed between multiple SNPs and type 2 diabetes. The most consistent evidence for association occurred with SNPs spanning the 3′ end of intron 1 of PTPN1 through intron 8 (P values ranging from 0.043 to 0.004 in one case-control set and 0.038–0.002 in a second case-control set). Analysis of the combined case-control data increased the evidence of SNP association with type 2 diabetes (P = 0.005–0.0016). All of the associated SNPs lie in a single 100-kb haplotype block that encompasses the PTPN1 gene. Analysis of haplotypes indicates a significant difference between haplotype frequencies in type 2 diabetes case and control subjects (P = 0.0035–0.0056), with one common haplotype (36%) contributing strongly to the evidence for association with type 2 diabetes. Odds ratios calculated from single SNP or haplotype data are in the proximity of 1.3. Haplotype-based calculation of population-attributable risk (PAR) results in an estimated PAR of 17–20% based on different models and assumptions. These results suggest that PTPN1 is a significant contributor to type 2 diabetes susceptibility in the Caucasian population. This risk is likely due to noncoding polymorphisms.

We formed the GEnetics of Nephropathy-an International Effort (GENIE) consortium to examine previously reported genetic associations with diabetic nephropathy (DN) in type 1 diabetes. GENIE consists of 6,366 similarly ascertained participants of European ancestry with type 1 diabetes, with and without DN, from the All Ireland-Warren 3-Genetics of Kidneys in Diabetes U.K. and Republic of Ireland (U.K.-R.O.I.) collection and the Finnish Diabetic Nephropathy Study (FinnDiane), combined with reanalyzed data from the Genetics of Kidneys in Diabetes U.S. Study (U.S. GoKinD). We found little evidence for the association of the EPO promoter polymorphism, rs161740, with the combined phenotype of proliferative retinopathy and end-stage renal disease in U.K.-R.O.I. (odds ratio [OR] 1.14, P = 0.19) or FinnDiane (OR 1.06, P = 0.60). However, a fixed-effects meta-analysis that included the previously reported cohorts retained a genome-wide significant association with that phenotype (OR 1.31, P = 2 × 10(-9)). An expanded investigation of the ELMO1 locus and genetic regions reported to be associated with DN in the U.S. GoKinD yielded only nominal statistical significance for these loci. Finally, top candidates identified in a recent meta-analysis failed to reach genome-wide significance. In conclusion, we were unable to replicate most of the previously reported genetic associations for DN, and significance for the EPO promoter association was attenuated.

P11 Type 2 diabetes is recognized as a major risk factor for atherosclerotic cardiovascular disease including subclinical atherosclerosis as measured by non-invasive procedures. However, the role of genetic factors that contribute to various measures of subclinical atherosclerosis is largely unknown. We hypothesize that subclinical atherosclerosis, measured as coronary artery calcification (CAC), will be extensive in persons with type 2 diabetes, and that its presence depends on both genetic and environmental factors. The genetic factors will result in the familial aggregation of CAC. To determine the extent of familial aggregation of CAC in the presence of type 2 diabetes, we studied 122 persons with type 2 diabetes (mean age 60 years) and 13 persons without diabetes in 56 families. CAC was measured by fast gated helical computed tomography. Other measured factors included blood pressure, body size, lipids, HbA1c, and self-reported medical history. To test for an association between CAC and these factors while accounting for the potential familial correlation of CAC, generalized estimating equations were used. CAC was detectable in 80% of persons with diabetes (median score = 84, range 0 - 5776). Extent of CAC, adjusted for age, was associated with male gender (p=0.0003), reduced HDL (p=0.02), albumin-creatinine ratio (p=0.008), and cigarette pack-years (p=0.03). CAC was also associated with a history of angina, myocardial infarction, stroke and vascular procedure (all p 2 = 0.50, p=0.009). In multivariate analysis adjusting for HDL, BMI, hypertension, and smoking, h 2 = 0.40 (p=0.038). These results suggest that strong (independent) genetic factors as well as environmental factors contribute to the variance of CAC in persons with type 2 diabetes. In these data, CAC appears heritable and may serve as an important feature in designing studies to map genes contributing to both atherosclerosis and type 2 diabetes.