Background

African Americans (AAs) have increased susceptibility to non-diabetic nephropathy relative to European Americans.

Study Design

Follow-up of a pooled genome-wide association study (GWAS) in AA dialysis patients with nondiabetic nephropathy; novel gene-gene interaction analyses.

Setting & Participants

Wake Forest sample: 962 AA nondiabetic nephropathy cases; 931 non-nephropathy controls. Replication sample: 668 Family Investigation of Nephropathy and Diabetes (FIND) AA nondiabetic nephropathy cases; 804 non-nephropathy controls.

Predictors

Individual genotyping of top 1420 pooled GWAS-associated single nucleotide polymorphisms (SNPs) and 54 SNPs in six nephropathy susceptibility genes.

Outcomes

APOL1 genetic association and additional candidate susceptibility loci interacting with, or independently from, APOL1.

Results

The strongest GWAS associations included two non-coding APOL1 SNPs, rs2239785 (odds ratio [OR], 0.33; dominant; p = 5.9 × 10−24) and rs136148 (OR, 0.54; additive; p = 1.1 × 10−7) with replication in FIND (p = 5.0 × 10−21 and 1.9 × 10−05, respectively). Rs2239785 remained significantly associated after controlling for the APOL1 G1 and G2 coding variants. Additional top hits included a CFH SNP(OR from meta-analysis in above 3367 AA cases and controls, 0.81; additive; p = 6.8 × 10−4). The 1420 SNPs were tested for interaction with APOL1 G1 and G2 variants. Several interactive SNPs were detected, the most significant was rs16854341 in the podocin gene (NPHS2) (p = 0.0001).

Limitations

Non-pooled GWAS have not been performed in AA nondiabetic nephropathy.

Conclusions

This follow-up of a pooled GWAS provides additional and independent evidence that APOL1 variants contribute to nondiabetic nephropathy in AAs and identified additional associated and interactive non-diabetic nephropathy susceptibility genes.

Features of melanocortin-4 receptor (MC4R) deficiency have been observed to be more pronounced in childhood. Longitudinal data from a population-based study were used to separate the phenotypic effects of MC4R deficiency during childhood and adulthood. The MC4R exon was sequenced in 6,760 individuals of predominantly Pima Indian heritage, and discovered mutations were functionally assessed in vitro. Effects on BMI, height, and slope of BMI change were assessed during childhood (ages 5–20 years) and adulthood (ages 20–45 years). Six mutations affecting MC4R function, including three that may be private to Pima Indians, were found in 159 individuals (2.4%). The slope of BMI increase was greater in individuals carrying an MC4R mutation compared with noncarriers during childhood but not during adulthood. The final adult height obtained was higher in individuals with MC4R deficiency. There was an increased risk for developing type 2 diabetes in individuals with a defective MC4R during childhood and adulthood, but this was only independent of BMI in childhood. The greater rates of body mass accumulation and risk of type 2 diabetes before the age of 20 years in individuals with MC4R deficiency indicate that the effects of these mutations are more apparent during the active growth of childhood.

Genetic variation in SIRT1 affects obesity-related phenotypes in several populations. The purpose of this study was to determine whether variation in SIRT1 affects susceptibility to obesity or type 2 diabetes in Pima Indians, a population with very high prevalence and incidence rates of these diseases. Genotypic data from single nucleotide polymorphisms (SNPs) identified by sequencing regions of SIRT1 combined with SNPs in/near SIRT1 from a prior genome-wide association study determined that 4 tag SNPs (rs7895833, rs10509291, rs7896005, and rs4746720) could capture information across this gene and its adjacent 5′ region. The tag SNPs were genotyped in a population-based sample of 3501 Pima Indians (44% had diabetes, 58% female) for association with type 2 diabetes and BMI. Metabolic trait data and adipose biopsies were available on a subset of these subjects. Two tag SNPs, rs10509291 and rs7896005, were nominally associated with type 2 diabetes (P = 0.01, OR = 1.25 95%CI 1.05-1.48, and P = 0.02, OR = 1.17 95%CI 1.02-1.34, respectively; additive P values adjusted for age, sex, birth year, and family membership), but not BMI (adjusted P values 0.52 and 0.45, respectively). Among metabolically characterized subjects with normal glucose tolerance (N = 243), those carrying the diabetes risk allele (T) for rs10509291 and (G) for rs7896005 had a reduced acute insulin response (AIR) to an intravenous glucose bolus (adjusted P = 0.045 and 0.035, respectively). SIRT1 expression in adipose biopsies was negatively correlated with BMI (adjusted P = 0.00001). We conclude that variation in SIRT1 is nominally associated with reduced AIR and increased risk for type 2 diabetes. SIRT1 expression in adipose is correlated with BMI, but it remains unknown whether this is a cause or consequence of obesity.

Objective

We examined the prognostic significance of elevated albuminuria in youth with type 2 diabetes.

Patients and Methods

Cross-sectional and prospective studies were conducted in Pima Indian youth aged 5-19 years at baseline who were examined between July 1, 1982 and December 31, 2007. Prevalence and sequential changes in the level of microalbuminuria (30≤ albumin-to-creatinine ratio <300 mg/g) and macroalbuminuria (albumin-to-creatinine ratio ≥300 mg/g) and incidence of macroalbuminuria were computed according to the presence or absence of type 2 diabetes.

Results

The prevalence of micro- and macroalbuminuria was 6.5% and 0.6% in the 3,856 nondiabetic youth and 18.5% and 2.9% in the 103 youth with diabetes. One-hundred-forty-one (75.4%) of 187 nondiabetic youth, but only one (7.1%) of 14 diabetic youth with elevated albumin-to-creatinine ratio (≥30 mg/g) regressed to undetectable or normal albumin-to-creatinine ratio (<30 mg/g) on subsequent examination. In a subset of 2,666 youth with a median follow-up of 8.1 years, 36 nondiabetic and 30 diabetic youth with baseline albumin-to-creatinine ratio <300 mg/g developed macroalbuminuria. For a given albumin-to-creatinine ratio level, the incidence of macroalbuminuria was 15.9-fold (95% CI = 11.1 to 22.6) higher in the diabetic than in the nondiabetic youth.

Conclusions

Elevated albuminuria is infrequent and largely transient in nondiabetic youth, but is relatively frequent and largely persistent in those with diabetes. Microalbuminuria in youth with type 2 diabetes strongly predicts progression to macroalbuminuria, supporting annual screening for albuminuria.

Diabetes affects American Indians disproportionately compared with other racial/ethnic groups in the United States and is almost exclusively type 2 diabetes. Much of our knowledge about diabetes in American Indians comes from studies in a few tribes. The most extensively studied American Indians are the Pima Indians from the Gila River Indian Community in Arizona, who participated in a longitudinal study of diabetes and its complications between 1965 and 2007. They have one of the highest reported incidence and prevalence of type 2 diabetes in the world, and kidney disease attributable to diabetes is a major cause of morbidity and mortality. In this article, we examine the course, determinants, and trends of diabetic kidney disease in American Indians, with special emphasis on studies conducted in the Pima Indians. We also review therapeutic strategies for managing diabetic kidney disease.

CNDP1 is located on 18q22.3, where linkage with diabetic nephropathy has been observed in several populations, including Pima Indians. However, evidence for association between CNDP1 alleles and diabetic nephropathy is equivocal and population-dependent. This study investigated CNDP1 as a candidate for diabetic kidney disease in Pima Indians. Nineteen tag single nucleotide polymorphisms spanning the CNDP1 locus were selected using genotype data from Chinese individuals in the HapMap resource along with 2 variants previously associated with diabetic nephropathy. All variants were genotyped in 3 different samples including a diabetic end-stage renal disease (ESRD) case-control study, a family-based study of diabetic individuals who participated in the linkage study for nephropathy, and a cohort of diabetic individuals in whom longitudinal measures of glomerular filtration rates (GFR) were performed. There was no statistically significant evidence for association with diabetic ESRD. However, nominal evidence for association was found in the family study, where markers rs12957330 (Odds ratio [OR]=0.29 per copy of G allele; p=0.04) and rs17817077 (OR=0.46 per copy of G allele; p=0.05) were associated with diabetic nephropathy. In addition, markers rs12964454, rs7244647, and rs7229005 were associated with changes in GFR (−8.5 ml/min per copy of the G allele; p=0.04; 18.8 ml/min per copy of the C allele; p=0.03; and −13.4 ml/min per copy of the C allele; p=0.001, respectively). These findings provide nominal evidence supporting a role between CNDP1 variants and diabetic kidney disease.

Background

Diabetic nephropathy (DN) is a leading cause of mortality and morbidity in patients with type 1 and type 2 diabetes. The multicenter FIND consortium aims to identify genes for DN and its associated quantitative traits, e.g. the urine albumin:creatinine ratio (ACR). Herein, the results of whole-genome linkage analysis and a sparse association scan for ACR and a dichotomous DN phenotype are reported in diabetic individuals.

Methods

A genomewide scan comprising more than 5,500 autosomal single nucleotide polymorphism markers (average spacing of 0.6 cM) was performed on 1,235 nuclear and extended pedigrees (3,972 diabetic participants) ascertained for DN from African-American (AA), American-Indian (AI), European-American (EA) and Mexican-American (MA) populations.

Results

Strong evidence for linkage to DN was detected on chromosome 6p (p = 8.0 × 10−5, LOD = 3.09) in EA families as well as suggestive evidence for linkage to chromosome 7p in AI families. Regions on chromosomes 3p in AA, 7q in EA, 16q in AA and 22q in MA displayed suggestive evidence of linkage for urine ACR. The linkage peak on chromosome 22q overlaps the MYH9/APOL1 gene region, previously implicated in AA diabetic and nondiabetic nephropathies.

Conclusion

These results strengthen the evidence for previously identified genomic regions and implicate several novel loci potentially involved in the pathogenesis of DN.

OBJECTIVE

Treatment guidelines for diabetes have become increasingly stringent as most research shows that more aggressive intervention reduces the risks for complications. Community data on the effect of these interventions are lacking.

RESEARCH DESIGN AND METHODS

Changes in the pharmacologic treatment of diabetes, blood pressure, and cholesterol in adults with diabetes were analyzed in a longitudinal population-based study of American Indians from 10 independent 3-year time intervals between 1975 and 2004. Trends in drug use were assessed by logistic regression models and trends in glycemia, blood pressure, and cholesterol were assessed by linear models.

RESULTS

Among the study participants, the use of any medicine for the treatment of diabetes increased from 53% in 1975–1978 to 67% in 2002–2004, Ptrend < 0.0001. The use of insulin as a single agent declined, and the use of combinations of insulin and oral agents increased. In 1990–1992, 23% of subjects had an A1C <7% and by 2002–2004, the proportion had increased to 33%, Ptrend < 0.0001. The use of anti-hypertensive medicine increased from 21% in 1975–1977 to 58% in 2002–2004, Ptrend < 0.0001, coincident with a decline in mean systolic blood pressure from 137 mmHg in 1975–1977 to 123 mmHg in 2002–2004, Ptrend < 0.0001. The use of lipid-lowering medicine also increased with an accompanying increase in HDL and a decrease in non-HDL cholesterol concentration.

CONCLUSIONS

Major changes in community treatment patterns for diabetes and related conditions coincided with improvements in glycemia, blood pressure, and cholesterol.

OBJECTIVE

We examined the effect of intrauterine diabetes exposure (IDE) on the incidence of diabetic end-stage renal disease (ESRD) in Pima Indians with type 2 diabetes.

RESEARCH DESIGN AND METHODS

Individuals were followed from their first diabetic examination until December 2006, death, ESRD, or age of 45 years.

RESULTS

Among the 1,850 diabetic participants, 102 had IDE. ESRD developed in 57, 5 of whom had IDE. Cumulative incidence of ESRD by age 45 was 19.3% in participants with IDE and 5.1% in those without; the age- and sex-adjusted incidence rate ratio was 4.12 (95% CI 1.54–11.02). After additional adjustment for age at diabetes onset, ESRD incidence was similar in the two groups (incidence rate ratio 1.38, 95% CI 0.45–4.24).

CONCLUSIONS

IDE increases the age- and sex-adjusted incidence of ESRD fourfold in young adults with type 2 diabetes, mediated primarily by the earlier onset of type 2 diabetes in those with IDE.

OBJECTIVE

A genome-wide association study (GWAS) in Pima Indians (n = 413) identified variation in the ataxin-2 binding protein 1 gene (A2BP1) that was associated with percent body fat. On the basis of this association and the obese phenotype of ataxin-2 knockout mice, A2BP1 was genetically and functionally analyzed to assess its potential role in human obesity.

RESEARCH DESIGN AND METHODS

Variants spanning A2BP1 were genotyped in a population-based sample of 3,234 full-heritage Pima Indians, 2,843 of whom were not part of the initial GWAS study and therefore could serve as a sample to assess replication. Published GWAS data across A2BP1 were additionally analyzed in French adult (n = 1,426) and children case/control subjects (n = 1,392) (Meyre et al. Nat Genet 2009;41:157–159). Selected variants were genotyped in two additional samples of Caucasians (Amish, n = 1,149, and German children case/control subjects, n = 998) and one additional Native American (n = 2,531) sample. Small interfering RNA was used to knockdown A2bp1 message levels in mouse embryonic hypothalamus cells.

RESULTS

No single variant in A2BP1 was reproducibly associated with obesity across the different populations. However, different variants within intron 1 of A2BP1 were associated with BMI in full-heritage Pima Indians (rs10500331, P = 1.9 × 10−7) and obesity in French Caucasian adult (rs4786847, P = 1.9 × 10−10) and children (rs8054147, P = 9.2 × 10−6) case/control subjects. Reduction of A2bp1 in mouse embryonic hypothalamus cells decreased expression of Atxn2, Insr, and Mc4r.

CONCLUSIONS

Association analysis suggests that variation in A2BP1 influences obesity, and functional studies suggest that A2BP1 could potentially affect adiposity via the hypothalamic MC4R pathway.

OBJECTIVE

Genome-wide association studies have begun to elucidate the genetic architecture of type 2 diabetes. We examined whether single nucleotide polymorphisms (SNPs) identified through targeted complementary approaches affect diabetes incidence in the at-risk population of the Diabetes Prevention Program (DPP) and whether they influence a response to preventive interventions.

RESEARCH DESIGN AND METHODS

We selected SNPs identified by prior genome-wide association studies for type 2 diabetes and related traits, or capturing common variation in 40 candidate genes previously associated with type 2 diabetes, implicated in monogenic diabetes, encoding type 2 diabetes drug targets or drug-metabolizing/transporting enzymes, or involved in relevant physiological processes. We analyzed 1,590 SNPs for association with incident diabetes and their interaction with response to metformin or lifestyle interventions in 2,994 DPP participants. We controlled for multiple hypothesis testing by assessing false discovery rates.

RESULTS

We replicated the association of variants in the metformin transporter gene SLC47A1 with metformin response and detected nominal interactions in the AMP kinase (AMPK) gene STK11, the AMPK subunit genes PRKAA1 and PRKAA2, and a missense SNP in SLC22A1, which encodes another metformin transporter. The most significant association with diabetes incidence occurred in the AMPK subunit gene PRKAG2 (hazard ratio 1.24, 95% CI 1.09–1.40, P = 7 × 10−4). Overall, there were nominal associations with diabetes incidence at 85 SNPs and nominal interactions with the metformin and lifestyle interventions at 91 and 69 mostly nonoverlapping SNPs, respectively. The lowest P values were consistent with experiment-wide 33% false discovery rates.

CONCLUSIONS

We have identified potential genetic determinants of metformin response. These results merit confirmation in independent samples.

OBJECTIVE

MBL2 encodes the mannose-binding lectin, which is a key player in the innate immune system and has recently been found to play a role in insulin resistance and development of type 1 diabetes and gestational diabetes mellitus. To assess the role of MBL2 in diabetes susceptibility, this gene was analyzed in the Pima Indian population, which has a high prevalence of type 2 diabetes.

RESEARCH DESIGN AND METHODS

Nineteen tag single nucleotide polymorphisms (SNPs) were genotyped in a population-based sample of 3,501 full-heritage Pima Indians, and selected SNPs were further genotyped in independent samples of Native American (n = 3,723) and Old Order Amish (n = 486) subjects.

RESULTS

Two variants, a promoter SNP (rs11003125) at −550 bp with a risk allele frequency of 0.77 and a Gly54Asp (rs1800450) with a risk allele frequency of 0.83, were associated with type 2 diabetes in the full-heritage Pima Indians (odds ratio 1.30 per copy of the G allele for rs1103125, P = 0.0007, and 1.30 per copy of the glycine allele for rs1800450, P = 0.002, adjusted for age, sex, birth year, and family membership). These associations replicated in an independent Native American sample (1.19, P = 0.04, for rs11003125) and a Caucasian sample, the Old Order Amish (1.51, P = 0.004, for rs1103125 and 2.38, P = 0.003, for rs1800450). Among Pima Indians with normal glucose tolerance, the diabetes risk allele glycine of Gly54Asp was associated with a decreased acute insulin response to an intravenous glucose bolus infusion (P = 0.004, adjusted for age, sex, percent body fat, glucose disposal under physiological insulin stimulation, and family membership).

CONCLUSIONS

Our data suggest that the functional variants in MBL2 contribute to type 2 diabetes susceptibility in both Native Americans and the Old Order Amish.

OBJECTIVE

Prior genome-wide association and exon array expression studies both provided suggestive evidence that apoptosis signal regulating kinase 1 (ASK1) may influence in vivo insulin action in Pima Indians. Genetic variants in or near ASK1 were analyzed to assess the role of this gene in insulin action and type 2 diabetes.

RESEARCH DESIGN AND METHODS

Genotypic data from 31 variants were used to determine the linkage disequilibrium pattern across ASK1 in Pima Indians. Eight tag SNPs were initially genotyped in 3,501 full-heritage Pima Indians. Replication for association with diabetes was assessed in a second population-based sample of 3,723 Native Americans and the published DIAGRAM study. Quantitative traits were analyzed in 536 nondiabetic Native Americans, and ASK1 expression was examined in skeletal muscle of 153 nondiabetic Native Americans.

RESULTS

Three tag SNPs were associated with type 2 diabetes (rs35898099, P = 0.003, odds ratio [95% CI] 1.27 [1.08–1.47]; rs1570056, P = 0.007, 1.19 [1.05–1.36]; rs7775356, P = 0.04, 1.14 [1.01–1.28]) in the full-heritage Pima Indians. The association with rs35898099 was replicated in a second sample of Native Americans (P = 0.04, 1.22 [1.01–1.47]), while that for rs1570056 was replicated in the DIAGRAM study of Caucasians (Z statistic based P = 0.026; fixed-effect model, 1.06 [1.00–1.12]). The diabetes risk allele for rs1570056 was associated with reduced insulin action as assessed by either HOMA-IR in 2,549 nondiabetic full-heritage Pima Indians (P = 0.027) or a hyperinsulinemic-euglycemic clamp among 536 nondiabetic Native Americans (P = 0.02). Real-time PCR identified a positive correlation between ASK1 expression in skeletal muscle biopsies and in vivo insulin action (P = 0.02, r = 0.23), and the risk allele for rs1570056 was associated with lower ASK1 expression (P = 0.003, r = −0.22).

CONCLUSIONS

ASK1 variants may increase susceptibility to type 2 diabetes by decreasing insulin sensitivity via reduced ASK1 expression.

Acetyl coenzyme A carboxylase B gene (ACACB) single nucleotide polymorphism (SNP) rs2268388 is reproducibly associated with type 2 diabetes (T2DM)-associated nephropathy (DN). ACACB knock-out mice are also protected from obesity. This study assessed relationships between rs2268388, body mass index (BMI) and gene expression in multiple populations, with and without T2DM. Among subjects without T2DM, rs2268388 DN risk allele (T) associated with higher BMI in Pima Indian children (n = 2021; p-additive = 0.029) and African Americans (AAs) (n = 177; p-additive = 0.05), with a trend in European Americans (EAs) (n = 512; p-additive = 0.09), but not Germans (n = 858; p-additive = 0.765). Association with BMI was seen in a meta-analysis including all non-T2DM subjects (n = 3568; p-additive = 0.02). Among subjects with T2DM, rs2268388 was not associated with BMI in Japanese (n = 2912) or EAs (n = 1149); however, the T allele associated with higher BMI in the subset with BMI≥30 kg/m2 (n = 568 EAs; p-additive = 0.049, n = 196 Japanese; p-additive = 0.049). Association with BMI was strengthened in a T2DM meta-analysis that included an additional 756 AAs (p-additive = 0.080) and 48 Hong Kong Chinese (p-additive = 0.81) with BMI≥30 kg/m2 (n = 1575; p-additive = 0.0033). The effect of rs2268388 on gene expression revealed that the T risk allele associated with higher ACACB messenger levels in adipose tissue (41 EAs and 20 AAs with BMI>30 kg/m2; p-additive = 0.018) and ACACB protein levels in the liver tissue (mixed model p-additive = 0.03, in 25 EA bariatric surgery patients with BMI>30 kg/m2 for 75 exams). The T allele also associated with higher hepatic triglyceride levels. These data support a role for ACACB in obesity and potential roles for altered lipid metabolism in susceptibility to DN.

Background

Many human diseases and phenotypes are related to RNA expression, levels of which are influenced by a wide spectrum of genetic and exposure-related factors. In a large genome-wide study of muscle tissue expression, we found that some genes exhibited a bimodal distribution of RNA expression, in contrast to what is usually assumed in studies of a single healthy tissue. As bimodality has classically been considered a hallmark of genetic control, we assessed the genome-wide prevalence, cause, and association of this phenomenon with diabetes-related phenotypes in skeletal muscle tissue from 225 healthy Pima Indians using exon array expression chips.

Results

Two independent batches of microarrays were used for bimodal assessment and comparison. Of the 17,881 genes analyzed, eight (GSTM1, HLA-DRB1, ERAP2, HLA-DRB5, MAOA, ACTN3, NR4A2, and THNSL2) were found to have bimodal expression replicated in the separate batch groups, while 24 other genes had evidence of bimodality in only one group. Some bimodally expressed genes had modest associations with pre-diabetic phenotypes, of note ACTN3 with insulin resistance. Most of the other bimodal genes have been reported to be involved with various other diseases and characteristics. Association of expression with cis genetic variation in a subset of 149 individuals found all but one of the confirmed bimodal genes and nearly half of all potential ones to be highly significant expression quantitative trait loci (eQTL). The rare prevalence of these bimodally expressed genes found after controlling for batch effects was much lower than the prevalence reported in other studies. Additional validation in data from separate muscle expression studies confirmed the low prevalence of bimodality we observed.

Conclusions

We conclude that the prevalence of bimodal gene expression is quite rare in healthy muscle tissue (<0.2%), and is much lower than limited reports from other studies. The major cause of these clearly bimodal expression patterns in homogeneous tissue appears to be cis-polymorphisms, indicating that such bimodal genes are, for the most part, eQTL. The high frequency of disease associations reported with these genes gives hope that this unique feature may identify or actually be an underlying factor responsible for disease development.

Background

A limited body of evidence, mostly based on self-report, is available regarding physical activity levels among American-Indian adults.

Purpose

This study aims to examine physical activity levels objectively by pedometer among a large cohort of American Indian adult participants in the Strong Heart Family Study.

Methods

Physical activity levels in 2604 American-Indian adults, aged 18–91 years, from 13 American-Indian communities were assessed using an Accusplit AE120 pedometer over a period of 7 days during 2001–2003. Anthropometric measurements were also assessed. All data analyses were conducted in 2008. Age-adjusted Pearson correlations were used to examine the relationship between average steps per day and age and anthropometric variables. Subjects were placed in age and BMI categories (according to NHLBI cutpoints) to examine trends in PA with increasing age and BMI.

Results

Daily pedometer steps ranged from 1001 to 38,755. Mean step counts by age group for men were: 5384 (18–29 years), 5120 (30–39 years), 5040 (40–49 years), 4561(50–59 years),4321 (60–69 years), and 3768 (≥70 years) and for women: 5038 (18–29 years), 5112 (30– 39 years), 5054 (40–49 years), 4582 (50–59 years), 3653 (60–69 years), and 3770 (>70 years). A significant linear trend in physical activity was noted with increasing age (P= 0.002 for men, P<0.0001 for women) and with increasing BMI (P = 0.05 for men, P = 0.04 for women).

Conclusions

Objectively measured data suggest that inactivity is a problem among American Indian adults and that a majority of American Indian adults in the SHFS may not be meeting the minimum physical activity public health recommendations. Efforts to increase physical activity levels in this population are warranted.

Background

The effect of childhood risk factors for cardiovascular disease on adult mortality is poorly understood.

Methods

In a cohort of 4857 American Indian children without diabetes (mean age, 11.3 years; 12,659 examinations) who were born between 1945 and 1984, we assessed whether body-mass index (BMI), glucose tolerance, and blood pressure and cholesterol levels predicted premature death. Risk factors were standardized according to sex and age. Proportional-hazards models were used to assess whether each risk factor was associated with time to death occurring before 55 years of age. Models were adjusted for baseline age, sex, birth cohort, and Pima or Tohono O'odham Indian heritage.

Results

There were 166 deaths from endogenous causes (3.4% of the cohort) during a median follow-up period of 23.9 years. Rates of death from endogenous causes among children in the highest quartile of BMI were more than double those among children in the lowest BMI quartile (incidence-rate ratio, 2.30; 95% confidence interval [CI], 1.46 to 3.62). Rates of death from endogenous causes among children in the highest quartile of glucose intolerance were 73% higher than those among children in the lowest quartile (incidence-rate ratio, 1.73; 95% CI, 1.09 to 2.74). No significant associations were seen between rates of death from endogenous or external causes and childhood cholesterol levels or systolic or diastolic blood-pressure levels on a continuous scale, although childhood hypertension was significantly associated with premature death from endogenous causes (incidence-rate ratio, 1.57; 95% CI, 1.10 to 2.24).

Conclusions

Obesity, glucose intolerance, and hypertension in childhood were strongly associated with increased rates of premature death from endogenous causes in this population. In contrast, childhood hypercholesterolemia was not a major predictor of premature death from endogenous causes.

OBJECTIVE

Linkage of the chromosome 1q21–25 region to type 2 diabetes has been demonstrated in multiple ethnic groups. We performed common variant fine-mapping across a 23-Mb interval in a multiethnic sample to search for variants responsible for this linkage signal.

RESEARCH DESIGN AND METHODS

In all, 5,290 single nucleotide polymorphisms (SNPs) were successfully genotyped in 3,179 type 2 diabetes case and control subjects from eight populations with evidence of 1q linkage. Samples were ascertained using strategies designed to enhance power to detect variants causal for 1q linkage. After imputation, we estimate ∼80% coverage of common variation across the region (r 2 > 0.8, Europeans). Association signals of interest were evaluated through in silico replication and de novo genotyping in ∼8,500 case subjects and 12,400 control subjects.

RESULTS

Association mapping of the 23-Mb region identified two strong signals, both of which were restricted to the subset of European-descent samples. The first mapped to the NOS1AP (CAPON) gene region (lead SNP: rs7538490, odds ratio 1.38 [95% CI 1.21–1.57], P = 1.4 × 10−6, in 999 case subjects and 1,190 control subjects); the second mapped within an extensive region of linkage disequilibrium that includes the ASH1L and PKLR genes (lead SNP: rs11264371, odds ratio 1.48 [1.18–1.76], P = 1.0 × 10−5, under a dominant model). However, there was no evidence for association at either signal on replication, and, across all data (>24,000 subjects), there was no indication that these variants were causally related to type 2 diabetes status.

CONCLUSIONS

Detailed fine-mapping of the 23-Mb region of replicated linkage has failed to identify common variant signals contributing to the observed signal. Future studies should focus on identification of causal alleles of lower frequency and higher penetrance.

OBJECTIVE

Haploinsufficiency of SIM1 is a cause of rare monogenic obesity. To assess the role of SIM1 in polygenic obesity, this gene was analyzed in the Pima Indian population, which has a high prevalence of obesity.

RESEARCH DESIGN AND METHODS

SIM1 was sequenced in 96 individuals. Variants (n = 46) were genotyped in a population-based sample of 3,250 full-heritage Pima Indians and in a separate replication sample of 2,944 predominately non–full-heritage subjects from the same community.

RESULTS

Variants spanning the upstream region of SIM1 through intron 8 were associated with BMI in the full-heritage Pima Indians, where the strongest associations (P ∼ 10−4 to 10−6) were with common variants (risk allele frequency 0.61–0.67). The difference in mean BMI between individuals homozygous for the major allele compared with homozygotes for the minor allele was ∼2.2 kg/m2 (P = 2 × 10−5 for rs3213541). These associations replicated in the separate sample of subjects from the same community (P = 5 × 10−3 for rs3213541). The strongest associations (P = 4 × 10−7, controlled for age, sex, birth year, and heritage) were seen in the combined sample (n = 6,194). The risk allele for obesity was more common in full-heritage Pimas than in the mixed-heritage subjects. Two variants (rs3734353 and rs3213541) were also genotyped in 1,275 severely obese and 1,395 lean control subjects of French European ancestry. The Pima risk alleles were the minor alleles in the European samples, and these variants did not display any significant association (P > 0.05).

CONCLUSIONS

Common variation in SIM1 is associated with BMI on a population level in Pima Indians where the risk allele is the major allele.

OBJECTIVE—In recent genome-wide association studies, variants in CDKAL1, SLC30A8, HHEX, EXT2, IGF2BP2, CDKN2B, LOC387761, and FTO were associated with risk for type 2 diabetes in Caucasians. We investigated the association of these single nucleotide polymorphisms (SNPs) and some additional tag SNPs with type 2 diabetes and related quantitative traits in Pima Indians.

RESEARCH DESIGN AND METHODS—Forty-seven SNPs were genotyped in 3,501 Pima Indians informative for type 2 diabetes and BMI, among whom 370 had measures of quantitative traits.

RESULTS—FTO provided the strongest evidence for replication, where SNPs were associated with type 2 diabetes (odds ratio = 1.20 per copy of the risk allele, P = 0.03) and BMI (P = 0.002). None of the other previously reported SNPs were associated with type 2 diabetes; however, associations were found between CDKAL1 and HHEX variants and acute insulin response (AIR), where the Caucasian risk alleles for type 2 diabetes were associated with reduced insulin secretion in normoglycemic Pima Indians. Multiallelic analyses of carrying risk alleles for multiple genes showed correlations between number of risk alleles and type 2 diabetes and impaired insulin secretion in normoglycemic subjects (P = 0.006 and 0.0001 for type 2 diabetes and AIR, respectively), supporting the hypothesis that many of these genes influence diabetes risk by affecting insulin secretion.

CONCLUSIONS—Variation in FTO impacts BMI, but the implicated common variants in the other genes did not confer a significant risk for type 2 diabetes in Pima Indians. However, confidence intervals for their estimated effects were consistent with the small effects reported in Caucasians, and the multiallelic “genetic risk profile” identified in Caucasians is associated with diminished early insulin secretion in Pima Indians.

Objective

Linkage of the chromosome 1q21-25 region to type 2 diabetes has been demonstrated in multiple ethnic groups. We performed common variant fine-mapping across a 23Mb interval in a multiethnic sample to search for variants responsible for this linkage signal.

Research Design and Methods

In all, 5,290 SNPs were successfully genotyped in 3,179 T2D cases and controls from eight populations with evidence of 1q linkage. Samples were ascertained using strategies designed to enhance power to detect variants causal for 1q-linkage. Following imputation, we estimate ~80% coverage of common variation across the region (r2>0.8, Europeans). Association signals of interest were evaluated through in silico replication and de novo genotyping in approximately 8,500 cases and 12,400 controls.

Results

Association mapping of the 23Mb region identified two strong signals, both restricted to the subset of European-descent samples. The first mapped to the NOS1AP (CAPON) gene region (lead SNP: rs7538490, OR 1.38 (95% CI, 1.21-1.57), p=1.4×10-6 in 999 cases and 1,190 controls): the second within an extensive region of linkage disequilibrium that includes the ASH1L and PKLR genes (lead SNP: rs11264371, OR 1.48 [1.18-1.76], p=1.0×10-5, under a dominant model). However, there was no evidence for association at either signal on replication, and, across all data (>24,000 subjects), no indication that these variants were causally-related to T2D status.

Conclusion

Detailed fine-mapping of the 23Mb region of replicated linkage has failed to identify common variant signals contributing to the observed signal. Future studies should focus on identification of causal alleles of lower frequency and higher penetrance.

OBJECTIVE—Humans with functional variants in the melanocortin 4 receptor (MC4R) are obese, hyperphagic, and hyperinsulinemic but have been reported to have no difference in energy expenditure.

RESEARCH DESIGN AND METHODS—We investigated the association of two MC4R variants, Arg165Gln (R165Q) and A insertion at nucleotide 100 (NT100), with adiposity in 3,074 full-heritage Pima Indians, a subset of whom had metabolic measures including 24-h energy expenditure (n = 252) and resting metabolic rate (RMR) (n = 364).

RESULTS—Among the 3,074 subjects, 43 were heterozygous for R165Q and 14 for NT100 (frequency = 0.007 and 0.002). Mean (± SD) BMI was higher among subjects with R165Q (39.3 ± 8.6 kg/m2) or NT100 (41.2 ± 7.8) than subjects without either variant (37.1 ± 8.4) (P = 0.04 and 0.02, adjusted for age, sex, and birth year and accounting for family membership). The 24-h energy expenditure (four with NT100; three with R165Q) or RMR (six with NT100; two with R165Q) was lower in heterozygous subjects but only met statistical significance when heterozygous subjects were combined and compared with subjects without either variant: least-squares means, 2,163 kcal/24 h (95% CI 2,035–2,291) vs. 2,307 kcal/24 h (2,285–2,328), P = 0.03 for 24-h energy expenditure, and 1,617 kcal/24 h (1,499–1,734) vs. 1,754 kcal/24 h (1,736–1,772), P = 0.02 for RMR; adjusted for age, sex, fat-free mass, and fat mass). For RMR, this difference persisted, even after accounting for family membership.

CONCLUSIONS—Pima Indians heterozygous for R165Q or NT100 in MC4R have higher BMIs and lower energy expenditure (by ∼140 kcal/day), indicating that lower energy expenditure was a component of the increased adiposity.

Pima Indians from the Gila River Indian Community in Arizona have a high incidence rate of type 2 diabetes, and kidney disease attributable to diabetes is a major cause of morbidity and mortality in this population. Since 1965, each member of the population at least 5 years of age is invited to participate in a research examination every other year. During the past 43 years, the overall incidence of diabetes in the Pima Indians has not changed, but the incidence of diabetes among those less than 15 years of age has increased nearly 6-fold, as an increasing prevalence and degree of obesity in the youth has shifted the onset of diabetes to younger ages. The rising frequency of diabetes in the youth has led, in turn, to the emergence in mid-life of the major complications of diabetes, including kidney disease. On the other hand, the introduction and widespread use of medicines to control blood pressure, reduce hyperglycemia, and block the renin-angiotensin system has lead to improvements in the average blood pressure and glycosylated hemoglobin levels in the diabetic population. These countervailing forces have influenced the course of diabetic nephropathy in a generally favorable direction in the past few years, as evidenced by the decline in the overall incidence of end-stage kidney disease since 1990. A continued increase in the incidence of type 2 diabetes in youth, however, threatens to reverse this trend.

OBJECTIVE—A prior genome-wide association (GWA) study in Pima Indians identified variants within PCLO that were associated with early-onset type 2 diabetes. PCLO encodes a presynaptic cytomatrix protein that functions as a Ca2+ sensor that may be involved in insulin secretion and/or insulin action. Therefore, PCLO was analyzed as a candidate gene for type 2 diabetes.

RESEARCH DESIGN AND METHODS—Sequencing of PCLO identified four nonsynonymous variants and a 10–amino acid insertion. These variants, together with 100 additional variants identified by sequencing or chosen from databases, were genotyped for association analysis in the same 895 subjects analyzed in the prior GWA study (300 case subjects with diabetes onset at aged <25 years, 334 nondiabetic control subjects aged >45 years, and 261 discordant siblings of the case or control subjects for within-family analyses), as well as 415 nondiabetic Pima Indians who had been metabolically phenotyped for predictors of diabetes. Selected variants were further genotyped in a population-based sample of 3,501 Pima Indians.

RESULTS—Four variants were modestly associated with early-onset type 2 diabetes in both general and within-family analyses (P = 0.004–0.04, recessive model), where the diabetes risk allele was also nominally associated with a lower insulin-mediated glucose disposal rate (P = 0.009–0.14, recessive model) in nondiabetic Pima Indians. However, their association with diabetes in the population-based sample was weaker (P = 0.02–0.20, recessive model).

CONCLUSIONS—Variation within PCLO may have a modest effect on early-onset type 2 diabetes, possibly as a result of reduced insulin action, but has minimal, if any, impact on population-based risk for type 2 diabetes.

OBJECTIVE— Genome-wide association scans (GWASs) have identified novel diabetes-associated genes. We evaluated how these variants impact diabetes incidence, quantitative glycemic traits, and response to preventive interventions in 3,548 subjects at high risk of type 2 diabetes enrolled in the Diabetes Prevention Program (DPP), which examined the effects of lifestyle intervention, metformin, and troglitazone versus placebo.

RESEARCH DESIGN AND METHODS— We genotyped selected single nucleotide polymorphisms (SNPs) in or near diabetes-associated loci, including EXT2, CDKAL1, CDKN2A/B, IGF2BP2, HHEX, LOC387761, and SLC30A8 in DPP participants and performed Cox regression analyses using genotype, intervention, and their interactions as predictors of diabetes incidence. We evaluated their effect on insulin resistance and secretion at 1 year.

RESULTS— None of the selected SNPs were associated with increased diabetes incidence in this population. After adjustments for ethnicity, baseline insulin secretion was lower in subjects with the risk genotype at HHEX rs1111875 (P = 0.01); there were no significant differences in baseline insulin sensitivity. Both at baseline and at 1 year, subjects with the risk genotype at LOC387761 had paradoxically increased insulin secretion; adjustment for self-reported ethnicity abolished these differences. In ethnicity-adjusted analyses, we noted a nominal differential improvement in β-cell function for carriers of the protective genotype at CDKN2A/B after 1 year of troglitazone treatment (P = 0.01) and possibly lifestyle modification (P = 0.05).

CONCLUSIONS— We were unable to replicate the GWAS findings regarding diabetes risk in the DPP. We did observe genotype associations with differences in baseline insulin secretion at the HHEX locus and a possible pharmacogenetic interaction at CDKNA2/B.