We aimed to identify factors that are independently associated with the metabolic clearance rate of insulin (MCRI) and to examine the association of MCRI with incident type 2 diabetes in nondiabetic Hispanics and African Americans.
RESEARCH DESIGN AND METHODS
We investigated 1,116 participants in the Insulin Resistance Atherosclerosis Study (IRAS) Family Study with baseline examinations from 2000 to 2002 and follow-up examinations from 2005 to 2006. Insulin sensitivity (SI), acute insulin response (AIR), and MCRI were determined at baseline from frequently sampled intravenous glucose tolerance tests. MCRI was calculated as the ratio of the insulin dose over the incremental area under the curve of insulin. Incident diabetes was defined as fasting glucose ≥126 mg/dL or antidiabetic medication use by self-report.
We observed that SI and HDL cholesterol were independent positive correlates of MCRI, whereas fasting insulin, fasting glucose, subcutaneous adipose tissue, visceral adipose tissue, and AIR were independent negative correlates (all P < 0.05) at baseline. After 5 years of follow-up, 71 (6.4%) participants developed type 2 diabetes. Lower MCRI was associated with a higher risk of incident diabetes after adjusting for demographics, lifestyle factors, HDL cholesterol, indexes of obesity and adiposity, and insulin secretion (odds ratio 2.01 [95% CI 1.30–3.10], P = 0.0064, per one-SD decrease in loge-transformed MCRI).
Our data showed that lower MCRI predicts the incidence of type 2 diabetes.
Common genetic variation frequently accounts for only a modest amount of inter-individual variation in quantitative traits and complex disease susceptibility. Circulating adiponectin, an adipocytokine implicated in metabolic disease, is a model for assessing the contribution of genetic and clinical factors to quantitative trait variation. The adiponectin locus, ADIPOQ, is the primary source of genetically-mediated variation in plasma adiponectin levels. This study sought to define the genetic architecture of ADIPOQ in the comprehensively phenotyped Hispanic (n=1151) and African American (n=574) participants from the Insulin Resistance Atherosclerosis Family Study (IRASFS). Through resequencing and bioinformatic analysis, rare/low frequency (<5% MAF) and common variants (>5% MAF) in ADIPOQ were identified. Genetic variants and clinical variables were assessed for association with adiponectin levels and contribution to adiponectin variance in the Hispanic and African American cohorts. Clinical traits accounted for the greatest proportion of variance (POV) at 31% (p=1.16×10−47) and 47% (p=5.82×10−20), respectively. Rare/low frequency variants contributed more than common variants to variance in Hispanics: POV=18% (p= 6.40×10−15) and POV=5% (p=0.19), respectively. In African Americans, rare/low frequency and common variants both contributed approximately equally to variance: POV=6% (p=5.44×10−12) and POV=9% (P=1.44×10−10), respectively. Importantly, single low frequency alleles in each ethnic group were as important as, or more important than, common variants in explaining variation in adiponectin. Cumulatively, these clinical and ethnicity-specific genetic contributors explained half or more of the variance in Hispanic and African Americans and provide new insight into the sources of variation for this important adipocytokine.
adiponectin; proportion of variation; rare variants; common variants; clinical traits
The objective of this study was to examine whether lifestyle factors were associated with 5-year change in abdominal fat measured by computed tomography (CT) in the Insulin Resistance and Atherosclerosis (IRAS) Family Study. We obtained abdominal CT scans at baseline and at 5 years, from African Americans (AA) (N = 339) and Hispanic Americans (N = 775), aged 18–81 years. Visceral (VAT) and subcutaneous (SAT) adipose tissue was measured at the L4/L5 vertebral level. Physical activity was documented by self-report of vigorous activity and a 1-year recall instrument. Dietary intake was assessed at follow-up using a semi-quantitative food frequency questionnaire referencing the previous year. Generalized linear models, accounting for family structure, were used to assess the associations between percent change in fat accumulation and smoking, physical activity, total calories, polyunsaturated, monounsaturated, protein, and saturated fat intake, percent of calories from sweets, and soluble and insoluble fiber. Soluble fiber intake and participation in vigorous activity were inversely related to change in VAT, independent of change in BMI. For each 10 g increase in soluble fiber, rate of VAT accumulation decreased by 3.7% (P = 0.01). Soluble fiber was not associated with change in SAT (0.2%, P = 0.82). Moderately active participants had a 7.4% decrease in rate of VAT accumulation and a 3.6% decrease in rate of SAT accumulation versus less active participants (P = 0.003 and P = 0.01, respectively). Total energy expenditure was also inversely associated with accumulation of VAT. Soluble fiber intake and increased physical activity were related to decreased VAT accumulation over 5 years.
Previously, we examined 20 non-HLA SNPs for association with islet autoimmunity (IA) and/or progression to type 1 diabetes (T1D). Our objective was to investigate fourteen additional non-HLA T1D candidate SNPs for stage- and age-related heterogeneity in the etiology of T1D. Of 1634 non-Hispanic white DAISY children genotyped, 132 developed IA (positive for GAD, insulin, or IA-2 autoantibodies at two or more consecutive visits); 50 IA positive children progressed to T1D. Cox regression was used to analyze risk of IA and progression to T1D in IA positive children. Restricted cubic splines were used to model SNPs when there was evidence that risk was not constant with age. C1QTNF6 (rs229541) predicted increased IA risk (HR: 1.57, CI: 1.20–2.05) but not progression to T1D (HR: 1.13, CI: 0.75–1.71). SNP (rs10517086) appears to exhibit an age-related effect on risk of IA, with increased risk before age 2 years (age 2 HR: 1.67, CI: 1.08–2.56) but not older ages (age 4 HR: 0.84, CI: 0.43–1.62). C1QTNF6 (rs229541), SNP (rs10517086), and UBASH3A (rs3788013) were associated with development of T1D. This prospective investigation of non-HLA T1D candidate loci shows that some SNPs may exhibit stage- and age-related heterogeneity in the etiology of T1D.
Adiponectin is an adipocytokine associated with a variety of metabolic traits. These associations in human studies, in conjunction with functional studies in model systems, have implicated adiponectin in multiple metabolic processes.
We hypothesize that genetic variants associated with plasma adiponectin would also be associated with glucose homeostasis and adiposity phenotypes.
Design and Setting
The Insulin Resistance Atherosclerosis Family Study was designed to identify the genetic and environmental basis of insulin resistance and adiposity in the Hispanic- (n=1,424) and African-American (n=604) population.
Main Outcome Measures
High quality metabolic phenotypes, e.g. insulin sensitivity (SI), acute insulin response (AIR), disposition index (DI), fasting glucose, body mass index (BMI), visceral adipose tissue (VAT), subcutaneous adipose tissue (SAT), and waist circumference, were explored.
Based on association analysis of more than 40 genetic polymorphisms in the adiponectin gene (ADIPOQ), we found no consistent association of ADIPOQ variants with plasma adiponectin levels and adiposity phenotypes. However, there were two promoter variants, rs17300539 and rs822387, associated with plasma adiponectin levels (P=0.0079 and 0.021, respectively) in the Hispanic-American cohort that were also associated with SI (P=0.0067 and 0.013, respectively). In contrast, there was only a single promoter SNP, rs17300539, associated with plasma adiponectin levels (P=0.0018) and fasting glucose (P=0.042) in the African-American cohort. Strikingly, high impact coding variants did not show evidence of association.
The lack of consistent patterns of association between variants, adiponectin levels, glucose homeostasis, and adiposity phenotypes suggests a reassessment of the influence of adiponectin in these pathways.
adiponectin; single nucleotide polymorphisms; glucose homeostasis; adiposity; African Americans; Hispanic Americans
Type 1 diabetes is a common chronic childhood disease, and the incidence is increasing globally. Childhood infections are considered a potential environmental trigger of type 1 diabetes. Alternatively, improved hygiene and reduced childhood infections could explain the increase in type 1 diabetes in developed countries. The association of reported illnesses during infancy and later development of islet autoimmunity (IA) were examined in the Diabetes Autoimmunity Study in the Young.
RESEARCH DESIGN AND METHODS
Complete illness interviews through 9 months of age were collected for 1,729 children—1,174 without a family history of type 1 diabetes and 555 with a first-degree relative with type 1 diabetes. Persistent IA was defined as positive antibodies to insulin, glutamic acid decarboxylase, or tyrosine phosphatase on at least two consecutive study visits.
There were 109 children with persistent IA among the 1,729 children with illness records. A greater number of gastrointestinal illnesses were associated with an increased risk of IA, but only among children who were exposed to gluten-containing grains (wheat or barley) either <4 months of age (hazard ratio 1.37 [95% CI 1.22–1.55]; P < 0.0001) or ≥7 months of age (1.12 [1.05–1.19]; P = 0.0005) compared with 4–6 months of age (P for interaction = 0.02). There were no associations of upper respiratory symptoms, respiratory illnesses, or fevers with IA.
Specific pathogens such as enteroviruses or rotavirus may increase the risk of IA in the presence of existing inflammation induced by diet.
Autoimmune diseases (AID) are a collection of many complex disorders of unknown etiology resulting in immune responses to self-antigens and are thought to result from interactions between genetic and environmental factors. Here we review the epidemiologic evidence for the role of environmental factors in the development of human AID, the conclusions that can be drawn from the existing data, critical knowledge gaps, and research needed to fill these gaps and to resolve uncertainties. We specifically summarize the state of knowledge and our levels of confidence in the role of specific agents in the development of autoimmune diseases, and we define the areas of greatest impact for future investigations. Among our consensus findings we are confident that: 1) crystalline silica exposure can contribute to the development of several AID; 2) solvent exposure can contribute to the development of systemic sclerosis; 3) smoking can contribute to the development of seropositive rheumatoid arthritis; and 4) an inverse association exists between ultraviolet radiation exposure and the risk of development of multiple sclerosis. We suggest that more studies of phenotypes, genotypes, and multiple exposures are needed. Additional knowledge gaps needing investigation include: defining important windows in the timing of exposures and latencies relating to age, developmental state, and hormonal changes; understanding dose-response relationships; and elucidating mechanisms for disease development. Addressing these essential issues will require more resources to support research, particularly of rare AID, but knowledge of the risks conferred by environmental factors in specific genetic contexts could pave the way for prevention of AID in the future.
autoimmune disease; environmental risk factors; biologic agents; chemical agents; physical factors; research priorities
To examine the relationship of Porphyromonas gingivalis (Pg) with the presence of autoantibodies in individuals at risk for rheumatoid arthritis (RA).
Participants included: 1) a cohort enriched with HLA-DR4 and 2) those at risk for RA by virtue of having a first-degree relative with RA. None satisfied 1987 ACR RA classification criteria. Autoantibodies measured included anti-citrullinated protein antibody (ACPA) and rheumatoid factor (RF; nephelometry, IgA, IgM, IgG). Individuals were considered autoantibody positive (n = 113) with ≥ 1 positive autoantibody with individuals further categorized as `high-risk' (n = 38; positive ACPA or ≥ 2 RF assays). Autoantibody negative individuals served as comparators (n = 171). Antibody to Pg, P. intermedia (Pi), and F. nucleatum (Fn) were measured. Associations of bacterial antibodies with group status were examined using logistic regression.
Anti-Pg concentrations were higher in high-risk (p = 0.011) and autoantibody positive group (p = 0.010) than in the autoantibody negative group. There were no group differences in anti-Pi or anti-Fn concentrations. After multivariable adjustment, anti-Pg concentrations (but not anti-Pi or anti-Fn) were significantly associated with autoantibody positive and high-risk status (p < 0.05).
Immunity to Pg, but not Pi or Fn, is significantly associated with the presence of RA-related autoantibodies in individuals at risk for RA. These results support the hypothesis that infection with Pg may play a central role in the early loss of tolerance to self-antigens in RA pathogenesis.
rheumatoid arthritis; periodontitis; Porphyromonas gingivalis; Prevotella intermedia; Fusobacterium nucleatum; rheumatoid factor; anti-citrullinated protein antibody
To examine whether oral contraceptive use is associated with the presence of serum rheumatoid factor in women of reproductive age without rheumatoid arthritis.
304 women selected from parents of children who were at increased risk of developing type 1 diabetes were studied, because they were enriched with the human leucocyte antigen‐DR4 allele, a susceptibility marker for both type 1 diabetes and rheumatoid arthritis. Participants visited a clinic where blood was drawn for rheumatoid factor testing, and exposure data were collected via questionnaires. A medical history and joint examination were performed to rule out rheumatoid arthritis. Participants and examiners were unaware of the participants' rheumatoid factor status at the time of examination and questionnaire.
Use of oral contraceptives at any time was inversely associated with rheumatoid factor positivity (adjusted odds ratio (OR) 0.2, 95% confidence interval (CI) 0.07 to 0.52) independent of age, education and smoking. Smoking ⩾20 pack‐years was also associated with rheumatoid factor positivity (adjusted OR 56.38, 95% CI 4.31 to 736.98) compared with never smoking. Smoking 1–19 pack‐years was not associated with a positive rheumatoid factor.
Our results suggest that oral contraceptive use, and possibly cigarette smoking, act early in the development of the immune dysregulation that occurs in rheumatoid arthritis.
Non-alcoholic fatty liver disease (NAFLD) is a highly prevalent condition, particularly among Hispanic Americans. A genetic variant in PNPLA3 (rs738409) has been identified as a strong predictor of hepatic fat content.
To confirm the association of this variant with NAFLD in two minority cohorts, Hispanic Americans and African Americans, in whom liver density was quantified by computed tomography (CT).
This analysis was conducted in the Insulin Resistance Atherosclerosis (IRAS) Family Study. Participants were recruited from the general community and included 843 Hispanic American and 371 African American adults aged 18–81 years. A single variant in PNPLA3 (rs738409) was genotyped. Liver density was calculated in Hounsfield Units from abdominal CT scans.
Single nucleotide polymorphism (SNP) rs738409 was strongly associated with reduced liver density (i.e. NAFLD) in Hispanic Americans (1.18 × 10−9) and in African Americans (P = 4.99 × 10−6). The association followed an additive genetic model with the G allele conferring risk. The allele was two times more common in Hispanic Americans than in African Americans (40 vs 19%), consistent with the greater prevalence of NAFLD in Hispanic Americans (24 vs 9%). The SNP explained 4.4 and 5.6% of the variance of the adjusted liver density outcome in Hispanic Americans and African Americans, respectively.
We confirmed the association of a PNPLA3 variant with NAFLD in Hispanic Americans and African Americans, suggesting that PNPLA3 contributes to the variation in NAFLD across multiple ethnicities. This study adds to the growing evidence that some of the ethnic variation in NAFLD is genetic.
African Americans; computed tomography; genetic epidemiology; hepatic steatosis; Hispanic Americans; non-alcoholic fatty liver disease; PNPLA3
Recently, a genome-wide association scan was completed in the IRAS (Insulin Resistance Atherosclerosis Study) Family Study (IRASFS) Hispanic-American cohort. Multiple single-nucleotide polymorphisms (SNPs) in the G-protein signaling 6 (RGS6) gene were found to be associated with adiposity phenotypes. RGS6 has shown downstream antagonistic interplay with opioid receptors, targets of fatty/sugary food agonists. The possibility that RGS6 promotes tolerance and tachyphylaxis among the opioid receptor is a plausible pathway for overconsuming fat/sugar-laden food. Therefore, we hypothesized that RGS6 variants are associated with intake of fatty/sugary foods. In 932 Hispanics from San Antonio and San Luis Valley, CO, the following dietary intake variables were assessed using the Block Brief 2000 food frequency questionnaire: total calories, total fat, % calories from fat, % calories from saturated fat, protein, % calories from protein, carbohydrates, % calories from carbohydrates, and daily frequency of servings of fats/oils/sweets. We tested for association between 23 SNPs in RGS6 and dietary intake using a variance components measured genotype approach. All models were adjusted for gender, recruitment site, admixture, BMI, and age. Using an additive genetic model, rs1402064 was associated with higher intake of fats/oils/sweets, total calories, total fat and saturated fat (P = 0.0007, 0.026, 0.023, and 0.024). SNPs rs847330 and rs847354 were associated with higher intake of fats/oils/sweets (P = 0.002 and 0.018), total fat (P = 0.040 and 0.048) and saturated fat (P = 0.044 and 0.041). Finally, rs769148 was associated with higher intake of fats/oils/sweets (P = 0.002). RGS6 is a new candidate gene for adiposity traits that may be associated with a behavioral tendency toward fat-laden food intake.
To evaluate the presence of pulmonary abnormalities in subjects with rheumatoid arthritis (RA)-related autoantibody (Ab) positivity without inflammatory arthritis (IA).
42 subjects without IA but with elevations of anti-cyclic citrullinated peptide antibodies and/or 2 or more rheumatoid factor isotypes (a profile that is 96% specific for RA), 15 Ab(−) controls and 12 patients with early established seropositive RA (<1 year duration) underwent spirometry and high-resolution computed tomographic (HRCT) lung imaging.
The median age of Ab(+) subjects was 54 years-old, 52% were female and 38% were smokers (not significantly different than Ab(−) controls). No Ab(+) subject had IA on joint examination. On HRCT, 76% of Ab(+) subjects had airways abnormalities including bronchial wall thickening, bronchiectasis, centrilobular opacities and air trapping, compared to 33% of Ab(−) controls (p=0.005). The Ab(+) subjects had similar prevalence and type of lung abnormalities compared to patients with early RA. Two Ab(+) subjects with airways disease developed IA classifiable as articular RA ~13 months after lung evaluation.
Airways abnormalities that are consistent with inflammation are common in Ab(+) subjects without IA, and similar to airways abnormalities seen in early RA. These findings suggest that the lung may be an early site of autoimmune-related injury, and potentially a site of generation of RA-related autoimmunity. Further studies are needed to define the mechanistic role of lung inflammation in the development of RA.
Rheumatoid arthritis; etiology; autoantibodies; preclinical; lung disease
We assessed the effects of non-HLA gene polymorphisms on the risk of islet autoimmunity (IA) and progression to type 1 diabetes in the Diabetes Autoimmunity Study in the Young. A total of 1,743 non-Hispanic, white children were included: 861 first-degree relatives and 882 general population children identified as having high-risk HLA-DR/DQ genotypes for type 1 diabetes. Of those, 109 developed IA and 61 progressed to diabetes. Study participants were genotyped for 20 non-HLA polymorphisms, previously confirmed as type 1 diabetes susceptibility loci. PTPN22 and UBASH3A predicted both IA and diabetes in regression models controlling for family history of type 1 diabetes and presence of HLA-DR3/4-DQB1*0302 genotype. In addition, PTPN2 predicted IA whereas INS predicted type 1 diabetes. The final multivariate regression models for both IA and type 1 diabetes included PTPN22, UBASH3A, and INS, in addition to family history of type 1 diabetes and HLA-DR3/4. In general population children, the most frequent combinations including these five significant predictors conferred hazard ratio of up to 13 for IA and >40 for type 1 diabetes. Non-HLA susceptibility alleles may help estimate risk for development of type 1 diabetes in the general population. These findings require replication in different populations.
We investigated whether omega-3 fatty acid intake and erythrocyte membrane omega-3 fatty acid levels are associated with conversion to type 1 diabetes in children with islet autoimmunity (IA).
The Diabetes Autoimmunity Study in the Young is following children at increased genetic risk for type 1 diabetes for the development of persistent IA, as defined as being positive for glutamic acid decarboxylase 65, i, or insulin autoantibodies on two consecutive visits, and then for the development of type 1 diabetes, as diagnosed by a physician. One hundred and sixty-seven children with persistent IA were followed for a mean of 4.8 yr, and 45 of these developed type 1 diabetes at a mean age of 8.7 yr. Erythrocyte membrane fatty acids (as a percent of total lipid) and dietary fatty acid intake (estimated via food frequency questionnaire) were analyzed as time-varying covariates in proportional hazards survival analysis, with follow-up time starting at detection of the first autoantibody.
Neither dietary intake of omega-3 fatty acids nor omega-6 fatty acids were associated with conversion to type 1 diabetes, adjusting for human leukocyte antigen (HLA)-DR, family history of type 1 diabetes, age at first IA positivity, maternal age, maternal education, and maternal ethnicity. Adjusting for HLA-DR, family history of type 1 diabetes and age at first IA positivity, omega-3 and omega-6 fatty acid levels of erythrocyte membranes were not associated with conversion to type 1 diabetes.
In this observational study, omega-3 fatty acid intake and status are not associated with conversion to type 1 diabetes in children with IA.
dietary intake; IA; omega-3 fatty acids; type 1 diabetes mellitus
A recent meta-analysis of 13 prospective studies reported that higher levels of adiponectin were significantly associated with lower risk of type 2 diabetes. Most previous studies, however, were limited in their ability to adjust for appropriate confounding variables. Our objective, therefore, was to study this association after adjustment for directly measured adiposity and insulin sensitivity, expressed as the insulin sensitivity index (SI).
RESEARCH DESIGN AND METHODS
The study included 1,096 Hispanic and African American participants free of diabetes at baseline (2000–2002) who returned for follow-up after 5 years. SI was determined from frequently sampled intravenous glucose tolerance tests with minimal model analysis. Visceral adipose tissue (VAT) area was determined by computed tomography. Diabetes and impaired fasting glucose (IFG) were defined using American Diabetes Association criteria. Multivariate generalized estimating equation logistic regression models were used to account for correlations within families.
A total of 82 subjects met criteria for incident diabetes. After adjustment for age, sex, ethnicity, and smoking, adiponectin was significantly inversely associated with diabetes (odds ratio [OR] 0.54 per 1 SD difference [95% CI 0.38–0.76]). The association remained significant after additional adjustment in individual models for BMI, homeostasis model assessment of insulin resistance, or VAT (all P < 0.05). However, adiponectin was no longer associated in separate models adjusted for SI or IFG (OR 0.81 [0.56–1.16] and 0.75 [0.53–1.06], respectively).
Adiponectin was inversely associated with incident diabetes after adjustment for conventional anthropometric and metabolic variables or VAT. Adjustment for detailed measures of SI attenuated this relationship, however, suggesting that the link between adiponectin and diabetes may operate at least in part through insulin resistance.
To examine associations between exposure to maternal diabetes in utero and body mass index (BMI) growth trajectories from birth through 13 years of age among a diverse cohort of youth.
Mixed linear effects models were constructed to assess differences in BMI and BMI growth velocity from birth through 13 years of age for 95 subjects exposed to diabetes in utero and 409 unexposed subjects enrolled in a retrospective cohort study.
The overall BMI growth trajectory (adjusted for sex and race/ethnicity) was not significantly different for exposed and unexposed subjects from birth through 26 months of age (p=0.48). However, the overall growth trajectory from 27 months of age through 13 years differed by exposure status (p=0.008), adjusted for sex and race/ethnicity. The difference was primarily due to a significantly higher BMI growth velocity among exposed youth between 10–13 years, increasing by 4.56 kg/m2 compared to 3.51 kg/m2 in the unexposed (p=0.005). Control for demographic variables, socioeconomic factors and maternal pre-pregnancy BMI did not alter the observed associations.
Exposure to maternal diabetes in utero accelerates BMI growth in late childhood thus increasing long-term obesity risk.
Gestational diabetes; fetal overnutrition; fetal exposure to diabetes; childhood obesity; childhood BMI; growth trajectory
To evaluate whether breastfeeding attenuates increased childhood adiposity associated with exposure to diabetes in utero.
RESEARCH DESIGN AND METHODS
Retrospective cohort study of 89 children exposed to diabetes in utero and 379 unexposed youth with measured BMI, waist circumference, skinfolds, visceral (VAT) and subcutaneous (SAT) abdominal fat. A measure of breast milk–months was derived from maternal self-report and used to categorize breastfeeding status as low (<6) and adequate (≥6 breast milk–months). Multiple linear regression was used to model the relationship between exposure to diabetes in utero and offspring adiposity outcomes among youth stratified according to breastfeeding status.
Adequate (vs. low) breastfeeding status was associated with significantly lower BMI, waist circumference, SAT, and VAT at ages 6–13 years. Among youth in the low breastfeeding category, exposure to diabetes in utero was associated with a 1.7 kg/m2 higher BMI (P = 0.03), 5.8 cm higher waist circumference (P = 0.008), 6.1 cm2 higher VAT (P = 0.06), 44.6 cm2 higher SAT (P = 0.03), and 0.11 higher ratio of subscapular-to-triceps skinfold ratio (P = 0.008). Among those with adequate breastfeeding in infancy, the effect of prenatal exposure to diabetes on childhood adiposity outcomes was not significant.
Adequate breastfeeding protects against childhood adiposity and reduces the increased adiposity levels associated with exposure to diabetes in utero. These data provide support for mothers with diabetes during pregnancy to breastfeed their infants in order to reduce the risk of childhood obesity.
To investigate whether enterovirus infections predict progression to type 1 diabetes in genetically predisposed children repeatedly positive for islet autoantibodies.
RESEARCH DESIGN AND METHODS
Since 1993, the Diabetes and Autoimmunity Study in the Young (DAISY) has followed 2,365 genetically predisposed children for islet autoimmunity and type 1 diabetes. Venous blood and rectal swabs were collected every 3–6 months after seroconversion for islet autoantibodies (against GAD, insulin, or insulinoma-associated antigen-2 [IA-2]) until diagnosis of diabetes. Enteroviral RNA in serum or rectal swabs was detected using reverse transcriptase PCR with primers specific for the conserved 5′ noncoding region, detecting essentially all enterovirus serotypes.
Of 140 children who seroconverted to repeated positivity for islet autoantibodies at a median age of 4.0 years, 50 progressed to type 1 diabetes during a median follow-up of 4.2 years. The risk of progression to clinical type 1 diabetes in the sample interval following detection of enteroviral RNA in serum (three diabetes cases diagnosed among 17 intervals) was significantly increased compared with that in intervals following a negative serum enteroviral RNA test (33 cases diagnosed among 1,064 intervals; hazard ratio 7.02 [95% CI 1.95–25.3] after adjusting for number of autoantibodies). Results remained significant after adjustment for ZnT8-autoantibodies and after restriction to various subgroups. Enteroviral RNA in rectal swabs was not predictive of progression to type 1 diabetes. No evidence for viral persistence was found.
This novel observation suggests that progression from islet autoimmunity to type 1 diabetes may increase after an enterovirus infection characterized by the presence of viral RNA in blood.
Pre-clinical rheumatoid arthritis (RA) biomarker elevations were evaluated and utilized to develop a model for the prediction of time to future diagnosis of seropositive RA.
Stored samples from 73 military seropositive RA cases (and controls) from pre-RA diagnosis (mean 2.9 samples per case; samples collected a mean of 6.6 years prior-to-diagnosis) were tested for rheumatoid factor (RF) isotypes, anti-cyclic citrullinated peptide (anti-CCP) antibodies, 14 cytokines/chemokines (bead-based assay) and C-reactive protein (CRP).
Pre-clinical positivity of anti-CCP and/or 2 or more RF isotypes was >96% specific for future RA. In pre-clinical RA, levels of the following were positive in a significantly greater proportion of RA cases versus controls: interleukin (IL)-1α, IL-1β, IL-6, IL-10, IL-12p40, IL-12p70, IL-15, fibroblast growth factor-2, Flt-3 ligand, tumor necrosis factor-α, interferon gamma induced protein-10, granulocyte macrophage colony-stimulating factor, and CRP. Also, increasing numbers of elevated cytokines/chemokines were present in cases nearer to the time of diagnosis. RA cases ≥40 years-old at diagnosis had a higher proportion of samples positive for cytokines/chemokines 5-10 years prior-to-diagnosis, compared to cases <40 at diagnosis (p<0.01). In regression modeling using only case samples positive for autoantibodies highly specific for future RA, increasing numbers of cytokines/chemokines predicted decreased time-to-diagnosis, and the predicted time-to-diagnosis based on cytokines/chemokines was longer in older compared to younger cases.
Autoantibodies, cytokines/chemokines and CRP are elevated in the pre-clinical period of RA development. In pre-clinical autoantibody positive cases, the number of elevated cytokines/chemokines predicts the time of diagnosis of future RA in an age-dependent manner.
pre-clinical rheumatoid arthritis; rheumatoid arthritis; cytokines; chemokines; prediction model
Family-based linkage analysis has been a powerful tool for identification of genes contributing to traits with monogenic patterns of inheritance. These approaches have been of limited utility in identification of genes underlying complex traits. In contrast, searches for common genetic variants associated with complex traits have been highly successful. It is now widely recognized that common variations frequently explain only part of the inter-individual variation in populations. ‘Rare’ genetic variants have been hypothesized to contribute significantly to phenotypic variation in the population. We have developed a combination of family-based linkage, whole-exome sequencing, direct sequencing and association methods to efficiently identify rare variants of large effect. Key to the successful application of the method was the recognition that only a few families in a sample contribute significantly to a linkage signal. Thus, a search for mutations can be targeted to a small number of families in a chromosome interval restricted to the linkage peak. This approach has been used to identify a rare (1.1%) G45R mutation in the gene encoding adiponectin, ADIPOQ. This variant explains a strong linkage signal (LOD > 8.0) and accounts for ∼17% of the variance in plasma adiponectin levels in a sample of 1240 Hispanic Americans and 63% of the variance in families carrying the mutation. Individuals carrying the G45R mutation have mean adiponectin levels that are 19% of non-carriers. We propose that rare variants may be a common explanation for linkage peaks observed in complex trait genetics. This approach is applicable to a wide range of family studies and has potential to be a discovery tool for identification of novel genes influencing complex traits.
Vitamin D deficiency is associated with many adverse health outcomes. There are several well established environmental predictors of vitamin D concentrations, yet studies of the genetic determinants of vitamin D concentrations are in their infancy. Our objective was to conduct a pilot genome-wide association (GWA) study of 25-hydroxyvitamin D (25[OH]D) and 1,25-dihydroxyvitamin D (1,25[OH]2D) concentrations in a subset of 229 Hispanic subjects, followed by replication genotyping of 50 single nucleotide polymorphisms (SNPs) in the entire sample of 1,190 Hispanics from San Antonio, Texas and San Luis Valley, Colorado. Of the 309,200 SNPs that met all quality control criteria, three SNPs in high linkage disequilibrium (LD) with each other were significantly associated with 1,25[OH]2D (rs6680429, rs9970802, and rs10889028) at a Bonferroni corrected P-value threshold of 1.62 × 10−7, however none met the threshold for 25[OH]D. Of the 50 SNPs selected for replication genotyping, five for 25[OH]D (rs2806508, rs10141935, rs4778359, rs1507023, and rs9937918) and eight for 1,25[OH]2D (rs6680429, rs1348864, rs4559029, rs12667374, rs7781309, rs10505337, rs2486443, and rs2154175) were replicated in the entire sample of Hispanics (P < 0.01). In conclusion, we identified several SNPs that were associated with vitamin D metabolite concentrations in Hispanics. These candidate polymorphisms merit further investigation in independent populations and other ethnicities.
Vitamin D; 25-hydroxyvitamin D; 1,25-dihydroxyvitamin D; genome-wide association study; Hispanic
In this observational study, we compared erythrocyte membrane fatty acids in infants consuming formula supplemented with docosahexaenoic acid (DHA) and arachidonic acid (ARA) with those consuming other types of milks. In 110 infants who were participants in a cohort study of otherwise healthy children at risk for developing type 1 diabetes, erythrocytes were collected at approximately 9 months of age, and fatty acid content was measured as a percent of total lipids. Parents reported the type of milk the infants consumed in the month of and prior to erythrocyte collection – infant formula supplemented with ARA and DHA (supplemented formula), formula with no ARA and DHA supplements (non-supplemented formula), breast-milk, or non-supplemented formula plus breast-milk. Membrane DHA (4.42 versus 1.79, p < 0.001) and omega-3 fatty acid (5.81 versus 3.43, p < 0.001) levels were higher in infants consuming supplemented versus non-supplemented formula. Omega-6 fatty acids were lower in infants consuming supplemented versus non-supplemented formula (26.32 versus 29.68, p = 0.023); ARA did not differ between groups. Infants given supplemented formula had higher DHA (4.42 versus 2.81, p < 0.001) and omega-3 fatty acids (5.81 versus 4.45, p = 0.008) than infants drinking breast-milk. In infants whose mothers did not receive any dietary advice, use of supplemented formula is associated with higher omega-3 and lower omega-6 fatty acid status.
Arachidonic Acid; Docosahexaenoic Acid; Breastfeeding; Infant Feeding; Infant Formula; Infant Feeding Behavior
To determine if antibodies against peptidyl arginine deiminase Type 4 (PAD-4) are present in the pre-clinical phase of rheumatoid arthritis (RA), and to compare their appearance to other pre-clinical autoantibodies.
Prediagnosis serum samples from 83 subjects with RA were evaluated for presence of anti-PAD-4 antibody, anti-cyclic citrullinated peptide (anti-CCP) antibody, and rheumatoid factor (RF). In addition, a control cohort (N = 83) matched on age, gender, race, number of samples, and duration of serum storage were tested for antibody against PAD-4 to determine its sensitivity and specificity for future RA.
Fifteen of 83 (18.1%) subjects with RA had at least one prediagnosis sample positive for anti-PAD-4. One of 83 (1.2%) control subjects had at least one sample positive, resulting in a sensitivity and specificity of anti-PAD-4 for the future development of RA of 18.1% and 98.8%, respectively. The mean time of first positivity for anti-PAD-4 was ~4.6 years prior to diagnosis. Anti-PAD-4 positivity was associated with anti-CCP positivity (OR 5.13, 95%CI 1.07–24.5, p = 0.04). In subjects with prediagnosis samples positive for both antibodies, anti-CCP positivity predated anti-PAD-4 in 9 of 13 (69%) cases.
Autoantibodies to PAD-4 are present in the pre-clinical phase of RA in a subset of patients and are associated with anti-CCP positivity. Further exploration is needed regarding the timing of appearance and disease-related effects of PAD-4 autoimmunity.
Rheumatoid arthritis; pre-clinical; peptidyl arginine deiminase type 4; anti-citrullinated peptide antibodies