Mutations in the genes for hepatocyte nuclear factor (HNF)-1alpha, -4alpha, -1beta, and -3beta; the dimerization cofactor of HNF-1; and insulin promoter factor 1 are not common causes of early-onset type 2 diabetes in Pima Indians

Glycemic Measures in Childhood as Predictors of Future Diabetes-Related Microvascular Complications in an Indigenous American Population

OBJECTIVE

To examine the role of glycemic measures performed during childhood in predicting future diabetes-related nephropathy and retinopathy in a high-risk indigenous American cohort.

RESEARCH DESIGN AND METHODS

We studied associations between glycated hemoglobin (HbA1c) and 2-h plasma glucose (PG), measured during childhood (age 5 to <20 years) in a longitudinal observational study of diabetes and its complications (1965-2007), and future albuminuria (albumin creatinine ratio [ACR] ≥30 mg/g), severe albuminuria (ACR ≥300 mg/g), and retinopathy (at least one microaneurysm or hemorrhage or proliferative retinopathy on direct ophthalmoscopy). Areas under the receiver operating characteristic curve (AUCs) for childhood glycemic measures when predicting nephropathy and retinopathy were compared.

RESULTS

Higher baseline levels of HbA1c and 2-h PG significantly increased the risk of future severe albuminuria (HbA1c: hazard ratio [HR] 1.45 per %; 95% CI 1.02-2.05 and 2-h PG: HR 1.21 per mmol/L; 95% CI 1.16-1.27). When categorized by baseline HbA1c, children with prediabetes had a higher incidence of albuminuria (29.7 cases per 1,000 person-years [PY]), severe albuminuria (3.8 cases per 1,000 PY), and retinopathy (7.1 cases per 1,000 PY) than children with normal HbA1c levels (23.8, 2.4, and 1.7 cases per 1,000 PY, respectively); children with diabetes at baseline had the highest incidence of the three complications. No significant differences were observed between AUCs for models with HbA1c, 2-h PG, and fasting PG when predicting albuminuria, severe albuminuria, or retinopathy.

CONCLUSIONS

In this study, higher glycemia levels ascertained by HbA1c and 2-h PG during childhood were associated with future microvascular complications; this demonstrates the potential utility of screening tests performed in high-risk children in predicting long-term health outcomes.

HbA1c and the Prediction of Type 2 Diabetes in Children and Adults

OBJECTIVE

Long-term data validating glycated hemoglobin (HbA_1c) in assessing the risk of type 2 diabetes in children are limited. HbA_1c, fasting plasma glucose (FPG), and 2-h postload plasma glucose (2hPG) concentrations were measured in a longitudinal study of American Indians to determine their utility in predicting incident diabetes, all of which is thought to be type 2 in this population.

RESEARCH DESIGN AND METHODS

Incident diabetes (FPG ≥126 mg/dL [7.0 mmol/L], 2hPG ≥200 mg/dL [11.1 mmol/L], HbA_1c ≥6.5% [8 mmol/mol], or clinical diagnosis) was determined in 2,095 children without diabetes ages 10-19 years monitored through age 39, and in 2,005 adults ages 20-39 monitored through age 59. Areas under the receiver operating characteristic (ROC) curve for HbA_1c, FPG, and 2hPG in predicting diabetes within 10 years were compared.

RESULTS

During long-term follow-up of children and adolescents who did not initially have diabetes, the incidence rate of subsequent diabetes was fourfold (in boys) as high and more than sevenfold (in girls) as high in those with HbA_1c ≥5.7% as in those with HbA_1c ≤5.3%-greater rate ratios than experienced by adults in the same HbA_1c categories. Analyses of ROCs revealed no significant differences between HbA_1c, FPG, and 2hPG in sensitivity and specificity for identifying children and adolescents who later developed diabetes.

CONCLUSIONS

HbA_1c is a useful predictor of diabetes risk in children and can be used to identify prediabetes in children with other type 2 diabetes risk factors with the same predictive value as FPG and 2hPG.

Identification and functional analysis of c.422_423InsT, a novel mutation of the HNF1A gene in a patient with diabetes

BACKGROUND

HNF1A gene regulates liver-specific genes, and genes that have a role in glucose metabolism, transport, and secretion of insulin. HNF1A gene mutations are frequently associated with type 2 diabetes. HNF1A protein has three domains: the dimerization domain, the DNA-binding domain, and the trans-activation domain. Some mutations in the dimerization or DNA-binding domains have no influence on the normal allele, while others have dominant negative effects. The I27L, A98V, and S487N polymorphisms are common variants of the HNF1A gene; they have been found in T2D and non-diabetic subjects.

METHODS AND RESULTS

We searched for mutations in the first three exons of the HNF1A gen in an Amerindian population of 71 diabetic patients. DNA sequencing revealed the previously reported I27L polymorphism (c.79A>C) in 53% of diabetic patients and in 67% of the control group. Thus, the I27L/L27L polymorphism might be a marker of Amerindians. In addition, we found the c.422_423InsT mutation in the HNF1A gene of one patient, which had not been previously reported. This mutation resulted in a frame shift of the open reading frame and a new translation stop in codon 187, leading to a truncated polypeptide of 186 amino acids (Q141Hfs*47). This novel mutation affects the DNA-binding capacity of the mutant HNF1A protein by EMSA; its intracellular localization by fluorescence and confocal microscopy, and a dominant-negative effect affecting the DNA-binding capacity of the normal HNF1A by EMSA. We also studied the homology modeling structure to understand the effect of this mutation on its DNA-binding capacity and its dominant negative effect.

CONCLUSION

The HNF1A Q141Hfs*47 mutant polypeptide has no DNA-binding capacity and exerts a dominant negative effect on the HNF1A protein. Therefore, it might produce severe phenotypic effects on the expression levels of a set of β-cell genes. Consequently, its screening should be included in the genetic analysis of diabetic patients after more functional studies are performed.

Metabolic Risk Factors and Type 2 Diabetes Incidence in American Indian Children

CONTEXT

Data are lacking on how metabolic risk factors during childhood affect the long-term risk of type 2 diabetes.

OBJECTIVES

Assess four metabolic risk factors as predictors of type 2 diabetes and determine whether the risk differs between younger and older children.

DESIGN

In a prospective cohort study conducted between 1965 and 2007, participants were followed for development of diabetes. Baseline measurements included body mass index (BMI), blood pressure, serum cholesterol, and 2-hour plasma glucose after an oral glucose tolerance test. Additional analyses divided subjects into two groups according to baseline age, 5–11 and 12–19 years.

SETTING

Gila River Indian Community in Arizona.

PARTICIPANTS

A total of 5532 nondiabetic Pima Indian children 5–19 years old.

RESULTS

A total of 1281 children developed diabetes (median follow-up, 12.4 years). Diabetes incidence was higher in overweight children (BMI ≥ 85th percentile) than in nonoverweight children. Nonoverweight children had the lowest risk of diabetes (20-year cumulative incidence, 9.5%), whereas overweight children with impaired glucose tolerance (2-hour glucose ≥ 140 mg/dL) had the highest (79.0%). The relative risk for children with metabolic abnormalities compared with their healthy counterparts was higher in younger children than in older children early in follow-up. BMI and 2-hour glucose were related to incident diabetes in multivariable models (predicted 15-year cumulative incidence for the highest vs lowest quartile was 3.9 and 1.8 times as high for BMI and 2-hour glucose, respectively; P < .001), whereas blood pressure and cholesterol were not.

CONCLUSIONS

BMI and impaired glucose tolerance in children are strong predictors of type 2 diabetes. Other components of the “metabolic syndrome” are not.

Association analyses of variants in the DIO2 gene with early-onset type 2 diabetes mellitus in Pima Indians

BACKGROUND

The type 2 deiodinase gene (DIO2) encodes a deiodinase that converts the thyroid prohormone, thyroxine, to the biologically active triiodothyronine. Thyroid hormones regulate energy balance and may also influence glucose metabolism. Therefore, we hypothesized that variations in DIO2 could contribute to obesity or type 2 diabetes mellitus (T2DM) in Pima Indians.

METHODS

Sequencing of the DIO2 gene in DNA from 83 Pima Indians identified 12 single-nucleotide polymorphisms (SNPs). Several of these SNPs were in perfect genotypic concordance among the 83 samples that were sequenced, and all 12 could be divided into five linkage disequilibrium groups. One representative SNP from each group (Thr92Ala, rs225011, rs225015, rs6574549, and a rare 5' flanking SNP) was selected for further genotyping for association analyses. In this study, the five selected variants in DIO2, as described above, were genotyped in three groups of Pima Indians: (i) a case (n=150)/control (n=150) group for early-onset T2DM (onset age <25 years); (ii) a case (n=362)/control (n=127) group for obesity; (iii) a large (n=1,311, cases n=810/controls n=501) family-based group, of which 256 nondiabetic subjects had undergone detailed metabolic phenotyping.

RESULTS

The Thr92Ala variant common in Pima Indians, rs225011, and rs225015 were modestly associated with early-onset T2DM (p=0.01-0.04) in the case-control study, but were not associated with obesity in the obesity case-control study, nor associated with T2DM (at any age) or body-mass index (BMI; as a quantitative trait) in the family-based analysis. Thr92Ala, rs225011, rs225015, and rs6574549 were also nominally associated with hepatic glucose output (p=0.02). rs6574549 was associated with fasting insulin (p=0.02), insulin action (p=0.04), and energy expenditure (p=0.02). None of these nominal associations remained statistically significant after corrections for multiple testing.

CONCLUSIONS

We propose that variation in DIO2 may have a subtle role in altering metabolic processes that lead to early-onset T2DM, but this gene does not have a large impact on T2DM at older ages, nor does DIO2 influence BMI in the Pima Indian population.

Increasing incidence of proteinuria and declining incidence of end-stage renal disease in diabetic Pima Indians

The introduction of more efficacious treatments for diabetic kidney disease may slow its progression, but evidence for their effectiveness in populations is sparse. We examined trends in the incidence of clinical proteinuria, defined as a urinary protein-to-creatinine ratio >0.5 g/g, and diabetic end-stage renal disease (ESRD), defined as death from diabetic nephropathy or onset of dialysis, in Pima Indians with type 2 diabetes between 1967 and 2002. The study included 2189 diabetic subjects >/=25 years old. During follow-up, 366 incident cases of proteinuria occurred in the subset of 1715 subjects without proteinuria at baseline. The age-sex-adjusted incidence rate of proteinuria increased from 24.3 cases/1000 person-years (pyrs) (95% confidence interval (CI) 18.7-30.0) in 1967-1978 to 35.4 cases/1000 pyrs (95% CI 28.1-42.8) in 1979-1990 and 38.9 cases/1000 pyrs (95% CI 31.2-46.5) in 1991-2002 (P(trend)<0.0002). In each period, the age-sex-adjusted incidence of proteinuria increased with diabetes duration, but diabetes duration-specific incidence was stable throughout the study period (P=0.8). The age-sex-adjusted incidence of ESRD increased between 1967 and 1990 and declined thereafter. The incidence of proteinuria increased over 36 years in Pima Indians as the proportion of people with diabetes of long duration increased. On the other hand, the incidence of ESRD declined after 1990, coinciding with improved control of blood pressure, hyperglycemia, and perhaps other risk factors.

Missense mutations in the human insulin promoter factor-1 gene are not a common cause of type 2 diabetes mellitus in Taiwan

Type 2 diabetes mellitus (T2DM) is a common metabolic disorder characterized by a hyperglycemia resulting from defect in insulin secretion and insulin action. Recent studies showed that dominant negative mutations in the insulin promoter factor-1 (IPF-1), a pancreatic beta-cell specific transcription factor, cause maturity-onset diabetes of the young (MODY), a subtype of T2DM with early onset and monogenic autosomal inheritance. In addition to MODY, IPF-1 mutations are suggested to predispose to common late-onset T2DM with different penetration of the mutations reflected in their in vitro activity. Thus, we investigated IPF-1 C18R, Q59L, D76N and R197H mutations in Taiwanese patients with common late-onset T2DM, because research into IPF-1 variants in Taiwanese diabetic patients--a population with the lowest range of diabetic incidence--has never been documented. Peripheral blood samples were collected and genomic DNA was extracted from 434 patients with T2DM and 194 non-diabetes control study subjects. IPF-1 genetic variations were analyzed by PCR and restriction fragment length polymorphism (RFLP) analysis. We did not find any of these four IPF-1 mutations in our patients. Our results suggested that IPF-1 mutations were not a common cause associated with Taiwanese T2DM.

Incidence of retinopathy and nephropathy in youth-onset compared with adult-onset type 2 diabetes

OBJECTIVE

To examine the risk of retinopathy and nephropathy in participants in whom type 2 diabetes was diagnosed in youth (before 20 years of age) compared with those in whom type 2 diabetes was diagnosed at older ages.

RESEARCH DESIGN AND METHODS

Subjects in whom youth-onset or adult-onset diabetes was diagnosed in the longitudinal study of health in the Pima Indians of Arizona were followed for microvascular complications. Diabetes was diagnosed in 178 subjects before 20 years of age (youth), in 1,359 subjects at 20-39 years of age (younger adults), and in 971 subjects at 40-59 years of age (older adults). Incidence rates of diabetic retinopathy diagnosed by direct ophthalmoscopy through dilated pupils and nephropathy (protein-to-creatinine ratio > or =0.5 g/g) were calculated by age at diagnosis.

RESULTS

Over 25 years, nephropathy developed in 35 of the participants with youth-onset type 2 diabetes; this incidence rate was not significantly different from that in patients with adult-onset diabetes (P = 0.77). Incidence rates of retinopathy, however, were significantly lower for the youth-onset group (P = 0.007). Adjusted for sex, glycemia, and blood pressure, risk of retinopathy was lower in patients with youth-onset diabetes than in those with adult-onset diabetes (hazard rate ratio [HRR] 0.42, 95% CI 0.24-0.74, P = 0.003), but risk of nephropathy was not different (HRR 1.2, 95% CI 0.77-1.3, P = 0.38).

CONCLUSIONS

In Pima Indians, the risk of nephropathy as a function of duration of diabetes is similar in all age groups. By contrast, the risk of retinopathy is lower in patients with youth-onset type 2 diabetes.

Skeletal muscle insulin resistance in normoglycemic subjects with a strong family history of type 2 diabetes is associated with decreased insulin-stimulated insulin receptor substrate-1 tyrosine phosphorylation

Normoglycemic subjects with a strong family history of type 2 diabetes are insulin resistant, but the mechanism of insulin resistance in skeletal muscle of such individuals is unknown. The present study was undertaken to determine whether abnormalities in insulin-signaling events are present in normoglycemic, nonobese subjects with a strong family history of type 2 diabetes. Hyperinsulinemic-euglycemic clamps with percutaneous muscle biopsies were performed in eight normoglycemic relatives of type 2 diabetic patients (FH(+)) and eight control subjects who had no family history of diabetes (FH(-)), with each group matched for age, sex, body composition, and ethnicity. The FH(+) group had decreased insulin-stimulated glucose disposal (6.64 +/- 0.52 vs. 8.45 +/- 0.54 mg. kg(-1) fat-free mass. min(-1); P < 0.05 vs. FH(-)). In skeletal muscle, the FH(+) and FH(-) groups had equivalent insulin stimulation of insulin receptor tyrosine phosphorylation. In contrast, the FH(+) group had decreased insulin stimulation of insulin receptor substrate (IRS)-1 tyrosine phosphorylation (0.522 +/- 0.077 vs. 1.328 +/- 0.115 density units; P < 0.01) and association of PI 3-kinase activity with IRS-1 (0.299 +/- 0.053 vs. 0.466 +/- 0.098 activity units; P < 0.05). PI 3-kinase activity was correlated with the glucose disposal rate (r = 0.567, P = 0.02). In five subjects with sufficient biopsy material for further study, phosphorylation of Akt was 0.266 +/- 0.061 vs. 0.404 +/- 0.078 density units (P < 0.10) and glycogen synthase activity was 0.31 +/- 0.06 vs. 0.50 +/- 0.12 ng. min(-1). mg(-1) (P < 0.10) for FH(+) and FH(-) subjects, respectively. Therefore, despite normal insulin receptor phosphorylation, postreceptor signaling was reduced and was correlated with glucose disposal in muscle of individuals with a strong genetic background for type 2 diabetes.

Comparison of the effect of plasma glucose concentrations on microvascular disease between Pima Indian youths and adults

OBJECTIVE

To examine whether the current adult guidelines for diagnosis of diabetes are applicable to youth (age <20 years).

RESEARCH DESIGN AND METHODS

We analyzed fasting plasma glucose (FPG) and 2-h plasma glucose (PG) in two groups of Pima Indians, youths aged 5-19 years and adults aged 20-34 years, in relation to the incidence of microvascular disease when subjects were reexamined at ages 25-39 (youths) and 40-54 (adults). Microvascular disease was defined as retinopathy or a urine protein-to-creatinine ratio > or =0.5 g.

RESULTS

An increase in the incidence of microvascular disease occurred at nearly the same level of glycemia in both groups. For youths, this increase occurred at FPG approximately 7.3 mmol/l and 2-h PG approximately 10.0 mmol/l; for adults, this increase occurred at FPG approximately 7.5 mmol/l and 2-h PG approximately 10.3 mmol/l. Sensitivity of the adult diagnostic guidelines of FPG > or =7.0 mmol/l and 2-h PG > or =11.1 mmol/l for the detection of microvascular disease was much lower (with higher specificity) in youths than in adults. Receiver operating characteristics (ROC) curve areas were lower for FPG and 2-h PG for youths, suggesting that microvascular disease was less strongly predicted by baseline glucose.

CONCLUSION

The current adult guidelines for diagnosis of diabetes are applicable to youth, as they identify a population at high risk of microvascular complications.

Genes and environment in type 2 diabetes and atherosclerosis in aboriginal Canadians

The incidence of coronary heart disease (CHD) among aboriginal people in northern Ontario has tripled over the past 20 years. This is inextricably linked to the remarkably high prevalence of type 2 diabetes in these native communities. Approximately 40% of the Oji-Cree of northern Ontario have typical obesity-related type 2 diabetes, which represents a drastic increase from virtually unreportable levels 50 years ago. The Oji-Cree have a private mutation in the HNF1A gene, namely G319S, which is absent from other ethnic groups and aboriginal populations. The most compelling reasons that HNF1A S319 is a diabetes-susceptibility allele are its consistent statistical association with the presence and severity of diabetes. Also, HNF1A S319 has specificity and positive predictive values of 97% and 95%, respectively, for the development of diabetes in the Oji-Cree by 50 years of age. This makes the HNF1A G319S genotype the most specific predictive genetic test for diabetes in any human population. HNF1A S319 has all the attributes of a thrifty allele in the Oji-Cree. It is possible that the recent increase in CHD in the aboriginal people of northern Ontario is the result of the expression of diabetes susceptibility due to HNF1A S319 as a consequence of rapid changes in environment and lifestyle.