A Bayesian population analysis of the development of type 2 diabetes in the offspring of diabetic parents.

Disease progression of type 2 diabetes (T2D) has received considerable attention, but little is known about the disease development of T2D. The purposes of this study were to identify disease development variables (DDV) for development of T2D and to compare corresponding models for disease development. All subjects included in this study were the offspring of diabetic parents and were followed up to 25 years. Repeated fasting blood samples were collected during the follow-up. Longitudinal data of four DDVs, namely fasting blood glucose (FBG), fasting serum insulin (FSI), homeostatic model assessment of insulin resistance (HOMA-IR) and body mass index (BMI) were recorded and compared. According to the diabetes status at the end of the follow-up, the data analysis involved a progressor group of 25 subjects, and a non-progressor group of 127 subjects. The temporal changes in the four DDVs over the time course of the disease development were evaluated by a single-slope and a dual-slope population-based Bayesian model. A dual-slope model based on FBG was found to be the best disease development model. For non-progressors, the FBG baseline stayed at 69.2 [66.5, 72.1] mg/dl (Bayes estimate [95% Bayesian credible set]) and increased with age by a rate of 0.227 mg/dl [0.149, 0.3] per year. For the progressors, the FBG increase with age the same rate as non-progressors and started to have an additional increase of 2.27 [0.505, 4.52] mg/dl per year, starting 8.73 [-10.8, -6.93] years before the diagnosis of T2D. No significant longitudinal increasing or decreasing temporal pattern was found for FSI, HOMA-IR and BMI by the population-based Bayesian approach. The proposed model, which enables a quantitative, time-based evaluation of the development of T2D in this higher risk population, may be used to quantify the effect of interventions/prevention strategies such as drug treatment and lifestyle changes.

Lack of association between polymorphisms in the gene encoding protein tyrosine phosphatase 1B (PTPN1) and risk of Type 2 diabetes.

AIMS: Recently, an association of Type 2 diabetes (T2DM) with polymorphisms in PTPN1 located on chromosome 20q was reported. We attempted to replicate this finding in an ethnically homogeneous Polish population. METHODS: The study groups comprised 474 cases with T2DM and 411 control subjects with normal fasting glucose. All individuals were genotyped for the five previously reported PTPN1 polymorphisms using a fluorescence polarization method. HAPLO.STAT software was used to infer and compare haplotype distributions. RESULTS: The distributions of alleles and genotypes for the five genotyped PTPN1 polymorphisms did not differ between the T2DM cases and control subjects (lowest P = 0.6). Similarly, the frequency of the common haplotype reported to be associated with T2DM did not differ in cases and control subjects. We also failed to find such an association in Whites by performing a meta-analysis of all the available data on the association of those five SNPs with T2DM. CONCLUSION: This case-control study in a Polish population did not confirm the reported association between polymorphisms in PTPN1 and T2DM.

A genome-wide linkage scan for genes controlling variation in urinary albumin excretion in type II diabetes.

The main hallmark of diabetic nephropathy is elevation in urinary albumin excretion. We performed a genome-wide linkage scan in 63 extended families with multiple members with type II diabetes. Urinary albumin excretion, measured as the albumin-to-creatinine ratio (ACR), was determined in 426 diabetic and 431 nondiabetic relatives who were genotyped for 383 markers. The data were analyzed using variance components linkage analysis. Heritability (h2) of ACR was significant in diabetic (h2=0.23, P=0.0007), and nondiabetic (h2=0.39, P=0.0001) relatives. There was no significant difference in genetic variance of ACR between diabetic and nondiabetic relatives (P=0.16), and the genetic correlation (rG=0.64) for ACR between these two groups was not different from 1 (P=0.12). These results suggested that similar genes contribute to variation in ACR in diabetic and nondiabetic relatives. This hypothesis was supported further by the linkage results. Support for linkage to ACR was suggestive in diabetic relatives and became significant in all relatives for chromosome 22q (logarithm of odds, LOD=3.7) and chromosome 7q (LOD=3.1). When analyses were restricted to 59 Caucasian families, support for linkage in all relatives increased and became significant for 5q (LOD=3.4). In conclusion, genes on chromosomes 22q, 5q and 7q may contribute to variation in urinary albumin excretion in diabetic and nondiabetic individuals.

Risk of diabetes in siblings of index cases with Type 2 diabetes: implications for genetic studies.

AIMS: The goal was to estimate the sibling recurrence-risk ratio for Type 2 diabetes in families with diabetes occurring in middle age. Because diabetes aetiology involves environmental exposures and genetic susceptibility, we sought to identify determinants of the recurrence risk. METHODS: We surveyed patients diagnosed at ages 35-59 years (n = 563) to obtain information on the occurrence of diabetes in their relatives, particularly siblings (n = 1675). Age-specific prevalences of diabetes in the US population were used for comparison. RESULTS: The overall sibling recurrence-risk ratio for diabetes was low, about 1.8 in the Joslin families and even lower in three other studies that were reanalysed for comparison. In all studies, the diabetes risk in siblings of index cases without a history of diabetes in a parent was similar to that in the general population, suggesting that genetic factors contributed to the occurrence of diabetes in only a minority of these siblings. The fact that recurrence-risk ratios were elevated only in families with one or two diabetic parents indicates that susceptibility to Type 2 diabetes is transmitted primarily through an affected parent. In addition, the sibling recurrence-risk ratios were elevated even further in families with diabetes in both a parent and grandparent of the index case, and in siblings of non-obese index cases (percent ideal body weight < 120%). CONCLUSIONS: The selection of families with non-obese index cases and vertical transmission of diabetes through three generations may improve the success of efforts to map susceptibility genes for Type 2 diabetes.

A nonlinear effect of hyperglycemia and current cigarette smoking are major determinants of the onset of microalbuminuria in type 1 diabetes.

Cigarette smoking and poor glycemic control are risk factors for diabetic nephropathy in type 1 diabetes. However, the specifics of the relation of these risk factors to the onset of this complication have not been elucidated. To investigate these issues, we followed for 4 years 943 Joslin Clinic patients aged 15-44 years with type 1 diabetes who had normoalbuminuria during the 2-year baseline period. Microalbuminuria developed in 109 of the 943 individuals, giving an incidence rate of 3.3/100 person-years. The risk of onset of microalbuminuria was predicted somewhat more precisely by the measurements during the 1st and 2nd years preceding onset than by all the measurements during the longer (4-year) interval, suggesting attenuation of the impact of past hyperglycemia over time. Point estimates of the incidence rate (per 100 person-years) according to quartiles of HbA(1c) during the 1st and 2nd years preceding the outcome were 1.3 in the 1st, 1.5 in the 2nd, 3.1 in the 3rd, and 6.9 in the 4th (P = 1.3 x 10(-9)). Point estimates of the incidence rate (per 100 person-years) according to smoking status were 7.9 for current smokers, 1.8 for past smokers, and 2.2 for those who had never smoked (P = 2.0 x 10(-7)). In a multiple logistic model, the independent effects of HbA(1c) level and cigarette smoking remained highly significant, but their magnitudes were reduced. Using the same covariates in a generalized additive model, we examined the shape of the relationship between HbA(1c) and onset of microalbuminuria and found significant nonlinearity in the logarithm of odds scale (P = 0.04). The slope was steeper with HbA(1c) >8% than <8%. Furthermore, the change in the slope was magnified among current smokers. In conclusion, patients with type 1 diabetes who smoke and have an HbA(1c) >8% have the highest risk of onset of microalbuminuria.

Mutation screening of the neurogenin-3 gene in autosomal dominant diabetes.

We investigated whether genetic variability in neurogenin-3, a basic helix-loop-helix transcription factor that is expressed in the developing pancreas, contributes to the etiology of maturity-onset diabetes of the young or other forms of autosomal dominant diabetes. Ninety-one probands of families with autosomal dominant diabetes were screened for neurogenin-3 mutations by dideoxy fingerprinting. Three sequence differences were identified: a polymorphism not affecting the amino acid sequence (L75L), a CA insertion/deletion in intron 1 (-44ins/del), and a C to T transition causing a serine to phenylalanine substitution (S199F). None of these sequence differences were more frequent in the family probands than in 179 nondiabetic controls. In contrast, allele 199F was weakly, but significantly, associated with common type 2 diabetes (199F frequencies = 0.436 in 132 cases with type 2 diabetes vs. 0.346 in the family probands and 0.346 in controls; P = 0.05). The relative risk of type 2 diabetes for 199F carriers was 1.7 (95% confidence interval, 1.04-2.7). We conclude that sequence differences in the neurogenin-3 gene do not play a major role in the development of autosomal dominant diabetes. Rather, they might contribute to common type 2 diabetes, although this finding must be replicated in other populations.

Type 2 diabetes locus on 12q15. Further mapping and mutation screening of two candidate genes.

We recently reported evidence of a novel type 2 diabetes locus placed on chromosome 12q15 between markers D12S375 and D12S1684 (Diabetes 48:2246-2251, 1999). Four multigenerational families having logarithm of odds (LOD) scores >1.0 in the original analysis were genotyped for 11 additional markers in this interval to refine this mapping; this allowed us to narrow the linked region to the interval between markers D12S1693 and D12S326. In a multipoint parametric analysis using the VITESSE software, the LOD score for linkage at this location reached 3.1 in one of these families. This interval contains the gene for protein tyrosine phosphatase receptor type R (PTPRR)--a protein that may be involved in both insulin secretion and action. After determining PTPRR exon-intron structure, we identified several polymorphisms in this gene but no mutation segregating with diabetes. The search for mutations was also negative for carboxypeptidase M (CPM)--another candidate gene mapped to this region. In summary, our data provide further evidence for the existence of a type 2 diabetes locus on chromosome 12q15. This locus, however, does not appear to correspond to the PTPRR or CPM, although a contribution of mutations in regulatory regions cannot be excluded at this time.

APOE polymorphisms and the development of diabetic nephropathy in type 1 diabetes: results of case-control and family-based studies.

The goal of this study was to examine the association between known polymorphisms in the apolipoprotein E gene (APOE) and diabetic nephropathy (DN) in type 1 diabetes. We used both a case-control comparison and a family-based study design known as the transmission/disequilibrium test (TDT). For the case-control comparison, we collected DNA from 223 subjects with clinically diagnosed DN and 196 control subjects with normoalbuminuria and long-duration type 1 diabetes (> or = 15 years). For the family-based study, we obtained DNA from both parents of 154 DN subjects and 81 control subjects. The frequency of the epsilon2 allele of exon 4 of APOE was significantly higher in DN subjects than in control subjects. The risk of DN was 3.1 times higher (95% CI 1.6-5.9) in carriers of this allele than in noncarriers. In the family study, heterozygous parents for the E2 allele preferentially transmitted epsilon2 to DN offspring (64 vs. 36%, P < 0.03). Four additional polymorphisms (i.e., -491 A/T, -219 G/T, IE1 G/C, and APOCI insertion/deletion [I/D]) that flank the APOE locus were not associated with DN in either the case-control comparison or in the family-based study. In conclusion, the results of the case-control as well as the family-based study provide evidence that the epsilon2 allele of APOE increases the risk of DN in type 1 diabetes. The molecular mechanisms underlying this risk are unclear at present.

Further evidence for a susceptibility locus for type 2 diabetes on chromosome 20q13.1-q13.2.

We previously reported suggestive linkage between type 2 diabetes and markers in a region on chromosome 20q using data from a collection of 29 Caucasian families in which type 2 diabetes with middle-age-onset was segregated as an autosomal-dominant disorder. To map more precisely the susceptibility locus (or loci) within this broad region, we increased the family collection and genotyped all families for additional markers, both within the critical region and spaced over the rest of chromosome 20. Altogether 526 individuals (including 241 with diabetes) from the total collection of 43 families were included in the study. All individuals were genotyped for 23 highly polymorphic markers. Positive evidence for linkage was found for a 10-cM region on the long arm of chromosome 20q13.1-q13.2 between markers D20S119 and D20S428. The strongest evidence in two-point as well as multipoint linkage analysis (P = 1.8 x 10(-5)) occurred at the position corresponding to marker D20S196. The individuals with diabetes in the seven most strongly linked families had high serum insulin levels during fasting and 2-h post-glucose load periods. We did not find any evidence for linkage between type 2 diabetes and any other region on chromosome 20. In conclusion, our larger and more comprehensive study showed very strong evidence for a susceptibility gene for insulin-resistant type 2 diabetes located on the long arm of chromosome 20 around marker D20S196.

Segregation analysis of urinary albumin excretion in families with type 2 diabetes.

Elevated urinary albumin excretion (UAE) is a predictor of the development of nephropathy and cardiovascular mortality. To study whether genetic factors may determine UAE, we examined familial aggregation of UAE in 96 large multigenerational pedigrees ascertained for type 2 diabetes. A total of 1,269 subjects had UAE measured as the urinary albumin-to-creatinine ratio (ACR). This included 630 subjects with type 2 diabetes and 639 subjects without diabetes. A significant correlation (Spearman's correlation 0.34, P < 0.001) was found between the median ACR values determined separately in nondiabetic and diabetic members of the same family. To determine whether this familial aggregation of ACR could be explained by the transmission of 1 or more major genes and thus be suitable for gene mapping studies, segregation analyses were performed. In these analyses, ACR was modeled as a continuous trait with the inclusion of age, sex, and duration of diabetes as covariates. Likelihood ratio tests were performed to test competing hypotheses, and Akaike's information criterion was used to determine the most parsimonious models. The Mendelian model with multifactorial inheritance was supported more strongly than Mendelian inheritance alone. These analyses suggested that the best model for ACR levels was multifactorial with evidence for a common major gene. When the analyses were repeated for diabetic subjects only, the evidence for Mendelian inheritance was improved, although a single major locus with additional multifactorial effects was more strongly supported. The results from the current study suggest that levels of UAE are determined by a mixture of genes with large and small effects as well as other measured covariates, such as diabetes.

Aldose reductase gene polymorphisms and susceptibility to diabetic nephropathy in Type 1 diabetes mellitus.

AIMS: To investigate association and linkage between DNA sequence variants in the aldose reductase (AR) gene on chromosome 7q35 and diabetic nephropathy (DN) in Type 1 diabetes mellitus. METHODS: By sequencing the promoter region and 10 exons in eight DN cases and eight controls, a frequent bi-allelic polymorphism (C-106T) was discovered. This polymorphism and the known 5'ALR2 dinucleotide repeat polymorphism were genotyped in unrelated cases with advanced nephropathy (n = 221) and unrelated controls with normoalbuminuria (n = 193). For a family based study, 166 case-trios (case and both parents) and 83 control-trios (control and both parents) were also genotyped. RESULTS: In the case-control study, carriers of the Z-2 allele of the 5'ALR2 polymorphism had a significantly higher risk of DN than non-carriers (odds ratios: 1.6 for heterozygotes and 2.1 for homozygotes, P<0.05 for each). The same was true for carriers of the T allele of the C-106T polymorphism (odds ratios: 1.6 for heterozygotes and 1.9 for homozygotes, P<0.05 for each). Moreover, the haplotype carrying both risk alleles was in excess in DN cases. In the family study, transmission of risk alleles from heterozygous parents was consistent with the case-control study, excess transmission in case-trios and deficient in control-trios. CONCLUSIONS: Association between DN and two DNA sequence variants in the promoter region of the AR gene implicates the polyol pathway in the development of kidney complications in Type 1 diabetes mellitus. Further examination of the molecular mechanisms underlying these findings may provide insight into the pathogenesis of DN.

Progression of microalbuminuria to proteinuria in type 1 diabetes: nonlinear relationship with hyperglycemia.

While small clinical trials have shown that improved glycemic control reduces the risk of progression of microalbuminuria to proteinuria, two recent clinical trials did not confirm this finding. We sought to reconcile the contradictory evidence by examining the dose-response relationship between hyperglycemia and progression of microalbuminuria to proteinuria in individuals with type 1 diabetes and microalbuminuria (n = 312) who were followed for 4 years with repeated assessments of urinary albumin excretion. Since 33 patients did not participate in follow-up (10.6%), data for 279 patients were analyzed. Urinary albumin excretion level worsened to proteinuria in 40 (4.1 per 100 person-years). To examine the dose-response relationship, baseline HbA1c was divided into four roughly equal groups using the cut points 8, 9, and 10%. The incidence rate varied significantly among the four groups (P = 0.008). Among those with HbA1c <8.0%, the incidence rate of progression was only 1.3 per 100 person-years, while it was 5.1, 4.2, and 6.7 per 100 person-years in the three other groups. We used generalized additive models to examine the dose-response curve using HbA1c as a continuous variable and found that the risk of progression rises steeply between an HbA1c of 7.5-8.5% and then remains approximately constant across higher levels. In conclusion, the results of this study suggest that, in patients with microalbuminuria, the risk of progression to overt proteinuria can be reduced by improved glycemic control only if the HbA1c is maintained below 8.5%. Moreover, below that value, the risk declines as the level of HbA1c decreases.

Urinary albumin excretion in families with type 2 diabetes is heritable and genetically correlated to blood pressure.

UNLABELLED: Urinary albumin excretion in families with type 2 diabetes is heritable and genetically correlated to blood pressure. BACKGROUND: Levels of urinary albumin excretion (UAE) are used to define both the diagnosis of diabetic nephropathy and its progression. Predisposition to high blood pressure is also a risk factor for susceptibility to nephropathy, but its relationship with UAE in type 2 diabetes remains unclear. In this study, we have estimated heritabilities of UAE and blood pressure and their correlation attributable to genetic effects using 96 large families ascertained for type 2 diabetes. METHODS: In these families, 630 individuals with type 2 diabetes and 639 individuals with normoglycemia were examined. All of them had a determination of UAE as the urinary albumin creatinine ratio (ACR), a convenient index of UAE, together with blood pressure and other variables, such as age, sex, and body mass index. A variance components approach was used to estimate heritability and genetic correlations for ACR and systolic and diastolic blood pressures (SBP and DBP) after adjustment for relevant covariates. RESULTS: In the 96 pedigrees, 6481 usable pairs of relatives were identified. In the total collection of pairs, heritability for ACR (h2 = 0.27, P < 0.001) was similar to that for blood pressure. When only pairs of diabetic relatives were analyzed (N = 1732), the estimates of heritability increased slightly for ACR (h2 = 0.31), SBP (h2 = 0.33), and DBP (h2 = 0.23). A significant genetic correlation was found between ACR and SBP (rg 0.27) and DBP (rg 0.26) in all pairs of relatives (P < 0.001). In pairs of diabetic relatives, these values were higher for SBP and DBP, 0.38 and 0.52, respectively. CONCLUSION: In families with type 2 diabetes, UAE is a heritable trait, with a heritability similar to that for blood pressure. A significant genetic correlation between UAE and blood pressure, particularly in the presence of diabetes, indicates that these traits share common genetic determinants.

Risk of advanced diabetic nephropathy in type 1 diabetes is associated with endothelial nitric oxide synthase gene polymorphism.

UNLABELLED: Risk of advanced diabetic nephropathy in type 1 diabetes is associated with endothelial nitric oxide synthase gene polymorphism. BACKGROUND: Polymorphisms in the endothelial nitric oxide synthase gene (eNOS) may be implicated in the development of nephropathy in patients with type 1 or insulin-dependent diabetes mellitus (IDDM). METHODS: Three groups of IDDM patients were selected to study this hypothesis: cases with advanced diabetic nephropathy (N = 78), cases with overt proteinuria but normal serum creatinine (N = 74), and controls with normoalbuminuria despite 15 years of diabetes (N = 195). Parents of 132 cases and 53 controls were also examined and were used for the transmission disequilibrium test, a family-based study design to test association. RESULTS: We examined four eNOS polymorphisms, and two were associated with diabetic nephropathy in the case-control comparisons: a T to C substitution in the promoter at position -786 and the a-deletion/b-insertion in intron 4. For the former, the risk of developing advanced nephropathy was higher for C allele homozygotes than for the other two genotypes (odds ratio 2.8, 95% CI, 1.4 to 5.6). For the latter polymorphism, it was the a-deletion carriers that had the higher risk (odds ratio 2.3, 95% CI, 1.3 to 4.0) in comparison with noncarriers. Both polymorphisms were analyzed together as haplotypes in a family-based study using the transmission disequilibrium test. The C/a-deletion haplotype was transmitted from heterozygous parents to cases with advanced diabetic nephropathy with a significantly higher frequency than expected (P = 0.004). CONCLUSION: The findings of the case-control and family-based studies demonstrate clearly that DNA sequence differences in eNOS influence the risk of advanced nephropathy in type 1 diabetes.

Polymorphisms of human paraoxonase 1 gene (PON1) and susceptibility to diabetic nephropathy in type I diabetes mellitus.

AIMS/HYPOTHESIS: Oxidative stress is a putative mechanism in the development of diabetic nephropathy. Paraoxonase gene 1 is an HDL-bound enzyme that protects tissues against oxidative damage. Three common polymorphisms of paraoxonase gene 1, T-107C in the promoter, Leu54Met and Gln192Arg, that modify paraoxonase activity have been associated with cardiovascular disease. This study aimed to find whether these polymorphisms also contribute to the development of diabetic nephropathy. METHODS: The association between diabetic nephropathy and these three polymorphisms was examined in a case-control study. For this purpose, genomic DNA was collected from 188 patients with Type I (insulin-dependent) diabetes mellitus and diabetic nephropathy and from 179 unrelated patients with Type I diabetes but without diabetic nephropathy despite the duration of diabetes of 15 or more years. RESULTS: The genotype and allele frequencies for each of the three polymorphisms (T-107C, Leu54Met and Gln192Arg) were similar in cases and control subjects. CONCLUSION/INTERPRETATION: The three polymorphisms in paraoxonase gene 1 that have been associated with serum levels of paraoxonase are not associated with diabetic nephropathy. We show that this genetically determined component of the antioxidant capacity of HDL does not play a critical part in the development of diabetic nephropathy.

Mutations in NEUROD1 are associated with the development of type 2 diabetes mellitus.

The helix-loop-helix (HLH) protein NEUROD1 (also known as BETA2) functions as a regulatory switch for endocrine pancreatic development. In mice homozygous for a targeted disruption of Neurod, pancreatic islet morphogenesis is abnormal and overt diabetes develops due in part to inadequate expression of the insulin gene (Ins2). NEUROD1, following its heterodimerization with the ubiquitous HLH protein E47, regulates insulin gene (INS) expression by binding to a critical E-box motif on the INS promoter. Here we describe two mutations in NEUROD1, which are associated with the development of type 2 diabetes in the heterozygous state. The first, a missense mutation at Arg 111 in the DNA-binding domain, abolishes E-box binding activity of NEUROD1. The second mutation gives rise to a truncated polypeptide lacking the carboxy-terminal trans-activation domain, a region that associates with the co-activators CBP and p300 (refs 3,4). The clinical profile of patients with the truncated NEUROD1 polypeptide is more severe than that of patients with the Arg 111 mutation. Our findings suggest that deficient binding of NEUROD1 or binding of a transcriptionally inactive NEUROD1 polypeptide to target promoters in pancreatic islets leads to the development of type 2 diabetes in humans.