NeuroD/BETA2 gene variability and diabetes: no associations to late-onset type 2 diabetes but an A45 allele may represent a susceptibility marker for type 1 diabetes among Danes. Danish Study Group of Diabetes in Childhood, and the Danish IDDM Epidemiology and Genetics Group

Mutations in the NeuroD/BETA2 gene have been shown to associate with type 2 diabetes. In the present study, we examined mutations in the NeuroD/BETA2 gene for association with either type 1 or 2 diabetes. Three variants were identified in patients with type 2 diabetes: Ala45Thr (allelic frequency 0.36, 95% CI 0.31-0.41), Pro197His (0.01), and Ser259Ser (0.01). Ala45Thr and Pro197His were not associated with type 2 diabetes, but the transmission disequilibrium test showed unequal transmission of the A45 allele to offspring with type 1 diabetes (chi2 = 5.90, P < 0.02, odds ratio 1.55, 95% CI 0.91-2.63). This association could not be explained by linkage disequilibrium between the Ala45 allele and IDDM7 (D2S152), which is also located on chromosome 2q32. When tested in vitro, the biological activity of Thr45 (117+/-36% vs. Ala45) and His197 (90+/-28% vs. Pro197) on the regulation of the human insulin gene promoter appeared normal. In conclusion, mutations in the NeuroD/BETA2 gene are not a common cause of late-onset type 2 diabetes among Danes. However, in the type 1 diabetic Danish population, the Ala45Thr variant of NeuroD/BETA2 may represent a susceptibility marker independent of IDDM7 on chromosome 2q32.     

The peroxisome proliferator-activated receptor-gamma2 Pro12A1a variant: association with type 2 diabetes and trait differences

Recent studies have identified a common proline-to-alanine substitution (Pro12Ala) in the peroxisome proliferator-activated receptor-gamma2 (PPAR-gamma2), a nuclear receptor that regulates adipocyte differentiation and possibly insulin sensitivity. The Pro12Ala variant has been associated in some studies with diabetes-related traits and/or protection against type 2 diabetes. We examined this variant in 935 Finnish subjects, including 522 subjects with type 2 diabetes, 193 nondiabetic spouses, and 220 elderly nondiabetic control subjects. The frequency of the Pro12Ala variant was significantly lower in diabetic subjects than in nondiabetic subjects (0.15 vs. 0.21; P = 0.001). We also compared diabetes-related traits between subjects with and without the Pro12Ala variant within subgroups. Among diabetic subjects, the variant was associated with greater weight gain after age 20 years (P = 0.023) and lower triglyceride levels (P = 0.033). Diastolic blood pressure was higher in grossly obese (BMI >40 kg/m2) diabetic subjects with the variant. In nondiabetic spouses, the variant was associated with higher fasting insulin (P = 0.033), systolic blood pressure (P = 0.021), and diastolic blood pressure (P = 0.045). These findings support a role for the PPAR-gamma2 Pro12Ala variant in the etiology of type 2 diabetes and the insulin resistance syndrome.     

The PPARG Pro12Ala polymorphism is associated with a decreased risk of developing hyperglycemia over 6 years and combines with the effect of the APM1 G-11391A single nucleotide polymorphism: the Data From an Epidemiological Study on the Insulin Resistance Syndrome (DESIR) study

Although cross-sectional studies have associated the Pro12Ala polymorphism of PPARG with type 2 diabetes, prospective studies offer more opportunities to investigate genetic variants. Associations between PPARG polymorphisms with insulin resistance parameters and with the 6-year incidence of impaired fasting glucose or type 2 diabetes were tested in 3,914 French Caucasians from the DESIR (Data From an Epidemiological Study on the Insulin Resistance Syndrome) cohort. In subjects normoglycemic at baseline (n = 3,498), the 6-year risk of hyperglycemia was lower in PPARG Ala carriers (odds ratio [OR] vs. ProPro = 0.66 [95% CI 0.44-0.99], P = 0.046 adjusted for sex, age, and BMI). Similar results were found with the PPARG C1431T single nucleotide polymorphism (SNP; adjusted OR = 0.65 [0.44-0.96], P = 0.036). Both alleles are in strong linkage disequilibrium (D' = 0.669, P < 0.001). The baseline mean fasting insulin and homeostasis model assessment of insulin resistance (HOMA-IR) were lower in Ala carriers compared with ProPro homozygotes (P = 0.001 for both), with smaller increases in mean insulin and HOMA-IR during follow-up (P = 0.007 and 0.018, respectively). No association with insulin levels or HOMA-IR was found with C1431T. In this cohort, the APM1 G-11391A SNP is associated with the development of hyperglycemia. The combined effects of PPARG Pro12Ala and APM1 G-11391A SNPs showed no interaction on the risk of 6-year hyperglycemia. The PPARG Ala allele showed a relatively high protective effect in developing hyperglycemia and hyperinsulinemia during a 6-year period. Cumulative rather than synergistic effects of PPARG Pro12Ala and APM1 SNPs on diabetes risk are suggested.     

Impact of two common polymorphisms in the PPARgamma gene on glucose tolerance and plasma insulin profiles in monozygotic and dizygotic twins: thrifty genotype,thrifty phenotype,or both?

The Pro12Ala polymorphism in the PPARgamma2 gene has been associated with reduced risk of type 2 diabetes and insulin resistance. Recently, an association between dizygotic twinning and PPARgamma gene polymorphisms has been proposed. We investigated the phenotypic appearance of the two polymorphisms (Pro12Ala and exon 6 C-->T) in PPARgamma among elderly twins (207 monozygotic [MZ] and 342 dizygotic [DZ]) and evaluated whether they could explain previously reported differences in plasma glucose and insulin profiles among MZ and DZ twins. We demonstrated a significant impact of the Pro12Ala polymorphism on glucose tolerance, diabetic status, homeostasis model assessment for insulin resistance, and plasma insulin profiles in twins. No impact of the silent exon 6 polymorphism on glucose homeostasis or plasma insulin profiles was found. Independent of the polymorphisms, we observed a significant impact of zygosity status per se on the plasma insulin profile after oral glucose ingestion, with the MZ twins being more hyperinsulinemic, indicating insulin resistance, than the DZ twins. Nonsignificantly higher glucose concentrations were observed among MZ compared with DZ twins. We demonstrated an association between the Ala allele and reduced risk of diabetes and insulin resistance in twins. However, the differences in metabolic profiles among MZ and DZ twins were not explained by differences in frequencies of the genetic variants and may be due to intrauterine environmental factors operating in twins independent of genotype. Accordingly, our study simultaneously supports a role for both the intrauterine environment (thrifty phenotype) and for genetics (thrifty genotype) in the etiology of insulin resistance and perhaps glucose intolerance in twins.     

The effects of the Pro12Ala polymorphism of the peroxisome proliferator-activated receptor-gamma2 gene on insulin sensitivity and insulin metabolism interact with size at birth

Type 2 diabetes is known to be associated with a small body size at birth. Body size at birth is an indicator of the intrauterine environment. There is also a well-established association between the peroxisome proliferator-activated receptor (PPAR)-gamma2 gene and type 2 diabetes. We therefore assessed whether the effects of the Pro12Ala polymorphism of the PPAR-gamma2 gene on insulin sensitivity and insulin concentrations in adult life are modified by size at birth. We found that the effects of the Pro12Pro and Pro12Ala polymorphisms of the PPAR-gamma2 gene in elderly people depended on their body size at birth. The well-known association between small body size at birth and insulin resistance was seen only in individuals with the high-risk Pro12Pro allele. In those who had low birth weight, the Pro12Pro polymorphism of the PPAR-gamma2 gene was associated with increased insulin resistance (P < 0.002) and elevated insulin concentrations (P < 0.003). These interactions between the effects of the Pro12Ala polymorphisms of the PPAR-gamma2 gene on adult traits and the effects of birth weight link two previously unknown associations together within the context of type 2 diabetes. We suggest that these findings reflect gene-environment interaction.     

Association of the Pro12Ala polymorphism in the PPAR-gamma2 gene with 3-year incidence of type 2 diabetes and body weight change in the Finnish Diabetes Prevention Study

The association of the Pro12Ala polymorphism of the PPAR-gamma2 gene with the incidence of type 2 diabetes was investigated in 522 subjects with impaired glucose tolerance (IGT) participating in the Finnish Diabetes Prevention Study. Subjects were randomized to either an intensive diet and exercise group or a control group. By 3 years of intervention, the odds ratio of the development of type 2 diabetes for subjects with the Ala12 allele was 2.11-fold compared with that for subjects with the Pro12Pro genotype (95% CI 1.20-3.72). The risk for type 2 diabetes increased also in subjects who gained weight or belonged to the control group. In the intervention group, subjects with the Ala12Ala genotype lost more weight during the follow-up than subjects with other genotypes (Pro12Pro vs. Ala12Ala P = 0.043), and none of subjects with the Ala12Ala genotype developed type 2 diabetes in this group. In conclusion, the Ala12 allele may predispose to the development of type 2 diabetes in obese subjects with IGT. However, beneficial changes in diet, increases in physical activity, and weight loss may reverse, to some extent, the diabetogenic impact of the Ala12 allele, possibly due to an improved insulin sensitivity.     

Variations in peptide YY and Y2 receptor genes are associated with severe obesity in Pima Indian men

Peptide YY (PYY) and Y2 receptor (Y2R) may be important in the central regulation of body weight and food intake. To determine whether genetic variation in PYY and/or Y2R may contribute to morbid obesity in humans, these genes were sequenced in 83 extremely obese Pima Indians (BMI > or = 50 kg/m2). Sequencing of PYY identified three single nucleotide polymorphisms (SNPs) in the untranslated region. Sequencing of the Y2R coding region identified one missense (Ala172Thr) substitution and two silent substitutions. Eight additional SNPs in the 5' untranslated region of Y2R were identified from public databases. These SNPs were genotyped in 489 full-heritage adult Pimas (362 severely obese and 127 nondiabetic, nonobese subjects), who are not first-degree relatives, for association analysis. The PYY variants were not associated with obesity, whereas four variants from two haplotype blocks in Y2R were marginally associated (P = 0.054-0.067) with obesity. However, if the analysis was restricted to men (n = 167, 100 obese and 67 lean), the PYY variants and two SNPs in Y2R that were in complete linkage disequilibrium were significantly associated with severe obesity (P = 0.001 and P = 0.002, respectively). Our data suggest that the PYY-Y2R pathway may influence body weight through a sex-specific mechanism, but this finding requires confirmation in other populations.     

Analysis of the type 2 diabetes-associated single nucleotide polymorphisms in the genes IRS1, KCNJ11, and PPARG2 in type 1 diabetes

It has been proposed that type 1 and 2 diabetes might share common pathophysiological pathways and, to some extent, genetic background. However, to date there has been no convincing data to establish a molecular genetic link between them. We have genotyped three single nucleotide polymorphisms associated with type 2 diabetes in a large type 1 diabetic family collection of European descent: Gly972Arg in the insulin receptor substrate 1 (IRS1) gene, Glu23Lys in the potassium inwardly-rectifying channel gene (KCNJ11), and Pro12Ala in the peroxisome proliferative-activated receptor gamma2 gene (PPARG2). We were unable to confirm a recently published association of the IRS1 Gly972Arg variant with type 1 diabetes. Moreover, KCNJ11 Glu23Lys showed no association with type 1 diabetes (P > 0.05). However, the PPARG2 Pro12Ala variant showed evidence of association (RR 1.15, 95% CI 1.04-1.28, P = 0.008). Additional studies need to be conducted to confirm this result.     

过氧化物酶体增殖物激活受体-γ及其共激活蛋白1的单核苷酸多态性与多囊卵巢综合征表型的关系

目的研究过氧化物酶体增殖物激活受体-γ2(PPAR-γ2)和过氧化物酶体增殖物激活受体-γ共激活蛋白1(PGC-1)α的单核苷酸多态性与多囊卵巢综合征(PCOS)发病及生殖激素的关系。方法收集PCOS患者和非PCOS妇女正常对照的血液标本。记录两组的初潮年龄,身高、体重,分离血清测定生殖激素,分离血液中的淋巴细胞提取总DNA,特异引物扩增后限制性酶切(PCR-RFLP),电泳分离,溴化乙锭(EB)染色。结果PCOS患者的PPAR-γ2(Pro12Pro,Pro12Ala和Ala12Ala)基因型分布(分别为0.910,0.090,0)与正常人的分布(分别为0.925,0.068,0.007)无显著差异。PCOS患者的PGC-1α(Gly482Gly,Gly482Ser和Ser482Ser)基因型分布(分别为0.328,0.402,0.269)与正常人的分布(分别为0.333,0.374,0.293)无显著差异。体重指数(BMI)、血清总睾酮(T)和卵泡刺激素(FSH)、黄体生成素(LH)、LH/FSH、孕酮(P)和雌二醇(E2)在PPAR-γ2和PGC-1α各基因型之间无显著差异。与其他人种比较,中国人PPAR-γ2中Ala等位基因频率较低(4.4%),但PGC-1α的频率较高(48%)。结论结果提示PPARγ2 Pro12Ala和PGC-1αGly482Ser这两种单核苷酸多态性与PCOS的发病无相关性。     

PCLO variants are nominally associated with early-onset type 2 diabetes and insulin resistance in Pima Indians

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.The Pima Indians of Arizona have an extremely high prevalence of type 2 diabetes (1). Their diabetes is characterized by obesity, dysfunction of insulin secretion, insulin resistance (decreased insulin-mediated glucose disposal), and increased rate of endogenous glucose output (2). Studies have shown that type 2 diabetes, insulin action, acute insulin response to glucose, and obesity are highly heritable in this population (3–5). To identify genes that underlie the development of type 2 diabetes in Pima Indians, we recently completed a genome-wide association (GWA) study using the Affymetrix 100K SNP genotyping array (6). Two single nucleotide polymorphisms (SNPs), rs10487656 and rs10487657, that ranked among the top 1% for a general association with early-onset type 2 diabetes (defined as age of onset <25 years) mapped within an intron of the PCLO gene. PCLO is located on chromosome 7q21 and encodes for a presynaptic cytomatrix protein that functions as a Ca²⁺ sensor that could potentially have a role in insulin secretion and/or insulin action (7–10); therefore, PCLO was analyzed as a positional and physiological candidate gene for type 2 diabetes.     

New amino acid substitutions in the IRS-2 gene in Finnish and Chinese subjects with late-onset type 2 diabetes

We investigated the significance of the variants of the IRS-2 gene in patients with type 2 diabetes. The entire coding part of the IRS-2 gene was screened by single-strand conformation polymorphism analysis in 40 Chinese and 40 Finnish patients with late-onset type 2 diabetes. The association of the variants of the IRS-2 gene with type 2 diabetes was studied in 85 Finnish diabetic patients and 82 Finnish control subjects and in 100 Chinese diabetic patients and 85 Chinese control subjects. The four variants predicting structural changes in the insulin receptor substrate (IRS)-2 protein included an insertion of AAC (Asn) in the Asn repeat sequence centered around codons 29-36 (allele frequencies of 0 vs. 0.6% and 1.5 vs. 0%), the Ala157Thr substitution (0 vs. 0% and 0.5 vs. 0%), the Leu647Val substitution (0.6 vs. 0% and 0 vs. 0%), and the Gly1057Asp polymorphism (31 vs. 31% and 35 vs. 30%) (P = NS for all comparisons). Furthermore, six silent variants were observed (CGC147CGG, CCC155CCG, GCC156GCT, AGT723AGC, TGT816TGC, and CCC829CCT). The Gly1057Asp polymorphism was not associated with insulin resistance or impaired insulin secretion in Finnish subjects with normal glucose tolerance (n = 295) or impaired glucose tolerance (n = 38). These data indicate that structural variants of the IRS-2 gene were uncommon in Finnish and Chinese patients with type 2 diabetes. Thus, the variants in the coding part of the IRS-2 gene are unlikely to have a major role in the development of type 2 diabetes in Finnish or Chinese subjects.     

The human peroxisome proliferator-activated receptor gamma2 (PPARgamma2) Pro12Ala polymorphism is associated with decreased risk of diabetic nephropathy in patients with type 2 diabetes

The peroxisome proliferator-activated receptor gamma2 (PPARgamma2) Pro12Ala polymorphism has been associated with a decreased risk of type 2 diabetes and a lower albumin excretion rate (AER) in patients with established diabetes. We performed a case-control study aiming to evaluate the association between the Pro12Ala polymorphism and diabetic nephropathy. Genomic DNA was obtained from 104 type 2 diabetic patients (case subjects) with chronic renal insufficiency (78 on dialysis and 26 with proteinuria [AER >or=200 microg/min] and serum creatinine >or=2.0 mg/dl) and 212 normoalbuminuric patients (AER <20 microg/min) with known diabetes duration >or=10 years (control subjects). The genotypic distribution of the PPARgamma2 Pro12Ala polymorphism in these diabetic patients was in Hardy-Weinberg equilibrium, and the Ala allele frequency was 9%. The frequency of Ala carriers (Ala/Ala or Ala/Pro) was 20.3% in control subjects and 10.6% in case subjects (P = 0.031). The odds ratio of having diabetic nephropathy for Ala carriers was 0.465 (95% CI 0.229-0.945; P = 0.034). Carriers of the Ala allele were not different from noncarriers (Pro/Pro) regarding sex (38.9 vs. 44.1% males) or ethnicity (77.4 vs. 71.7% white) distribution, age (61 +/- 10 vs. 61 +/- 10 years), known diabetes duration (17 +/- 7 vs. 16 +/- 7 years), BMI (27 +/- 4 vs. 28 +/- 5 kg/m(2)), fasting plasma glucose (184 +/- 81 vs. 176 +/- 72 mg/dl), HbA(1c) (6.7 +/- 2.3 vs. 6.9 +/- 2.4%; high-performance liquid chromatography reference range: 2.7-4.3%), and systolic (145 +/- 27 vs. 0.144 +/- 24 mmHg) or diastolic (87 +/- 14 vs. 85 +/- 14 mmHg) blood pressure, respectively. In conclusion, the presence of the Ala allele may confer protection from diabetic nephropathy in patients with type 2 diabetes.     

Variation in the interleukin-6 receptor gene associates with type 2 diabetes in Danish whites

Interleukin-6 (IL-6) is a pleiotropic cytokine involved in the pathophysiology of various human diseases such as type 2 diabetes and obesity. IL-6 signals via a heterodimeric receptor complex consisting of a soluble IL-6 alpha-subunit (IL-6 receptor [IL6R]) and a signal transducing subunit (gp130). The IL6R gene maps to an important candidate locus for type 2 diabetes on chromosome 1q21. An Asp358Ala polymorphism of the IL6R has been reported to associate with obesity in Pima Indians. We investigated the Asp358Ala polymorphism in relation to type 2 diabetes, obesity, and other pre-diabetic quantitative traits among Danish whites. By applying a recessive genetic model in a case-control study of 1,349 type 2 diabetic patients and 4,596 glucose-tolerant control subjects, we found a significant difference in genotype distribution (P = 0.008) and in allele frequency (Ala-allele 38.3% [95% CI 36.5-40.1] in diabetic subjects vs. 41.2% [40.2-42.2] in control subjects; P = 0.007). The odds ratio for the Asp/Asp carriers versus Ala/Ala carriers was 1.38 (1.09-1.71). Among 4,251 middle-aged glucose-tolerant subjects, the Asp358Ala polymorphism was not associated with estimates of obesity, post-oral glucose tolerance test serum insulin release, or the homeostasis model assessment of insulin resistance index. In conclusion, the Asp358Ala polymorphism of the IL6R associates with type 2 diabetes in Danish whites.     

Pro12Ala of the peroxisome proliferator-activated receptor-gamma2 gene is associated with lower serum insulin levels in nonobese African Americans: the Atherosclerosis Risk in Communities Study

Recent research suggests that the Pro12Ala variant in peroxisome proliferator-activated receptor-gamma2 (PPAR-gamma2) is associated with diabetes- and obesity-related traits, and that its effects may be modified by obesity status. We characterized this variant in a population-based sample of 1,441 middle-aged African-American individuals with respect to diabetes-, obesity-, and other cardiovascular-related traits, both cross-sectionally and prospectively. The overall frequency of Ala12 was 1.9% (95% CI 1.5-2.5%), significantly lower than in Caucasian populations. Consistent with previous findings in Caucasians, African Americans with type 2 diabetes tended to be less likely to have the Pro/Ala genotype than those without (odds ratio [OR] 0.64, 95% CI 0.34-1.20); however, this OR was not statistically significant. Among nonobese individuals, the Pro/Ala genotype was associated with significantly lower ln(insulin) (P = 0.001), lower ln(HOMA-IR) (homeostasis model assessment of insulin resistance) (P = 0.002), higher fasting glucose-to-insulin ratio (P = 0.005), and lower diastolic blood pressure (P = 0.02). Among overweight individuals (BMI 25-29.9 kg/m(2)), the Pro/Ala genotype was associated with greater BMI (P = 0.02), waist-to-hip ratio (P = 0.01), and waist circumference (P = 0.04). Among obese individuals, there was no association between any of the diabetes- or obesity-related traits and the Pro12Ala PPAR-gamma2 variant. We conclude that among nonobese African Americans, the Pro/Ala genotype is associated with markers of greater insulin sensitivity.     

Hyperglycemia and a common variant of GCKR are associated with the levels of eight amino acids in 9,369 Finnish men

We investigated the association of glycemia and 43 genetic risk variants for hyperglycemia/type 2 diabetes with amino acid levels in the population-based Metabolic Syndrome in Men (METSIM) Study, including 9,369 nondiabetic or newly diagnosed type 2 diabetic Finnish men. Plasma levels of eight amino acids were measured with proton nuclear magnetic resonance spectroscopy. Increasing fasting and 2-h plasma glucose levels were associated with increasing levels of several amino acids and decreasing levels of histidine and glutamine. Alanine, leucine, isoleucine, tyrosine, and glutamine predicted incident type 2 diabetes in a 4.7-year follow-up of the METSIM Study, and their effects were largely mediated by insulin resistance (except for glutamine). We also found significant correlations between insulin sensitivity (Matsuda insulin sensitivity index) and mRNA expression of genes regulating amino acid degradation in 200 subcutaneous adipose tissue samples. Only 1 of 43 risk single nucleotide polymorphisms for type 2 diabetes or hyperglycemia, the glucose-increasing major C allele of rs780094 of GCKR, was significantly associated with decreased levels of alanine and isoleucine and elevated levels of glutamine. In conclusion, the levels of branched-chain, aromatic amino acids and alanine increased and the levels of glutamine and histidine decreased with increasing glycemia, reflecting, at least in part, insulin resistance. Only one single nucleotide polymorphism regulating hyperglycemia was significantly associated with amino acid levels.