Variants of the insulin receptor substrate-1 and fatty acid binding protein 2 genes and the risk of type 2 diabetes, obesity, and hyperinsulinemia in African-Americans: the Atherosclerosis Risk in Communities Study.

We conducted a community-based case-control study of African-American men and women in the Atherosclerosis Risk in Communities Study. The allele frequencies of the Gly972Arg variant of the insulin receptor substrate-1 (IRS-1) gene and the Ala54Thr variant of the fatty acid binding protein 2 (FABP2) gene were compared in 992 normal control subjects and three patient groups: 1) 321 type 2 diabetic individuals, 2) 260 severely obese individuals, and 3) 258 markedly hyperinsulinemic individuals without diabetes. Allele frequencies of Gly972Arg IRS-1 and Ala54Thr FABP2 were 0.07 and 0.22, respectively; there were no differences in allele or genotype frequencies between patients and control subjects for either gene variant. In weighted linear regression of all patients and control subjects, the presence of the IRS-1 gene variant was associated with a 0.85 (0.42) kg/m2 higher BMI (P = 0.04). In addition, individuals with at least one IRS-1 Arg972 allele and two FABP2 Thr54 alleles had a BMI of 33.3 (7.9) kg/m2, compared with 30.0 (6.3) kg/m2 for those with neither allele (P = 0.05). These results suggest that in African-Americans, these variants in the IRS-1 and FABP2 genes are not associated with the risk of type 2 diabetes, severe obesity, or marked hyperinsulinemia, but that their independent and joint effects may be associated with small increases in BMI.     

Genetic variation at the adiponectin locus and risk of type 2 diabetes in women

Previous data suggesting that polymorphisms in the adiponectin gene were associated with insulin resistance or type 2 diabetes have been inconsistent. We assessed the relationship between five common haplotype-tagging single nucleotide polymorphisms (SNPs) in the adiponectin gene (-11365C>G, -4034A>C, -3964A>G, +45T>G, and +276G>T), haplotypes defined by these SNPs, and the risk of type 2 diabetes by conducting a nested case-control study of 642 incident cases of type 2 diabetes and 995 matching control subjects in the Nurses' Health Study. Overall, we did not observe significant differences in genotype or allele frequencies for the five SNPs between the case and control subjects. After adjustment for diabetes risk factors, the -4034 C/C genotype was associated with a reduced risk of diabetes (odds ratio [OR] compared with the A/A genotype = 0.70, 95% CI 0.50-0.99, P = 0.04). In subgroup analyses, the +276 genotype was significantly associated with diabetes risk only among subjects with peroxisome proliferator-activated receptor-gamma (PPAR gamma) variant 12Ala allele (OR comparing +276 T alleles with the G/G genotype = 1.69, 1.04-2.75, P = 0.035) or among obese subjects (1.46, 1.03-2.08, P = 0.03). These data suggest a potential interaction between the adiponectin genotype and PPAR gamma genotype or obesity, but these analyses should be considered exploratory and require further investigation in larger studies.     

Studies of the peptide YY and neuropeptide Y2 receptor genes in relation to human obesity and obesity-related traits

Peptide-YY (PYY) is secreted from endocrine L-cells of the gastrointestinal tract in response to caloric ingestion and may mediate postprandial satiety through the hypothalamic neuropeptide Y2 receptor (Y2R). We examined whether variants in the genes encoding PYY and Y2R might be associated with obesity-related phenotypes in humans. Among 101 subjects with severe early-onset obesity and a history of hyperphagia, we found two rare sequence variants-L73P and IVS2 + 32delG-in PYY and three rare missense mutations-L40F, F87I, and A172T-in Y2R. Although none of these were found in 100 normal-weight white control subjects, L73P in PYY and F87I and A172T in Y2R did not segregate with obesity in family studies, and family data were unavailable for IVS2 + 32delG in PYY and L40F in Y2R. Two common single nucleotide polymorphisms (SNPs), R72T and IVS3 + 68C>T, in PYY were in tight linkage disequilibrium but showed no association with BMI in a large white population. In the Y2R, two SNPs, 585T>C and 936T>C, were found and were in tight linkage disequilibrium. Men, homozygous for the rarer variant, had significantly lower BMI (P = 0.017), waist-to-hip ratio (P = 0.013), and, surprisingly, higher nonesterified fatty acid levels (P = 0.01). In conclusion, mutations in PYY and Y2R are not commonly found in humans with severe early-onset obesity. The relationship between common variants in Y2R and obesity-related traits deserves further exploration in other populations.     

Low plasma ghrelin is associated with insulin resistance, hypertension, and the prevalence of type 2 diabetes

Experimental studies have suggested that ghrelin plays a role in glucose homeostasis and in the regulation of blood pressure (BP). We therefore assessed the hypothesis that a low ghrelin concentration may be a risk factor for type 2 diabetes and hypertension. We also characterized the effect of the ghrelin Arg51Gln and Leu72Met mutations on ghrelin concentrations in the population-based hypertensive (n = 519) and control (n = 526) cohorts of our OPERA (Oulu Project Elucidating Risk of Atherosclerosis) study. The fasting plasma ghrelin concentrations of 1,040 subjects were analyzed using the radioimmunoassay method. Insulin sensitivity was assessed using the quantitative insulin sensitivity check index (QUICKI). Ghrelin concentrations were negatively associated with fasting insulin (P < 0.001), systolic (P = 0.026) and diastolic BP (P = 0.018), and the prevalence of type 2 diabetes (P = 0.015) and insulin resistance (P < 0.001) in the multivariate models. In the control cohort, low ghrelin was associated with hypertension (BP >140/90 mmHg) (P = 0.031). The subjects with the ghrelin 51Gln allele had lower ghrelin concentrations than the Arg51Arg homozygotes (P = 0.001). We conclude that low ghrelin is independently associated with type 2 diabetes, insulin concentration, insulin resistance, and elevated BP. Therefore, it might have some role in the etiology of type 2 diabetes and the regulation of BP. The ghrelin Arg51Gln mutation is associated with low plasma ghrelin concentrations.     

Genetic variation of the GLUT10 glucose transporter (SLC2A10) and relationships to type 2 diabetes and intermediary traits

The SLC2A10 gene encodes the GLUT10 facilitative glucose transporter, which is expressed in high amounts in liver and pancreas. The gene is mapped to chromosome 20q12-q13.1, a region that has been shown to be linked to type 2 diabetes. The gene was examined in 61 Danish type 2 diabetic patients, and a total of six variants (-27C-->T, Ala206Thr, Ala272Ala, IVS2 + 10G-->A, IVS4 + 18T-->G, and IVS4 + 26G-->A) were identified and investigated in an association study, which included 503 type 2 diabetic patients and 510 glucose-tolerant control subjects. None of the variants were associated with type 2 diabetes. Interestingly, carriers of the codon 206 Thr allele had 18% lower fasting serum insulin levels (P = 0.002) and 20% lower insulinogenic index (P = 0.03) than homozygous carriers of the Ala allele. These results suggest that variation in the coding region of SLC2A10 does not contribute substantially to the pathogenesis of type 2 diabetes in the examined study population. However, the codon 206 polymorphism may be related to the interindividual variation in fasting and oral glucose-induced serum insulin levels.     

A common promoter polymorphism in the hepatic lipase gene (LIPC-480C>T) is associated with an increase in coronary calcification in type 1 diabetes

Type 1 diabetes is associated with coronary heart disease (CHD) and coronary artery calcification (CAC), a measure of subclinical CHD. The hepatic lipase gene promoter polymorphism (LIPC-480C>T) is a common variant affecting lipid metabolism. This study examined the relation between the LIPC-480C>T and CAC in type 1 diabetes. In the type 1 diabetic patients studied, 56% had CAC >0 Agatston units (AU). These subjects had a longer duration of diabetes (26.2 +/- 1.3 vs. 17.8 +/- 1.4 years; P < 0.001), lower HDL cholesterol levels (55.7 +/- 2.4 vs. 61.0 +/- 2.5 mg/dl; P = 0.05), higher triglyceride levels (101 +/- 17.3 vs. 66 +/- 7.6 mg/dl; P < 0.05), and higher diastolic blood pressure (79.7 +/- 1.0 vs. 76.0 +/- 1.4 mmHg; P < 0.05). The LIPC-480 T allele was more common in subjects with CAC (frequency = 0.31 +/- 0.05 vs. 0.14 +/- 0.04; P = 0.006). The proportion with CAC was 44% in LIPC-480CC subjects, 71% in heterozygotes, and 83% in LIPC-480TT subjects (P < 0.01). LIPC-480 T allele frequency increased as the amount of CAC increased (P = 0.007). LIPC-480 genotype was independently associated with the CAC (odds ratio = 2.90, 95% CI 1.22-6.92, P < 0.05) after adjusting for duration of diabetes, age, sex, diastolic blood pressure, HDL cholesterol, and triglyceride levels. In conclusion, the LIPC-480C>T polymorphism was associated with subclinical CHD in type 1 diabetes. This genetic variant may identify subjects in which early intervention to prevent CHD may be appropriate.     

COL18A1 is highly expressed during human adipocyte differentiation and the SNP c.1136C > T in its "frizzled" motif is associated with obesity in diabetes type 2 patients

Collagen XVIII can generate two fragments, NC11-728 containing a frizzled motif which possibly acts in Wnt signaling and Endostatin, which is cleaved from the NC1 and is a potent inhibitor of angiogenesis. Collagen XVIII and Wnt signaling have recently been associated with adipogenic differentiation and obesity in some animal models, but not in humans. In the present report, we have shown that COL18A1 expression increases during human adipogenic differentiation. We also tested if polymorphisms in the Frizzled (c.1136C>T; Thr379Met) and Endostatin (c.4349G>A; Asp1437Asn) regions contribute towards susceptibility to obesity in patients with type 2 diabetes (113 obese, BMI > or =30; 232 non-obese, BMI < 30) of European ancestry. No evidence of association was observed between the allele c.4349G>A and obesity, but we observed a significantly higher frequency of homozygotes c.1136TT in obese (19.5%) than in non-obese individuals (10.9%) [P = 0.02; OR = 2.0 (95%CI: 1.07-3.73)], suggesting that the allele c.1136T is associated to obesity in a recessive model. This genotype, after controlling for cholesterol, LDL cholesterol, and triglycerides, was independently associated with obesity (P = 0.048), and increases the chance of obesity in 2.8 times. Therefore, our data suggest the involvement of collagen XVIII in human adipogenesis and susceptibility to obesity.     

No evidence of association of ENPP1 variants with type 2 diabetes or obesity in a study of 8,089 U.K. Caucasians

Ectoenzyme nucleotide pyrophosphate phosphodiesterase 1 (ENPP1) is an inhibitor of insulin-induced activation of the insulin receptor. There is strong evidence from several previous studies that a common coding variant of ENPP1 (K121Q) and a three-marker haplotype (Q121, IVS20delT-11, and G+1044TGA) are associated with type 2 diabetes and obesity. We examined the impact of ENPP1 variation on type 2 diabetes and obesity in a large U.K. genetic association study. We genotyped the three previously associated polymorphisms in 2,363 type 2 diabetic case and 4,045 control subjects, as well as 1,681 subjects from 529 type 2 diabetic families. We used the same subjects for morbid and moderate obesity association studies. For type 2 diabetes, moderate and morbid obesity, and for both the Q121 and three-marker haplotype, our results exclude with >95% confidence the effect sizes from previous studies (Q121 allele: odds ratio 1.02 [95% CI 0.93-1.12], P = 0.61; 1.00 [0.85-1.18], P = 0.99; and 0.92 [0.70-1.20], P = 0.41; three-marker haplotype: 1.10 [0.96-1.26], P = 0.17; 0.97 [0.77-1.23], P = 0.81; and 0.86 [0.57-1.30], P = 0.46 for type 2 diabetes, moderate, and morbid obesity, respectively). A K121Q type 2 diabetes meta-analysis of all previously published studies remained significant after the inclusion of this study (1.25 [1.10-1.43], P = 0.0007), although there was some evidence of publication bias. In conclusion, we find no evidence that previously associated variants of ENPP1 are associated with type 2 diabetes or obesity in the U.K. population.     

Paraoxonase 192 Gln/Arg gene polymorphism, coronary artery disease, and myocardial infarction in type 2 diabetes

Paraoxonase is an HDL-associated enzyme implicated in the pathogenesis of atherosclerosis by protecting lipoproteins against peroxidation. Its biallelic gene polymorphism at codon 192 (glutamine/arginine) has been associated with coronary artery disease (CAD). To further evaluate the role of this paraoxonase gene polymorphism for CAD in type 2 diabetes, we determined the paraoxonase genotype in 288 type 2 diabetic patients (170 with and 118 without angiographically documented CAD). The paraoxonase 192 Gln/Arg genotype was assessed using polymerase chain reaction followed by AlwI digestion. The frequency of the Gln allele was 0.656 in the CAD patients and 0.746 in the controls (chi2 = 5.36, P = 0.02). Compared with the Gln/Gln genotypes, the age-adjusted odds ratio for CAD was 1.78 (95% CI 1.08-2.96, P = 0.02) in subjects carrying at least one Arg allele. In the multivariate analysis, this association was even stronger after correction for the possible confounders age, sex, smoking history, and hypertension. Among current and former smokers, the odds ratio (OR) for having CAD among patients with at least one Arg allele was 3.58 (1.45-9.53, P < 0.01). The paraoxonase Arg allele was not associated with the history of myocardial infarction (OR 1.20 [0.73-1.99, NS]), but was with the extent of CAD (OR for three-vessel disease 1.92 [1.15-3.27, P = 0.01]). Our data indicate that the 192 Arg allele of the human paraoxonase gene is a risk factor for CAD but not myocardial infarction in type 2 diabetic patients, a risk factor further modified by cigarette smoking. This risk could possibly be explained by a reduced ability of the paraoxonase Arg isoform to protect lipoproteins against peroxidation.     

Positional candidate gene analysis of Lim domain homeobox gene (Isl-1) on chromosome 5q11-q13 in a French morbidly obese population suggests indication for association with type 2 diabetes

The Lim domain homeobox gene (Isl-1) is a positional candidate gene for obesity that maps on chromosome 5q11-q13, a locus linked to BMI and leptin levels in French Caucasians. Isl-1 might be involved in body weight regulation and glucose homeostasis via the activation of proglucagon gene expression, which encodes for glucagon and glucagon-like peptides. By mutation screening of 72 obese subjects, we identified three single-nucleotide polymorphisms (SNPs) in the Isl1 gene. The allele frequencies in the morbidly obese group did not differ from that of the control group. In the obese group, the -47G allele was associated with a decreased risk of type 2 diabetes (odds ratio 0.41, P = 0.019). The AG bearers displayed a higher maximal BMI than the AA bearers in the whole obese group (P = 0.026) as well as in the type 2 diabetic obese subgroup (P = 0.014). In obese families, this allele was not preferentially transmitted from heterozygous parents to their obese siblings, indicating that Isl-1 does not contribute to the linkage with obesity on 5cen-q. However, in French Caucasian morbidly obese subjects, the Isl1-47A-->G SNP may modulate the risk for type 2 diabetes and may increase body weight in diabetic morbidly obese subjects.     

Impaired capacity to lose visceral adipose tissue during weight reduction in obese postmenopausal women with the Trp64Arg beta3-adrenoceptor gene variant

Controversy exists regarding the association between the Trp64Arg variant of the beta3-adrenoceptor gene and visceral obesity. The cross-sectional nature of most studies, the modest effect of the variant, and sex or ethnic differences between groups have contributed to discrepancies among investigations. To overcome these confounding factors, we examined the effect of the Trp64Arg variant on total and visceral adipose tissue loss, insulin sensitivity, and cardiovascular disease risk factors in response to weight reduction in obese older women. A total of 24 women (age 57 +/- 4 years), including 1 Trp64Arg homozygote, 10 Trp64Arg heterozygotes, and 13 normal homozygotes, were admitted to a weight reduction program of 13 +/- 3 months, with weight and nutritional intake stabilization established before testing. Total and regional adiposity were measured with dual-energy X-ray absorptiometry and computed tomography, insulin sensitivity was measured by the hyperinsulinemic-euglycemic clamp technique, and a blood lipid profile was obtained. No baseline differences were noted in adiposity measurements, glucose disposal, and lipid profiles among carriers and noncarriers of the variant allele. In response to weight loss, carriers and noncarriers of the Trp64Arg allele had similar reductions in body weight (-16.4 +/- 5.0 vs. -14.1 +/- 6.2 kg, NS) and body fat (-10.0 +/- 5.2 vs. -11.5 +/- 3.9 kg, NS). However, loss of visceral adipose tissue was 43% lower in carriers of the Trp64Arg allele compared with noncarriers (-46 +/- 27 vs. -81 +/- 51 cm2, P = 0.05). Furthermore, there was less improvement in the total cholesterol-to-HDL cholesterol ratio (-0.18 +/- 0.54 vs. -0.72 +/- 0.56, P = 0.04) in carriers compared with noncarriers of the allele. Although glucose disposal improved in both groups, there was no difference in the magnitude of improvement between carriers and noncarriers of the variant allele. In conclusion, older obese women carrying the Trp64Arg beta3-adrenoceptor gene variant have an impaired capacity to lose visceral adipose tissue in response to prolonged caloric restriction. Despite these genetic differences in loss of intraabdominal adipose tissue, improvement in glucose disposal was similar between groups.     

Metabolic effects of the Gly1057Asp polymorphism in IRS-2 and interactions with obesity

Insulin receptor substrate (IRS)-2 plays an important role in insulin signaling and its disruption results in diabetes in mice. In humans, the IRS-2 Gly1057Asp substitution was associated with lower risk of type 2 diabetes in lean individuals, but with a higher risk in obese individuals. To clarify the role of IRS-2 on the development of type 2 diabetes and obesity in Pima Indians, and particularly to investigate whether the effects of the Gly1057Asp polymorphism on metabolism are mediated by obesity, molecular scanning of the gene for mutations was performed and interaction of the polymorphism with obesity was tested. We identified the previously described Gly1057Asp mutation as well as a rare Asp819His mutation and four silent polymorphisms. The effect of the Gly1057Asp mutation on type 2 diabetes and obesity was tested in a large cohort of Pima Indians (n = 998). A subgroup of nondiabetic full-heritage Pima Indians (n = 233) had measurements of body composition, glucose tolerance, insulin action (M), endogenous glucose production (EGP; hyperinsulinemic clamp), acute insulin response (AIR, 25-g intravenous glucose tolerance test, n = 118 normal glucose-tolerant subjects), and percutaneous fat biopsy specimens from the periumbilical region (n = 160). A total of 132 nondiabetic subjects were included in longitudinal analyses. The frequency of the Asp1057 allele was 0.6. In cross-sectional analyses, subjects homozygous for the Asp1057 allele (Asp/Asp) had a higher prevalence of type 2 diabetes than heterozygote individuals and subjects homozygous for the Gly1057 allele (X/Gly, P = 0.04). There was no effect on BMI (P = 0.78) or gene-BMI interaction on the prevalence of type 2 diabetes (P = 0.57). In the nondiabetic subgroup, subjects with Asp/Asp had higher percent body fat (P = 0.01), BMI (P = 0.02), and waist circumference (P = 0.004), but there was no difference in metabolic characteristics (all P > 0.2). However, the relationship between percent body fat and fasting glucose, basal EGP, EGP during the clamp, AIR, and subcutaneous abdominal adipocyte size was significantly different in the Asp/Asp group (P for interaction = 0.02, 0.06, 0.0007, 0.08, and 0.006, respectively) compared with the X/Gly group, suggesting a more detrimental effect of Asp homozygosity on these traits with increasing percent body fat. In longitudinal analyses, among subjects in the upper tertile of change in percent body fat, those with Asp/Asp had a larger increase in fasting and postprandial glycemia and basal EGP and a larger decrease in M and AIR than subjects with X/Gly, independent of change in obesity (all P < 0.05). In conclusion, our findings suggest that the association of homozygosity for the Asp1057 allele in IRS-2 with type 2 diabetes in Pima Indians may be mediated by interaction of the polymorphism with obesity on several diabetes-related traits.     

New polymorphism of ENPP1 (PC-1) is associated with increased risk of type 2 diabetes among obese individuals

The K121Q polymorphism in ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1) is associated with type 2 diabetes and obesity. The possibility of other ENPP1 polymorphisms influencing these phenotypes has received little attention. Our aim was to examine the associations of tagging single nucleotide polymorphisms (SNPs) and haplotypes of the linkage disequilibrium (LD) block containing K121Q polymorphism with type 2 diabetes in a Polish population, controlling for any effect of obesity. We genotyped 426 type 2 diabetic case and 370 control subjects for seven SNPs in ENPP1. In the total group, neither type 2 diabetes nor obesity was significantly associated with any SNP. However, in obese subjects, two SNPs were significantly associated with type 2 diabetes: the Q allele of K121Q (odds ratio 1.6 [95% CI 1.003-2.6]) and T allele of rs997509 (4.7 [1.6-13.9]). In the LD block, four SNPs plus the K121Q polymorphism distinguished six haplotypes, three of which carried the Q allele. Interestingly, the T allele of rs997509 sufficed to distinguish a 121Q-carrying haplotype that was significantly more associated with type 2 diabetes than the other two (4.2 [1.3-13.5]). These other two 121Q-carrying haplotypes were not associated with type 2 diabetes. In conclusion, we found a new SNP, rs997509, in intron 1 that is strongly associated with risk of type 2 diabetes in obese individuals. The molecular mechanisms underlying this association are unknown.     

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.     

Variation in the UCP2-UCP3 gene cluster predicts the development of type 2 diabetes in healthy middle-aged men

The impact of the UCP2 -866G>A and UCP3 -55C>T variants on prospective risk of type 2 diabetes was examined over 15 years in 2,936 healthy middle-aged men (mean age 56 years). Conversion to diabetes (n = 169) was associated with higher BMI, blood pressure, cholesterol, triglycerides and C-reactive protein. The hazard ratio (HR) for diabetes of a BMI >30 kg/m(2) was 3.96 (95% CI 2.87-5.47). Homozygosity for the UCP2A or UCP3T alleles accelerated the onset of diabetes, with significant differences in risk of diabetes at 10 years (HR [95% CI] UCP2AA vs. GA+GG 1.94 [1.18-3.19], P = 0.009; UCP3TT vs. CC+ CT 2.06 [1.06-3.99], P = 0.03) but less so at 15 years (UCP2AA 1.42 [0.92-2.19], P = 0.1; UCP3TT 1.57 [0.87-2.04], P = 0.13). Men who were homozygous for both UCP2AA and UCP3TT (1.5% of men) had a risk for diabetes at 10 years of 4.20 (1.70-10.37), P = 0.002. These genotype effects were additive with obesity, and men with a BMI >30 kg/m(2) and this genotype combination had a 10-year risk of diabetes of 19.23 [5.63-63.69], P < 0.0001. Functional promoter variants UCP2 and UCP3 increase the prospective risk of diabetes. Although the mechanism of the UCP2 effect is likely to be caused by increased expression in the pancreas and subsequent reduced insulin secretion, the mechanism of the UCP3 effect is currently unknown. Both effects are exacerbated by obesity.     

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.     

Association testing in 9,000 people fails to confirm the association of the insulin receptor substrate-1 G972R polymorphism with type 2 diabetes

The insulin receptor substrate (IRS)-1 is an important component of the insulin signal transduction cascade. Several reports suggest that a Gly-->Arg change in codon 972 is associated with type 2 diabetes and related traits, and a recent meta-analysis reported a modest but nominally significant association with type 2 diabetes (odds ratio [OR] 1.25 in favor of carriers of the Arg allele [95% CI 1.05-1.48). To test the reproducibility of the model in a recent meta-analysis, we examined genotype-phenotype correlation in three large Caucasian samples (not previously reported for this variant) totaling 9,000 individuals (estimated to have >95% power to obtain a P < 0.05 for the OR of 1.25 estimated in the meta-analysis). In our combined sample, comprising 4,279 case and 3,532 control subjects, as well as 1,189 siblings discordant for type 2 diabetes, G972R was not associated with type 2 diabetes (OR 0.96 [0.84-1.10], P = 0.60). Genotype at G972R had no significant effect on various measures of insulin secretion or insulin resistance in a set of Scandinavian samples in whom we had detailed phenotypic data. In contrast, the well-documented associations of peroxisome proliferator-activated receptor gamma P12A and Kir6.2 E23K with type 2 diabetes are both robustly observed in these 9,000 subjects, including an additional (previously unpublished) confirmation of Kir6.2 E23K and type 2 diabetes in the Polish and North American samples (combined OR 1.15 [1.05-1.26], P = 0.001). Despite genotyping 9,000 people and >95% power to reproduce the estimated OR from the recent meta-analysis, we were unable to replicate the association of the IRS-1 G972R polymorphism with type 2 diabetes.