Genetic analysis of ADIPOR1 and ADIPOR2 candidate polymorphisms for type 2 diabetes in the Caucasian population

Adiponectin is a metabolic link between adipose tissue and insulin action, mediating part of obesity-associated insulin resistance and type 2 diabetes. Two adiponectin receptors have been identified, and we investigated whether sequence variations in adiponectin receptor 1 (ADIPOR1) and adiponectin receptor 2 (ADIPOR2) genes could contribute to the genetic risk for type 2 diabetes in a case-control study of 1,498 Caucasian subjects. We sequenced the putative functional regions of the two genes in 48 subjects and selected single nucleotide polymorphisms (SNPs) from the public database. Five SNPs in ADIPOR1 and 12 in ADIPOR2 were tested for association with type 2 diabetes. No SNP of ADIPOR1 showed association in any of the samples from the French population. In contrast, three SNPs of ADIPOR2 showed nominal evidence for association with type 2 diabetes before correction for multiple testing (odds ratio [OR] 1.29-1.37, P = 0.034-0.014); only rs767870, located in intron 6, was replicated in an additional diabetes dataset (n = 636, OR 1.29, P = 0.020) with significant allelic association from the overall meta-analysis of 2,876 subjects (adjusted OR 1.25 [95% CI 1.07-1.45], P = 0.0051). In conclusion, our data suggest a modest contribution of ADIPOR2 variants in diabetes risk in the French population.     

Variations in adiponectin receptor genes and susceptibility to type 2 diabetes in women: a tagging-single nucleotide polymorphism haplotype analysis

Adiponectin has been associated with low diabetes risk. The metabolic effects of adiponectin are mediated by adiponectin receptors 1 (ADIPOR1) and 2 (ADIPOR2). We conducted a prospective, nested case-control study of 714 cases of type 2 diabetes and 1,120 control subjects. Six polymorphisms in ADIPOR1 and 16 polymorphisms in ADIPOR2 were determined. Haplotypes inferred from ADIPOR1 polymorphisms were significantly associated with diabetes risk (overall test, -2log-likelihood = 15.1 on 5 df; P = 0.0098). A single copy of haplotype 001100 (0, common allele; and 1, minor allele) was associated with 24% decreased risk (odds ratio [OR] 0.76 [95% CI 0.61-0.96], P = 0.02) compared with the most common haplotype, 110000, adjusting for age, BMI, and other covariates. A 3' untranslated region (UTR) polymorphism, rs1139646, showed the strongest and nominally significant association with greater diabetes risk (unadjusted OR 1.26 [1.03-1.53] and adjusted OR 1.36 [1.10-1.70]). However, such an association became marginal after controlling for multiple comparisons by permutation test (P = 0.08 on the basis of 10,000 permutations). There were not significant associations between ADIPOR2 polymorphisms, individually or in haplotypes, and the risk of type 2 diabetes. In conclusion, our data indicate significant associations between ADIPOR1 haplotypes and diabetes risk but do not support a relation between ADIPOR2 variability and the disease.     

Common haplotypes at the adiponectin receptor 1 (ADIPOR1) locus are associated with increased risk of coronary artery disease in type 2 diabetes

Adiponectin, an adipokine facilitating insulin action, has antiatherogenic effects. This study investigated whether common polymorphisms in the adiponectin receptor 1 (ADIPOR1) gene mediating these effects influence the risk of coronary artery disease (CAD) in type 2 diabetes. Linkage disequilibrium analysis of 28 single nucleotide polymorphisms (SNPs) spanning the entire ADIPOR1 locus revealed two haplotype blocks that could be tagged by six SNPs. These six markers were typed in two populations of CAD-positive and -negative subjects with type 2 diabetes, one from Boston (n = 411) and the other from Italy (n = 533). In the Boston population, the three tags of the more 3' block were all significantly associated with CAD (P = 0.001-0.01). A similar trend, although not significant, was found in Italian subjects. Haplotype analysis of the combined populations revealed different haplotype distributions in case and control subjects (P = 0.0002), with one common haplotype being associated in homozygotes with a greater than threefold increase in cardiovascular risk (odds ratio 3.6 [95% CI 1.8-7.2]). Some of the genotypes associated with increased cardiovascular risk were associated with 30-40% lower ADIPOR1 mRNA levels in blood mononuclear cells (n = 60) and adipose tissue biopsies (n = 28) (P = 0.001-0.014). Our findings point to genetic variability at the ADIPOR1 locus as a strong determinant of CAD susceptibility in type 2 diabetes.     

Single nucleotide polymorphisms in the proximal promoter region of the adiponectin (APM1) gene are associated with type 2 diabetes in Swedish caucasians

Adiponectin (APM1) is an adipocyte-derived peptide. The APM1 gene is located on chromosome 3q27 and linked to type 2 diabetes. In patients with type 2 diabetes, the adiponectin level in plasma is decreased in comparison to healthy subjects. To identify genetic defects of the APM1 gene that contribute to the development of type 2 diabetes, we genotyped 13 single nucleotide polymorphisms (SNPs) in 106 patients with type 2 diabetes, 325 patients with impaired glucose tolerance (IGT), and 497 nondiabetic control subjects in Swedish Caucasians by using dynamic allele-specific hybridization (DASH). We found that SNPs -11426(A/G) and -11377(G/C) in the proximal promoter region had significant differences of allele frequencies between type 2 diabetic patients and nondiabetic control subjects (P = 0.02 and P = 0.04, respectively). SNP-11426(A/G) was significantly associated with fasting plasma glucose in type 2 diabetic patients (P = 0.02) and in IGT subjects (P = 0.04), while the patients carrying CC and CG genotypes for SNP-11377(G/C) had a higher BMI than the patients with the GG genotype (P = 0.03). Haplotype analysis of 13 SNPs in the APM1 gene showed that estimates of haplotype frequencies in Swedish Caucasians are similar to those estimated in French Caucasians. However, no significant association of haplotypes with type 2 diabetes and IGT was detected in our study. The present study provides additional evidence that SNPs in the proximal promoter region of the APM1 gene contribute to the development of type 2 diabetes.     

Evidence that Rho guanine nucleotide exchange factor 11 (ARHGEF11) on 1q21 is a type 2 diabetes susceptibility gene in the Old Order Amish

Rho guanine nucleotide exchange factor 11 (ARHGEF11), located on chromosome 1q21, is involved in G protein signaling and is a pathway known to play a role in both insulin secretion and action. We genotyped 52 single nucleotide polymorphims (SNPs) in ARHGEF11 and compared the genotype frequencies of subjects with type 2 diabetes (n = 145) or type 2 diabetes/impaired glucose tolerance (IGT) (n = 293) with those of control subjects with normal glucose tolerance (NGT) (n = 358). Thirty SNPs, spanning the entire gene, were significantly associated with type 2 diabetes or type 2 diabetes/IGT. The most significantly associated SNP was rs6427340 (intron 2), in which the less common allele was the risk allele (odds ratio [OR] 1.82 [95% CI 1.20-2.70], P = 0.005 for type 2 diabetes vs. NGT and 1.79 [1.27-2.50], P = 0.0008 for type 2 diabetes/IGT vs. NGT). In an expanded set of nondiabetic subjects (n = 754), most of the type 2 diabetes-and IGT-associated SNPs were significantly associated with glucose levels during an oral glucose tolerance test, with the same SNP (rs6427340) showing the most significant associations (P = 0.007). All type 2 diabetes-and IGT-associated SNPs were in high linkage disequilibrium and constitute a single 133-kb haplotype block. These results, coupled with similar findings in Pima Indians, suggest that sequence variation in ARHGEF11 may influence risk of type 2 diabetes.     

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.     

Adiponectin receptor 1 gene (ADIPOR1) as a candidate for type 2 diabetes and insulin resistance

Considerable data support adiponectin as an important adipose-derived insulin sensitizer that enhances fatty acid oxidation and alters hepatic gluconeogenesis. Adiponectin acts by way of two receptors, ADIPOR1 and ADIPOR2. ADIPOR1 is widely expressed in tissues, including muscle, liver, and pancreas, and binds the globular form of adiponectin with high affinity. To test the hypothesis that sequence variations in or near the ADIPOR1 gene contribute to the risk of developing type 2 diabetes and the metabolic syndrome, we screened the eight exons (including the untranslated exon 1) of the ADIPOR1 gene with flanking intronic sequences and the 5' and 3' flanking sequences. We identified 22 single nucleotide polymorphisms (SNPs) in Caucasian and African-American subjects, of which a single nonsynonymous SNP (N44K) in exon 2 was present only in African-American subjects. We typed 14 sequence variants that had minor allele frequencies >5%. No SNP was associated with type 2 diabetes in Caucasians or African Americans, and no SNP was a determinant of insulin sensitivity or insulin secretion among nondiabetic members of high-risk Caucasian families. However, the two alleles of a SNP in the 3' untranslated region were expressed unequally, and ADIPOR1 mRNA levels were significantly lower among transformed lymphocytes from diabetic African-American individuals than among control cell lines. This altered gene expression might suggest a role for ADIPOR1 in the metabolic syndrome.     

Polymorphisms in the SLC2A2 (GLUT2) gene are associated with the conversion from impaired glucose tolerance to type 2 diabetes: the Finnish Diabetes Prevention Study

Impaired insulin secretion is a fundamental defect in type 2 diabetes. The aim of this study was to investigate whether single nucleotide polymorphisms (SNPs) in the genes regulating insulin secretion (SLC2A2 [encoding GLUT2], GCK, TCF1 [encoding HNF-1alpha], HNF4A, GIP, and GLP1R) are associated with the conversion from impaired glucose tolerance (IGT) to type 2 diabetes in participants of the Finnish Diabetes Prevention Study. With the exception of SLC2A2, other genes were not associated with the risk of type 2 diabetes. All four SNPs of SLC2A2 predicted the conversion to diabetes, and rs5393 (AA genotype) increased the risk of type 2 diabetes in the entire study population by threefold (odds ratio 3.04, 95% CI 1.34-6.88, P = 0.008). The risk for type 2 diabetes in the AA genotype carriers was increased in the control group (5.56 [1.78-17.39], P = 0.003) but not in the intervention group. We conclude that the SNPs of SLC2A2 predict the conversion to diabetes in obese subjects with IGT.     

Single nucleotide polymorphisms of PPARD in combination with the Gly482Ser substitution of PGC-1A and the Pro12Ala substitution of PPARG2 predict the conversion from impaired glucose tolerance to type 2 diabetes: the STOP-NIDDM trial

Peroxisome proliferator-activated receptor (PPAR)-delta regulates fatty acid oxidation and improves insulin sensitivity. We screened six single nucleotide polymorphisms (SNPs) of the PPAR-delta gene (PPARD) for an association with the conversion from impaired glucose tolerance (IGT) to type 2 diabetes in 769 subjects participating in the STOP-NIDDM trial. A 2.7-fold increase in the risk of diabetes was observed in female carriers of the C allele of rs6902123 (95% CI 1.44-5.30; adjusted P = 0.002). In the placebo group, subjects possessing both the 482Ser allele of the PPAR-gamma coactivator-1alpha gene (PGC-1A) and the rare allele of two SNPs of PPARD (rs6902123 and rs3734254) had up to 2.5-fold increased risk for diabetes. Furthermore, women carrying the C allele of rs6902123 of PPARD and the Pro12Pro genotype of the PPAR-gamma2 gene (PPARG2) had a 3.9-fold (95% CI 1.79-8.63; P = 0.001)-higher risk for diabetes than women with protective genotypes. Expression levels of PPAR-delta in subcutaneous adipose tissue of 87 offspring of Finnish patients with type 2 diabetes did not differ among the genotype groups of SNPs of PPARD. We conclude that SNPs in PPARD modify the conversion from IGT to type 2 diabetes, particularly in combination with the SNPs of PGC-1A and PPARG2.     

Polymorphism in the calsequestrin 1 (CASQ1) gene on chromosome 1q21 is associated with type 2 diabetes in the old order Amish

Calsequestrin (CASQ)1 is involved in intracellular storage and release of calcium, a process that has been shown to mediate glucose transport in muscle. Its gene, CASQ1, is encoded on chromosome 1q21, a region that has been linked to type 2 diabetes in the Amish and several other populations. We screened all 11 exons, exon-intron junctions, and the proximal regulatory region of CASQ1 for mutations. We detected four novel single nucleotide polymorphisms (SNPs) (-1470C-->T, -1456delG, -1366insG, and 593C-->T). Ten informative SNPs within CASQ1 were genotyped in Amish subjects with type 2 diabetes (n = 145), impaired glucose tolerance (n = 148), and normal glucose tolerance (n = 358). Rs2275703 and rs617698 in introns 4 and 2 were significantly associated with type 2 diabetes (P = 0.008 and 0.04, respectively); three other SNPs showed borderline evidence for association to type 2 diabetes (P = 0.076-0.093). Furthermore, in nondiabetic subjects (n = 754), both rs2275703 and rs617698 were significantly associated with glucose area under the curve during an oral glucose tolerance test (P = 0.035 and 0.013, respectively). Haplotype analysis suggested that no haplotype could explain these associations better than rs2275703. These findings, coupled with similar findings in Utah Caucasians, suggest that sequence variation in CASQ1 may influence risk of type 2 diabetes.     

Adiponectin gene polymorphisms and adiponectin levels are independently associated with the development of hyperglycemia during a 3-year period: the epidemiologic data on the insulin resistance syndrome prospective study

The plasma concentration of the adipocyte-derived peptide adiponectin is decreased in patients with obesity and type 2 diabetes. The adiponectin gene is located on chromosome 3q27, where a diabetes susceptibility locus has been mapped. Adiponectin gene polymorphisms (single nucleotide polymorphisms [SNPs]) have been associated with BMI, insulin sensitivity, and type 2 diabetes in some cross-sectional studies. Our aim was to assess the contribution of these SNPs in the development of features of the insulin resistance syndrome in a 3-year prospective study in approximately 4,500 French Caucasian subjects from the Epidemiologic Data on the Insulin Resistance Syndrome (DESIR) cohort. For subjects who were normoglycemic at baseline, the 3-year risk of becoming hyperglycemic (diabetes or impaired fasting glucose) was affected by two SNPs: G-11391A and T45G. For G-11391A, the risk was increased in GA carriers (odds ratio [OR] adjusted for sex [versus GG] = 1.60 [95% CI 1.16-2.20]; P = 0.004). For T45G, it was increased in GG carriers (OR [versus TT] = 2.71 [1.31-5.60]; P = 0.007). After 3 years, GG subjects had a greater increase in BMI (P = 0.009) and waist-to-hip ratio (P = 0.007). Adiponectin levels at baseline were associated with the development of hyperglycemia (P = 0.005), but the predictive effects on the risk for hyperglycemia were independent of adiponectin genotypes. In conclusion, in the DESIR study, variations at the adiponectin locus affect body weight gain, body fat distribution, and onset of hyperglycemia, as well as adiponectin levels. Adiponectin gene SNPs may have several phenotypic effects that co-occur with the development of the metabolic syndrome.     

Opposing effects of adiponectin receptors 1 and 2 on energy metabolism

The adipocyte-derived hormone adiponectin regulates glucose and lipid metabolism and influences the risk for developing obesity, type 2 diabetes, and cardiovascular disease. Adiponectin binds to two different seven-transmembrane domain receptors termed AdipoR1 and AdipoR2. To study the physiological importance of these receptors, AdipoR1 gene knockout mice (AdipoR1(-/-)) and AdipoR2 gene knockout mice (AdipoR2(-/-)) were generated. AdipoR1(-/-) mice showed increased adiposity associated with decreased glucose tolerance, spontaneous locomotor activity, and energy expenditure. However, AdipoR2(-/-) mice were lean and resistant to high-fat diet-induced obesity associated with improved glucose tolerance and higher spontaneous locomotor activity and energy expenditure and reduced plasma cholesterol levels. Thus, AdipoR1 and AdipoR2 are clearly involved in energy metabolism but have opposing effects.     

The common polymorphisms (single nucleotide polymorphism [SNP] +45 and SNP +276) of the adiponectin gene predict the conversion from impaired glucose tolerance to type 2 diabetes: the STOP-NIDDM trial

Adiponectin is an adipose tissue-specific protein with insulin-sensitizing and antiatherogenic properties. Therefore, the adiponectin gene is a promising candidate gene for type 2 diabetes. We investigated the single nucleotide polymorphisms (SNPs) +45T/G and +276G/T of the adiponectin gene as predictors for the conversion from impaired glucose tolerance to type 2 diabetes in the STOP-NIDDM trial, which aimed to investigate the effect of acarbose compared with placebo on the prevention of type 2 diabetes. Compared with the TT genotype, the G-allele of SNP +45 was associated with a 1.8-fold risk for type 2 diabetes (95% CI 1.12-3.00, P = 0.015) in the placebo group. Subjects treated with placebo and simultaneously having the G-allele of SNP +45 and the T-allele of SNP +276 (the risk genotype combination) had a 4.5-fold (1.78-11.3, P = 0.001) higher risk of developing type 2 diabetes compared with subjects carrying neither of these alleles. Women carrying the risk genotype combination had an especially high risk of conversion to diabetes (odds ratio 22.2, 95% CI 2.7-183.3, P = 0.004). In conclusion, the G-allele of SNP +45 is a predictor for the conversion to type 2 diabetes. Furthermore, the combined effect of SNP +45 and SNP +276 on the development of type 2 diabetes was stronger than that of each SNP alone.     

Plasma adiponectin concentration is associated with skeletal muscle insulin receptor tyrosine phosphorylation,and low plasma concentration precedes a decrease in whole-body insulin sensitivity in humans

Adiponectin, the most abundant adipose-specific protein, has been found to be negatively associated with degree of adiposity and positively associated with insulin sensitivity in Pima Indians and other populations. Moreover, adiponectin administration to rodents has been shown to increase insulin-induced tyrosine phosphorylation of the insulin receptor (IR) and also increase whole-body insulin sensitivity. To further characterize the relationship between plasma adiponectin concentration and insulin sensitivity in humans, we examined 1) the cross-sectional association between plasma adiponectin concentration and skeletal muscle IR tyrosine phosphorylation and 2) the prospective effect of plasma adiponectin concentration at baseline on change in insulin sensitivity. Fasting plasma adiponectin concentration, body composition (hydrodensitometry or dual energy X-ray absorptiometry), insulin sensitivity (insulin-stimulated glucose disposal, hyperinsulinemic clamp), and glucose tolerance (75-g oral glucose tolerance test) were measured in 55 Pima Indians (47 men and 8 women, aged 31 +/- 8 years, body fat 29 +/- 8% [mean +/- SD]; 50 with normal glucose tolerance, 3 with impaired glucose tolerance, and 2 with diabetes). Group 1 (19 subjects) underwent skeletal muscle biopsies for the measurement of basal and insulin-stimulated tyrosine phosphorylation of the IR (stimulated by 100 nmol/l insulin). The fold increase after insulin stimulation was calculated as the ratio between maximal and basal phosphorylation. Group 2 (38 subjects) had follow-up measurements of insulin-stimulated glucose disposal. Cross-sectionally, plasma adiponectin concentration was positively associated with insulin-stimulated glucose disposal (r = 0.58, P < 0.0001) and negatively associated with percent body fat (r = -0.62, P < 0.0001) in the whole group. In group 1 plasma adiponectin was negatively associated with the basal (r = -0.65, P = 0.003) and positively associated with the fold increase in IR tyrosine phosphorylation (r = 0.69, P = 0.001) before and after the adjustment for percent body fat (r = -0.58, P = 0.01 and r = 0.54, P = 0.02, respectively). Longitudinally, after adjustment for age, sex, and percent body fat, low plasma adiponectin concentration at baseline was associated with a decrease in insulin sensitivity (P = 0.04). In conclusion, our cross-sectional data suggest a role of physiological concentration of fasting plasma adiponectin in the regulation of skeletal muscle IR tyrosine phosphorylation. Prospectively, low plasma adiponectin concentration at baseline precedes a decrease in insulin sensitivity. Our data indicate that adiponectin plays an important role in regulation of insulin sensitivity in humans.     

A haplotype at the adiponectin locus is associated with obesity and other features of the insulin resistance syndrome

Adiponectin is a protein secreted by adipocytes that modulates insulin action. To assess whether variants of this gene contribute to the prevalence of insulin resistance in Caucasians, we genotyped 413 nondiabetic individuals for two single nucleotide polymorphisms (SNPs) at this locus. The two SNPs (45T-->G and 276G-->T) were chosen because of their association with type 2 diabetes in Japanese. Whereas each polymorphism was significantly associated with some correlate of insulin resistance, the haplotype defined by the two together was strongly associated with many components of the insulin resistance syndrome. Homozygotes for the risk haplotype had higher body weight (P = 0.03), waist circumference (P = 0.004), systolic (P = 0.01) and diastolic (P = 0.003) blood pressure, fasting glucose (P = 0.02) and insulin (P = 0.005) levels, homeostasis model assessment (HOMA) for insulin resistance (P = 0.003), and total to HDL cholesterol ratio (P = 0.01). Homozygotes also had significantly lower plasma levels of adiponectin (P = 0.03), independent of sex, age, and body weight. In an independent study group of 614 Caucasians, including 310 with type 2 diabetes, the risk haplotype was confirmed to be associated with increased body weight (P = 0.03) but not with type 2 diabetes per se. We conclude that variability at the adiponectin locus is associated with obesity and other features of the insulin resistance syndrome, but given the nature of the two SNPs, the risk haplotype is most probably a marker in linkage disequilibrium with an as yet unidentified polymorphism that affects plasma adiponectin levels and insulin sensitivity.     

Type I diabetes manifested solely by 2-h oral glucose tolerance test criteria

The clinical presentation of type 1 diabetes usually involves symptoms such as polyuria and polydipsia. However, investigators in the Diabetes Prevention Trial of Type 1 Diabetes (DPT-1) have detected a group of subjects with type 1 diabetes who have a different phenotype. These subjects are asymptomatic, have normal (<6.1 mmol/l) (group A) or impaired (6.1- <7.0 mmol/l) (group B) fasting glucose, but have 2-h glucose values >11.1 mmol/l on their oral glucose tolerance tests (OGTT). Of the 585 OGTTs performed on islet cell antibody (ICA)-positive relatives with insulin autoantibodies (IAA) or low first-phase insulin response (FPIR), normal glucose tolerance (NGT) was found in 427 subjects; impaired glucose tolerance (IGT) was found in 87 subjects, and diabetes was found by 2-h OGTT criteria alone in 61 subjects. Despite marked differences in 2-h glucose values (NGT 5.8 +/- 1.1 mmol/l, IGT 8.9 +/- 0.9 mmol/l, and group A 13.5 +/- 2.5 mmol/l), there were no significant differences in fasting glucose values among NGT (4.8 +/- 0.5 mmol/l), IGT (5.03 +/- 0.5 mmol/l), and group A (4.99 +/- 0.7 mmol/l) categories. Mean FPIR was higher in subjects with NGT compared with subjects with IGT and subjects diagnosed by 2-h OGTT criteria alone. However, the correlation between FPIR and 2-h glucose value was low (r2 = 0.114). Multivariate analysis demonstrated that additional independent variables provide smaller contributions to the 2-h glucose value. In conclusion, there are asymptomatic type 1 diabetic subjects whose diabetes was diagnosed by the 2-h criteria on OGTT alone. Despite the importance of beta-cell dysfunction in the pathogenesis of type I diabetes, factors other than impaired FPIR must also contribute to postprandial glucose tolerance in these subjects.     

Toward further mapping of the association between the IL2RA locus and type 1 diabetes

A novel type 1 diabetes locus was mapped to the interleukin-2 receptor alpha gene (IL2RA) on chromosome 10p15.1, encoding an important modulator of immunity. The aim of the current study was to confirm the association of IL2RA with type 1 diabetes and to attempt further mapping of the genetic effect with a new set of 12 single nucleotide polymorphisms (SNPs). We genotyped 949 nuclear family trios with one type 1 diabetes-affected offspring and two parents (2,847 individuals). Two of the 12 IL2RA SNPs genotyped (rs706778 and rs3118470) had statistically significant type 1 diabetes association (P = 6.96 x 10(-4) and 8.63 x 10(-4), respectively). Both SNPs are located in the 5' end of the long intron 1 within 3 kb of each other and are in high linkage disequilibrium (D' = 0.997, r(2) = 0.613). The A-C haplotype (frequency = 0.331) was associated with increased type 1 diabetes risk (P = 3.02 x 10(-4)). Our study identifies two markers in the IL2RA gene that are significantly associated with type 1 diabetes, supporting IL2RA as a promising candidate gene for type 1 diabetes and suggesting a potential role of IL2Ralpha in the pathogenesis of type 1 diabetes, likely involving regulatory T-cells.