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Shanghai Clinical Center for Endocrine and Metabolic Diseases (J.X., X.-Y.L., M.X., J.H., Y.H., J.-R.T., X.L., M.D., G.N.), Shanghai Institute of Endocrinology and Metabolism and Shanghai Key Laboratory for Endocrine Tumors, Rui-Jin Hospital, Shanghai Jiao-Tong University School of Medicine, Shanghai 200025, China; and Department of Molecular and Clinical Genetics (B.Y.), Royal Prince Alfred Hospital and Central Clinical School, University of Sydney, Sydney 2050, Australia
Address all correspondence and requests for reprints to: Guang Ning, M.D., Ph.D., Department of Endocrinology and Metabolism, Rui-Jin Hospital, Shanghai Jiao-Tong University School of Medicine, Rui-Jin 2nd Road, Shanghai 200025, China. E-mail: guangning{at}medmail.com.cn.
| Abstract |
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Objective: The objective of the study was to investigate the association of SLC30A8 with type 2 diabetes in Chinese.
Design: A comprehensive gene-based association study was performed using 14 tagging single-nucleotide polymorphism (SNPs) of SLC30A8 in Han Chinese subjects with normal glucose tolerance (NGT; n = 721), impaired glucose regulation (IGR; n = 375), and type 2 diabetes (n = 521).
Results: A significant association for SNP rs13266634 was observed between patients with type 2 diabetes and NGT controls (P = 0.016). The association was also observed between combined type 2 diabetes/IGR and NGT subjects (P = 0.002). The adjusted odds ratios for homozygote CC vs. TT at this locus were 1.71 for type 2 diabetes (95% confidence interval 1.19–2.45, P = 0.002) and 1.77 for type 2 diabetes and IGR (95% confidence interval 1.29–2.42, P = 0.0001). We further studied the genotype-phenotype correlation in 70 Han Chinese using iv glucose tolerance test and found an association between SNP rs13266634 and acute insulin response to glucose and disposition index (adjusted P = 0.012 and 0.004, respectively).
Conclusions: Our results provide evidence that SLC30A8 is a susceptible locus for type 2 diabetes in Chinese population, and its variant can influence insulin secretion.
| Introduction |
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Several studies independently revealed a strong association of single-nucleotide polymorphism (SNP) rs13266634, a nonsynonymous Arg325Trp (C>T) variant in SLC30A8 with type 2 diabetes. The C allele of this variant is the risk allele for type 2 diabetes (7, 8, 9, 10) and is associated with decreased pancreatic β-cell function (11, 12, 13). Although this particular SNP rs13266634 has also been replicated in Hong Kong Han Chinese (11), the in-depth gene-based association study in Chinese population has not been reported between SLC30A8 and type 2 diabetes. In this study, we presented the comprehensive association results in 1617 unrelated subjects from a Han Chinese population in Shanghai using 14 tagging SNPs.
| Subjects and Methods |
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The studied subjects were recruited from a two-step blood glucose survey in a single urban community of Shanghai in 2004. First, all permanent residents aged 40–80 yr were invited for the survey. A total of 9219 subjects participated in this investigation including a questionnaire about lifestyle and use of medications and anthropometrical measurements and fasting capillary glucose tests. In the second step, after exclusion of subjects with self-reported diabetes mellitus, 1835 subjects were randomly selected and invited for further investigation, including a 75-g oral glucose tolerance test (OGTT) and blood and urine sampling. The clinical characteristics were not significantly different between the selected 1835 and the other 7384 subjects, including age, gender, systolic blood pressure, diastolic blood pressure, and fasting capillary glucose.
The 1835 subjects were allocated into normal glucose tolerance [NGT, n = 721, average age 59.7 yr; 270 males, 451 females; body mass index (BMI); 24.09 kg/m2], impaired glucose regulation (IGR, n = 375, average age 63.7 yr; 140 males, 235 females; BMI 25.68 kg/m2); and type 2 diabetic patients (n = 521, average age 62.6 yr; 210 males, 311 females; BMI 26.27 kg/m2). IGR was defined as impaired fasting glucose (fasting plasma glucose level
6.1 mmol/liter and <7.0 mmol/liter) and/or impaired glucose tolerance (2 h OGTT plasma glucose level
7.8 mmol/liter and <11.1 mmol/liter). Type 2 diabetes was diagnosed according to the 1999 World Health Organization criteria (fasting plasma glucose level
7.0 mmol/liter or 2 h OGTT plasma glucose level
11.1 mmol/liter). A fasting plasma glucose level less than 6.1 mmol/liter and a 2-h OGTT plasma glucose level less than 7.8 mmol/liter was defined as normoglycemia.
Body height and weight and waist and hip circumferences were measured by the same physician. Blood pressure was measured at the right arm with an automated electronic device (model 1 Plus; Omron; Omron, Japan). The fasting and 2-h OGTT plasma glucose, serum triglycerides, total cholesterol, high-density lipoprotein, and low-density lipoprotein were determined. Fasting plasma insulin was measured by RIA (Sangon Co., Shanghai, China). Using the homeostasis model assessment of insulin resistance index (HOMA-IR) was assessed as fasting plasma insulin (in milliunits per milliliter) fasting plasma glucose (in millimoles per liter)/22.5, and homeostasis model assessment of β-cell function (HOMA-β) was assessed as fasting plasma insulin (in milliunits per milliliter) · 20/fasting plasma glucose – 3.5) (in millimoles per liter)/22.5 (14). The study protocol was approved by the Institutional Review Board of the Rui-Jin Hospital, Shanghai. Informed consent was obtained from each participant.
Genotyping
Genomic DNA was extracted from peripheral blood leukocytes with standard phenol/chloroform-based method (15). Genotyping was performed using the Sequenom iPLEX assay (Sequenom, Cambridge, MA). Locus-specific PCR primers and allele-specific detection primers were designed using the MassARRAY Assay Design 3.0 software (Sequenom). Allele detection was performed by primer extension of multiplex products with detection using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The mass spectrograms were analyzed by the MassARRAY TYPER software (Sequenom). The detailed list of SNPs and their genotyping assays can be found in supplemental Table 1, published as supplemental data on The Endocrine Societys Journals Online Web site at http://jcem.endojournals.org.
SLC30A8 genomic sequence of 41.62 kb, along with an additional 5 kb of it up- and downstream, was retrieved from the HapMap database (data release 22/phase II, April 2007, on National Center for Biotechnology Information B36 assembly; http://www.hapmap.org/) (16). Eighteen tagging SNPs were selected using the standard pairwise method in Tagger (17), which is implemented in Haploview (version 3.32; http://www.broad.mit.edu/mpg/haploview/) (18) based on the minor allele frequencies of Han Chinese in HapMap database with a threshold of 1%, r2 of 0.8, and limit of detection of 3.0. This method also allows the user to force in the marker of interest; the SNP previously verified associated with type 2 diabetes in this region (rs13266634) was included in the 18 tagging SNPs (7). These tagging SNPs were able to capture all 59 (100%) of the common SNPs at r2 >0.8 (Fig. 1
and supplemental Table 2). This meant that any marker that was not eventually chosen as a tagging marker was already strongly correlated with at least one of the tagging markers with r2 >0.8. Two SNPs (rs12542770 and rs16889471) failed to meet the criteria from the Sequenom platform. Another two SNPs, rs7002176 and rs7015338, were also excluded due to a low call rate (57%) and incompatibility with Hardy-Weinberg expectations (P < 0.001), respectively. Finally, the remaining 14 tagging SNPs were used in the analyses, which had an average call rate of 98.6% and captured 91.5% of the variants (54 of 59) in the region. The average concordance rate for the 14 tagging SNPs was 99.6% based on 243 blind comparisons.
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Statistical analyses
Deviation from Hardy-Weinberg equilibrium for genotypes at individual locus was assessed using the
2 test. For association analysis of each SNP with disease states (type 2 diabetes vs. NGT and type 2 diabetes/IGR vs. NGT), we used simple
2 test implemented in Haploview software (18). The strength of the association between the presence of the disease and the constitutionally determined alleles was estimated by the odds ratio (OR) with 95% confidence interval (CI). Allelic ORs were obtained from Pearsons goodness-of-fit
2 test. Logistic regression was performed for the two associated SNPs with type 2 diabetes status under an additive genetic model with or without adjustment for age, gender, and waist circumference. We performed tests for association with quantitative traits in the combined NGT subjects, IGR subjects and type 2 diabetic patients. Tests for association between genotypes and quantitative traits in the combined large samples were performed using linear regression model under an additive model with or without adjustment as suggested by the others studies (11, 12). The association tests for traits in the small set of the samples were also performed under an additive model. Indices of insulin secretion were adjusted for age, gender, waist circumference, and indices of insulin sensitivity, and other associated traits were adjusted for age, gender, and waist circumference. The statistical analyses were performed using SAS version 8.1 (SAS Institute, Cary, NC). Measurements with a skewed distribution were normalized by logarithmic transformation.
| Results |
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The clinical and biochemical characteristics of all subjects in the association study are summarized in Table 1
, whereas those of the subset individuals who received IVGTT are detailed in supplemental Table 3.
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The 59 common SNPs and the 18 tagging SNPs in the region are shown in Fig. 1
. The genomic position, nucleic acid composition, and minor allele frequencies of the 14 genotyped SNPs are shown in Table 2
. The standardized pairwise LD coefficients D' and r2 are shown in supplemental Table 4.
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The allelic distributions of the 14 tagging SNPs for SLC30A8 were not significantly different between the IGR and type 2 diabetic subjects in this study (data not shown). However, the same allelic distributions were interesting with some significant differences between the cases (type 2 diabetes or combined type 2 diabetes and IGR) and controls (NGT) (Table 2
). The variant rs13266634 was significantly associated with type 2 diabetes or combined type 2 diabetes and IGR (P = 0.016 and 0.002, respectively). The C allele of rs13266634 was significantly associated with the increased risk for type 2 diabetes and combined type 2 diabetes and IGR. The ORs for homozygous genotypes CC vs. TT of this locus were 1.52 for type 2 diabetes (95% CI 1.08–2.14, P = 0.01) and 1.57 for combined type 2 diabetes and IGR (95% CI 1.17–2.11, P = 0.0009), and adjustment for age, gender, and waist circumference did not change the result (adjusted OR 1.71 and 1.77, P = 0.002 and 0.0001, respectively). The ORs for the heterozygotes were not significant for type 2 diabetes and IGR before or after adjustment (P > 0.05).
An additional SNP rs2466293, which is located in the 3'-untranslated region, showed a significance in the association analysis (P = 0.012) between the combined type 2 diabetes/IGR and NGT controls (P = 0.012) but not between the type 2 diabetes and NGT (P = 0.063, Table 2
). Homozygous carriers of the risk allele G had ORs of 1.46 (95% CI 1.02–2.09, P = 0.048) and 1.50 (95% CI 1.09–2.07, P = 0.03) relative to noncarriers of G allele for type 2 diabetes and combined type 2 diabetes and IGR, respectively. The adjusted ORs for type 2 diabetes and combined type 2 diabetes and IGR were 1.41 (95% CI 0.96–2.06, P = 0.14) and 1.49 (95% CI 1.06–2.08, P = 0.07), respectively.
Metabolic traits association
The genotype-phenotype correlation was performed between the two significant SNPs (rs13266634 and rs2466293) and body weight, plasma glucose, plasma insulin, HOMA-IR, and HOMA-β in all subjects with NGT, IGR, and type 2 diabetes. We did not find any association between these metabolic traits and the two SNPs before or after adjustment for age, gender, waist circumference, and diabetes status (supplemental Table 5).
Table 3
summarizes the association between rs13266634 and IVGTT-derived metabolic traits in the subjects (n = 70) with NGT and IGR. The risk allele C was correlated with lower AIRg after adjustment for age, gender, waist circumference, and Si (P = 0.012 by linear regression). The correlation between the genotype and Si was not observed by linear regression before or after adjustment for age, gender, and waist circumference (P > 0.05). Moreover, the C allele was correlated with lower DI by linear regression before and after adjustment for age, gender, and waist circumference (P = 0.014 and 0.004, respectively).
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| Discussion |
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We found a significant association of risk allele C of SNP rs13266634 with type 2 diabetes in Chinese. The association between the combined type 2 diabetes/IGR and NGT controls was more significant than the association between the type 2 diabetes and NGT controls (21, 22), which was probably due to the limited sample size. These results emphasize again that the association study is sensitive to sample size, especially in detection of modest effect of a multifactorial trait such as type 2 diabetes. Some negative association results seen in European ancestry population could suffer from the similar problem with an insufficient power in the case-control studies (23). Negative association results could also be found in a different ethnic population (24), suggesting different ethnic groups may not share identical genetic risk factors.
In addition, we identified a novel marginal association of SNP rs2466293 located in 3'-untranslated region of SLC30A8 with combined type 2 diabetes and IGR. Neither the association for type 2 diabetes alone nor for the combined type 2 diabetes and IGR remained significant after the adjustment for age, gender, and waist circumference in the logistic regression analysis. This variant was associated with the verified SNP rs13266634 in a very strong LD (D' = 0.99 and r2 = 0.47). These results suggest that SNP rs13266634 may be the real causative allele associated with decreased β-cell function. SNP rs13266634 of SLC30A8, located at the COOH-terminal region of the protein structure, results in a nonsynonymous mutation (Arg325Trp, CGG>TGG). This DNA variant might be gain of function and affect the posttranslational modification mechanism in the COOH terminus of ZnT-8 (25).
The other nonsynonymous SNP rs16889462 (Arg325Gln) in SLC30A8 was not genotyped because this variant is perfectly in LD (D' = 1.00 and r2 = 1.00) with rs3802178 according to the Han Chinese HapMap (16) (Table 2
). We failed to identify any association of SNP rs3802178 with type 2 diabetes, and the most likely explanation was that there were no true associations at this SNP rs3802178 and the nonsynonymous SNP rs16889462.
We further evaluated the pancreatic β-cell function associated with SNP rs13266634 and rs2466293 in all subjects including NGT, IGR, and naïve type 2 diabetic patients. None of the two SNPs were associated with insulin secretion indices derived from OGTT. However, we adopted the AIRg derived from IVGTTs to evaluate the first-phase insulin secretion stimulated by glucose in another independent group of subjects with NGT and IGR. The subjects with homozygous risk allele C had a decreased insulin secretion by AIRg, and SNP rs13266634 was associated with a decrease in glucose DI. These results support the correlation of SNP rs13266634 with pancreatic β-cell function. We cannot explain the discrepancy between the lack of association of SNP rs13266634 with insulin secretion parameter derived from OGTT and the association with insulin secretion parameter derived from IVGTT. It could be that HOMA-β is not a sensitive parameter to assess pancreatic β-cell function. The association of SNP rs13266634 with insulin sensitivity was not identified either using OGTT or IVGTT, which was also consistent with the other studies (12, 13).
In conclusion, SNP rs13266634 of SLC30A8 gene is associated with type 2 diabetes, and combined type 2 diabetes and IGR in Chinese Hans. Moreover, SNP rs13266634 is correlated with glucose-stimulated insulin secretion.
| Acknowledgments |
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| Footnotes |
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Disclosure Information: All authors have nothing to declare.
First Published Online July 15, 2008
1 J.Y., J.-Y.L., and M.X. contributed equally to this work. ![]()
Abbreviations: AIRg, Acute insulin response to glucose; BMI, body mass index; CI, confidence interval; DI, disposition index; HOMA-β, homeostasis model assessment of β-cell function; HOMA-IR, homeostasis model assessment of insulin resistance index; IGR, impaired glucose regulation; IVGTT, iv glucose tolerance test; LD, linkage disequilibrium; NGT, normal glucose tolerance; OGTT, oral glucose tolerance test; OR, odds ratio; Si, insulin sensitivity index; SNP, single-nucleotide polymorphism.
Received January 22, 2008.
Accepted July 3, 2008.
| References |
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2 gene in Chinese. Mol Genet Metab 86:372–378[CrossRef][Medline]This article has been cited by other articles:
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H. Staiger, F. Machicao, A. Fritsche, and H.-U. Haring Pathomechanisms of Type 2 Diabetes Genes Endocr. Rev., October 1, 2009; 30(6): 557 - 585. [Abstract] [Full Text] [PDF] |
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