Adiponectin (ACRP30), an adipocyte-secreted protein encoded by the APM1 gene, is known to modulate insulin sensitivity and glucose homeostasis, those effects protecting obese mice from diabetes. Plasma adiponectin levels correlate well with insulin sensitivity in humans, and are decreased in both type 2 diabetes (T2D) and obesity. We screened for single-nucleotide polymorphisms (SNPs) the APM1 gene coding and 5' sequences in 40 French Caucasians: 12 SNPs and 4 rare non-synonymous mutations of exon 3 were detected. The 10 most frequent SNPs were genotyped in 1373 T2D and obese French Caucasian subjects and in all subjects available from 148 T2D multiplex families. The screening for rare mutations of exon 3 was extended to 1246 T2D and obese French subjects and to the members of the 148 T2D multiplex families. A haplotype including SNPs -11391 and -11377, both located in the 5' sequences, was associated with adiponectin levels (P<0.0001) and with T2D (P=0.004). The presence of at least one non-synonymous mutation in exon 3 showed evidence of association with adiponectin levels (P=0.0009) and with T2D (P=0.005). We failed to detect an association with insulin resistance indexes. Although family-based association analysis with T2D did not reach significance, our results suggest that an at-risk haplotype of common variants located in the promoter and rare mutations in exon 3 contribute to the variation of the adipocyte-secreted adiponectin hormone level, and may be part of the genetic determinants for T2D in the French Caucasian population.

Single-nucleotide polymorphism haplotypes in the both proximal promoter and exon 3 of the APM1 gene modulate adipocyte-secreted adiponectin hormone levels and contribute to the genetic risk for type 2 diabetes in French Caucasians

To investigate the underlying mechanisms of T2D pathogenesis, we looked for diabetes susceptibility genes that increase the risk of type 2 diabetes (T2D) in a Han Chinese population. A two-stage genome-wide association (GWA) study was conducted, in which 995 patients and 894 controls were genotyped using the Illumina HumanHap550-Duo BeadChip for the first genome scan stage. This was further replicated in 1,803 patients and 1,473 controls in stage 2. We found two loci not previously associated with diabetes susceptibility in and around the genes protein tyrosine phosphatase receptor type D (PTPRD) (P = 8.54x10(-10); odds ratio [OR] = 1.57; 95% confidence interval [CI] = 1.36-1.82), and serine racemase (SRR) (P = 3.06x10(-9); OR = 1.28; 95% CI = 1.18-1.39). We also confirmed that variants in KCNQ1 were associated with T2D risk, with the strongest signal at rs2237895 (P = 9.65x10(-10); OR = 1.29, 95% CI = 1.19-1.40). By identifying two novel genetic susceptibility loci in a Han Chinese population and confirming the involvement of KCNQ1, which was previously reported to be associated with T2D in Japanese and European descent populations, our results may lead to a better understanding of differences in the molecular pathogenesis of T2D among various populations.

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A Genome-Wide Association Study Identifies Susceptibility Variants for Type 2 Diabetes in Han Chinese

We identified a locus on chromosome 6q16.3-q24.2 (ref. 1) associated with childhood obesity that includes 2.4 Mb common to eight genome scans for type 2 diabetes (T2D) or obesity. Analysis of the gene ENPP1 (also called PC-1), a candidate for insulin resistance, in 6,147 subjects showed association between a three-allele risk haplotype (K121Q, IVS20delT-11 and A-->G+1044TGA; QdelTG) and childhood obesity (odds ratio (OR) = 1.69, P = 0.0006), morbid or moderate obesity in adults (OR = 1.50, P = 0.006 or OR = 1.37, P = 0.02, respectively) and T2D (OR = 1.56, P = 0.00002). The Genotype IBD Sharing Test suggested that this obesity-associated ENPP1 risk haplotype contributes to the observed chromosome 6q linkage with childhood obesity. The haplotype confers a higher risk of glucose intolerance and T2D to obese children and their parents and associates with increased serum levels of soluble ENPP1 protein in children. Expression of a long ENPP1 mRNA isoform, which includes the obesity-associated A-->G+1044TGA SNP, was specific for pancreatic islet beta cells, adipocytes and liver. These findings suggest that several variants of ENPP1 have a primary role in mediating insulin resistance and in the development of both obesity and T2D, suggesting that an underlying molecular mechanism is common to both conditions.

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Variants of ENPP1 are associated with childhood and adult obesity and increase the risk of glucose intolerance and type 2 diabetes

Faced with a global epidemic of type 2 diabetes (T2D), it is critical that researchers improve our understanding of the pathogenesis of T2D and related vascular complications. These findings may ultimately lead to novel treatment options for disease prevention or delaying progression. Two major paradigms jointly underlie the development of T2D and related coronary artery disease, diabetic nephropathy, and diabetic retinopathy. These paradigms include the genetic risk variants and behavioral/environmental factors. This article systematically reviews the literature supporting genetic determinants in the pathogenesis of T2D and diabetic vasculopathy, and the functional implications of these gene variants on the regulation of beta-cell function and glucose homeostasis. We update the discovery of diabetes and diabetic vasculopathy risk variants, and describe the genetic technologies that have uncovered them. Also, genomic linkage between obesity and T2D is discussed. There is a complementary role for behavioral and environmental factors modulating the genetic susceptibility and diabetes risk. Epidemiological and clinical data demonstrating the effects of behavioral and novel environmental exposures on disease expression are reviewed. Finally, a succinct overview of recent landmark clinical trials addressing glycemic control and its impact on rates of vascular complications is presented. It is expected that novel strategies to exploit the gene- and exposure-related underpinnings of T2D will soon result.

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Genetic and environmental factors associated with type 2 diabetes and diabetic vascular complications.

Type 2 diabetes (T2D) has become a health-care problem worldwide, with the rise in disease prevalence being all the more worrying as it not only affects the developed world but also developing nations with fewer resources to cope with yet another major disease burden. Furthermore, the problem is no longer restricted to the ageing population, as young adults and children are also being diagnosed with T2D. In recent years, there has been a surge in the number of genetic studies of T2D in attempts to identify some of the underlying risk factors. In this review, I highlight the main genes known to cause uncommon monogenic forms of diabetes (e.g. maturity-onset diabetes of the young--MODY--and insulin resistance syndromes), as well as describe some of the main approaches used to identify genes involved in the more common forms of T2D that result from the interaction between environmental risk factors and predisposing genotypes. Linkage and candidate gene studies have been highly successful in the identification of genes that cause the monogenic variants of diabetes and, although progress in the more common forms of T2D has been slow, a number of genes have now been reproducibly associated with T2D risk in multiple studies. These are discussed, as well as the main implications that the diabetes gene discoveries will have in diabetes treatment and prevention.

Genetics of Type 2 diabetes.

This genome-wide search for susceptibility genes to type 2 diabetes/impaired glucose homeostasis (IGH) was performed on a relatively homogeneous Chinese sample with a total number of 257 pedigrees and 385 affected sibpairs. Two regions showed significant linkage to type 2 diabetes/IGH in the Chinese. The region showing linkage to type 2 diabetes/IGH from the entire sample group analysis was located on chromosome 6q21-q23 (128.93 cM, 1-LOD [logarithm of odds] support interval between 124 and 142 cM, according to the Marshfield genetic map), with a maximum likelihood score of 6.23, a nonparametric linkage (all) score of 4.48, and empirical P value <0.001. With a subanalysis based on 101 affected sibpairs with age at diagnosis of type 2 diabetes/IGH <40 years, we detected significant evidence for linkage to chromosome 1q21-q24 (192.1 cM, 1-LOD support interval between 182 and 197 cM), with a maximum likelihood score of 8.91, a nonparametric linkage (all) score of 5.70, and empirical P value <0.001. No interaction was observed between these two regions. Our independent replication of the region on chromosome 1q that has been shown to be linked significantly to type 2 diabetes/IGH in Chinese supports the notion that gene(s) in this region may be universally important in the development of human type 2 diabetes.

https://diabetes.diabetesjournals.org/content/diabetes/53/1/228.full.pdf

Genome-wide search for type 2 diabetes/impaired glucose homeostasis susceptibility genes in the Chinese: Significant linkage to chromosome 6q21-q23 and chromosome 1q21-q24

OBJECTIVE To study the contribution of single nucleotide polymorphism-UCSNP44 at calpain-10 gene (CAPN-10) on NIDDM1 locus to type 2 diabetes mellitus (T2DM) in Chinese. METHODS 276 Chinese living in Shanghai, 148 with normal glucose tolerance (NGT) and 128 with T2DM were given 75 g glucose. O, 30, 60, 120, and 180 minutes later their plasma glucose (PG), insulin (INS), C-peptide (CP), and free fatty acids (FFA) were measured and the areas under curve (AUC) were calculated. The islet beta-cell insulin secretion and tissue insulin sensitivity were estimated by formulae of homeostasis model assessment and increment ratio of insulin to glucose levels 30 minutes after glucose challenge. The CAPN-10 UCSNP44 as well as UCSNP43 were genotyped by automated DNA direct sequencing. RESULTS (1) The major genotype of CAPN-10 UCSNP44 in persons with NGT was TT (with a frequency of 0.82); the major allele was T (0.91). The most frequent genotype combination between UCSNP44 and UCSNP43 was TT-GG (corresponding to haplotype combination TG/TG) (0.64). The most frequent haplotype was TG (0.80). The D value for linkage disequilibrium between UCSNP44 and UCSNP43 was -0.11. (2) The frequencies of UCSNP44 and UCSNP44/UCSNP43 haplotype combination did not differ significantly between subjects with NGT and those with T2DM. (3) The PG levels in T2DM subjects with UCSNP44 TT genotype both at fasting and after glucose challenge were statistically significantly higher than those in subjects with non-TT (TC + CC) genotype, especially the PG levels 0, 60, 120, and 180 minutes after glucose challenge (P = 0.036, 0.040, 0.020, and 0.017) and the PG-AUC (P = 0.013). The PG levels and PG-AUC 0 and 120 minutes after glucose challenge were still significant after adjusted with age, sex, and body mass index and waist circumference. Similar results were observed in comparison between the TG/TG and TG/CG subgroups of UCSNP44/UCSNP43 haplotype combination. In addition, T2DM subjects with UCSNP44 TT genotype had lower CP levels after glucose challenge than those with non-TT genotype. However, the difference became not statistically significant after adjusted with above-mentioned variables. CONCLUSION The variation of CAPN-10 UCSNP44 has an impact on plasma glucose levels at fasting and after glucose challenge in subjects with type 2 diabetes. The relevant mechanism remains to be elucidated.

Kunxue Shen

Papers

Genome-wide search for type 2 diabetes/impaired glucose homeostasis susceptibility genes in the Chinese: Significant linkage to chromosome 6q21-q23 and chromosome 1q21-q24

The UCSNP44 variation of calpain 10 gene on NIDDM1 locus and its impact on plasma glucose levels in type 2 diabetic patients