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.

The allelic variant of LAR gene promoter -127 bp T-->A is associated with reduced risk of obesity and other features related to insulin resistance.

Insulin resistance, which is pathogenic for type 2 diabetes (T2D), is under the control of largely unknown genetic determinants. LAR, a protein-tyrosine phosphatase which inhibits insulin signalling, is overexpressed in animal and human models of insulin resistance. We studied the entire sequence of the LAR gene by SSCP analysis and automatic DNA sequencing, with the aim of verifying whether its sequence variants might be associated with insulin resistance. In the 276 bp sequence upstream of the transcriptional start site (i.e. a region we have identified as having basal promoter activity) a -127 bp T-->A SNP (5% frequency) was associated with lower body mass index (BMI) ( P=0.03), waist circumference ( P=0.01), blood pressure ( P=0.01) and urinary albumin/creatinine ratio ( P=0.04) in 589 non-diabetic unrelated individuals from the Gargano region (central east coast of Italy). To quantify the risk for a high body weight conferred by the -127 T-->A SNP, the whole cohort was divided into tertiles according to the individual BMI. The risk of belonging to the heavier tertile, as compared to the leaner one, was reduced by approximately 60%. In a population from East Sicily ( n=307), T/A genotype carriers ( n=13) showed lower triglyceride levels ( P=0.04) and higher insulin sensitivity as indicated by lower plasma glucose ( P=0.03) and serum insulin ( P=0.006) during oral glucose tolerance testing (OGTT). Promoter activity, studied by cDNA transfection experiments, was similar for the A and T alleles. In conclusion, a genetic variant of the LAR gene promoter is consistently associated with features of insulin resistance in two different Caucasian populations. Although the biological relevance of this variant has yet to be determined, this finding underlines the potential importance of the LAR gene in dysregulation of insulin sensitivity and related disorders.

The -318 C>G single-nucleotide polymorphism in GNAI2 gene promoter region impairs transcriptional activity through specific binding of Sp1 transcription factor and is associated with high blood pressure in Caucasians from Italy.

Inhibiting Galpha subunit 2 protein, which is encoded by the GNAI2 gene, is suggested to be pathogenic for essential hypertension and/or insulin resistance. The aim of this study was to determine whether GNAI2 variations modulate the risk for these abnormalities. Seven single-nucleotide polymorphisms (SNP) at the GNAI2 locus were identified. Because of either low allelic frequency or unlikely biologic relevance (i.e., synonymous or intronic), six SNP were not studied further. The -318C>G SNP (allelic frequency 6%) in the promoter region was studied for association with adiposity, systolic BP (SBP) and diastolic BP, fasting insulin and glucose, and lipids levels in 655 nondiabetic Caucasians from Italy. As compared with individuals who carry the C/C genotype, G carriers (i.e., individuals who carry either the G/G or the C/G genotype) had higher SBP (117.8 +/- 16 versus 113.6 +/- 12.6 mmHg; P = 0.010) and were at increased risk for hypertension (odds ratio 2.2; 95% confidence interval 1.1 to 4.5). Compared with the C, the G allele had 2.5-fold reduced transcriptional activity in transfected HEK293 cells. As predicted by the TRANSFAC database, competition with YY1 or Sp1 transcription factors specifically reduced the binding of HeLa cell nuclear proteins to -318C or -318G allele, respectively, as indicated by shifted electrophoretic mobility. A "supershift" of the nuclear proteins/-318G allele complex was observed after anti-Sp1 was added but not anti-YY1 antibody. The GNAI2 -318 C>G SNP impairs transcriptional activity through specific binding of Sp1 and is associated with high SBP in Caucasians from Italy.

A variation in 3' UTR of hPTP1B increases specific gene expression and associates with insulin resistance.

Protein tyrosine phosphatase 1B (PTP1B) inhibits insulin signaling and, when overexpressed, plays a role in insulin resistance (Ahmad et al. 1997). We identified, in the 3' untranslated region of the PTP1B gene, a 1484insG variation that, in two different populations, is associated with several features of insulin resistance: among male individuals, higher values of the insulin resistance HOMA(IR) index (P=.006), serum triglycerides (P=.0002), and total/HDL cholesterol ratio (P=.025) and, among female individuals, higher blood pressure (P=.01). Similar data were also obtained in a family-based association study by use of sib pairs discordant for genotype (Gu et al. 2000). Subjects carrying the 1484insG variant showed also PTP1B mRNA overexpression in skeletal muscle (6,166 plus minus 1,879 copies/40 ng RNA vs. 2,983 plus minus 1,620; P<.01). Finally, PTP1B mRNA stability was significantly higher (P<.01) in human embryo kidney 293 cells transfected with 1484insG PTP1B, as compared with those transfected with wild-type PTP1B. Our data indicate that the 1484insG allele causes PTP1B overexpression and plays a role in insulin resistance. Therefore, individuals carrying the 1484insG variant might particularly benefit from PTP1B inhibitors, a promising new tool for treatment of insulin resistance (Kennedy and Ramachandran 2000).

A common haplotype at the CD36 locus is associated with high free fatty acid levels and increased cardiovascular risk in Caucasians.

CD36 is a class B scavenger receptor recognizing a variety of ligands including long-chain fatty acids and modified LDL. We investigated whether genetic variability at this locus is a determinant of free fatty acid (FFA) plasma levels and risk of coronary artery disease (CAD) in Caucasians. Typing of 21 polymorphic markers, evenly spanning the CD36 gene, revealed two linkage disequilibrium (LD) blocks that could be tagged by five polymorphisms (-33137A>G, -31118G>A, 25444G>A, 27645del>ins and 30294G>C). In 585 non-diabetic individuals of Caucasian origin, the 30294G>C polymorphism was significantly associated with FFA levels (P = 0.02)--an effect that was especially visible among men (P = 0.009). A similar association was observed in this gender at -33137 (P = 0.008) and -31118 (P = 0.028). When the five tag polymorphisms were considered together, men carrying the AGGIG haplotype had 31% higher FFA (P = 0.0002) and 20% higher triglycerides (P = 0.025) than non-carriers. The same haplotype was associated with increased risk of CAD in 197 type 2 diabetic individuals from the US (OR = 2.3, 95% CI 1.2-4.2). A similar tendency was observed in a group of 321 type 2 diabetic individuals from Italy (OR = 1.4, 0.9-2.3), resulting in an overall relative risk of 1.6 (1.1-2.3, P = 0.015) in the two populations considered together. By targeted resequencing, we identified a common variant in the CD36 promoter that is in strong LD with the AGGIG haplotype and could be partly responsible for these findings. In conclusion, this comprehensive study of CD36 variability indicates that the common polymorphisms at this locus modulate lipid metabolism and cardiovascular risk in Caucasians.