Allelic variants at insulin-receptor and insulin gene loci and susceptibility to NIDDM in Welsh population

Influence of Insulin Receptor Single Nucleotide Polymorphisms on Glycaemic Control and Formation of Anti-Insulin Antibodies in Diabetes Mellitus

Single nucleotide polymorphisms (SNPs) in insulin and insulin receptor genes may influence the interaction between the two molecules, as may anti-insulin antibodies (IAs), commonly found in patients with type 1 diabetes mellitus (T1D) or type 2 diabetes mellitus (T2D) treated with exogenous insulin. We examined the impact of two SNPs in the human insulin gene (INS), rs3842752 and rs689, and two in the insulin receptor gene (INSR) rs2245649 and rs2229429, on disease susceptibility, glycaemic control, and IAs formation in 100 T1D patients and 101 T2D patients treated with insulin. 79 individuals without diabetes were typed as healthy controls. The minor alleles of rs3842752 and rs689 in INS protected against T1D (OR: 0.50, p = 0.01 and OR: 0.44; p = 0.002, respectively). The minor alleles of both rs2245649 and rs2229429 in INSR were risk factors for poor glycaemic control (HbA1c ≥ 80 mmol/mol) in T1D (OR: 5.35, p = 0.009 and OR: 3.10, p = 0.01, respectively). Surprisingly, the minor alleles of rs2245649 and rs2229429 in INSR associated strongly with the absence of IAs in T1D (OR = 0.28, p = 0.008 and OR = 0.30, p = 0.002, respectively). In conclusion, the minor alleles of the investigated INS SNPs protect against T1D, and the minor alleles of the investigated INSR SNPs are associated with poor glycaemic control and the absence of IAs in T1D.

Insulin Receptor Trafficking: Consequences for Insulin Sensitivity and Diabetes

Insulin receptor (INSR) has been extensively studied in the area of cell proliferation and energy metabolism. Impaired INSR activities lead to insulin resistance, the key factor in the pathology of metabolic disorders including type 2 diabetes mellitus (T2DM). The mainstream opinion is that insulin resistance begins at a post-receptor level. The role of INSR activities and trafficking in insulin resistance pathogenesis has been largely ignored. Ligand-activated INSR is internalized and trafficked to early endosome (EE), where INSR is dephosphorylated and sorted. INSR can be subsequently conducted to lysosome for degradation or recycled back to the plasma membrane. The metabolic fate of INSR in cellular events implies the profound influence of INSR on insulin signaling pathways. Disruption of INSR-coupled activities has been identified in a wide range of insulin resistance-related diseases such as T2DM. Accumulating evidence suggests that alterations in INSR trafficking may lead to severe insulin resistance. However, there is very little understanding of how altered INSR activities undermine complex signaling pathways to the development of insulin resistance and T2DM. Here, we focus this review on summarizing previous findings on the molecular pathways of INSR trafficking in normal and diseased states. Through this review, we provide insights into the mechanistic role of INSR intracellular processes and activities in the development of insulin resistance and diabetes.

An exon variant in insulin receptor gene is associated with susceptibility to colorectal cancer in women

Given the role of insulin resistance in colorectal cancer (CRC), we explored whether genetic variants in insulin (INS), insulin receptor (INSR), insulin receptor substrate 1 (IRS1), insulin receptor substrate 2 (IRS2), insulin-like growth factor 1 (IGF1), and insulin-like growth factor binding protein 3 (IGFBP3) genes were associated with CRC risk. A total of 600 subjects, including 261 cases with CRC and 339 controls, were enrolled in this case-control study. Six polymorphisms in INS (rs689), INSR (rs1799817), IRS1 (rs1801278), IRS2 (rs1805097), IGF1 (rs5742612), and IGFBP3 (rs2854744) genes were genotyped using PCR-RFLP method. No significant difference was observed for INS, INSR, IRS1, IRS2, IGF1, and IGFBP3 genes between the cases and controls. However, the INSR rs1799817 "TT + CT" genotype and "CT" genotype compared with "CC" genotype occurred more frequently in the women with CRC than women controls (P = 0.007; OR = 1.93, 95 %CI = 1.20-3.11 and P = 0.002, OR = 2.15, 95 %CI = 1.31-3.53, respectively), and the difference remained significant after adjustment for confounding factors including age, BMI, smoking status, NSAID use, and family history of CRC (P = 0.018; OR = 1.86, 95 %CI = 1.11-3.10 and P = 0.004, OR = 2.18, 95 %CI = 1.28-3.71, respectively). In conclusion, to our knowledge, this study indicated for the first time that the INSR rs1799817 TT + CT genotype and CT genotype compared with the CC genotype had 1.86-fold and 2.18-fold increased risks for CRC among women, respectively. Furthermore, this finding is in line with previous studies which found significant associations between other variants of the INSR gene and CRC risk. Nevertheless, further studies are required to confirm our findings.

Influence of socioeconomic lifestyle factors and genetic polymorphism on type 2 diabetes occurrences among Tunisian Arab and Berber groups of Djerba Island

Type 2 diabetes mellitus (T2DM) is characterized by three major metabolic abnormalities: impaired insulin-stimulated glucose uptake in muscle and adipose tissues, alterations in glucose-stimulated insulin secretion, and increased hepatic glucose production. Both genetic and environmental factors contribute to its development. The insulin gene (INS), insulin receptor gene (INSR), and insulin receptor substrate 1 gene (IRS1), identified by polymerase chain reaction and digestion with selected restriction enzymes PstI, NsiI, and BstnI, have been proposed as T2DM candidate genes. To determine the contribution of genetic and environmental factors on the occurrence of T2DM, we examined the frequency of T2DM among two ethnically diverse populations, Arabs and Berbers, who have shared the same environment, the island of Djerba, for thousands of years. Both populations have a high prevalence of obesity,T2DM, and a high consanguinity rate. A total of 162 T2DM men and women were matched to 110 healthy male and female controls. Results showed that the NsiI polymorphism in INSR and BstnI polymorphism of IRS1 were significantly associated with T2DM only among the Berber group. The PstI polymorphism in INS, was not associated with T2DM in either group. Sedentary lifestyles, lower physical activity, and lower educational levels were associated with T2DM among the Berber group. These findings suggest that the insulin receptor gene and lifestyle factors in combination may contribute to the occurrence of T2DM in the Berber portion of this island population.

The genetics of gestational diabetes mellitus: evidence for relationship with type 2 diabetes mellitus

Gestational diabetes is a major public health problem because of its prevalence, its associated complications during pregnancy, and its increased risk for type 2 diabetes later in life. Insulin resistance is one of many physiological changes occurring during pregnancy, and when insulin resistance is accompanied by pancreatic beta-cell insufficiency, gestational diabetes may develop. Several lines of evidence suggest that gestational diabetes shares a common etiology with type 2 diabetes and support the hypothesis that gestational diabetes serves as a window to reveal a predisposition to type 2 diabetes. Pregnancy is an environmental stressor that may catalyze the progression to a diabetic state in genetically predisposed women; therefore, identification of these women during pregnancy could decrease the occurrence of type 2 diabetes through targeted prevention. This review presents an overview of the genetics of gestational diabetes, focusing on human association studies with candidate genes common to both type 2 diabetes and gestational diabetes.

Polymorphisms at the GLUT2 (β-cell/liver) glucose transporter gene and non-insulin-dependent diabetes mellitus (NIDDM): analysis in affected pedigree members

The precise genetic defects underlying the etiology of non-insulin-dependent diabetes mellitus (NIDDM) have yet to be identified. The beta-cell/liver glucose transporter gene GLUT2 represents a good candidate for the etiology of the disease, being involved in the glucose signalling for beta-cell insulin release. Population association studies of the GLUT2 gene in NIDDM have so far yielded controversial results. In order to determine the possible contribution of this gene to the inheritance of NIDDM, we have employed a new approach, where two polymorphic markers of the GLUT2 locus, detected with the restriction enzyme Taq-1, were examined for linkage with the disease in a group of 22 Italian pedigrees with affected members (n = 50). Departure from independent segregation between markers and disease was analyzed by the Affected-Pedigree-Members (APM) statistical method. Furthermore, association analysis between the Taq-1 RFLPs at the GLUT2 locus and NIDDM was performed in a group of diabetics with a strong family history, comprising the 22 probands and 23 other diabetics with an affected first-degree relative. The results indicate that there was no segregation distortion between the Taq-1 markers of the GLUT2 gene and the disease in the pedigrees examined. Also, no significant difference in genotype distribution, haplotype and allele frequencies was found between diabetics and controls for the two Taq-1 RFLPs. We conclude that genetic variation at the GLUT2 transporter gene is unlikely to contribute in a major way to the inheritance for NIDDM in this Italian population.

The insulin gene in diabetes

Lack of insulin production or abnormalities affecting insulin secretion are key to the development of almost all forms of diabetes, including the common type 1 (insulin-dependent) and type 2 (non-insulin-dependent) diabetes and the more rare forms of maturity-onset diabetes of the young (MODY). Because insulin has such a central role in the pathogenesis of both forms of diabetes, the insulin gene (INS) has always been considered a candidate susceptibility gene. A number of studies have shown that the allelic variation and parent-of-origin effects affect the transmission and expression of the insulin gene in pancreatic beta-cells and extra-pancreatic tissues. These observations have led to the formulation of new hypotheses to explain the biological mechanisms by which functional differences in the expression of the insulin gene may contribute to diabetes susceptibility.

Insulin receptor gene in hypertension

The first molecular genetic association with human essential hypertension (HT) involved the insulin receptor gene (INSR). This highly significant result in Caucasians was for an insertion/deletion polymorphism in intron 9. A polymorphism in exon 8 showed a weak association, but a microsatellite in intron 2 proved negative for HT, although has shown an association with plasma insulin in Japanese. A similar spectrum of genetic associations for variants spanning INSR has been noted for insulin-dependent diabetic patients with rapidly-progressing renal disease, a subgroup having a strong family history of essential HT. Association with HT has also been found for an INSR variant in CHinese. Insulin resistance secondary to an INSR 'defect', or other causes, would increase insulin, which has cardiovascular effects, and insulin can raise angiotensinogen. Also, insulin is co-secreted with amylin, which can increase renin secretion. In the spontaneously HT rat there is evidence for reduced down-regulation of INSR expression in response to NaCl-loading, consistent with a promoter effect. When combined with observations of insulin resistance in essential HT patients and their pre-HT offspring, the possibility of dys-regulation of INSR merits attention in disease etiology in a proportion of essential HT patients.

Two microsatellite repeat polymorphisms flanking opposite ends of the human glucokinase gene: use in haplotype analysis of Welsh Caucasians with type 2 (non-insulin-dependent) diabetes mellitus

The purpose of this study was to evaluate the role of potential glucokinase defects contributing to susceptibility to Type 2 (non-insulin-dependent) diabetes mellitus in Welsh Caucasians. For this analysis, two microsatellite repeat polymorphisms flanking opposite ends of the gene were employed. For a recently described microsatellite (GCK2), located 6 kilobases upstream of islet exon 1, six different sized alleles were observed, with heterozygosity of 0.50 and polymorphism information content 0.44. Combined heterozygosity with another microsatellite repeat (GCK1) was 0.72. Significant linkage disequilibrium was noted between GCK2 and GCK1, suggesting that haplotypes may be a better predictor of Type 2 diabetes than analysis with either microsatellite alone. Using these two markers, the association with Type 2 diabetes was examined. The frequencies of alleles and genotypes at GCK1 did not differ between the patients with Type 2 diabetes (n = 157) and control subjects (n = 73). Similarly no differences were observed in GCK2 alleles or genotypes. The frequencies of haplotypes, derived from the two markers, also did not differ between the two groups. To investigate the possibility of minor metabolic effects of glucokinase defects, we also studied the association between the GCK alleles or haplotypes and the response profiles to meal tolerance tests. No association was observed between plasma glucose or insulin responses to meal tolerance tests with GCK haplotypes or alleles. These results suggest that glucokinase mutations in Welsh Caucasians are not major determinants of susceptibility to the common type of Type 2 diabetes.

Polymorphisms at the GLUT1 (HepG2) and GLUT4 (muscle/adipocyte) glucose transporter genes and non-insulin-dependent diabetes mellitus (NIDDM)

In order to determine the possible contribution of the GLUT1 (HepG2) glucose transporter gene to the inheritance of non-insulin-dependent diabetes mellitus (NIDDM), two restriction fragment length polymorphisms (RFLPs) and the related haplotypes at this locus were studied in 48 Italian diabetic patients and 58 normal subjects. Genotype frequencies for the XbaI polymorphism were significantly different between patients and controls (XbaI: chi 2 = 9.80, df = 2, P less than 0.0079). A significant difference was also found in the allele frequencies between NIDDM patients and controls (chi 2 = 9.39, df = 1, P less than 0.0022), whereas no differences were found for the StuI RFLP. No linkage disequilibrium was detected between the XbaI and StuI RFLPs in this sample. The analysis of the four haplotype frequencies (X1S1, X1S2, X2S1, X2S2) revealed a significant difference between diabetic patients and controls (chi 2 = 14.26, df = 3, P less than 0.002). By comparing single haplotype frequencies, a significant difference between the two groups was found for the X1S1 and X2S2 haplotypes. A two-allele RFLP at the GLUT4 (muscle/adipocyte) glucose transporter gene, detected with the restriction enzyme KpnI, was also examined; no differences were found between patients and controls for this RFLP. The finding of an association between polymorphic markers at the GLUT1 transporter and NIDDM suggests that this locus may contribute to the inherited susceptibility to the disease in this Italian population.

Genetic variation in insulin receptor beta-chain exons among members of familial type 2 (non-insulin-dependent) diabetic pedigrees

Insulin resistance appears to be an essential component of Type 2 (non-insulin-dependent) diabetes mellitus. Both hyperinsulinaemia and insulin resistance are inherited and may precede the onset of Type 2 diabetes. To determine whether insulin receptor gene mutations, and specifically whether mutations of the beta-chain could account for the observed insulin resistance, we studied members of 16 pedigrees ascertained for two or more Type 2 diabetic siblings and members of four additional pedigrees ascertained for a mixture of Type 1 and Type 2 diabetes. We previously demonstrated insulin resistance among unaffected members of these pedigrees. Each pedigree was initially examined with insulin receptor restriction fragment length polymorphisms to determine whether any allele segregated with Type 2 diabetes in these pedigrees. Of the 16 pedigrees ascertained for Type 2 diabetes, at least one recombinant event between diabetes and the insulin receptor locus was present in seven pedigrees. An additional two pedigrees showed no linkage if individuals with impaired glucose tolerance were also considered affected. In all but one of the remaining pedigrees, apparent sharing of haplotypes may have resulted from insufficient polymorphism to distinguish all parental alleles. Subsequently, exons 13-21 of each allele which appeared in a Type 2 diabetic individual were examined by single strand conformation polymorphisms to detect any mutations in this region. A total of five mutations were detected, but DNA sequence analysis showed each mutation to be silent and thus not likely to result in defective insulin receptor function. No mutation detected in this fashion was present on an allele which appeared to segregate with Type 2 diabetes.(ABSTRACT TRUNCATED AT 250 WORDS)