Insulin receptor gene polymorphisms in type 2 (non-insulin-dependent) diabetes mellitus

Analysis of three glucose transporter genes in a Caucasian population: no associations with non-insulin-dependent diabetes and obesity

The significance of variation within the genes coding for three glucose transporter proteins in the aetiology of non-insulin dependent diabetes mellitus was assessed by analysing restriction fragment length polymorphisms in an English Caucasian population. Two polymorphisms at the HepG2/erythrocyte glucose transporter (GLUT1) locus, four at the liver/pancreatic glucose transporter (GLUT2) locus and one at the muscle/adipocyte glucose transporter (GLUT4) were analysed in a sample of diabetic and non-diabetic subjects. No significant differences in the allelic, genotypic or haplotypic frequencies of the polymorphisms at these three loci were observed between the diabetic or non-diabetic populations. No significant linkage disequilibrium was observed between the two GLUT1 polymorphic sites, whereas the four polymorphic sites at the GLUT2 locus, one of which appears to be due to a 100-200 base pair DNA insertion/deletion, were found to be in significant linkage disequilibrium. In order to study the possible role of glucose transporter gene variants contributing to the development of obesity, the body mass indexes were compared in the different genotypic groups of diabetic and non-diabetic subjects. No differences in body mass index between genotype groups were found at the p < 0.005 level of significance.

Progress in determining the genes for hypertension, insulin resistance, and dyslipidemia

For the first time, we have techniques available that may enable us to determine cause and effect in common cardiovascular diseases. The observations presented herein require cautious interpretation until replicated. There are currently several large programs under way that seek to establish substantial family resources for investigation of the genetic basis of hypertension. When interpreting the results of genome screens, it will be necessary to consider that we may link genetic loci for coexistent features such as dyslipidemia and insulin resistance to hypertension. Therefore, careful phenotypic data will be necessary to dissect out the causes of hypertension.

Genetics of non-insulin-dependent (type-II) diabetes mellitus

Both genetic and environmental factors contribute to the etiology of non-insulin-dependent diabetes. The genetic component is heterogeneous and in some patients is probably complex, involving multiple genes. Specific genetic defects have been identified for rate monogenic forms of NIDDM: maturity-onset diabetes of the young, or MODY (which is due to glucokinase mutations in about 40% of families), syndromes of extreme insulin resistance (which often involve the insulin receptor), and diabetes-deafness syndromes (with defects in mitochondrial genes). In contrast, the genes involved in common forms of NIDDM are still uncertain. Mutations have been extensively searched in genes regulating insulin signaling and secretion. Some evidence of involvement has been produced for insulin-receptor substrate-1, glycogen synthase, the glucagon receptor, a ras-related protein (Rad), histocompatibility antigens, PC-1, and fatty acid binding protein, but the contributions of these genes to NIDDM is probably small. Other candidate genes (e.g. insulin, insulin receptor, glucose transporters) have been excluded as major diabetogenes. New insights are expected in the near future from the systematic scanning of the genome for linkage with NIDDM.

Insulin resistance in offspring of hypertensive parents

OBJECTIVE

To determine if insulin resistance is present in normotensive adults at increased risk of developing hypertension.

DESIGN

Normotensive subjects with at least one hypertensive parent were paired with offspring of normotensive parents (controls), being matched for age, sex, social class, and physical activity.

SETTING

Outpatient clinic.

SUBJECTS

30 paired subjects (16 men and 14 women) with and without a family history of hypertension, aged 18-32, with a body mass index < 25 kg/m2, with blood pressure < 130/85 mm Hg, and not taking drugs.

INTERVENTIONS

Euglycaemic glucose clamp (two hour infusion of insulin 1 mU/kg/min) and intravenous glucose tolerance test (injection of 100 ml 20% glucose).

MAIN OUTCOME MEASURES

Insulin mediated glucose disposal and insulin secretion.

RESULTS

The offspring of hypertensive parents had slightly higher blood pressure than did the controls (mean 117 (SD 6) v 108 (5) mm Hg systolic, p = 0.013; 76 (7) v 67 (6) mm Hg diastolic, p = 0.017). Their insulin mediated glucose disposal was lower than that of controls (29.5 (6.5) v 40.1 (8.6) mumol/kg/min, p = 0.002), but, after adjustment for blood pressure, the difference was not significant (difference 6.9 (95% confidence interval -1.5 to 15.3), p = 0.10). Insulin secretion in the first hour after injection of glucose was slightly but not significantly higher in the offspring of hypertensive patients (9320 (5484) v 6723 (3751) pmol.min/l). The two groups had similar concentrations of plasma glucose (5.2 (0.3) v 5.1 (0.4) mmol/l), serum cholesterol (4.4 (0.8) v 4.6 (0.8) mmol/l), serum triglyceride (0.89 (0.52) v 0.68 (0.27) mmol/l), and serum low density lipoprotein cholesterol (2.81 (0.65) v 2.79 (0.61) mmol/l). The offspring of hypertensive parents, however, had lower serum concentrations of high density lipoprotein cholesterol (1.24 (0.31) v 1.56 (0.35) mmol/l, p = 0.002) and higher serum concentrations of non-esterified fatty acids (0.7 (0.4) v 0.4 (0.4) mmol/l, p = 0.039).

CONCLUSIONS

Young normotensive subjects who are at increased risk of developing hypertension are insulin resistant.

Molecular studies of the genetics of non-insulin-dependent diabetes mellitus

Non-insulin-dependent mellitus (NIDDM) is a common, multifactorial disease with a significant genetic component to disease susceptibility. Biometrical analysis of family data has consistently found evidence of the action of a major gene in determining susceptibility to NIDDM in families. However, the identity of the gene or genes that contribute to NIDDM in the general population is still not known. Recent advances in molecular biology have given investigators access to a number of plausible candidate genes for NIDDM and these have been used as test loci in association and linkage studies with inconsistent results. A review of the candidate gene studies in NIDDM suggests that the failure of these studies to identify specific loci involved in conferring susceptibility to NIDDM is, in part, due to failure to incorporate a number of biological features of the disease. The frequency of NIDDM in the population suggests that the alleles involved in NIDDM are common and their individual impact too small to be detected by simple single locus methods of analysis. Studies of other phenotypic forms of diabetes mellitus suggest that susceptibility to NIDDM is probably determined by alleles at more than one locus acting independently or in concert. The evolutionary history of certain populations may have isolated alleles conferring susceptibility to NIDDM in ethnically defined populations at high risk of NIDDM. These populations may provide a unique opportunity to identify specific genes involved in the complex etiology of NIDDM. © 1993 Wiley-Liss, Inc.