Segregation analysis of NIDDM in Caucasian families

The impact of parental history of type 2 diabetes on hyperinsulinemia and insulin resistance in subjects from central Mexico

AIMS

Hyperinsulinemia and insulin resistance are both associated with the development of Type 2 Diabetes and other pathologies; however, the influence of parental history of Type 2 diabetes (PH-T2D) has yet to be investigated. Therefore, this study was conducted to determine the effect of PH-T2D has on the risk of developing hyperinsulinemia and IR.

MATERIALS AND METHODS

1092 subjects (703 non-pregnant females and 389 males) were enrolled for a cross-sectional study. Clinical and biochemical parameters were collected. Subjects were allocated according to their PH-T2D: no parents, one parent, or both parents. Insulin resistance was calculated using the HOMA1 equation (HOMA1-IR). Logistic regression was used to determine the association (odds ratio) between PH-T2D and hyperinsulinemia or insulin resistance.

RESULTS

Increasing degrees of PH-T2D were associated with significant increases in fasting plasma glucose, insulin, and HOMA1-IR (p <0.05). Subjects having one or both parents were associated with an increase risk of developing hyperinsulinemia (odds ratio=1.53, 95%CI: 1.12-2.09, and odds ratio=1.92, 95%CI: 1.21-3.06, respectively) and insulin resistance (odds ratio=1.47, 95%CI: 1.08-2.00 and odds ratio=1.77, 95%CI: 1.09-2.87, respectively), when adjusting for age, sex, BMI, fasting plasma glucose, and triglycerides.

CONCLUSION

The presences of PH-T2D significantly increased the risk of developing hyperinsulinemia and insulin resistance.

Familial aggregation of insulin resistance and cardiovascular risk factors in hypertension

The authors assessed the familial aggregation of cardiometabolic abnormalities (elevated homeostasis model assessment [HOMA], triglycerides [TG], and low-density lipoprotein [LDL] and reduced high-density lipoprotein [HDL]) among hypertensive siblings (N=287 from 138 families). Evidence for familial aggregation required sibling-pair concordance of outcome variables dichotomized according to predefined values (concordance for highest-quartile HOMA [>3.3], TG [>170 mg/dL], and LDL [>138 mg/dL] and lowest-quartile HOMA for HDL [<32 mg/dL]). Hypertensive individuals with insulin resistance (high-quartile HOMA) had higher TG and lower HDL and LDL levels compared with insulin-sensitive hypertensives. High-quartile HOMA, TG, and LDL aggregated in hypertensive families, and TG plus HOMA coaggregated. HDL did not show aggregation. In a multivariate logistic regression, the only significant predictor of an individual's HOMA status was a sibling's HOMA status in a model including age, sex, race, and body mass index (odds ratio=9.12; 95% confidence interval, 3.64-23.14; P<.001). Cardiometabolic variables demonstrate heritability in hypertensive families. Further exploration of common genetic susceptibility loci in hypertension involving these factors is warranted.

Differences in the association between type 2 diabetes and impaired microvascular function among Europeans and African Caribbeans

AIMS/HYPOTHESIS

Diabetes is associated with microvascular damage in all populations, but diabetic patients of Black African descent (African Caribbeans) have a greater risk of vascular target organ damage than would be anticipated for any given blood pressure level. We investigated whether this may be due to differences in the microvasculature.

MATERIALS AND METHODS

To assess the maximum hyperaemic response to heating and the post-ischaemic response, Laser Doppler fluximetry was performed on 51 and 100 Europeans, and on 66 and 88 African Caribbeans with and without diabetes, respectively. Subjects were aged between 40 and 65 years and recruited from the general population. Echocardiographic interventricular septal thickness (IVST) was measured as a proxy for vascular target organ damage.

RESULTS

In diabetic subjects of both ethnic groups, the maximum hyperaemic response and peak response to ischaemia were attenuated as compared to the corresponding non-diabetic subjects (p=0.08 for diabetic and 0.03 for non-diabetic Europeans; p=0.03 and 0.1 for African Caribbeans). Adjustment for cardiovascular risk factors, in particular insulin and blood pressure, abolished these differences in Europeans (p=0.8 for diabetic and 0.2 for non-diabetic Europeans), but not in African Caribbeans (p=0.03 and 0.05).

CONCLUSIONS/INTERPRETATION

Persisting microvascular dysfunction in African Caribbeans may contribute to the increased risk of target organ damage observed in diabetes in this population. The weak contribution of conventional cardiovascular risk factors to these disturbances indicates that conventional therapeutic interventions may be less beneficial in these patients. There was a risk-factor-independent, inverse association between IVST and maximal hyperaemia. These ethnic differences in microvascular responses to temperature and arterial occlusion could account for increased target organ damage in African Caribbeans.

Genetic basis of type 2 diabetes mellitus: implications for therapy

Type 2 diabetes mellitus represents a multifactorial, heterogeneous group of disorders, which result from defects in insulin secretion, insulin action, or both. The prevalence of type 2 diabetes has increased dramatically worldwide over the past several decades, a trend that has been heavily influenced by the relatively recent changes in diet and physical activity levels. There is also strong evidence supporting a genetic component to type 2 diabetes susceptibility and several genes underlying monogenic forms of diabetes have already been identified. However, common type 2 diabetes is likely to result from the contribution of many genes interacting with different environmental factors to produce wide variation in the clinical course of the disease. Not surprisingly, the etiologic complexity underlying type 2 diabetes has made identification of the contributing genes difficult. Current therapies in the management of type 2 diabetes include lifestyle intervention through diet modification and exercise, and oral or injected hypoglycemic agents; however, not all individuals with type 2 diabetes respond in the same way to these treatments. Because of variability in the clinical course of the disease and in the responsiveness to pharmacologic therapies, identification and characterization of the genetic variants underlying type 2 diabetes susceptibility will be important in the development of individualized treatment. Findings from linkage analyses, candidate gene studies, and animal models will be valuable in the identification of novel pathways involved in the regulation of glucose homeostasis, and will augment our understanding of the gene-gene and gene-environment interactions, which impact on type 2 diabetes etiology and pathogenesis. In addition, identification of genetic variants that determine differences in antidiabetic drug responsiveness will be useful in assessing a first-line pharmacologic therapy for diabetic patients.

A genome-wide scan for loci linked to plasma levels of glucose and HbA(1c) in a community-based sample of Caucasian pedigrees: The Framingham Offspring Study

Elevated blood glucose levels are the hallmark of type 2 diabetes as well as a powerful risk factor for development of the disease. We conducted a genome-wide search for diabetes-related genes, using measures of glycemia as quantitative traits in 330 pedigrees from the Framingham Heart Study. Of 3,799 attendees at the 5th Offspring Study exam cycle (1991--1995), 1,461, 1,251, and 771 men (49%) and women provided information on levels of 20-year mean fasting glucose, current fasting glucose, and HbA(1c), respectively, and 1,308 contributed genotype data (using 401 microsatellite markers with an average spacing of 10 cM). Levels of glycemic traits were adjusted for age, cigarette smoking, alcohol and estrogen use, physical activity, and BMI. We ranked standardized residuals from these models, created normalized deviates from the ranks, and used the variance component model implemented in SOLAR (Sequential Oligogenic Linkage Analysis Routines) to evaluate linkage to normalized deviates as quantitative traits. We found peak evidence for linkage to 20-year mean fasting glucose levels on chromosome 1 at approximately 247 cM from p-telomere (pter) (multipoint logarithm of odds [LOD] 2.33) and on chromosome 10 at approximately 86 cM from pter (multipoint LOD 2.07); to current fasting glucose levels on chromosome 1 at approximately 218 cM from pter (multipoint LOD 1.80) and on chromosome 10 at approximately 96 cM from pter (multipoint LOD 2.15); and to HbA(1c) levels on chromosome 1 at approximately 187 cM (multipoint LOD 2.81). This analysis of unselected European Caucasian pedigrees suggests localization of quantitative trait loci influencing glucose homeostasis on chromosomes 1q and 10q. Findings at approximately 187--218 cM on chromosome 1 appear to replicate linkage reported in previous studies of other populations, pointing to this large chromosomal region as worthy of more detailed scrutiny in the search for type 2 diabetes susceptibility genes.

A serine/alanine polymorphism in the nucleotide-binding fold-2 of the sulphonylurea receptor-1 (S1369A) is associated with enhanced glucose-induced insulin secretion during pregnancy

The sulphonylurea receptor-1 (SUR-1) regulates glucose-induced insulin secretion by controlling K+-ATP channel activity of the pancreatic beta-cell membrane. In this study, we investigated the putative role of a T/G-polymorphism (exon 33, codon 1369; S1369A) in the adenosine diphosphate-sensing nucleotide-binding fold-2 (NBF-2) of the SUR-1 on glucose-induced insulin secretion during an oral glucose tolerance test in pregnant women (PW; n=182). Compared to PW with the T/T genotype, statistically significant elevated C-peptide concentrations were found 60 min after glucose intake in PW with the T/G and G/G genotype (T/T 9.0+/-0.4 ng/ml vs T/G 10.8+/-0.4 ng/ml or G/G 10.8+/-0.7 ng/ml, p=0.01). Furthermore, compared to PW with T/T genotype the deltaC-peptide (60/0 min) was significantly enhanced in PW with T/G or G/G genotype (T/T 6.7+/-0.3 vs T/G 8.9+/-0.4 or G/G 8.9+/-0.7, p=0.0009). A significant correlation of C-peptide concentrations with blood glucose (BG) 60 min after glucose intake was only found in PW with the T/T genotype (r=0.6, p<0.0004). Similarly, a significant correlation of insulin concentrations with BG 60 min after glucose intake was observed in PW with T/T genotype (r=0.5, p<0.0001) and T/G genotype (r=0.24, p<0.03) but not in PW with G/G genotype (r=0.01, p=0.9). From our data we conclude that in PW with the alanine substitution in the NBF-2 region, the insulin response of the pancreatic beta-cell after glucose intake is enhanced and does not correlate with actual BG levels.

Heritability of factors of the insulin resistance syndrome in women twins

The insulin resistance syndrome (IRS) is characterized by a combination of interrelated coronary heart disease (CHD) risk factors, including low high-density lipoprotein cholesterol (HDL-C) levels, obesity and increases in triglyceride (TG), blood pressure, small low-density lipoprotein particles (LDL), and both fasting and postload plasma insulin and glucose. Using factor analysis, we previously identified 3 uncorrelated factors that explained 66% of the variance among these variables, based on data from women participating in examination 2 of the Kaiser Permanente Women Twins Study in Oakland, CA during 1989-1990. The factors were interpreted as: 1) body mass/fat distribution, 2) insulin/glucose, and 3) lipids: TG, HDL-C, LDL peak particle diameter. In this analysis, heritability of each of the factors was estimated based on data from 140 monozygotic and 96 dizygotic pairs of non-diabetic women twins. Heritability estimates were calculated using the classical approach, the analysis of variance (ANOVA) approach, and the maximum likelihood approach. For the body mass/fat distribution factor heritability estimates suggest moderate genetic influences; 0.61 (P < 0.001), 0.14 (P > 0.05), and 0.71 (P < 0.001), respectively. The insulin/glucose factor appeared to be highly heritable, with estimates of 0.87, 0.92, and 0.57 (all P < 0.001), respectively. The heritability estimates for the lipid factor were moderate and consistent across methods: 0.25 (P < 0.10), 0.32 (P < 0.05), and 0.30 (P < 0.05), respectively. These results are consistent with genetic influences on each of the 3 "factors," and suggest that both genetic and environmental effects are involved in the clustering of IRS risk factors.

Paternal-maternal effects on phenotypic characteristics in spontaneously diabetic Nagoya-Shibata-Yasuda mice

The Nagoya-Shibata-Yasuda (NSY) mouse is an inbred strain with spontaneous development of type 2 (non-insulin-dependent) diabetes mellitus. The purpose of this study was to determine the mode of inheritance of various phenotypes related to diabetes in this strain. Two reciprocal outcrosses, female C3H/He x male NSY F1 (C3NF1) and female NSY x male C3H/He F1 (NC3F1) mice, were performed. The phenotypic characteristics in both F1 mice were investigated. The cumulative incidence of diabetes was 100% (25 of 25) in male C3NF1 mice and 97% (29 of 30) in male NC3F1 mice at 48 weeks of age, indicating that diabetes in NSY mice was transmitted to male F1 hybrids in an autosomal dominant manner. Fatty liver also showed an autosomal dominant mode of inheritance. In contrast, epididymal fat accumulation and impaired insulin secretion showed an autosomal recessive mode of inheritance. The body mass index (BMI) showed a codominant mode of inheritance. Paternal-maternal effects associated with the severity of diabetes were observed. Insulin resistance was much more severe in male F1 mice than in the parental NSY strain. These data indicate different modes of inheritance among phenotypes related to type 2 diabetes. The presence of more severe insulin resistance in F1 mice versus the parental strains suggests the interaction of both parental genomes in the development of insulin resistance. The F1 mouse is expected to be useful for studies of the pathogenesis and genetic synergism of the insulin resistance syndrome.

Potential errors resulting from sex and age difference in assessing family history of diabetes

BACKGROUND

Diabetes mellitus occurs nearly exponentially with aging and its occurrence differs between men and women in adulthood. Therefore, the sex and age of family members should be considered in assessing the family history. In this report the effects of sex and age on the positivity of family history were estimated numerically.

METHODS

Sex- and age-specific proportion of a positive history of diabetes mellitus among 24,273 family members was obtained from a questionnaire survey of 2,316 high school students in Japan. By analyzing the sex- and age-specific proportion with the logistic regression model, odds ratios were estimated which indicated potential bias or misclassification resulting from sex and age differences.

RESULTS

The odds ratios were 1.97 (95% confidence interval, 1.74-2.23) for the sex difference and 1.05 (95% confidence interval, 1.04-1.05) for an age difference of 1 year. This indicated that a male family member had a 1.97 times higher chance of having a positive history than a female member and that a positive history increased by (1.05)y, where y was age difference in years.

CONCLUSION

A control for sex and age of family members will be required in assessing the family history of diabetes mellitus as a risk factor.

Non-insulin-dependent diabetes mellitus--a collision between thrifty genes and an affluent society

Non-insulin-dependent diabetes mellitus (NIDDM) is one of the most common non-communicable diseases in the world. It has become obvious that NIDDM is the result of a collision between thrifty genes and an affluent society. Genes predisposing to NIDDM might have been survival genes for our ancestors, helping them to store energy during long periods of starvation. When these genes are exposed to a sedentary lifestyle and high caloric intake typical to the Western world, they predispose to obesity and insulin resistance. NIDDM results when beta cells cannot compensate for insulin resistance by increasing insulin secretion. Therefore, at least two inherited defects can be expected in NIDDM, one causing obesity and insulin resistance and the other inability to increase insulin secretion. In reality there may be more inherited defects. It has become quite clear that diabetes cannot simply be divided into NIDDM and insulin-dependent diabetes mellitus (IDDM). The disease is more heterogeneous; unmasking this heterogeneity and identifying new subgroups of diabetes presents a challenge to modern molecular biology.

Mapping of a gene for type 2 diabetes associated with an insulin secretion defect by a genome scan in Finnish families

Non-insulin dependent diabetes mellitus (NIDDM) affects more than 100 million people worldwide and is associated with severe metabolic defects, including peripheral insulin resistance, elevated hepatic glucose production, and inappropriate insulin secretion. Family studies point to a major genetic component, but specific susceptibility genes have not yet been identified-except for rare early-onset forms with monogenic or mitochondrial inheritance. We have screened over 4,000 individuals from a population isolate in western Finland, identified 26 families (comprising 217 individuals) enriched for NIDDM and performed a genome-wide scan using non-parametric linkage analysis. We found no significant evidence for linkage when the families were analysed together, but strong evidence for linkage when families were classified according to mean insulin levels in affecteds (in oral glucose tolerance tests). Specifically, families with the lowest insulin levels showed linkage (P = 2 x 10(-6)) to chromosome 12 near D12S1349. Interestingly, this region contains the gene causing the rare, dominant, early-onset form of diabetes MODY3. Unlike MODY3 families, the Finnish families with low insulin have an age-of-onset typical for NIDDM (mean = 58 years). We infer the existence of a gene NIDDM2 causing NIDDM associated with low insulin secretion, and suggest that NIDDM2 and MODY3 may represent different alleles of the same gene.

Candidate gene studies in pedigrees with maturity-onset diabetes of the young not linked with glucokinase

Maturity-onset diabetes of the young (MODY) is a form of non-insulin-dependent diabetes mellitus characterised by an early age of onset and an autosomal dominant mode of inheritance. Only a proportion of cases are due to mutations in the glucokinase gene. We have studied five Caucasian MODY families, including the first MODY family to be described, with five candidate genes implicated in regulation of insulin secretion. The affected subjects showed more marked hyperglycaemia than that found in subjects with glucokinase mutations. We assessed polymorphic markers close to the genes for glucokinase, hexokinase II, adenosine deaminase, pituitary adenylate cyclase-activating polypeptide receptor, and glucagon-like peptide-1 receptor. Linkage analysis with diabetes gave cumulative log of the odds (LOD) scores of less than -3, implying that mutations in these genes are unlikely to provide a major genetic contribution to this form of MODY.