Diabetes in identical twins. A study of 200 pairs

Inflammatory mediators and islet beta-cell failure: a link between type 1 and type 2 diabetes

Pancreatic islet beta-cell death occurs in type 1 and 2 diabetes mellitus, leading to absolute or relative insulin deficiency. beta-cell death in type 1 diabetes is due predominantly to autoimmunity. In type 2 diabetes beta-cell death occurs as the combined consequence of increased circulating glucose and saturated fatty acids together with adipocyte secreted factors and chronic activation of the innate immune system. In both diabetes types intra-islet inflammatory mediators seem to trigger a final common pathway leading to beta-cell apoptosis. Therefore anti-inflammatory therapeutic approaches designed to block beta-cell apoptosis could be a significant new development in type 1 and 2 diabetes.

Evidence for joint action of genes on diabetes status and CVD risk factors in American Indians: the strong heart family study

OBJECTIVES

Previous research among American Indians of the strong heart family study (SHFS) has demonstrated significant heritabilities for CVD risk factors and implicated diabetes as an important predictor of several of the phenotypes. Moreover, we recently demonstrated that genetic effects on CVD risk factors differed in diabetic and nondiabetic individuals. In this paper, we investigated whether a significant genetic influence on diabetes status could be identified, and whether there is evidence for joint action of genes on diabetes status and related CVD risk factors.

METHODS AND RESULTS

Approximately 950 men and women, age 18 or older, in 32 extended families, were examined between 1997 and 1999. We estimated the effects of genes and environmental covariates on diabetes status using a threshold model and a maximum likelihood variance component approach. Diabetes status exhibited a residual heritability of 22% (h2=0.22). We also estimated the genetic and environmental correlations between diabetes susceptibility and eight risk factors for CVD. All eight CVD risk factors displayed significant genetic correlations with diabetes status (BMI (rhoG=0.55), fibrinogen (rhoG=0.40), HDL-C (rhoG=-0.37), ln triglycerides (rhoG=0.65), FAT (rhoG=0.38 ), PAI-1 (rhoG=0.67), SBP (rhoG=0.57), and WHR (rhoG=0.58)). Three of eight traits (HDL-C (rhoE=-0.32), ln triglycerides (rhoE=0.33), and fibrinogen (rhoE=0.20)) displayed significant environmental correlations with diabetes status.

CONCLUSIONS

These findings suggest that in the context of a high prevalence of diabetes, still unidentified diabetes genes may play an important role in influencing variation in CVD risk factors.

Longitudinal changes in risk variables of insulin resistance syndrome from childhood to young adulthood in offspring of parents with type 2 diabetes: the Bogalusa Heart Study

The occurrence of metabolic abnormalities related to insulin resistance syndrome in nondiabetic offspring of type 2 diabetic parents is known. However, information is lacking on the timing and the course of development of the components of this syndrome from childhood to adulthood in the offspring of parents with diabetes. This aspect was examined in a community-based cohort with (n = 303) and without (n = 1,136) a parental history of type 2 diabetes followed longitudinally since childhood (ages 4 to 17 years; mean follow-up period, 15 years) by repeated surveys. Offspring with parental diabetes versus those without such history had significantly excess generalized and truncal adiposity as measured by body mass index (BMI) and subscapular skinfold beginning in childhood, higher levels of fasting insulin and glucose and homeostasis model assessment index of insulin resistance (HOMA-IR) from adolescence, and higher levels of low-density lipoprotein (LDL) cholesterol and triglycerides and lower levels of high-density lipoprotein (HDL) cholesterol in adulthood. Many of these risk variables changed adversely at an increased rate in offspring of diabetic parents. In a multivariate analysis, parental diabetes was an independent predictor of longitudinal changes in adiposity, glucose, insulin, HOM-IR, systolic and diastolic blood pressure, and LDL cholesterol in the offspring, regardless of race and gender. As young adults, the offspring of diabetic parents had a higher prevalence of generalized (BMI > 30, 36% v 16%, P =.0001) and visceral (waist > 100 cm, 15% v 6%, P =.0001) obesity, hyperinsulinemia indicative of insulin resistance (insulin > 18 microU/mL, 15% v 8%, P =.0001), hyperglycemia (>or=110 mg/dL, 2% v 0.5%, P =.02), high LDL cholesterol (>or=160 mg/dL, 11% v 7%, P =.02), low HDL cholesterol (<40 mg/dL for males and <50 mg/dL for females, 40% v 31%, P =.004), high triglycerides (>or=150 mg/dL, 23% v 15%, P =.0001), and hypertension (>140/90 mm Hg, 11% v 6%, P =.004). Thus, the offspring of diabetic parents displayed excess body fatness beginning in childhood and accelerated progression of adverse risk profile characteristics of insulin resistance syndrome from childhood to young adulthood. These observations have important implications for early prevention and intervention.

The search for type 2 diabetes genes

Type 2 diabetes (T2DM) is a serious disease with severe complications. Around one in 10 people alive today suffer from type 2 diabetes or are destined to develop it before they die. Inheritance plays an important role in the cause of type 2 diabetes. A considerable amount of research is devoted to defining the genes involved in the aetiology of this widespread disease. This information is crucial if we are to improve our methods of preventing and treating diabetes. Over the last 25 years there have been considerable advances in our understanding of the genetics of diabetes. Important discoveries have been made in dissecting the genes involved in rare monogenic forms of type 2 diabetes which has become a paradigm for genetic studies of type 2 diabetes. This review focuses on the main approaches currently adopted and our current understanding of the genes involved in susceptibility to type 2 diabetes.

High GAD65 autoantibody levels in nondiabetic adults are associated with HLA but not with CTLA-4 or INS VNTR

OBJECTIVES

To explore the relationship between genetic background and antibody levels in a nondiabetic population. We evaluated if high levels of autoantibodies against the 65 kDa isoform of glutamic acid decarboxylase (GAD65Ab), were associated with high-risk genes, i.e. HLA, CTLA-4 and INS VNTR genes.

DESIGN AND SUBJECTS

Seventy-five (M/F 39/36) subjects exceeding the 95th percentile of GAD65 autoantibody index and 75 age and sex matched subjects below the 95th percentile, randomly selected amongst participants in the Västerbotten Intervention Programme.

METHODS

The GAD65 Ab were measured in a radioligand-binding assay. HLA class II typing was performed by an oligoblot hybridization method. CTLA-4 repeat length was analysed and divided into short forms and long forms. Class I and class III alleles of INS VNTR were detected. Differences in distribution were tested by Pearson chi-square with Yates correction. Odds ratios (OR) were used to compare groups calculated with Cochran's and Mantel-Haenszel statistics.

RESULTS

The DQB1*0201-DQA1*0501-DRB1*03 haplotype was increased in subjects with high GAD65Ab levels (P = 0.04). This increase seemed to be explained by a difference in haplotype frequencies amongst men (P = 0.01). Calculating OR showed a significant association between the DQB1*0201-DQA1*0501-DRB1*03 haplotype and elevated levels of GAD65Ab in all subjects (OR 2.2, 95% CI 1.02-4.9) as well as in men (OR 4.6, 95% CI 1.3-15.9). There was no association between high levels of GAD65Ab and either INS VNTR or CTLA-4 polymorphisms.

CONCLUSION

Our study suggests that adult males with the DQB1*0201-DQA1*0501-DRB1*03 haplotype tend to develop high GAD65Ab titres. As none of these subjects have developed diabetes these data suggest that HLA may be important in GAD65Ab formation but that additional factors are required for the progression to overt type 1 diabetes.

Genetic liability of type 1 diabetes and the onset age among 22,650 young Finnish twin pairs: a nationwide follow-up study

Finland has the world's highest incidence of type 1 diabetes, and it is steadily increasing. We determined concordance rates and estimated heritability for type 1 diabetes in the Finnish Twin Cohort, a population-based twin cohort of 22,650 twin pairs. In addition, we studied age of onset in the first affected twin and discordance time between concordant twin pairs. Finnish twins born between 1958 and 1986 were followed for type 1 diabetes until 1998. We identified 228 twin pairs with type 1 diabetes: 44 monozygotic (MZ), 183 dizygotic (DZ), and 1 pair with unknown zygosity. The pairwise concordance for type 1 diabetes was 27.3% (95% CI 22.8-31.8) in MZ and 3.8% (2.7-4.9) in DZ twins. The probandwise concordance was 42.9% (26.7-59.2) and 7.4% (2.2-12.6), respectively. The longest discordance times were 6.9 years among concordant MZ twins and 23.6 years among DZ twins. The risk for type 1 diabetes was highest in cotwins of the index twins diagnosed at a very young age. The model with additive genetic and individual environmental effects was the best-fitting liability model, with 88% of phenotypic variance due to genetic factors and the remaining variance due to unshared environmental factors. In conclusion, these nationwide twin data demonstrated high genetic liability for type 1 diabetes. Early-onset diabetes increases the risk in cotwins. However, the majority of affected MZ twin pairs remain discordant for type 1 diabetes.

Large-scale search of SNPs for type 2 DM susceptibility genes in a Japanese population

The etiology of type 2 diabetes (DM) is polygenic. We investigated here genes and polymorphisms that associate with DM in the Japanese population. Single-nucleotide polymorphisms (SNPs) of 398 derived from 120 candidate genes were examined for association with DM in a population-based case-control study. The study group consisted of 148 cases and 227 controls recruited from Funagata, Japan. No evident subpopulation structure was detected for the tested population. The association tests were conducted with standard allele positivity tables (chi(2) tests) between SNP genotype frequency and case-control status. The independent association of the SNPs from serum triglyceride levels and body mass index was examined by multiple logistic regression analysis. A value of P<0.01 was accepted as statistically significant. Six genes (met proto-oncogene, ATP-binding cassette transporter A1, fatty acid binding protein 2, LDL receptor defect C complementing, aldolase B, and sulfonylurea receptor) were shown to be associated with DM.

Condições de saúde bucal e diabetes mellitus na população nipo-brasileira de Bauru-SP

Este estudo transversal foi delineado para estimar a prevalência de diabetes mellitus, intolerância à glicose e condições de saúde bucal na população de origem japonesa, na faixa de 40 a 79 anos de idade, residente no município de Bauru-Brasil. Todos os indivíduos da primeira geração (isseis) e uma amostra casualizada de um terço da segunda geração (niseis) foram submetidos a entrevista domiciliar, totalizando 530 indivíduos. O exame clínico e teste oral de tolerância à glicose, e exame das condições de saúde bucal, foram realizados no Hospital de Reabilitação de Anomalias Crânio-Faciais - USP. Os dados foram processados através do programa Epi-Info, sendo que 22,9% apresentaram ocorrência de diabetes mellitus (grupo I), 15,1% tolerância à glicose diminuída (grupo II) e 61,9% foram considerados normoglicêmicos (grupo III). O percentual de indivíduos desdentados totais foi de 45,9% para a amostra e valores de 58,4%, 46,7% e 41,2% foram verificados para os grupos I, II e III, respectivamente. Entre os indivíduos edêntulos, nenhum apresentava necessidade de confecção de prótese total, em contraposição aos dados encontrados para a população brasileira em levantamento realizado pelo Ministério da Saúde (1986), cuja necessidade era da ordem de 8,3% na faixa etária de 35 a 59 anos. Pôde-se concluir que o edentulismo apresenta associação significante com a ocorrência de diabetes mellitus, porém não com a intolerância à glicose.

Modern obstetrical and infertility care may increase the prevalence of disease: an evolutionary concept

OBJECTIVE

To explore the hypothesis that the increasing prevalence of some polygenetically inherited conditions, may, to a degree, be the consequence of treatment successes of modern health care that have overcome evolutionary blocks to reproductive success.

DESIGN

Hypothesis, based on a selective review of the literature.

SETTING

University-affiliated private infertility center. Patient(s)None.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Occurrence of polygenetically inherited diseases.

RESULT(S)

Successfully treated evolutionary blocks to the inheritance of polygenetically inherited diseases result in an increased prevalence of these diseases in subsequent generations.

CONCLUSION(S)

Evolutionary processes have erected barriers to successful reproduction for many polygenetically inherited diseases, which are now overcome by successful treatment, leading to an increased prevalence, younger age of occurrence, and greater severity of these diseases in next generation offspring.

Impaired primary immune response in type-1 diabetes. Functional impairment at the level of APCs and T-cells

We have recently described an impaired proliferative response of CD4(+) T-cells to primary antigens in patients with insulin-dependent diabetes mellitus (IDDM) [Clin. Immunol. 103 (2002) 249]. In order to further investigate possible mechanisms underlying this impairment, several factors known to be involved in the down-regulation of the immune response both at the level of APCs and CD4(+) T-cells were investigated: Monocyte-derived dendritic cells (MDDC) from IDDM patients were shown to express elevated amounts of CD86 (B7.2) (p=0.003) and reduced amounts of the adhesion molecule CD54 (ICAM-1) (p=0.03) on their cell surface compared to age-matched healthy controls and patients with non-insulin-dependent diabetes mellitus (NIDDM) as well as decreased SDS-PAGE stability of HLA-DQ and -DR peptide complexes directly isolated from the IDDM patients' peripheral blood mononuclear cells (PBMCs). Expression of CTLA-4 (CD152), known to be involved in the down-regulation of the immune response, was shown to be increased on CD4(+) T-cells from IDDM patients after exposure to the primary antigen KLH (keyhole limpet hemocyanin) presented by MDDC (p=0.0047). Likewise, purified CD4(+) T-cells from IDDM patients produced elevated levels of the cytokine TGF-beta1 after stimulation with immobilized monoclonal antibodies directed against CD3 and CD28 (p=0.014). When monocytes from IDDM patients were stimulated with lipopolysaccharide (LPS), an increased tendency to produce the inhibitory cytokine interleukin (IL)-10 (p=0.007) and the acute phase cytokine IL-6 (p=0.044) was observed, whereas the concentrations of tumor necrosis factor (TNF)-alpha, IL-1beta, and IL-12 were comparable to controls. Taken together, our data suggest that a deviation in the expression of certain molecules known to be involved in the peripheral control of the immune response is present in IDDM patients and is underlying the observed impairment of the primary immune response.

A new look at viruses in type 1 diabetes

Type 1 diabetes (T1D) results from the destruction of pancreatic beta cells. Genetic factors are believed to be a major component for the development of T1D, but the concordance rate for the development of diabetes in identical twins is only about 40%, suggesting that nongenetic factors play an important role in the expression of the disease. Viruses are one environmental factor that is implicated in the pathogenesis of T1D. To date, 14 different viruses have been reported to be associated with the development of T1D in humans and animal models. Viruses may be involved in the pathogenesis of T1D in at least two distinct ways: by inducing beta cell-specific autoimmunity, with or without infection of the beta cells, [e.g. Kilham rat virus (KRV)] and by cytolytic infection and destruction of the beta cells (e.g. encephalomyocarditis virus in mice). With respect to virus-mediated autoimmunity, retrovirus, reovirus, KRV, bovine viral diarrhoea-mucosal disease virus, mumps virus, rubella virus, cytomegalovirus and Epstein-Barr virus (EBV) are discussed. With respect to the destruction of beta cells by cytolytic infection, encephalomyocarditis virus, mengovirus and Coxsackie B viruses are discussed. In addition, a review of transgenic animal models for virus-induced autoimmune diabetes is included, particularly with regard to lymphocytic choriomeningitis virus, influenza viral proteins and the Epstein-Barr viral receptor. Finally, the prevention of autoimmune diabetes by infection of viruses such as lymphocytic choriomeningitis virus is discussed.

Preventing type 1 diabetes mellitus: the promise of gene therapy

Type 1 (insulin-dependent) diabetes mellitus is an autoimmune disease that has no cure. Closed-loop insulin administration strategies and approaches for replacement of the insulin-producing beta cells may offer improved treatments, which could delay or prevent diabetes complications. In the long run, however, prevention of type 1 diabetes in susceptible individuals represents the best chance for reducing the toll of the disease. Prevention of type 1 diabetes will require reliable methods for early diagnosis of predisposition to the disease, using improved genetic and serological screening on a wide scale. Identification of the primary antigenic target(s) for autoimmunity will allow intervention in prediabetes stages aimed at the induction of antigen-specific tolerance. In addition to manipulation of the immune system, the susceptibility of beta cells to autoimmunity could be reduced. A number of genes have been shown to increase beta-cell resistance to immune effector molecules in animal models and cultured beta-cell lines. These genes could be used for preventive gene therapy of type 1 diabetes mellitus if expressed in beta cells prior to the onset of autoimmune destruction. This prospect depends on the development of safe and efficient vectors, and approaches for cell-specific targeting of these vectors to beta cells in vivo.

Challenges and strategies for investigating the genetic complexity of common human diseases

There is substantial interest in the identification of genes underlying susceptibility to complex human diseases because of the potential utility of such genes in disease prediction or therapy. Type 1 diabetes is an example of one such disorder and is presumed to arise from the effect of multiple genes and environmental factors. One identified locus has a major effect on type 1 diabetes susceptibility (IDDM1), whereas other loci have significant, yet small, individual effects (IDDM2, IDDM15). It is unclear whether susceptibility for type 1 diabetes arises because of the effects of loci acting independently or whether there are important interactions between loci. Although genetic tools are continuing to be developed to enable examination of candidate regions, the means to identify and narrow "true" susceptibility regions continues to be limited by the lack of statistical power resulting from inadequately sized collections of families. This report provides an evaluation of the approaches for identification of regions harboring type 1 diabetes genes, methods to identify the gene regions that interact to define the risk for type 1 diabetes, and efforts to fine-map the variants responsible.

Toward testing the hypothesis that group B coxsackieviruses (CVB) trigger insulin-dependent diabetes: inoculating nonobese diabetic mice with CVB markedly lowers diabetes incidence

Insulin-dependent (type 1) diabetes mellitus (T1D) onset is mediated by individual human genetics as well as undefined environmental influences such as viral infections. The group B coxsackieviruses (CVB) are commonly named as putative T1D-inducing agents. We studied CVB replication in nonobese diabetic (NOD) mice to assess how infection by diverse CVB strains affected T1D incidence in a model of human T1D. Inoculation of 4- or 8-week-old NOD mice with any of nine different CVB strains significantly reduced the incidence of T1D by 2- to 10-fold over a 10-month period relative to T1D incidences in mock-infected control mice. Greater protection was conferred by more-pathogenic CVB strains relative to less-virulent or avirulent strains. Two CVB3 strains were employed to further explore the relationship of CVB virulence phenotypes to T1D onset and incidence: a pathogenic strain (CVB3/M) and a nonvirulent strain (CVB3/GA). CVB3/M replicated to four- to fivefold-higher titers than CVB3/GA in the pancreas and induced widespread pancreatitis, whereas CVB3/GA induced no pancreatitis. Apoptotic nuclei were detected by TUNEL (terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling) assay in CVB3/M-infected pancreata but not in CVB3/GA-infected pancreata. In situ hybridization detected CVB3 RNA in acinar tissue but not in pancreatic islets. Although islets demonstrated inflammatory infiltrates in CVB3-protected mice, insulin remained detectable by immunohistochemistry in these islets but not in those from diabetic mice. Enzyme-linked immunosorbent assay-based examination of murine sera for immunoglobulin G1 (IgG1) and IgG2a immunoreactivity against diabetic autoantigens insulin and HSP60 revealed no statistically significant relationship between CVB3-protected mice or diabetic mice and specific autoimmunity. However, when pooled sera from CVB3/M-protected mice were used to probe a Western blot of pancreatic proteins, numerous proteins were detected, whereas only one band was detected by sera from CVB3/GA-protected mice. No proteins were detected by sera from diabetic or normal mice. Cumulatively, these data do not support the hypothesis that CVB are causative agents of T1D. To the contrary, CVB infections provide significant protection from T1D onset in NOD mice. Possible mechanisms by which this virus-induced protection may occur are discussed.

Mapping genes for autoimmunity in humans: type 1 diabetes as a model

Type 1 diabetes (T1D) arises from autoimmune destruction of the beta cells of the pancreas leading to a complete dependence on exogenous insulin for survival. Like many autoimmune disorders, the etiology of T1D is complex, resulting from the action of multiple genes and environmental factors. Identification of genes that contribute to T1D susceptibility should improve disease prediction and contribute to the understanding of the underlying pathology of the disorder. Two regions of the human genome, the human leukocyte antigen (HLA) region and the insulin gene region are generally thought to contain susceptibility loci for T1D. Although additional putative T1D loci have been reported, the supporting evidence has often been of modest significance and findings have displayed poor reproducibility across multiple studies. This review summarizes the current state of genetic linkage and association studies in T1D and suggests future directions. We argue that much of the difficulty in mapping T1D susceptibility loci has resulted from inadequate sample sizes and we illustrate the substantial gains in power that can be achieved by pooling data across studies. These findings suggest that substantial progress toward the identification of susceptibility genes in T1D and other genetically complex disorders may be achieved through increased collaboration and consortium mapping efforts.

Genetics of type 2 diabetes and insulin resistance: knowledge from human studies

Both type 2 diabetes mellitus (T2DM) and insulin resistance are complex traits in which multiple gene effects and metabolic and environmental factors combine to contribute to the overall pathogenesis of these conditions. This complexity has complicated the search for susceptibility genes and has led to different but complementary approaches being used for the detection of gene effects. These include the study of monogenic cases of insulin resistance and T2DM, association studies of candidate genes and genome-wide scans. The peroxisome proliferator-activated receptor gamma (PPARgamma) and calpain-10 (CAPN10) genes have recently been identified as T2DM susceptibility genes, and the lessons learnt from these studies are helping to shape future strategies to search for additional susceptibility genes in T2DM and insulin resistance.

Establishing the role of gene-environment interactions in the etiology of type 2 diabetes

The descriptive epidemiology of type 2 diabetes and findings from cohort studies suggest that this disorder originates in large part from a complex interaction between genetic and environmental factors. Determining the details of these interactions using the nested case-control design may be optimal, but is a long-term and expensive strategy. Quicker and cheaper results may be obtained by studying interaction on the quantitative traits that underlie diabetes; however, the power of such studies to detect interaction is highly dependent on the precision with which non-genetic exposures are measured. Unraveling these interactions will undoubtedly shed light on the etiology of diabetes and will, we hope, lead to opportunities for targeted prevention. Recent studies in high-risk groups such as people with impaired glucose tolerance suggest that the incidence of diabetes can be reduced by more than 50% by interventions aimed at changing dietary and physical activity behavior [39,40]; however, it may be that individuals with a particular genotype are particularly susceptible to the negative metabolic consequences of sedentary living, and that they conversely, therefore, would have most to gain from a targeted preventive intervention program. Understanding how to detect these individuals and which environmental factors a program should attempt to manipulate is a major goal of studies that attempt to unravel gene-environment interaction.

Space-time clustering of childhood Type 1 diabetes in Devon and Cornwall, England

AIMS

Several studies on space-time clustering have been reported in childhood diabetes, but the findings are conflicting. The present study was undertaken to examine whether such clustering could be detected at either birth or the time of diagnosis in the far South-west of England.

METHODS

A cohort of 518 children aged 0-15 years and diagnosed with Type 1 diabetes from 1975 to 1996 contained in the population-based Cornwall and Plymouth Children's Diabetes Register (CPCDR) were included in the analyses. The case ascertainment for this register is estimated to be 94.4% complete. Mantel's modification of Knox's method was employed. A method based on K-function was also used, for the first time, to investigate the space-time clustering of diabetes.

RESULTS

Significant space-time clustering at diagnosis was found by the Knox's test in the following combinations of critical cut-off thresholds: 25, 35 and 50 km and 90, 270 and 360 days (all P < 0.05), with the highest significance found at 35 km and 360 days (P = 0.0011). K-function analysis also confirmed the overall clustering (P = 0.013).

CONCLUSIONS

There is strong evidence of space-time clustering in the onset of childhood Type 1 diabetes in Devon and Cornwall, England. These results lend some support to the hypothesis that viral infections and some unknown localized environmental factors play a role in the development of childhood Type 1 diabetes.

Evidence from twins for acquired cellular immune hyperactivity in type 1 diabetes

Type 1 diabetes has been associated with an increased frequency of activated T cells and T-cell hyperactivity to non-specific and disease-specific stimuli including the islet autoantigen glutamic acid decarboxylase 65 (GAD). To address whether T-cell hyperactivity is genetic or acquired we measured whole blood cytokines in vitro in response to GAD or tetanus in 18 identical twin pairs, nine discordant for type 1 diabetes. In addition, the activity of 2', 5' oligoadenylate synthetase (OAS) in blood mononuclear cells was measured as a marker of viral infection. Interleukin-2 (IL-2) basally and IL-2 and interferon-gamma (IFN-gamma) in response to GAD, were detected more frequently and at higher levels in diabetic compared to non-diabetic twins. IL-10 was not different between groups. OAS activity was increased in diabetic compared to non-diabetic twins and showed a correlation with basal IL-2 and GAD-stimulated IFN-gamma and IL-10. These findings suggest that T-cell hyperactivity in type 1 diabetes is an acquired trait and could reflect persisting virus expression.

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.

Is reduced first-phase insulin release the earliest detectable abnormality in individuals destined to develop type 2 diabetes?

Insulin is released from the pancreas in a biphasic manner in response to a square-wave increase in arterial glucose concentration. The first phase consists of a brief spike lasting approximately 10 min followed by the second phase, which reaches a plateau at 2-3 h. It is widely thought that diminution of first-phase insulin release is the earliest detectable defect of beta-cell function in individuals destined to develop type 2 diabetes and that this defect largely represents beta-cell exhaustion after years of compensation for antecedent insulin resistance. In this article, the origins of these concepts are reviewed and recent evidence is presented suggesting that reductions in both phases of insulin release are equally early, that they precede insulin resistance other than that simply due to obesity, and that they therefore may represent the primary genetic risk factor predisposing individuals to type 2 diabetes.

Phenotyping of individual pancreatic islets locates genetic defects in stimulus secretion coupling to Niddm1i within the major diabetes locus in GK rats

The major diabetes quantitative trait locus (Niddm1), which segregates in crosses between GK rats affected with spontaneous type 2-like diabetes and normoglycemic F344 rats, encodes at least two different diabetes susceptibility genes. Congenic strains for the two subloci (Niddm1f and Niddm1i) have been generated by transfer of GK alleles onto the genome of F344 rats. Whereas the Niddm1f phenotype implicated insulin resistance, the Niddm1i phenotype displayed diabetes related to insulin deficiency. Individual islets from 16-week-old congenic rats were characterized for insulin release and oxygen tension (pO(2)). In the presence of 3 mmol/l glucose, insulin release from Niddm1f and Niddm1i islets was approximately 5 pmol. g(-1). s(-1) and pO(2) was 120 mmHg. Similar recordings were obtained from GK and F344 islets. When glucose was raised to 11 mmol/l, insulin release increased significantly in Niddm1f and F344 islets but was essentially unchanged in islets from GK and Niddm1i. The high glucose concentration lowered pO(2) to the same extent in islets from all strains. Addition of 1 mmol/l tolbutamide to the perifusion medium further increased pulsatile insulin release threefold in all islets. The pulse frequency was approximately 0.4 min(-1). alpha-Ketoisocaproate (11 mmol/l) alone increased pulsatile insulin release eightfold in islets from Niddm1f, Niddm1i, and control F344 rats but had no effect on insulin release from GK islets. These secretory patterns in response to alpha-ketoisocaproate were paralleled by reduction of pO(2) in Niddm1f, Niddm1i, and control F344 islets and no change of pO(2) in GK islets. The results demonstrate that Niddm1i carries alleles of gene(s) that reduce glucose-induced insulin release and that are amenable to molecular identification by genetic fine mapping.

Non-diabetic relatives of Type 2 diabetic families: dietary intake contributes to the increased risk of diabetes

AIMS

Non-diabetic first degree relatives of Type 2 diabetic patients are at increased risk of developing diabetes and cardiovascular disease. This is assumed to reflect a shared genetic predisposition. The aim of this study was to test the hypothesis that lifestyle factors, specifically dietary factors, are also important to the increased risk in non-diabetic relatives.

METHODS

Dietary intake was assessed using a validated food frequency questionnaire in 149 non-diabetic first degree relatives (age 20-65 years) from families of North European extraction with two or more living Type 2 diabetic family members, and 143 age- and sex-matched control subjects from the background population with no family history of diabetes.

RESULTS

Relatives reported higher absolute intakes of total fat (mean (95% confidence intervals) 83 (76-91) vs. 71 (66-76) g/day, P = 0.01), saturated fat (SFA; 39 (36-43) vs. 33 (30-36) g/day, P < 0.01) and cholesterol (391 (354-427) vs. 318 (287-349) mg/day, P < 0.01), and a lower intake of non-starch polysaccharide (P < 0.05). Considered as percentage of total daily energy intake, relatives had higher intakes of total fat (P < 0.01) and SFA (P < 0.02), and a lower intake of carbohydrate (P < 0.02). These differences remained after exclusion of suspected under- and over-reporters of dietary intake.

CONCLUSIONS

Non-diabetic relatives of Type 2 diabetic patients were found to consume diets that will promote rather than prevent the development of diabetes and cardiovascular disease. This suggests that the increased risk to non-diabetic relatives is therefore not entirely genetic, and there is scope for decreasing the risk through lifestyle modification.

The distribution of HLA class II susceptible/protective haplotypes could partially explain the low incidence of type 1 diabetes in continental Italy (Lazio region)

HLA class II is the primary susceptibility gene to type 1 diabetes and the analysis of HLA class II association could help to clarify the relative weight of genetic contribution to the incidence of the disease. Here we present an extensive typing for HLA class II alleles and their haplotypes in a homogenous population of type 1 diabetic patients (n=134) and controls (n=128) and in simplex (n=100) and multiplex families (n=50) from continental Italy (Lazio region). Among the various haplotypes tested, the DRB1*0301-DQA1*0501-DQB1*0201 was the most frequent found in type 1 diabetic patients and was transmitted in 82% of affected siblings, whereas DRB1*0402-DQA1*0301-DQB1*0302 appeared to have the highest odds ratio (10.4), this haplotype was transmitted in 96.3% of affected siblings, followed by DRB1*0405-DQA1*0301-DQB1*0302, DRB1*0405-DQA1*0301-DQB1*0201, DRB1*0401-DQA1*0301-DQB1*0302 and DRB1*0404-DQA1*0301-DQB1*0302. The following haplotypes showed a significant decreased transmission to diabetic siblings: DRB1*0701-DQA1*0201-DQB1*0303, DR2-DQA1*01-DQB1*0602, DR5-DQA1*0501-DQB1*0301. We suggest that the HLA DR/DQ haplotype/genotype frequencies observed could in part explain the low incidence of type 1 diabetes registered in Lazio region (8.1/100.000/year), for a number of reasons: i) the low frequency, in the general control population, of the most susceptible haplotypes and genotype for type 1 diabetes DRB1*0301-DQA1*0501-DQB1*0201 (14%), and DR4-DQA1*0301-DQB1*0302 (9%) and DRB1*0301-DQA1*0501-DQB1*0201/DR4-DQA1*0301-DQB1*0302 (0.8%) compared to other countries characterised by high incidence rate of the disease, Sardinia and Finland, respectively; ii) a significant lower ratio, in the control population, between the susceptible DRB1*0301-DQA1*0501-DQB1*0201 and the neutral DRB1*0701-DQA1*0501-DQB1*0201 haplotypes compared to the Sardinian population; iii) the high frequency of protection haplotypes/genotypes as the DR5-DQA1*0501-DQB1*0301, and DR5-DQA1*0501-DQB1*0301/DR5-DQA1*0501-DQB1*0301 very common in the control population of Lazio region and the DRB1*1401-DQA1*0101-DQB1*0503 haplotype.

Pathogenesis of type 2 diabetes. Insulin resistance

This article addresses the role of insulin resistance in the pathogenesis of type 2 diabetes. The major causes of acquired insulin resistance including aging, pregnancy, lack of physical activity, and obesity are discussed briefly. The role of free fatty acids (FFAs) as a link between obesity and insulin resistance/type 2 diabetes is discussed in detail. Evidence is provided showing that increased plasma FFA levels produce insulin resistance dosage dependently, acutely, and chronically. Mechanisms by which FFA can cause insulin resistance are outlined. Lastly, normalizing plasma FFA levels is proposed as a new approach to reducing insulin resistance and the risk for type 2 diabetes mellitus, and atherosclerotic vascular disease.

Skeletal muscle insulin resistance in normoglycemic subjects with a strong family history of type 2 diabetes is associated with decreased insulin-stimulated insulin receptor substrate-1 tyrosine phosphorylation

Normoglycemic subjects with a strong family history of type 2 diabetes are insulin resistant, but the mechanism of insulin resistance in skeletal muscle of such individuals is unknown. The present study was undertaken to determine whether abnormalities in insulin-signaling events are present in normoglycemic, nonobese subjects with a strong family history of type 2 diabetes. Hyperinsulinemic-euglycemic clamps with percutaneous muscle biopsies were performed in eight normoglycemic relatives of type 2 diabetic patients (FH(+)) and eight control subjects who had no family history of diabetes (FH(-)), with each group matched for age, sex, body composition, and ethnicity. The FH(+) group had decreased insulin-stimulated glucose disposal (6.64 +/- 0.52 vs. 8.45 +/- 0.54 mg. kg(-1) fat-free mass. min(-1); P < 0.05 vs. FH(-)). In skeletal muscle, the FH(+) and FH(-) groups had equivalent insulin stimulation of insulin receptor tyrosine phosphorylation. In contrast, the FH(+) group had decreased insulin stimulation of insulin receptor substrate (IRS)-1 tyrosine phosphorylation (0.522 +/- 0.077 vs. 1.328 +/- 0.115 density units; P < 0.01) and association of PI 3-kinase activity with IRS-1 (0.299 +/- 0.053 vs. 0.466 +/- 0.098 activity units; P < 0.05). PI 3-kinase activity was correlated with the glucose disposal rate (r = 0.567, P = 0.02). In five subjects with sufficient biopsy material for further study, phosphorylation of Akt was 0.266 +/- 0.061 vs. 0.404 +/- 0.078 density units (P < 0.10) and glycogen synthase activity was 0.31 +/- 0.06 vs. 0.50 +/- 0.12 ng. min(-1). mg(-1) (P < 0.10) for FH(+) and FH(-) subjects, respectively. Therefore, despite normal insulin receptor phosphorylation, postreceptor signaling was reduced and was correlated with glucose disposal in muscle of individuals with a strong genetic background for type 2 diabetes.

Medical care from childhood to adulthood in type 1 and type 2 diabetes

Diabetes mellitus comprises a heterogeneous group of diseases that have in common the development of macro- and microvascular complications. It is now possible to identify subjects at high risk of Type 1 or Type 2 diabetes, especially in the patient's family members. Preventive interventions are quickly becoming available, and can help delay the onset of the disease and thereby reduce complications in these subjects. Furthermore the correct etiological diagnosis of diabetes is fundamental in providing the best treatment for the patient. Maturity-onset diabetes of the young (MODY) syndrome should be suspected in cases of a subtle onset of diabetes and autosomal dominant inheritance. Mitochondrial DNA mutations should be considered when a diabetic patient also suffers from deafness or if there is a family history of this combination in the mother side of the family. Atypical diabetes has to be identified by the physician to avoid mistakes when the patient enters the non-insulin-dependent phase. In the case of Wolfram's syndrome a gene analysis for each family member should be performed to identify heterozygote subjects. Recently, many discoveries in genetics help us better understand the pathogenesis of the diseases and diagnose the monogenic form of diabetes more easily. If all family members are followed in the same center, clues from the family history are readily available for differential diagnosis and preventive interventions can be established more effectively.

Uma amostra de pacientes com diabetes tipo 1 no sul do Brasil

Objetivos: Descrever uma população de pacientes com diabetes tipo 1 (DM1) em relação a fatores demográficos, ambientais, sócio-econômicos e manejo da doença. Delineamento: Série de casos. Participantes: Indivíduos com DM1, com até 10 anos de doença, até 30 anos de idade, residentes em onze municípios do sul do Brasil. Resultados: Foram estudados 126 indivíduos com DM1 (57 homens e 69 mulheres), sendo que a idade mais freqüente de início da doença foi dos 11 aos 15 anos (31%). Houve variação sazonal na época de apresentação. O diagnóstico foi feito por sintomas que motivaram uma dosagem de glicemia em 61%, por hospitalização, não em UTI, em 22% e por cetoacidose em 18%. Na amostra, 47% aplicava insulina uma vez ao dia. Sessenta por cento dos pacientes realizava algum tipo de automonitorização, um terço reutilizava seis ou mais vezes a seringa e 50% da insulina era fornecida pelo poder público. Quanto ao reconhecimento da hipoglicemia, 18% dos pacientes não sabiam citar nenhum dos sinais de alerta. Grande parte da amostra (73%) consultava médico especialista em DM. Dos pacientes com mais de 5 anos de doença, 16% nunca haviam feito fundoscopia e 17% haviam realizado o exame há 2 anos ou mais. As formas de apresentação da doença e da aquisição de insulina e a consulta com especialista estiveram associadas à renda familiar. As mulheres seguiam a dieta de modo mais adequado (p= 0,05) e auto-aplicavam insulina com mais freqüência, quando comparadas aos homens. Conclusões: Os fatores sócio-econômicos influenciaram neste estudo a forma de diagnóstico da doença, a obtenção de insulina e o acesso à especialistas. Os pacientes ainda carecem de conhecimentos básicos a respeito do manejo da doença.

Elevated plasma non-esterified fatty acid levels and insulin secretion in non-diabetic relatives of type 2 diabetic patients

OBJECTIVE

High non-esterified fatty acid (NEFA) levels impair glucose-stimulated insulin secretion from islets derived from non-diabetic Zucker rats that are genetically predisposed to diabetes. We therefore examined the effect of elevated plasma NEFA levels on insulin secretion in non-diabetic first-degree relatives of type 2 diabetic patients who are at increased risk of developing diabetes.

SUBJECTS AND STUDY DESIGN

Normal glucose tolerant relatives (n = 9) and control subjects with no family history of diabetes were pair-matched for age, sex, body mass index (BMI), insulin sensitivity and early insulin response during an oral glucose tolerance test (OGTT). Plasma NEFA levels were raised from 0 to 340 minutes by the infusion of 20% Intralipid and heparin. From 180 minutes, insulin secretion rates (IRSs) were assessed by stepped low-dose glucose infusion.

RESULTS

The mean (geometric mean +/- 95% CI) NEFA levels were comparable between relatives and control subjects (2.7 [2.1-3.6] and 2.1 [1.7-2.7] mmol/l, paired analysis, NS). Similarly, plasma glucose levels achieved at each glucose infusion step were comparable between the groups. However, there were no significant differences between the groups for ISR throughout the study.

CONCLUSIONS

Sustained elevation of plasma non-esterified fatty acid levels does not decrease insulin secretion in non-diabetic relatives of type 2 diabetic patients, and is therefore unlikely to be important in the development of the impaired pancreatic beta-cell function in type 2 diabetes mellitus.

The genetics of type 2 diabetes

Type 2 diabetes mellitus is not a single disease but a genetically heterogeneous group of metabolic disorders sharing glucose intolerance. The precise underlying biochemical defects are unknown and almost certainly include impairments of both insulin secretion and action. The rapidly increasing prevalence of T2D world wide makes it a major cause of morbidity and mortality. Understanding the genetic aetiology of T2D will facilitate its diagnosis, treatment and prevention. The results of linkage and association studies to date demonstrate that, as with other common diseases, multiple genes are involved in the susceptibility to T2D, each making a modest contribution to the overall risk. The completion of the draft human genome sequence and a brace of novel tools for genomic analysis promise to accelerate progress towards a more complete molecular description of T2D.

Genetic analysis of a new mouse model for non-insulin-dependent diabetes

The TallyHo (TH) mouse strain is a newly established model for non-insulin-dependent diabetes mellitus (NIDDM). TH mice show obesity, hyperinsulinemia, hyperlipidemia, and male-limited hyperglycemia. A genetic dissection of the diabetes syndrome has been carried out using male backcross 1 progeny obtained from crosses between (C57BL/6J x TH)F1 and TH mice or (CAST/Ei x TH)F1 and TH mice. A genome-wide scan reveals three quantitative trait loci (QTLs), Tanidd1-3 (TH-associated NIDDM) linked to hyperglycemia. The major QTL (common in both crosses), Tanidd1, maps to chromosome (Chr) 19. Additionally, gene-gene interactions contributing to hyperglycemia have been observed between Tanidd1 and a locus on Chr 18 as well as between Tanidd2 and a locus on Chr 16. The overt hyperglycemia in TH mice is, therefore, likely due to a mutation in a major diabetes susceptibility locus on Chr 19, which interacts with additional genes to lead to an observable phenotype.

Impaired fasting glycaemia in middle-aged women: a prospective study

OBJECTIVES

To investigate: (i) the incidence of impaired fasting glycaemia (IFG) developed over 5 y in a population-based sample of Australian-born women; (ii) prospectively the factors which are associated with the development of IFG; (iii) the association of the menopausal transition with the onset of IFG and an increase in serum insulin concentrations.

DESIGN AND METHODS

A total of 265 women (110 pre-, 138 peri-, 17 postmenopausal) participants in the longitudinal phase of the Melbourne Women's Midlife Health Project, aged 46-57 and with normal fasting plasma glucose concentrations at the time of the initial measure, were interviewed, had physical measurements and blood taken annually over a 5 y follow-up period.

RESULTS

During the study period 43 women (16%) recorded a fasting glucose concentration of > or =6.1 mmol/l (IFG). Women who recorded IFG prospectively had, at the time of the initial measure when fasting glucose concentrations were normal: higher body mass index (BMI), trunk skinfold thicknesses, waist and hip circumferences (P<0.005), lower SHBG, higher free androgen index and serum insulin concentrations (P<0.05), higher systolic blood pressure, serum triglyceride and lower HDL-cholesterol concentrations (P<0.05) than women whose fasting glucose concentrations remained normal. The onset of IFG was not triggered by the menopausal transition or hormone use. Changes in insulin concentration were associated with changes in BMI (P<0.05).

CONCLUSION

Women who developed IFG during the menopausal transition exhibited significantly higher levels of body fatness and dyslipidemia, premenopausally, compared with the women who did not develop IFG. The menopausal transition did not have an effect on the development of IFG, but weight gain during this period was associated with an increase in insulin concentration.

Concordance for type 1 diabetes in identical twins is affected by insulin genotype

OBJECTIVE

Monozygotic twins are usually discordant (only one twin affected) for type 1 diabetes. Discordance for disease between such twins implies a role for nongenetically determined factors but could also be influenced by a decreased load of diabetes susceptibility genes. The aim of this study was to determine whether two susceptibility genes were less prevalent in discordant twins compared with concordant twins.

RESEARCH DESIGN AND METHODS

We studied 77 monozygotic twin pairs (INS), 40 concordant and 37 discordant, for type 1 diabetes at polymorphism of the insulin gene region on chromosome 11 p and HLA-DQBI.

RESULTS

The disease-associated INS genotype (Hph I) was identified in 87.5% of the concordant twins but only in 59.5% (P = 0.005) of the discordant twins. Neither DQB1*0201 nor DQB1*0302 was seen in 2 of 40 (5%) concordant twins compared with 8 of 37 (22%) discordant twins (P = 0.04). No statistical differences were seen between concordant and discordant twins at individual alleles of DQB1. Combining insulin and DQ data, 5% of concordant twins compared with 32.4% of discordant twins had neither DQB1*0201/DQB1*0302 nor the high-risk Hph I INS "++" genotype (P = 0.002).

CONCLUSIONS

We conclude that the possession of the high-risk Hph I insulin genotype increases the likelihood of identical twins being concordant for type 1 diabetes and that the "load" of both major histocompatibility complex (MHC) and non-MHC susceptibility genes has an impact on the disease penetrance of type 1 diabetes.

Genomic variation in pancreatic ion channel genes in Japanese type 2 diabetic patients

BACKGROUND

Many genetic diseases are caused by mutations in ion channel genes. Because type 2 diabetes is characterized by pancreatic beta-cell insensitivity to glucose, the genes responsible for glucose metabolism and calcium signaling in pancreatic beta-cells are candidate type 2 diabetes susceptibility genes.

METHODS

We have examined genomic variations in two ion channel genes relevant to the molecular pathology of diabetes mellitus, the Kir6.2 subunit of the ATP-sensitive potassium channel gene and alpha(1D) subunit of the voltage-dependent calcium channel (VDCC) gene among Japanese type 2 diabetic patients.

RESULTS

There are two alleles in the Kir6.2 gene: EI, glutamic acid at codon 23 and isoleucine at codon 337 and KV, lysine at codon 23 and valine at codon 337. The allelic frequencies of these polymorphisms are similar in type 2 diabetic patients and normal subjects. We also detected trinucleotide repeat polymorphisms in the amino terminus and the carboxyl terminal region of the alpha(1D) gene. Expansion of the ATG trinucleotide repeat from seven to eight was detected only in type 2 diabetic patients, but the frequency was low and was similar in type 2 diabetic patients and normal subjects.

CONCLUSIONS

Although variations of the Kir6.2 and alpha(1D) genes are not associated with the development of common type 2 diabetes, further studies may determine the role of these genomic variations, especially those in the alpha(1D) VDCC gene, in the pathogenesis of certain subsets of type 2 diabetes, or as a co-factor in the polygenic disorder generally.

Importance of family history in type 2 black South African diabetic patients

OBJECTIVE

To assess the family history of diabetes in type 2 black South African diabetics with emphasis on the parental phenotype.

DESIGN

Prospective case-control study in which family histories were obtained from patients.

SETTING

Diabetic clinic of a provincial teaching hospital in the Transkei region of South Africa.

SUBJECTS

A total of 1111 type 2 diabetics attending the diabetic clinic and 687 controls.

MAIN OUTCOME MEASURES

History of diabetes in parents, siblings, maternal and paternal grandparents, aunts, and uncles.

RESULTS

Altogether 27.3% of diabetic subjects had a family history of diabetes compared with 8.4% in the control group (p<0.01). Among the group with positive family history 82.6% reported only one diabetic family member, while 17.4% reported at least two relatives; 6.6% had a diabetic relative from both maternal and paternal sides, and 87.8% had first degree relative with diabetes. Among them there was a significant maternal aggregation with 64.7% of patients having a diabetic mother compared with 27% who had a diabetic father (p<0.01). No maternal effect was observed among the second and third degree relatives. Patients with positive family history had an earlier onset of diabetes than those without family history (p<0.01).

CONCLUSION

These data suggest that type 2 diabetes is heritable in black South African diabetics. It is also likely that maternal influences may play an important part.

Complex trait analysis in the mouse: The strengths, the limitations and the promise yet to come

In 1990, David Baltimore predicted that the 1990s would be the decade of the mouse (). This certainly proved to be true: The mouse has contributed immensely to biological research through transgenic, embryonic stem cell (ES) knockout, and classical genetic technologies. But its usefulness as a model organism is by no means over; indeed it is still rising to its peak: The mouse as a model mammalian organism still has much to offer. This article reviews use of the mouse to dissect complex genetic traits using quantitative trait analysis, with a particular emphasis on medically important diseases.

Evaluation of features of syndrome X in offspring of Caribbean patients with Type 2 diabetes

OBJECTIVE

To determine whether the features of metabolic syndrome X are more common in offspring of patients with Type 2 diabetes than in control subjects without immediate family history of diabetes.

MATERIALS AND METHODS

Thirty-four young offspring of patients with Type 2 diabetes and 27 healthy control subjects underwent a standard oral glucose tolerance tests (OGTT; 75 g glucose in 300 ml water). Anthropometric indices, blood pressure, plasma glucose, serum lipids and insulin levels were measured. Homeostasis model assessment (HOMA) was used to assess basal insulin resistance (IR) and sensitivity (%S).

RESULTS

The offspring had significantly higher mean+/-SD BMI (p<0.01) and basal serum triglyceride (p<0.05), insulin (p<0.05), insulin/glucose ratio (p<0.01), and lower %S (p<0.001) than the control subjects, in spite of similar fasting plasma glucose concentrations. Multiple linear regression analysis showed that these differences were independent of BMI. Although, the two groups of subjects had similar serum HDL-Cholesterol, LDL-cholesterol and blood pressure levels, %S was significantly related to diastolic BP (p<0.01) and serum triglyceride levels (p<0.01).

CONCLUSIONS

In comparison with the healthy control subjects, the insulin resistant offspring have higher levels of the identified syndrome X features independent of obesity. These features were quantitatively lower than the values reported in offspring of white Caucasian and African-American patients.

Sick genes, sick individuals or sick populations with chronic disease? The emergence of diabetes and high blood pressure in African-origin populations

AIM AND METHODS

To discuss evidence for and against genetic 'causes' of type 2 diabetes, illustrated by standardized study of glucose intolerance and high blood pressure in four representative African origin populations. Comparison of two genetically closer sites: rural (site 1) and urban Cameroon (2); then Jamaica (3) and Caribbean migrants to Britain (80% from Jamaica-4).

BACKGROUND

Alternatives to the reductionist search for genetic 'causes' of chronic disease include Rose's concept that populations give rise to 'sick' individuals. Twin studies offer little support to genetic hypotheses because monozygotic twins share more than genes in utero and suffer from ascertainment bias. Non-genetic intergenerational mechanisms include amniotic fluid growth factors and maternal exposures. Type 2 diabetes and hypertension incidence accelerate in low-risk European populations from body mass > or =23 kg/m2, well within 'desirable' limits. Transition from subsistence agriculture in West Africa occurred this century and from western hemisphere slavery only six generations ago, with slow escape from intergenerational poverty since.

RESULTS

'Caseness' increased clearly within and between genetically similar populations: age-adjusted diabetes rates were 0.8, 2.4, 8.5 and 16.4% for sites 1-4, respectively; for 'hypertension', rates were 7, 16, 21 and 34%, with small shifts in risk factors. Body mass index rose similarly.

CONCLUSION

Energy imbalance and intergenerational socioeconomic influences are much more likely causes of diabetes (and most chronic disease) than ethnic/genetic variation, which does occur, poorly related to phenotype. The newer method of 'proteomics' holds promise for identifying environmental triggers influencing gene products. Even in lower prevalence 'westernized' societies, genetic screening per se for diabetes/chronic disease is likely to be imprecise and inefficient hence unreliable and expensive.

In search of susceptibility genes for type 2 diabetes in West Africa: the design and results of the first phase of the AADM study

PURPOSE

The purpose of this study is to map type 2 diabetes susceptibility genes in West African ancestral populations of African-Americans, through an international collaboration between West African and US investigators.

DESIGN AND METHODS

Affected sib-pairs (ASP) along with unaffected spouse controls are being enrolled and examined in West Africa, with two sites established in Ghana (Accra and Kumasi) and three in Nigeria (Enugu, Ibadan, and Lagos). Eligible participants are invited to study clinics to obtain detailed epidemiologic, family, and medical history information. Blood samples are drawn from each participant to measure glucose, insulin, C-peptide, total cholesterol, LDL, HDL, triglycerides, albumin, creatinine, urea, uric acid, total calcium and to detect autoantibodies to glutamic acid decarboxylase (GAD). DNA is isolated from frozen white blood cells obtained from 20 ml of EDTA whole blood samples.

RESULTS

With full informed consent, 162 individuals from 78 families have been enrolled and examined since the Africa America Diabetes Mellitus (AADM) study began in June of 1997. Logistics of field examinations and specimen shipping have been successfully established. At the end of the third year of field activity (September 2000) the AADM study will have enrolled and performed comprehensive examination on 400 ASP with type 2 diabetes, for a minimum of 800 cases and 200 controls from Ghana and Nigeria. At the current participation rate, the goal of 400 sib-pairs and 200 controls will be met before the scheduled closing date.

CONCLUSIONS

The AADM study will create a comprehensive epidemiologic and genetic resource that will facilitate a powerful genome-wide search for West African susceptibility genes to type 2 diabetes.

Familial predisposition of type 1 diabetes mellitus in Japan, a country with low incidence. Japan Diabetes Society Data Committee for Childhood Diabetes

The study group of the Japan Diabetes Society (JDS) carried out nationwide hospital-based and population-based surveys of childhood type 1 diabetes mellitus (DM) in Japan. According to the nationwide population-based survey, the incidence of childhood type 1 DM in Japan was 1.5 (1.4-1.6)/10(5), which did not differ for the 5 years from 1986-1990. Predisposition for DM and autoimmunity were studied in the first-degree relatives of the patients, including older and later cohorts. The prevalence of type 1 DM was 3.3% (12/369) among siblings and 2.2% (8/369) among parents, while the prevalence of type 2 DM was 0% among siblings and 4.3% (16/369) among parents. The risk of type 1 DM among siblings of the patients was 330 times higher than that among the general population in the Japanese population. The rate of positivity for autoantibodies, including ICA, IAA, GAD and IA-2, was 1.4-2.9% in parents (n=140) and 2.0-3.9% in siblings (n=203). The genetic susceptibility for type 1 DM is far lower in Japanese children than in Caucasian children, but predisposition to the disease and positive autoimmunity are almost the same in Japanese families of patients as in Caucasian families. The quality of life of Japanese parents of children with type 1 DM was less satisfactory that that of the Caucasian parents previously reported, which might be a result of the low incidence of type 1 DM in Japan.

Genomewide search for type 2 diabetes-susceptibility genes in French whites: evidence for a novel susceptibility locus for early-onset diabetes on chromosome 3q27-qter and independent replication of a type 2-diabetes locus on chromosome 1q21-q24

Despite recent advances in the molecular genetics of type 2 diabetes, the majority of susceptibility genes in humans remain to be identified. We therefore conducted a 10-cM genomewide search (401 microsatellite markers) for type 2 diabetes-related traits in 637 members of 143 French pedigrees ascertained through multiple diabetic siblings, to map such genes in the white population. Nonparametric two-point and multipoint linkage analyzes-using the MAPMAKER-SIBS (MLS) and MAXIMUM-BINOMIAL-LIKELIHOOD (MLB) programs for autosomal markers and the ASPEX program for chromosome X markers-were performed with six diabetic phenotypes: diabetes and diabetes or glucose intolerance (GI), as well as with each of the two phenotypes associated with normal body weight (body-mass index<27 kg/m(2)) or early age at diagnosis (<45 years). In a second step, high-resolution genetic mapping ( approximately 2 cM) was performed in regions on chromosomes 1 and 3 loci showing the strongest linkage to diabetic traits. We found evidence for linkage with diabetes or GI diagnosed at age <45 years in 92 affected sib pairs from 55 families at the D3S1580 locus on chromosome 3q27-qter using MAPMAKER-SIBS (MLS = 4.67, P=.000004), supported by the MLB statistic (MLB-LOD=3.43, P=.00003). We also found suggestive linkage between the lean diabetic status and markers APOA2-D1S484 (MLS = 3. 04, P=.00018; MLB-LOD=2.99, P=.00010) on chromosome 1q21-q24. Several other chromosomal regions showed indication of linkage with diabetic traits, including markers on chromosome 2p21-p16, 10q26, 20p, and 20q. These results (a) showed evidence for a novel susceptibility locus for type 2 diabetes in French whites on chromosome 3q27-qter and (b) confirmed the previously reported diabetes-susceptibility locus on chromosome 1q21-q24. Saturation on both chromosomes narrowed the regions of interest down to an interval of <7 cM.

Increased risk of cardiovascular disease in newly diagnosed type 2 diabetic patients in a primary health care center in Trinidad

The prevalence of cardiovascular diseases (CVD) has increased sharply in the developing countries and because Type 2 diabetic patients are at increased risk for CVD, we assessed CVD risk factors in newly diagnosed Type 2 diabetic patients presenting in a primary health care center in Trinidad. Fasting and 2 h postprandial blood samples were collected from 387 (269 females, 118 males) newly diagnosed Type 2 diabetic patients (mean age: 53.1+/-6.6 years) for the determination of plasma glucose, creatinine, cholesterol (chol), triglyceride (TG) and % glycated hemoglobin (HbA(1c)) concentrations. Blood pressure and anthropometric indices were also measured. There were high prevalence rates of obesity (37%), overweight (35%), hypertension (21%), hypercholesterolemia (25%) and hypertriglyceridemia (22.3%) among the patients and these were significantly higher in women than men (P<0.001). Patients of Indian descent had a significantly higher prevalence of diastolic hypertension and hypertriglyceridemia compared with patients of African origin or mixed race (P<0.001). In comparison with males, female diabetic patients were at greater risk of cardiovascular morbidity and mortality. Early detection of CVD risk factors and treatment, particularly in women, may be beneficial management strategy in all local diabetic clinics in Trinidad.

Incomplete penetrance of MHC susceptibility genes: prospective analysis of polygenic MHC-determined traits

We propose an approach to understanding incomplete penetrance of disease susceptibility genes as a method of studying the underlying mechanisms of polygenic diseases. Incomplete penetrance is the failure of genetically susceptible individuals to exhibit a trait. We define as baseline penetrance that which occurs in genetically identical (monozygotic) twins of an index subject with a major histocompatibility complex (MHC)-associated disease or trait. We consider two mechanisms for incomplete baseline penetrance: an extrinsic (environmental) trigger and an intrinsic stochastic, gene-associated process. The latter can be detected for dominant expression because susceptibility genes in homozygotes (with their two intrinsic triggers) will be up to twice as frequently penetrant as those in heterozygotes. The extent of MHC and non-MHC gene contribution determines differences between baseline penetrance and apparent penetrance in MHC-identical sib pairs, sib pairs in general and MHC-identical unrelated individuals. Inheritance patterns in families do not reveal modes of inheritance of incompletely penetrant polygenic MHC-determined traits. A method is proposed to study such traits prospectively in persons presumed to be homozygous, heterozygous or non-carrying for susceptibility genes by determining trait expression in homozygotes, heterozygotes or non-carriers of trait-associated conserved extended MHC haplotypes. The method provides direct estimates of apparent penetrance rates, modes of genetic determination, and, if the trait is dominant, the origin of penetrance. When applied to dominant MHC susceptibility gene-determined immunoglobulin deficiencies in two populations, the ratios of affected haplotype homozygotes to heterozygotes near 2.0 were consistent with an intrinsic mechanism for baseline penetrance acting on the MHC susceptibility genes.