Studies of diabetic twins

Causal associations between human gut microbiota and osteomyelitis: a Mendelian randomization study

Background

Recent studies have emphasized the role of gut microbiota in the onset and progression of osteomyelitis. However, the exact types of gut microbiota and their mechanisms of action remain unclear. Additionally, there is a lack of theoretical support for treatments that improve osteomyelitis by altering the gut microbiota.

Methods

In our study, we utilized the largest genome-wide association study (GWAS) meta-analysis to date from the MiBioGen consortium, involving 13,400 participants. The GWAS data for osteomyelitis were sourced from the UK Biobank, which included 4,836 osteomyelitis cases and 486,484 controls. We employed a two-sample Mendelian randomization framework for a detailed investigation into the causal relationship between gut microbiota and osteomyelitis. Our methods included inverse variance weighting, MR-Egger, weighted median, and weighted mode approaches. Additionally, we applied Cochran's Q statistic to assess the heterogeneity of the instrumental variable.

Results

At the class level, Bacilli and Bacteroidia were positively correlated with the risk of osteomyelitis. At the order level, only Bacteroidales showed a positive association with osteomyelitis. At the genus level, an increased abundance of Butyricimonas, Coprococcus3, and Tyzzerella3 was positively associated with the risk of osteomyelitis, whereas Lachnospira was negatively associated. Sensitivity analyses showed no evidence of heterogeneity or pleiotropy.

Conclusion

This study reveals that classes Bacilli and Bacteroidia, order Bacteroidales, and genera Butyricimonas, Coprococcus3, and Tyzzerella3 are implicated in increasing the risk of osteomyelitis, while the genus Lachnospira is associated with a reduced risk. Future investigations are warranted to elucidate the precise mechanisms through which these specific bacterial groups influence the pathophysiology of osteomyelitis.

Spatiotemporal Dynamics of Insulitis in Human Type 1 Diabetes

Type 1 diabetes (T1D) is an auto-immune disease characterized by the selective destruction of the insulin secreting beta cells in the pancreas during an inflammatory phase known as insulitis. Patients with T1D are typically dependent on the administration of externally provided insulin in order to manage blood glucose levels. Whilst technological developments have significantly improved both the life expectancy and quality of life of these patients, an understanding of the mechanisms of the disease remains elusive. Animal models, such as the NOD mouse model, have been widely used to probe the process of insulitis, but there exist very few data from humans studied at disease onset. In this manuscript, we employ data from human pancreases collected close to the onset of T1D and propose a spatio-temporal computational model for the progression of insulitis in human T1D, with particular focus on the mechanisms underlying the development of insulitis in pancreatic islets. This framework allows us to investigate how the time-course of insulitis progression is affected by altering key parameters, such as the number of the CD20+ B cells present in the inflammatory infiltrate, which has recently been proposed to influence the aggressiveness of the disease. Through the analysis of repeated simulations of our stochastic model, which track the number of beta cells within an islet, we find that increased numbers of B cells in the peri-islet space lead to faster destruction of the beta cells. We also find that the balance between the degradation and repair of the basement membrane surrounding the islet is a critical component in governing the overall destruction rate of the beta cells and their remaining number. Our model provides a framework for continued and improved spatio-temporal modeling of human T1D.

Viral infections and molecular mimicry in type 1 diabetes

Type 1 diabetes (T1D) is a disease characterized by inflammation of pancreatic islets associated with autoimmunity against insulin-producing beta cells, leading to their progressive destruction. The condition constitutes a significant and worldwide problem to human health, particularly because of its rapid, but thus far unexplained, increase in incidence. Environmental factors such as viral infections are thought to account for this trend. While there is no lack of reports associating viral infections toT1D, it has proven difficult to establish which immunological processes link viral infections to disease onset or progression. One of the commonly discussed pathways is molecular mimicry, a mechanism that encompasses cross-reactive immunity against epitopes shared between viruses and beta cells. In this review, we will take a closer look at mechanistic evidence for a potential role of viruses in T1D, with a special focus on molecular mimicry.

Type 2 Diabetes Genetics: Beyond GWAS

The global epidemic of type 2 diabetes mellitus (T2D) is one of the most challenging problems of the 21(st) century leading cause of and the fifth death worldwide. Substantial evidence suggests that T2D is a multifactorial disease with a strong genetic component. Recent genome-wide association studies (GWAS) have successfully identified and replicated nearly 75 susceptibility loci associated with T2D and related metabolic traits, mostly in Europeans, and some in African, and South Asian populations. The GWAS serve as a starting point for future genetic and functional studies since the mechanisms of action by which these associated loci influence disease is still unclear and it is difficult to predict potential implication of these findings in clinical settings. Despite extensive replication, no study has unequivocally demonstrated their clinical role in the disease management beyond progression to T2D from impaired glucose tolerance. However, these studies are revealing new molecular pathways underlying diabetes etiology, gene-environment interactions, epigenetic modifications, and gene function. This review highlights evolving progress made in the rapidly moving field of T2D genetics that is starting to unravel the pathophysiology of a complex phenotype and has potential to show clinical relevance in the near future.

Enteroviruses, type 1 diabetes and hygiene: a complex relationship

Type 1 diabetes (T1D) is an autoimmune disease in which the immune system mounts an attack on the host's insulin‐producing β cells. Because most cases of T1D cannot be attributed only to individual genetics, it is strongly inferred that there is a significant environmental contribution, such as infection, impacting disease development. The human enteroviruses (HEV) are common picornaviruses often implicated as triggers of human T1D, although precisely which of the numerous HEV may be involved in human T1D development is unknown. Experiments using non‐obese diabetic (NOD) mice, commonly used to model T1D, show that induction of T1D by HEV infection in NOD mice is a multifactorial process involving both the virus and the host. Interestingly, results demonstrate that HEV infection of NOD mice can also induce long‐term protection from T1D under certain conditions, suggesting that a similar mechanism may occur in humans. Based upon both experimental animal and observational human studies, we postulate that HEV have a dual role in T1D development and can either cause or prevent autoimmune disease. Whichever outcome occurs depends upon multiple variables in the host‐virus equation, many of which can be deduced from results obtained from NOD mouse studies. We propose that the background to the sharply rising T1D incidences observed in the 20th century correlates with increased levels of hygiene in human societies. Viewing T1D in this perspective suggests that potential preventative options could be developed. Copyright © 2009 John Wiley & Sons, Ltd.

Immunology of beta-cell destruction

The pancreatic islet beta-cells are the target for an autoimmune process that eventually results in an inability to control blood glucose due to the lack of insulin. The different steps that eventually lead to the complete loss of the beta-cells are reviewed to include the very first step of a triggering event that initiates the development of beta-cell autoimmunity to the last step of appearance of islet-cell autoantibodies, which may mark that insulitis is about to form. The observations that the initial beta-cell destruction by virus or other environmental factors triggers islet autoimmunity not in the islets but in the draining pancreatic lymph nodes are reviewed along with possible basic mechanisms of loss of tolerance to islet autoantigens. Once islet autoimmunity is established the question is how beta-cells are progressively killed by autoreactive lymphocytes which eventually results in chronic insulitis. Many of these series of events have been dissected in spontaneously diabetic mice or rats, but controlled clinical trials have shown that rodent observations are not always translated into mechanisms in humans. Attempts are therefore needed to clarify the step 1 triggering mechanisms and the step to chronic autoimmune insulitis to develop evidence-based treatment approaches to prevent type 1 diabetes.

Influence of microbial environment on autoimmunity

During protective immune responses, the adaptive arm of the immune system requires activation by signals provided by innate immunity and driven by microbial stimuli. Whether the same rules apply to autoimmune diseases involving clonal self-reactive T and B lymphocytes--a process referred to here as 'adaptive autoimmunity'--is not quite clear. Nevertheless, in these diseases, the innate-adaptive connection is likely to be influenced by the microbial environment. This review integrates the results of experiments analyzing autoimmunity in sterile versus nonsterile conditions and experiments testing the role of innate immune receptor signaling in autoimmunity. It proposes that autoimmune diseases can be divided into two groups, the pathogenesis of which either follows the rules of innate-adaptive connection or does not.

Antiviral effect of nicotinamide on enterovirus-infected human islets in vitro: effect on virus replication and chemokine secretion

Type 1 diabetes is a chronic disease characterized by the selective destruction of insulin-producing cells in the pancreas. Enterovirus (EV) is the prime candidate to initiate this destruction and several inflammatory chemokines are induced by EV infection. Nicotinamide has been shown to protect isolated human islets, and to modulate chemokine expression. The aim of this study was to evaluate the effect of nicotinamide on EV replication and EV-induced chemokine secretion and cytolysis of human islets. Two EV strains were used to infect human islets in vitro, one lytic (Adrian) isolated from a child at onset of type 1 diabetes, and one non-lytic (VD2921). Secretion of the chemokines IP-10 and MCP-1, viral replication, and virus-induced cytopathic effect (CPE), were measured at different time points post-infection. Addition of nicotinamide to the culture medium reduced viral replication and virus-induced islet destruction/CPE, significantly. Both EV strains increased secretion of IP-10 and MCP-1, when measured days 2-3, and days 5-7 post infection, compared to mock-infected control islets. IP-10 was not produced by uninfected isolated islets, whereas a basal secretion of MCP-1 was detected. Interestingly, addition of nicotinamide blocked completely (Adrian), or reduced significantly (VD2921), the virus-induced secretion of IP-10. Secretion of MCP-1 was also reduced in the presence of nicotinamide, from infected and uninfected islets. The reported antiviral effects of nicotinamide could have implications for the treatment/prevention of virus- and immune-mediated disease. Also, this study highlights a possible mechanism of virus-induced type 1 diabetes through the induction of MCP-1 and IP-10 in pancreatic islets.

Positional cloning of "Lisch-Like", a candidate modifier of susceptibility to type 2 diabetes in mice

In 404 Lep^ob/ob F2 progeny of a C57BL/6J (B6) x DBA/2J (DBA) intercross, we mapped a DBA-related quantitative trait locus (QTL) to distal Chr1 at 169.6 Mb, centered about D1Mit110, for diabetes-related phenotypes that included blood glucose, HbA1c, and pancreatic islet histology. The interval was refined to 1.8 Mb in a series of B6.DBA congenic/subcongenic lines also segregating for Lep^ob. The phenotypes of B6.DBA congenic mice include reduced β-cell replication rates accompanied by reduced β-cell mass, reduced insulin/glucose ratio in blood, reduced glucose tolerance, and persistent mild hypoinsulinemic hyperglycemia. Nucleotide sequence and expression analysis of 14 genes in this interval identified a predicted gene that we have designated “Lisch-like” (Ll) as the most likely candidate. The gene spans 62.7 kb on Chr1qH2.3, encoding a 10-exon, 646–amino acid polypeptide, homologous to Lsr on Chr7qB1 and to Ildr1 on Chr16qB3. The largest isoform of Ll is predicted to be a transmembrane molecule with an immunoglobulin-like extracellular domain and a serine/threonine-rich intracellular domain that contains a 14-3-3 binding domain. Morpholino knockdown of the zebrafish paralog of Ll resulted in a generalized delay in endodermal development in the gut region and dispersion of insulin-positive cells. Mice segregating for an ENU-induced null allele of Ll have phenotypes comparable to the B.D congenic lines. The human ortholog, C1orf32, is in the middle of a 30-Mb region of Chr1q23-25 that has been repeatedly associated with type 2 diabetes.

Type 2 diabetes (T2D) accounts for over 90% of instances of diabetes and is a leading cause of medical morbidity and mortality. Twin studies indicate a strong polygenic contribution to susceptibility within the context of obesity. Although approximately ten genes making important contributions to individual risk have been identified, it is clear that others remain to be identified. In this study, we intercrossed obese, diabetes-resistant and diabetes-prone mouse strains to implicate a genetic interval on mouse Chr1 associated with reduced β-cell numbers and elevated blood glucose. We narrowed the region using molecular genetics and computational approaches to identify a novel gene we designated “Lisch-like” (Ll). The orthologous human genetic interval has been repeatedly implicated in T2D. Mice with an induced mutation that reduces Ll expression are impaired in both β-cell development and glucose metabolism, and reduced expression of the homologous gene in zebrafish disrupts islet development. Ll is expressed in organs implicated in the pathophysiology of T2D (hypothalamus, islets, liver, and skeletal muscle) and is predicted to encode a transmembrane protein that could mediate cholesterol transport and/or convey signals related to cell division. Either mechanism could mediate effects on β-cell mass that would predispose to T2D.

Group B coxsackievirus diabetogenic phenotype correlates with replication efficiency

Group B coxsackieviruses can initiate rapid onset type 1 diabetes (T1D) in old nonobese diabetic (NOD) mice. Inoculating high doses of poorly pathogenic CVB3/GA per mouse initiated rapid onset T1D. Viral protein was detectable in islets shortly after inoculation in association with beta cells as well as other primary islet cell types. The virulent strain CVB3/28 replicated to higher titers more rapidly than CVB3/GA in the pancreas and in established beta cell cultures. Exchange of 5'-nontranslated regions between the two CVB3 strains demonstrated a variable impact on replication in beta cell cultures and suppression of in vivo replication for both strains. While any CVB strain may be able to induce T1D in prediabetic NOD mice, T1D onset is linked both to the viral replication rate and infectious dose.

Frequency of abnormal carbohydrate metabolism and diabetes in a population-based screening of adolescents

OBJECTIVE

To document the frequency of glucose intolerance in adolescents in a population-based study of primarily African-American/Non-Hispanic whites in an urban-suburban school district.

STUDY DESIGN

Measurement of fasting and 2-hour post-glucose load plasma glucose concentrations.

RESULTS

Carbohydrate intolerance (either impaired fasting glucose, impaired glucose tolerance, or both) was identified in 8.0%, near-diabetes (1 fasting glucose > or = 126 mg/dL [7.0 mmol/L] and/or 2-hour glucose > or = 200 mg/dL [11.1 mmol/L]) in 0.3%, and diabetes in 0.36% (type 1A = 0.24%; type 2 = 0.08%; undiagnosed type 2 = 0.04%). A model for abnormal carbohydrate metabolism was constructed with regression analysis in the Carbohydrate Intolerance (CI)/near-diabetes group and with logistic regression in the entire study population. Risk factors for the development of CI/near-diabetes included having a 1 unit increase in body mass index (BMI) z-score and either being non-Hispanic white or in the pubertal group. Increased fasting glucose correlated with having puberty and decreased BMI z-score, whereas 2-hour glucose correlated with increased BMI z-score. By using National Health and Nutrition Survey (NHANES) III (1988-1994) definitions, impaired fasting glucose was present in 2.0% in this study versus 1.7% (NHANES III).

CONCLUSION

The prevalence of CI/near-diabetes was 8.3%. Undiagnosed diabetes mellitus was rare. One third of adolescents with diabetes mellitus could be classified as having type 2 diabetes mellitus. The adult model of the progression of insulin resistance to type 2 diabetes mellitus in adolescents may be valid. Despite the increase in the overweight population since NHANES III, abnormalities in glucose metabolism have not changed significantly.

Coxsackievirus B3 infection and type 1 diabetes development in NOD mice: insulitis determines susceptibility of pancreatic islets to virus infection

Group B coxsackieviruses (CVB) are believed to trigger some cases of human type 1 diabetes (T1D), although the mechanism by which this may occur has not been shown. We demonstrated previously that inoculation of young nonobese diabetic (NOD) mice with any of several different CVB strains reduced T1D incidence. We also observed no evidence of CVB replication within islets of young NOD mice, suggesting no role for CVB in T1D induction in the NOD mouse model. The failure to observe CVB replication within islets of young NOD mice has been proposed to be due to interferon expression by insulin-producing beta cells or lack of expression of the CVB receptor CAR. We found that CAR protein is detectable within islets of young and older NOD mice and that a CVB3 strain, which expresses murine IL-4, can replicate in islets. Mice inoculated with the IL-4 expressing CVB3 chimeric strain were better protected from T1D onset than were mock-infected control mice despite intraislet viral replication. Having demonstrated that CVB can replicate in healthy islets of young NOD mice when the intraislet environment is suitably altered, we asked whether islets in old prediabetic mice were resistant to CVB infection. Unlike young mice in which insulitis is not yet apparent, older NOD mice demonstrate severe insulitis in all islets. Inoculating older prediabetic mice with different pathogenic CVB strains caused accelerated T1D onset relative to control mice, a phenomenon that was preceded by detection of virus within islets. Together, the results suggest a model for resolving conflicting data regarding the role of CVB in human T1D etiology.

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.

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.

Genetics of type 1 diabetes

Type 1 diabetes mellitus is a T-cell-mediated autoimmune disease characterized by the selective destruction of pancreatic beta cells. Susceptibility to the disease is determined by a combination of genetic and environmental factors. The genetic factors are termed 'susceptibility genes' as they modify the risk of diabetes but are neither necessary nor sufficient for disease to develop. A large number of chromosomal regions have been identified as containing potential diabetes susceptibility genes. The IDDM1 locus, which encompasses the major histocompatibility complex on chromosome 6, is the major genetic risk factor. The HLA-DQ genes are the primary susceptibility genes within this region, although other genes may also contribute. The IDDM2 locus maps to a variable number of tandem repeats in the insulin gene region on chromosome 11. Further research is necessary to determine the precise location and identity of other diabetes susceptibility genes.

Antidiabetic effect of glycyrrhizin in genetically diabetic KK-Ay mice

We, previously demonstrated that one shot administration of glycyrrhizin (Grz) reduced the postprandial blood glucose rise, using Std ddY mice. Subsequently, we evaluated the effects of long-term Grz treatment (2.7, 4.1 g/kg diet) on diabetic symptoms using genetically non-insulin dependent diabetic model mice (KK-Ay). Male KK-Ay mice were divided into 3 groups: the control group, 0.27% Grz diet (2.7 g of Grz/kg diet) group and 0.41% Grz diet (4.1 g of Grz/kg diet) group. The elevation of blood glucose concentration was almost entirely suppressed in mice fed the 0.41% Grz diet 7 weeks after the beginning of test feeding, although it was not suppressed in mice fed the control diet or the 0.27% Grz diet. Water intake in the control and 0.27% Grz diet groups increased gradually, whereas, this was not true in the 0.41% Grz diet group. Grz treatment significantly lowered blood insulin level. Throughout the experiment, Grz did not affect the food intake or body weight among the three groups. The mice fed the 0.41% Grz diet also improved their tolerance to oral glucose loading 9 weeks after the beginning of test feeding. This study shows that Grz has an antidiabetic effect in noninsulin-dependent diabetes model mice.

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.

Effects of acute hyperglycaemia on cardiac function: an echocardiographic study of monozygotic twins

BACKGROUND

A major cause of morbidity in type I diabetes is congestive heart failure due predominantly to left ventricular diastolic dysfunction. The mechanism of diastolic dysfunction remains unknown and does not relate to blood pressure, microvascular complications and glycated haemoglobin. Hyperglycaemia is the hallmark of diabetes and is a potential determinant of left ventricular diastolic dysfunction.

OBJECTIVE

To determine whether acute hyperglycaemia can induce changes in left ventricular diastolic function in normal subjects similar to those observed in insulin-dependent diabetes mellitus (IDDM).

DESIGN

Cross-sectional study.

SETTING

London teaching hospital.

SUBJECTS

Sixteen twins from eight identical twin pairs discordant for IDDM (age 18-38 years, five male) were studied; none had a history or evidence of myocardial ischaemia, valvular or primary heart muscle disease, systemic hypertension or nephropathy.

INTERVENTIONS

Non-diabetic twins underwent a hyperglycaemic clamp at 10 mmol/l.

MAIN OUTCOME MEASURES

Doppler echocardiography was performed in basal condition in identical twin pairs discordant for IDDM and repeated in the non-diabetic twins during hyperglycaemia. Blood glucose, insulin and catecholamines were measured at baseline and during hyperglycaemia.

RESULTS

Transmitral Doppler E/A velocity ratio was significantly lower in diabetic than non-diabetic twins at baseline (1.44 (0.38) vs. 1.51 (0.19), P<0.05). Glucose infusion in the non-diabetic twins resulted in an increase in their E/A ratio (1.51 (0.19) vs. 1.82 (0. 47), P<0.05) due to an increase in E velocity (68 (12) to 64.7 (10. 7), P<0.05) and a decrease in the peak A velocity (42.7 (3.85) to 38. 0 (4.1), P<0.05). No significant changes were observed in peak E velocity or isovolumic relaxation time in the non-diabetic twins between baseline and hyperglycaemia.

CONCLUSIONS

The alterations in left ventricular diastolic function induced by acute hyperglycaemia and consequent increase in plasma catecholamines do not mimic those demonstrated in IDDM patients.

The aetiology of Type I diabetes

The aetiology of Type I diabetes involves both genetic and environmental factors. The genes implicated are 'susceptibility genes', which modify risk. Individual susceptibility genes may not be required and are not sufficient for disease development. The strongest genetic risk component is encoded within the major histocompatibility complex (MHC) and is designated IDDM I. The HLA-DQ genes contribute to the risk, but so may other MHC-encoded genes. The susceptibility encoded by IDDM2 refers to a variable number of tandem repeats in the insulin gene region. Many other genomic regions have been designated as susceptibility intervals potentially containing candidate genes. Environmental factors appear to be important in disease expression in either a causative or a protective role. Epidemiological data indicate that such factors operate from early in life. Viral infection(s) may have a disease-initiating and/ or accelerating effect. A potential diabetogenic role for cows' milk protein remains unconfirmed. Further research is necessary to elucidate fully the aetiological factors involved and how they interact.

Viruses and other perinatal exposures as initiating events for beta-cell destruction

There is strong evidence that the aetiology of insulin-dependent diabetes mellitus (IDDM) is due to a complex interaction between genes and the environment and that the pathogenesis is autoimmune. In early perinatal life the immune system is induceable and exposures in this period may initiate autoimmunity. Recent findings of time and space clustering of birth dates for later diabetic cases together with the early observation of a very high prevalence of diabetes in cases with rubella embryopathy suggest that foetal virus exposure may be important. Recent findings from Sweden and Finland suggest that enterovirus exposure during foetal life may initiate autoimmunity which may lead to diabetes. Other immune events, such as maternal-foetal blood group incompatibility and pre-eclampsia in the mother have also been associated with IDDM risk. Other more unspecific events in the perinatal period, such as a short gestational age, caesarean section and neonatal respiratory disease, are also indicated to increase the risk. In addition, food components such as nitrosamine components, cow's milk protein and gliadin have been proposed to initiate the slowly progressing autoimmune beta-cell destruction. Most of these epidemiological findings are supported by experimental studies in the nonobese diabetic mice but their exact mechanisms of action are still unclear. It is concluded that new evidence is accumulating indicating that perinatal exposures may be important for the initiation of beta-cell destruction. As such risk factors may be targets for primary prevention strategies further studies are urgently warranted.

Relationship between obesity and concordance rate for type 2 (non-insulin-dependent) diabetes mellitus among twins

In order to analyse the relationship of genetic factors and the role of obesity in the pathogenesis of Type 2 (non-insulin-dependent) diabetes mellitus, we compared body mass index (BMI) and other parameters in 71 monozygotic and 17 dizygotic twins (MZT and DZT) with Type 2 diabetes, and analysed the relationship of maximal BMI in the past (max BMI) with the concordance and discordance for diabetes. Data were collected by mail from the members of the Japan Diabetes Society. Concordance rate for diabetes was higher in MZT than in DZT (72% vs. 41%, P = 0.017). Concordance rate in MZT varied in relation to the max BMI of the index twins who developed diabetes earlier. It was higher in non-obese and slightly obese groups (82% and 80% for those with max BMI < 24 and 24-27.9, respectively) than in obese group (36%, max BMI > or = 28) (P = 0.003). In MZT, diabetic twins of discordant pairs were significantly more obese at the survey and in the past than index twins of concordant pairs (mean BMI: 23.9 vs. 21.7, P = 0.007; mean max BMI, 27.7 vs. 24.3, P = 0.001). A similar tendency of differences in BMI was also observed in DZT. Intrapair comparison in discordant MZT and DZT pairs showed that diabetic twins were more obese than non-diabetic cotwins (mean max BMI, 27.7 vs. 24.7, P = 0.004 for MZT; and 27.3 vs. 23.9, P = 0.002 for DZT). In concordant DZT pairs, index twins with earlier onset of diabetes had been less obese than cotwins (mean max BMI, 23.6 vs. 26.0, P = 0.004). In conclusion, the comparison of the max BMI in twins suggests that the degree of diabetogenic role of obesity varies in heterogeneous genetic background. The index twins of discordant pairs had been more obese than those of concordant pairs, suggesting that obesity plays a more important role in those with weaker genetic susceptibility for diabetes.

Immunological studies on type 1 diabetes in identical twins

Diabetes is a multifactorial disease, the pathogenesis of which involves participation of the host immune system in beta cell destruction. Studies on identical twins offer the opportunity to define genetic and non-genetic factors which may contribute to susceptibility to the disease. Our own work indicates that the number and nature, as well as the intensity and persistence of immune abnormalities of cellular and humoral immune responses can be powerful predictors of the disease and also identify twins who have a degree of protection from the disease.

Metabolic changes in diabetes

Diabetes is not a single disease but a group of diseases characterised by hyperglycaemia. The most important regulator of glucose uptake from the blood is the hormone insulin, which is produced by islet beta cells and acts on insulin receptors to promote nutrient uptake and processing. A decrease in either insulin secretion or sensitivity can cause diabetes. Exposure to prolonged hyperglycaemia causes reversible and then irreversible changes to tissue metabolism and structure. These changes may be responsible for the potentially devastating complications of diabetes.