Metabolic studies in unaffected co-twins of non-insulin-dependent diabetics

Fasting plasma lactate as a possible early clinical marker for metabolic disease risk

BACKGROUND AND AIM

Elevated fasting plasma lactate concentrations are evident in individuals with metabolic diseases. However, it has yet to be determined if these associations exist in a young, healthy population as a possible early marker for metabolic disease risk. The purpose of this study was to determine if indices of the metabolic syndrome are related to plasma lactate concentrations in this population.

METHODS

Fifty (29 ± 7 yr) men (n = 19) and women (n = 31) classified as overweight (26.4 ± 1.8 kg/m2) participated in this observational study. Blood pressure and blood metabolites were measured after an overnight fast. Lactate was also measured before and after a three-day eucaloric high-fat (70 %) diet. The homeostatic model assessment for insulin resistance (HOMA-IR) was calculated as a measure of insulin resistance. Visceral adipose tissue mass was determined via dual X-ray absorptiometry.

RESULTS

Triglycerides (r = 0.55, p=<0.0001), HOMA-IR (r = 0.53, p=<0.0001), and systolic and diastolic (both, r = 0.36, p = 0.01) blood pressures associated with fasting plasma lactate. No differences in visceral adipose tissue existed between the sexes (p = 0.41); however, the relationship between visceral adipose tissue and lactate existed only in females (r = 0.59, p = 0.02) but not in males (p = 0.53). Fasting lactate and HOMA-IR increased in males (p = 0.01 and p = 0.02, respectively), but not females, following a three-day high-fat diet.

CONCLUSION

Indices of the metabolic syndrome associated with fasting plasma lactates in young relatively healthy individuals. Fasting lactate also increased in a sex-specific manner after a three-day high fat diet. Thus, lactate could become a clinical marker for metabolic disease risk.

What the Jackson Heart Study Has Taught Us About Diabetes and Cardiovascular Disease in the African American Community: a 20-year Appreciation

PURPOSE OF REVIEW

The burden of cardiometabolic diseases such as cardiovascular disease (CVD) and type 2 diabetes (T2D) is pronounced among African Americans. Research has shown that behavioral, social, metabolic, psychosocial, and genetic risk factors of CVD and T2D are closely interwoven. Approximately 20 years ago, the Jackson Heart Study (JHS) was established to investigate this constellation of risk factors.

RECENT FINDINGS

Findings from neighborhood studies emphasize the importance of social cohesion and physical environment in the context CVD and T2D risk. Socioeconomic status factors such as income and education were significant predictors for CVD and T2D. Behavioral studies indicate that modifiable risk factors such as smoking, physical inactivity, lack of sleep, and poor nutrition are associated with CVD risk and all-cause mortality. Mental health also was found to be associated with CVD and T2D. Genetic influences are associated with disease etiology. This review summarizes the joint contributions of CVD and cardiometabolic risk factors in an African American population.

Lactate, a Neglected Factor for Diabetes and Cancer Interaction

Increasing body of evidence suggests that there exists a connection between diabetes and cancer. Nevertheless, to date, the potential reasons for this association are still poorly understood and currently there is no clinical evidence available to direct the proper management of patients presenting with these two diseases concomitantly. Both cancer and diabetes have been associated with abnormal lactate metabolism and high level of lactate production is the key biological property of these diseases. Conversely, high lactate contribute to a higher insulin resistant status and a more malignant phenotype of cancer cells, promoting diabetes and cancer development and progression. In view of associations between diabetes and cancers, the role of high lactate production in diabetes and cancer interaction should not be neglected. Here, we review the available evidence of lactate's role in different biological characteristics of diabetes and cancer and interactive relationship between them. Understanding the molecular mechanisms behind metabolic remodeling of diabetes- and cancer-related signaling would endow novel preventive and therapeutic approaches for diabetes and cancer treatment.

The Concordance and Heritability of Type 2 Diabetes in 34,166 Twin Pairs From International Twin Registers: The Discordant Twin (DISCOTWIN) Consortium

Twin pairs discordant for disease may help elucidate the epigenetic mechanisms and causal environmental factors in disease development and progression. To obtain the numbers of pairs, especially monozygotic (MZ) twin pairs, necessary for in-depth studies while also allowing for replication, twin studies worldwide need to pool their resources. The Discordant Twin (DISCOTWIN) consortium was established for this goal. Here, we describe the DISCOTWIN Consortium and present an analysis of type 2 diabetes (T2D) data in nearly 35,000 twin pairs. Seven twin cohorts from Europe (Denmark, Finland, Norway, the Netherlands, Spain, Sweden, and the United Kingdom) and one from Australia investigated the rate of discordance for T2D in same-sex twin pairs aged 45 years and older. Data were available for 34,166 same-sex twin pairs, of which 13,970 were MZ, with T2D diagnosis based on self-reported diagnosis and medication use, fasting glucose and insulin measures, or medical records. The prevalence of T2D ranged from 2.6% to 12.3% across the cohorts depending on age, body mass index (BMI), and national diabetes prevalence. T2D discordance rate was lower for MZ (5.1%, range 2.9-11.2%) than for same-sex dizygotic (DZ) (8.0%, range 4.9-13.5%) pairs. Across DISCOTWIN, 720 discordant MZ pairs were identified. Except for the oldest of the Danish cohorts (mean age 79), heritability estimates based on contingency tables were moderate to high (0.47-0.77). From a meta-analysis of all data, the heritability was estimated at 72% (95% confidence interval 61-78%). This study demonstrated high T2D prevalence and high heritability for T2D liability across twin cohorts. Therefore, the number of discordant MZ pairs for T2D is limited. By combining national resources, the DISCOTWIN Consortium maximizes the number of discordant MZ pairs needed for in-depth genotyping, multi-omics, and phenotyping studies, which may provide unique insights into the pathways linking genes to the development of many diseases.

Comprehensive review on lactate metabolism in human health

Metabolic pathways involved in lactate metabolism are important to understand the physiological response to exercise and the pathogenesis of prevalent diseases such as diabetes and cancer. Monocarboxylate transporters are being investigated as potential targets for diagnosis and therapy of these and other disorders. Glucose and alanine produce pyruvate which is reduced to lactate by lactate dehydrogenase in the cytoplasm without oxygen consumption. Lactate removal takes place via its oxidation to pyruvate by lactate dehydrogenase. Pyruvate may be either oxidized to carbon dioxide producing energy or transformed into glucose. Pyruvate oxidation requires oxygen supply and the cooperation of pyruvate dehydrogenase, the tricarboxylic acid cycle, and the mitochondrial respiratory chain. Enzymes of the gluconeogenesis pathway sequentially convert pyruvate into glucose. Congenital or acquired deficiency on gluconeogenesis or pyruvate oxidation, including tissue hypoxia, may induce lactate accumulation. Both obese individuals and patients with diabetes show elevated plasma lactate concentration compared to healthy subjects, but there is no conclusive evidence of hyperlactatemia causing insulin resistance. Available evidence suggests an association between defective mitochondrial oxidative capacity in the pancreatic β-cells and diminished insulin secretion that may trigger the development of diabetes in patients already affected with insulin resistance. Several mutations in the mitochondrial DNA are associated with diabetes mellitus, although the pathogenesis remains unsettled. Mitochondrial DNA mutations have been detected in a number of human cancers. d-lactate is a lactate enantiomer normally formed during glycolysis. Excess d-lactate is generated in diabetes, particularly during diabetic ketoacidosis. d-lactic acidosis is typically associated with small bowel resection.

Diabetes-science, serendipity and common sense

This paper is dedicated to young researchers in diabetes. One such person was Frederick Banting who, with his colleagues, isolated insulin in 1921, saving the lives of literally millions of people. What factors allowed Banting and other scientists to produce work that has immensely benefited the human race? I propose that it is the combination of good scientific background (the 'prepared mind'), commonly some serendipity taken with a good dose of common sense and supplemented by enthusiasm, tenacity and good mentoring, which drives the 'power of observation' and the ability to take forward the good idea. I give examples from history to support this and then discuss some of the 'truths, perspectives and controversies' within the diabetes arena when I first started in diabetes research in the late 1970s. I describe how my appetite was initially 'whetted' for research by moving to an excellent clinical research environment with encouragement to test ideas and controversies initially in a clinical research programme, followed by more scientific/basic research. The work that I performed as a young doctor and research fellow led to a lifelong professional interest in three major areas-causes and interventions for diabetes vascular disease, studies of the molecular genetics of Type 1 and Type 2 diabetes and work on diabetes in different ethnic groups. I provide a summation of my own and other people's work to demonstrate how research can be progressed and lead to patient benefit as well as providing an incredibly rewarding career. I believe that we need to encourage and put more resources into development of young doctors and scientists wishing to undertake research in our discipline. Areas ripe for much-needed clinical research programmes, for example, include work on best practice/provision of health care, application of the evidence base from clinical trials to achieve public health gains, attention to adherence issues and better-tolerated therapies. Most importantly, a greater emphasis on prevention through public health measures and 'buy in' from the whole population is urgently required.

Impact of physical inactivity on subcutaneous adipose tissue metabolism in healthy young male offspring of patients with type 2 diabetes

OBJECTIVE

Physical inactivity is a risk factor for type 2 diabetes and may be more detrimental in first-degree relative (FDR) subjects, unmasking underlying defects of metabolism. Using a positive family history of type 2 diabetes as a marker of increased genetic risk, the aim of this study was to investigate the impact of physical inactivity on adipose tissue (AT) metabolism in FDR subjects.

RESEARCH DESIGN AND METHODS

A total of 13 FDR and 20 control (CON) subjects participated in the study. All were studied before and after 10 days of bed rest using the glucose clamp technique combined with measurements of glucose uptake, lipolysis, and lactate release from subcutaneous abdominal (SCAAT) and femoral (SCFAT) adipose tissue by the microdialysis technique. Additionally, mRNA expression of lipases was determined in biopsies from SCAAT.

RESULTS

Before bed rest, the FDR subjects revealed significantly increased glucose uptake in SCAAT. Furthermore, mRNA expression of lipases was significantly decreased in the SCAAT of FDR subjects. Bed rest significantly decreased lipolysis and tended to increase glucose uptake in the SCFAT of both CON and FDR subjects. In response to bed rest, SCAAT glucose uptake significantly increased in CON subjects but not in FDR subjects.

CONCLUSIONS

FDR subjects exhibit an abnormal AT metabolism including increased glucose uptake prior to bed rest. However, the differences between FDR and CON subjects in AT metabolism were attenuated during bed rest due to relatively more adverse changes in CON subjects compared with FDR subjects. Physical inactivity per se is not more deleterious in FDR subjects as compared with CON subjects with respect to derangements in AT metabolism.

Advances in diabetes for the millennium: understanding insulin resistance

Type 2 diabetes is a heterogeneous disorder in which both insulin resistance and impaired insulin secretion play important roles. Studies in monozygotic twins in which one is discordant for type 2 diabetes and studies of first-degree relatives of patients with type 2 diabetes who still have normal glucose tolerance indicate that impaired insulin secretion can be detected before insulin resistance, suggesting that impaired beta-cell function may be the primary genetic defect. The insulin resistance found in most individuals with impaired glucose tolerance and/or type 2 diabetes appears to be largely acquired and can be accounted for by obesity, physical inactivity, and glucose and lipotoxicity. Progressive deterioration in beta-cell function as demonstrated in the United Kingdom Prospective Diabetes Study (UKPDS) and/or worsening of insulin resistance leads to deterioration in glucose tolerance and to secondary failure of oral antidiabetic drugs. Therefore, agents that improve beta-cell function (such as sulfonylureas and meglitinides) and insulin sensitizers (such as metformin and thiazolidinediones) both are useful alone or in combination for treating type 2 diabetes.

Pathogenesis of type 2 diabetes mellitus

This article provides an overview of the pathogenesis of type 2 diabetes mellitus. Discussion begins by describing normal glucose homeostasis and ingestion of a typical meal and then discusses glucose homeostasis in diabetes. Topics covered include insulin secretion in type 2 diabetes mellitus and insulin resistance, the site of insulin resistance, the interaction between insulin sensitivity and secretion, the role of adipocytes in the pathogenesis of type 2 diabetes, cellular mechanisms of insulin resistance including glucose transport and phosphorylation, glycogen and synthesis,glucose and oxidation, glycolysis, and insulin signaling.

Redefining the clinical management of type 2 diabetes: matching therapy to pathophysiology

Conventional treatments for type 2 diabetes do not provide adequate glycaemic control to prevent the long-term progression of the disease. The introduction of increasingly intensive therapeutic regimens in stepwise management strategies aims to maintain glycaemic control in the face of progressive deterioration in beta-cell function. However, such an approach does not entirely address the underlying disease mechanisms. Although much remains unclear about the aetiology of type 2 diabetes, both beta-cell dysfunction and insulin resistance play important roles, and there is a complex, dynamic interaction between these two abnormalities. Growing evidence suggests that treatments that can reverse insulin resistance and improve beta-cell function may be able to slow or prevent the progression of the disease. The clinical management of type 2 diabetes therefore needs to be re-examined and redefined to reflect new insights into the underlying pathogenetic mechanisms, including consideration of the potential benefits of early, aggressive intervention to counter both beta-cell dysfunction and insulin resistance.

Diabetes mellitus and other metabolic disturbances induced by atypical antipsychotic agents

Atypical antipsychotic agents offer significant advantages over older conventional antipsychotic agents. The reduction in antipsychotic drug-associated extrapyramidal symptoms and the potential reduced risk for tardive dyskinesia, compared to conventional drugs, are major advances in the treatment of psychotic patients. However, recent reports of hyperglycemia, new-onset diabetes mellitus, diabetic ketoacidosis, weight gain, and lipid abnormalities associated with atypical antipsychotic agents have emerged. A review of the recent literature and an approach to the evaluation of risk factors to aide in the safe use of atypical antipsychotic agents in presented.

Atypical antipsychotic-induced diabetes mellitus: how strong is the evidence?

Atypical antipsychotics offer significant improvements over older, conventional antipsychotic agents. However, recently the newer agents have been linked to medical morbidity including hyperglycaemia, diabetes mellitus, bodyweight gain and abnormal lipid levels. Even more concerning, because of a significant risk of death, there have been numerous case reports of patients treated with clozapine or olanzapine developing diabetic ketoacidosis shortly after initiation of the drug. Much of the information concerning the medical morbidity of diabetes mellitus is based on case reports, retrospective chart reviews, naturalistic studies and cross-sectional studies. While definitive studies have yet to be reported, mounting evidence suggests that the atypical antipsychotic agents, particularly clozapine and olanzapine, may significantly impair glucose metabolism and increase the risk of diabetes in patients with schizophrenia. Diabetic ketoacidosis, although it appears to be uncommon, is of great concern secondary to the risk of death. Patients treated with atypical antipsychotic agents should be routinely screened for diabetes and other metabolic abnormalities including raised lipid levels. Patients with risk factors for diabetes should be monitored more closely. Reports and clinical experience suggest that in a case of atypical antipsychotic-associated diabetes or diabetic ketoacidosis, discontinuation of the antipsychotic agent may result in complete resolution of the hyperglycaemia and diabetes.

A reconsideration of the origins of the type 2 diabetes epidemic among Native Americans and the implications for intervention policy

Type 2 diabetes has reached epidemic proportions in many Native American communities in North America. The overwhelming majority of physicians, biomedical researchers, and medical ecologists continue to explain the astoundingly high prevalence rates of diabetes among Native Americans and other high prevalence populations in terms of yet-to-be-identified genetic factors. Recent experimental and epidemiological research, however, has brought to light an etiological alternative to the genetic-predisposition model. This body of research suggests that type 2 diabetes may result initially from fetal malnutrition and, in subsequent generations, be propagated via perturbations in the intrauterine environment. Native American populations at greatest risk for diabetes today are the ones most likely to have endured severe nutritional stress in their recent histories, thus experiencing the conditions that are most conducive to the diabetic developmental sequence. If further substantiated, the implications of the fetal-origin model of diabetes for diabetes intervention programs are profound.

Increased lactate release per fat cell in normoglycemic first-degree relatives of individuals with type 2 diabetes

The aim of this study was to examine subcutaneous lactate production in the relatives of individuals with type 2 diabetes. Therefore, we recruited seven healthy first-degree relatives of type 2 diabetic patients and seven pairwise, matched, healthy control subjects without any heredity for diabetes. All subjects were studied with a euglycemic insulin clamp at approximately 600 pmol/l, abdominal subcutaneous microdialysis, and (133)Xe clearance. Furthermore, a subcutaneous needle biopsy was performed to determine fat cell size. In the fasting state, interstitial lactate was 40% higher in relatives than in control subjects (P = 0.043), but net lactate production was similar in both groups. However, during the insulin clamp, interstitial lactate (2.50 +/- 0.29 vs. 1.98 +/- 0.26 mmol/l, P = 0.018), interstitial-arterial lactate concentration difference (1.08 +/- 0.30 vs. 0.53 +/- 0.24 mmol/l, P = 0.028), and net lactate release per fat cell (10.9 +/- 3.7 vs. 2.8 +/- 1.3 fmol. cell(-1). min(-1), P = 0.018) were increased in the relatives. We conclude that first-degree relatives of type 2 diabetic patients may have an enhanced net lactate release per fat cell in abdominal subcutaneous tissue. This could suggest a pathological regulation in adipose tissue that is of importance for the metabolic defects known in type 2 diabetic relatives.

Nutritional origins of insulin resistance: a rat model for diabetes-prone human populations

While there has been little success identifying the genetic bases of noninsulin-dependent (type-2) diabetes, current epidemiological data and animal models implicate fetal undernutrition in the development of type-2 diabetes. We examined the effects of fetal undernutrition on insulin responses and glucose tolerance in adulthood in genetically normal rats. Control rats were adequately nourished in utero and consumed nutritionally adequate (N) diets throughout life. Experimental rats (F1 generation) were undernourished in utero and consumed either N or high-energy, high-fat (HF) diets postweaning. The offspring of the experimental rats (F2 generation) received the respective diets of their parent. Body weights of experimental F1 rats at d 4 were 40% less than that of control pups, and they remained significantly smaller than controls throughout adulthood. The experimental F1 rats consuming N diets postweaning had a reduced insulin response (-30%) at 30-min postglucose challenge in adulthood (P > 0.05). However, their offspring (F2 generation) displayed a markedly elevated insulin response [+80% at 30 min (P < 0.05) and + 230% at 120 min (P < 0.001) postglucose challenge]. The insulin response of the F2 generation rats fed the high-energy, HF diet was even more pronounced [+130% at 30 min (P < 0.003) and + 250% at 120 min (P < 0.001) postglucose challenge]. Thus, undernourishment in utero produces striking insulin resistance in genetically normal, well-nourished second-generation rats.

Polymorphism in the angiotensin converting enzyme but not in the angiotensinogen gene is associated with hypertension and type 2 diabetes: the Skaraborg Hypertension and diabetes project

OBJECTIVE

To study the association between polymorphisms in the angiotensin converting enzyme (ACE) gene and angiotensinogen (AGT) gene and hypertension and/or type 2 diabetes in a community population.

PATIENTS AND METHODS

The insertion (I)/deletion (D) polymorphism of the ACE gene and the M235T polymorphism of the AGT gene were genotyped in 773 nondiabetic individuals with hypertension, 193 normotensive patients with type 2 diabetes, 243 patients with type 2 diabetes and hypertension, and in 820 normotensive control individuals identified in a community-based study.

RESULTS

The DD genotype was associated with hypertension in individuals less than 70 years [odds ratio (OR) = 1.54, confidence interval (CI) = 1.09-2.18] and remained so when patients with type 2 diabetes were excluded from the analysis (OR = 1.45, CI = 1.01-2.09). The strongest association was with the combination of type 2 diabetes and hypertension (OR = 2.19, CI = 1.09-4.38). There was no association with type 2 diabetes without hypertension. No association was observed between the M235T variant or the 3'-microsatellite polymorphism of the AGT gene and hypertension.

CONCLUSION

The D-allele of the ACE gene ID polymorphism increases susceptibility to hypertension, particularly when associated with type 2 diabetes. No association was observed between the M235T variant or 3'-microsatellite polymorphism of the AGT gene and hypertension.

The genetic basis of type 2 diabetes mellitus: impaired insulin secretion versus impaired insulin sensitivity

Despite the fact that it is the prevalent view that insulin resistance is the main genetic factor predisposing to development of type 2 diabetes, review of several lines of evidence in the literature indicates a lack of overwhelming support for this concept. In fact, the literature better supports the case of impaired insulin secretion being the initial and main genetic factor predisposing to type 2 diabetes, especially 1) the studies in people at high risk to subsequently develop type 2 diabetes (discordant monozygotic twins and women with previous gestational diabetes), 2) the studies demonstrating compete alleviation of insulin resistance with weight loss, and 3) the studies finding that people with type 2 diabetes or IGT can have impaired insulin secretion and no insulin resistance compared with well matched NGT subjects. The fact that insulin resistance may be largely an acquired problem in no way lessens its importance in the pathogenesis of type 2 diabetes. Life style changes (exercise, weight reduction) and pharmacological agents (e.g., biguanides and thiazolidendiones) that reduce insulin resistance or increase insulin sensitivity clearly have major beneficial effects (122, 144-146, 153-155).

Elevated plasma glucose 2 h postchallenge predicts defects in beta-cell function

Studies were performed in subjects with no known family history of diabetes, normoglycemic subjects who have first-degree relatives with non-insulin-dependent diabetes mellitus (NIDDM), and subjects with nondiagnostic oral glucose tolerance tests (NDX) or impaired glucose tolerance (IGT). Insulin sensitivity index (SI) was similar in all four groups. However, a number of defects in insulin secretion were seen in the NDX and IGT groups, including reduced first-phase insulin secretory responses in intravenous glucose in relation to the degree of insulin resistance, and reduced normalized spectral power of insulin secretion during oscillatory glucose infusion. The latter finding demonstrates a decreased ability of the beta-cell to detect and respond to the successive increases and decreases in glucose and therefore to be entrained by the exogenous glucose infusion. The ability of a low-dose glucose infusion to prime the insulin secretory response to a subsequent glucose stimulus was normal in subjects with IGT but reduced or absent in subjects with overt NIDDM. These studies demonstrate that a number of alterations in beta-cell function are detectable in nondiabetic first-degree relatives of subjects with NIDDM with mild elevations in the 2-h postchallenge glucose level, and these abnormalities antedate the onset of overt hyperglycemia and clinical diabetes.

Hyperinsulinemia in offspring of non-insulin-dependent diabetes mellitus patients: the role played by abnormal clearance of insulin

Insulin resistance and hyperinsulinemia are often found in first-degree relatives of non-insulin-dependent diabetes mellitus (NIDDM) patients, and are currently considered a familial trait of this population at increased risk for diabetes. This study was undertaken to determine the role played by the metabolic clearance rate (MCR) of insulin (MCR-I) in the hyperinsulinism of these subjects. The proband population, consisting of 48 subjects aged 29.2 +/- 4.4 (mean +/- SD) years (18 men and 30 women; body mass index, 24.6 +/- 0.8 kg/m2; fasting plasma glucose, 4.54 +/- 0.37 mmol/L), was assigned in random order to four groups (I, II, III, and IV), each receiving a double insulin/glucose infusion (I, 0.025/2.0; II, 0.050/3.5; III, 0.100/6.0; and IV, 0.200/8.0 U/kg.h and mg/kg.min, respectively) to calculate MCR-I and MCR of glucose (MCR-G). Forty (14 men and 26 women) age- and body mass index-matched healthy individuals served as controls. All subjects had a normal response to an oral glucose tolerance test (75 g) according to World Health Organization criteria. Basal plasma insulin and C-peptide levels in probands were significantly (P < .05) higher than in controls in each study group; similarly, MCR-I was significantly (at least P < .05) lower in probands than in controls in all groups. MCR-G was significantly (at least P < .05) decreased in probands as compared with controls of groups III and IV.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolic defects in persistent impaired glucose tolerance are related to the family history of non-insulin-dependent diabetes mellitus

Recent studies have suggested that the family history of non-insulin-dependent diabetes mellitus (NIDDM) influences glucose metabolism in subjects with normal glucose tolerance (NGT). However, it is not known whether the family history of NIDDM influences glucose metabolism in impaired glucose tolerance (IGT). We studied in a well-characterized group the impact of family history of NIDDM (diabetes mellitus [DM]-positive) in subjects with IGT on glucose disposal rate (GDR) measured by the euglycemic hyperinsulinemic clamp technique combined with indirect calorimetry. We recruited subjects from our previous population-based studies, and verified their glucose tolerance status twice during the follow-up period of 1 year. Subjects with NGT (n = 10) and IGT (n = 18) were comparable with respect to age, sex distribution, body mass index, smoking habits, and hypertension. As a group, IGT subjects showed lower GDR than the NGT group (28.6 +/- 12.1 v 38.9 +/- 13.6 mumol/kg/min, P < .05). IGT DM-positive subjects showed a 40% lower GDR than the NGT group (P < .05) and a 29% lower GDR than IGT DM-negative subjects (P = NS). IGT DM-positive subjects had lower glucose oxidation (P = NS, P < .01), glucose nonoxidation (P = NS, P = .01), and suppression of lipid oxidation (P = NS, P < .05) during the hyperinsulinemic euglycemic clamp as compared with IGT DM-negative and NGT groups, respectively. In conclusion, in subjects with persistent IGT, the family history of NIDDM is associated with the reduced total whole-body, oxidative, and nonoxidative GDR.

Molecular genetics of diabetes mellitus

As a result of advances in technology, genome searches have been carried out for susceptibility genes for type 1 diabetes in humans and in the NOD mouse. These have shown that, in the NOD mouse, diabetes susceptibility is under the control of at least ten separate chromosomal loci. In the human, in addition to HLA and INS, two new susceptibility genes have been localized, IDDM4 on chromosome 11q and IDDM5 on 6q, demonstrating the polygenic nature of type 1 diabetes and the role of HLA as the major locus. Candidate genes at these loci are the subject of current investigation. Genetic and immunological markers of disease may be of value in screening the general population for individuals at risk of developing type 1 diabetes. The predictive power of different screening strategies should be tested in order to work out the potential value to the general population of preventive therapies that are now undergoing clinical trials in high risk 'pre-diabetics'. Type 2 diabetes is genetically heterogeneous, and, since 1992, two distinct genetic subtypes have been identified. The first is defined by mutations in the GCK gene, which cause up to 60% of cases of MODY. The second, designated MIDD (maternally inherited diabetes and deafness), is defined by mutation in the mitochondrial gene for tRNA(Leu(UUR)). MIDD patients are less obese than is usual for typical type 2 diabetes, may present in early adult life or occasionally in childhood and may have been diagnosed as having autoimmune type 1 diabetes, type 2 diabetes or MODY. Typically, patients with MIDD require insulin earlier than do type 2 diabetics without mitochondrial mutations. Genetically complex diseases, such as diabetes, hypertension, cancer and coronary heart disease, are common in most populations. The approaches to the genetic analysis of diabetes outlined in this review are likely to be useful to the genetic analysis of many of these disorders. Progress in this area will have important implications for public health strategies in the next decade and beyond.

Increased secretion of 32,33 split proinsulin after intravenous glucose in glucose-tolerant first-degree relatives of patients with non-insulin dependent diabetes of European, but not Asian, origin

OBJECTIVE

The aetiology of non-insulin dependent diabetes is unknown, but defective insulin secretion is a feature. The disease also has a strong genetic basis and first-degree relatives of patients have an increased risk of future diabetes. To investigate whether beta-cell dysfunction is an early feature of the disease, we studied insulin secretion in healthy first-degree relatives of patients with non-insulin dependent diabetes.

DESIGN

Each subject underwent a 1-hour intravenous glucose tolerance test (0.3 g/kg).

PATIENTS

Seventeen first-degree relatives of patients (10 of European and 7 of Asian (Indian subcontinent) origin) with normal glucose tolerance were compared with 17 matched control subjects with no family history of diabetes.

MEASUREMENTS

Plasma immunoreactive insulin (IRI) was measured by radioimmunoassay, and specific insulin, intact and 32,33 split proinsulin were measured by specific immunoradiometric assays (IRMA) for the 1st phase (0-10 minutes) and 2nd phase (10-60 minutes) responses. Glucose and intermediary metabolites were measured enzymatically.

RESULTS

Fasting concentrations of IRI, IRMA insulin, intact and 32,33 split proinsulin were similar in relatives and controls in each group. Fasting glucose levels were similar in European relatives and controls but lower in Asian relatives compared to their controls (mean +/- SE 4.9 +/- 0.2 vs 5.5 +/- 0.2 mmol/l, P < 0.05). Following intravenous glucose, European relatives had similar IRI and glucose levels to their controls. Secretion of 32,33 split proinsulin was increased in European relatives compared to their controls, significantly so for 2nd phase secretion (1st phase median (range): 71 (7-352) vs 55 (17-118) pmol/l min, NS; 2nd phase: 433 (115-1459) vs 234 (55-745) pmol/l min, P < 0.05). Secretion of IRMA insulin and intact proinsulin were similar in European relatives and controls (IRMA insulin: 1st phase 2757 (700-10,969) vs 2830 (632-4682) pmol/l min; 2nd phase 6387 (3006-15,865) vs 5284 (2060-18,605) pmol/l min; intact proinsulin: 1st phase 31 (13-113) vs 32 (16-72) pmol/l min; 2nd phase: 174 (87-737) vs 159 (97-298) pmol/l min). European relatives had a greater percentage of proinsulin-like molecules (intact + 32,33 split proinsulin) to total insulin (sum of IRMA insulin + intact + 32,33 split proinsulin) during the 2nd phase of secretion (9.1 (5.0-11.8) vs 5.9 (4.3-12.6)%, P < 0.05). In contrast, Asian relatives had similar secretion of IRI, IRMA insulin, intact and 32,33 split proinsulin to their controls. Glucose disappearance (KG) was similar in relatives and controls within each ethnic group (Europeans: relatives 725 +/- 101 vs controls 668 +/- 47/min; Asian: relatives 610 +/- 97 vs controls 783 +/- 936/min). Asian relatives had higher fasting circulating glycerol (65 +/- 7 vs 44 +/- 4 mumol/l, P < 0.05), non-esterified fatty acid (569 +/- 59 vs 375 +/- 64 mumol/l, P < 0.05) and 3-hydroxybutyrate levels (147 (44-187) vs 35 (21-57) mumol/l, P < 0.01) than their controls and this persisted following intravenous glucose. This difference was not observed in the European group.

CONCLUSION

First-degree relatives of European patients with NIDDM possess early signs of beta-cell dysfunction, with increased and disproportionate secretion of 32,33 split proinsulin after intravenous glucose, whilst glucose tolerance is still normal.

Insulin secretion, insulin action, and hepatic glucose production in identical twins discordant for non-insulin-dependent diabetes mellitus

12 identical twin pairs discordant for non-insulin-dependent diabetes mellitus (NIDDM) were studied for insulin sensitivity (euglycemic insulin clamp, 40 mU/m2 per min), hepatic glucose production (HGP, [3-3H]glucose infusion), and insulin secretion (oral glucose tolerance test and hyperglycemic [12 mM] clamp, including glucagon administration). Five of the nondiabetic twins had normal and seven had impaired glucose tolerance. 13 matched, healthy subjects without a family history of diabetes were included as control subjects. The NIDDM twins were more obese compared with their non-diabetic co-twins. The nondiabetic twins were insulin resistant and had a delayed insulin and C-peptide response during oral glucose tolerance tests compared with controls. Furthermore, the nondiabetic twins had a decreased first-phase insulin response and a decreased maximal insulin secretion capacity during hyperglycemic clamping and intravenous glucagon administration. Nondiabetic twins and controls had similar rates of HGP. Compared with both nondiabetic twins and controls, the NIDDM twins had an elevated basal rate of HGP, a further decreased insulin sensitivity, and a further impaired insulin secretion pattern as determined by all tests. In conclusion, defects of both in vivo insulin secretion and insulin action are present in non- and possibly prediabetic twins who possess the necessary NIDDM susceptibility genes. However, all defects of both insulin secretion and glucose metabolism are expressed quantitatively more severely in their identical co-twins with overt NIDDM.

The genetics and pathophysiology of type II and gestational diabetes

The development of both type II diabetes and gestational diabetes is probably governed by a complex and variable interaction of genes and environment. Molecular genetics has so far failed to identify discrete gene mutations accounting for metabolic changes in NIDDM. Both beta cell dysfunction and insulin resistance are operative in the manifestation of these disorders. Specific and sensitive immunoradiometric assays found fasting hyperproinsulinemia and first-phase hypoinsulinemia early in the natural history of the disorder. A lack of specificity of early radioimmunoassays for insulin resulted in measuring not only insulin but also proinsulins, leading to overestimation of insulin and misleading conclusions about its role in diabetes. The major causes of insulin resistance are the genetic deficiency of glycogen synthase activation, compounded by additional defects due to metabolic disorders, receptor downregulation, and glucose transporter abnormalities, all contributing to the impairment in muscle glucose uptake. The liver is also resistant to insulin in NIDDM, reflected in persistent hepatic glucose production despite hyperglycemia. Insulin resistance is present in many nondiabetics, but in itself is insufficient to cause type II diabetes. Gestational diabetes is closely related to NIDDM, and the combination of insulin resistance and impaired insulin secretion is of importance in its pathogenesis.

Serum lipoprotein levels and plasma concentrations of insulin, intact and 32, 33 split proinsulin in normoglycaemic relatives of patients with type 2 diabetes

Type 2 diabetes is associated with abnormal lipoprotein levels and altered plasma concentrations of insulin, intact and 32, 33 split proinsulin. To investigate whether these are early features of the disease, we studied 36 normoglycaemic first-degree relatives of patients with Type 2 diabetes (13 European, 15 of Asian (Indian-subcontinent), and 8 of Afro-Caribbean origin) and 36 control subjects with no family history of diabetes. Relatives and controls were matched for age (mean +/- S.E. 33 +/- 2 vs 34 +/- 2 years), body mass index (23.7 +/- 0.5 vs 23.7 +/- 0.6 kg m-2), sex (17 M, 19 F) and ethnic origin. After an overnight fast, blood was sampled for measurement of serum lipids, plasma glucose and insulin, intact and 32, 33 split proinsulin by specific immunoradiometric assays. Relatives and controls had similar fasting concentrations of glucose (5.0 +/- 0.1 vs 4.9 +/- 0.1 mmol l-1), total cholesterol (4.51 +/- 0.13 vs 4.54 +/- 0.17 mmol l-1), HDL-cholesterol (1.21 +/- 0.06 vs 1.10 +/- 0.05 mmol l-1), LDL-cholesterol (2.84 +/- 0.14 vs 2.96 +/- 0.14 mmol l-1) and triglyceride (median (range) 0.78 (0.44-2.45) vs 0.83 (0.41-4.03) mmol l-1). Fasting levels of insulin (50.4 (18.9-174.0) vs 51.6 (10.0-118.0) pmol l-1, intact proinsulin (2.8 (0.1-15.0) vs 2.1 (0.6-6.4) pmol l-1 and 32, 33 split proinsulin (2.0(0-23.7) vs 1.6 (0.3-6.0) pmol l-1) were not significantly different between relatives and controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin sensitivity in non-diabetic relatives of patients with non-insulin-dependent diabetes from two ethnic groups

OBJECTIVE

Non-insulin-dependent diabetes is a heterogeneous disorder, the basis of which may differ in different ethnic groups. In order to investigate early metabolic abnormalities occurring during the development of the condition we assessed insulin secretion and insulin action in subjects predisposed to the later development of non-insulin-dependent diabetes from two different ethnic groups.

DESIGN

Subjects were studied on two separate occasions by an oral glucose tolerance test and a short insulin tolerance test.

PATIENTS

Twenty-four glucose-tolerant first-degree relatives of patients with non-insulin-dependent diabetes (12 of European and 12 of Asian origin) were compared with 24 ethnically matched control subjects with no family history of diabetes.

MEASUREMENTS

Insulin, proinsulin, glucose and intermediary metabolites were measured during a 75-g oral glucose tolerance test. Insulin sensitivity was assessed using a 15-minute insulin tolerance test (0.05 units/kg).

RESULTS

Asian relatives compared to Asian controls had significantly higher fasting levels of immunoreactive insulin (83 +/- 17 vs 40 +/- 6 pmol/l, P < 0.05), which were not due to increased proinsulin. Blood glycerol concentrations were elevated (83 +/- 9 vs 51 +/- 4 mumol/l, P < 0.005), but fasting glucose and non-esterified fatty acid (NEFA) concentrations were similar. Relatives of European origin did not differ from their European controls in any of these measurements. The glucose response to oral glucose was similar in relatives and controls, irrespective of ethnic group. The insulin responses were non-significantly greater in relatives from both ethnic groups. Proinsulin levels were not significantly different. Asian relatives had higher circulating glycerol and NEFA levels after oral glucose than Asian controls, but these differences were not observed in the European group. Insulin sensitivity was reduced in the Asian relatives compared to their controls (183 +/- 7 vs 139 +/- 12 mumol/l/min, P < 0.01) but there was no difference in insulin sensitivity between the European relatives and European controls (167 +/- 11 vs 160 +/- 11 mumol/l/min).

CONCLUSIONS

First-degree relatives of non-insulin-dependent diabetic patients of Asian, but not of European, origin are insulin insensitive in terms of both glucose metabolism and lipolysis, and have true hyperinsulinaemia. This suggests that insulin insensitivity may be an early abnormality in the development of non-insulin-dependent diabetes in the Asian population.

Lack of control by glucose of ultradian insulin secretory oscillations in impaired glucose tolerance and in non-insulin-dependent diabetes mellitus

Normal subjects demonstrate the presence of ultradian oscillations (period 80-150 min) in insulin secretion rate (ISR) tightly coupled to glucose oscillations of similar period. These oscillations appear to be a function of the feedback loop linking glucose and insulin. The present study was undertaken to determine whether the control by glucose of the ultradian oscillations in insulin secretion is altered in impaired glucose tolerance IGT and in non-insulin-dependent diabetes mellitus (NIDDM). Patients with NIDDM (n = 7), IGT (n = 4), and matched nondiabetic controls (n = 5) were studied under three separate protocols that involved administration of glucose at either a constant rate of 6 mg/kg per min for 28 h or in one of two oscillatory patterns at the same overall mean rate. The amplitude of the oscillations was 33% above and below the mean infusion rate, and their respective periods were 144 min (slow oscillatory infusion) or 96 min (rapid oscillatory infusion). Insulin, C-peptide, and glucose were sampled at 10-min intervals during the last 24 h of each study. ISRs were calculated by deconvolution of C-peptide levels. Analysis of the data showed that (a) the tight temporal coupling between glucose and ISR in the nondiabetic controls was impaired in the IGT and NIDDM groups as demonstrated by pulse analysis, cross-correlation analysis, and spectral analysis; (b) the absolute amplitude of the ISR pulses progressively declined with the transition from obesity to IGT to NIDDM; and (c) the absolute amplitude of the ISR oscillations failed to increase appropriately with increasing absolute amplitude of glucose oscillations in the IGT and NIDDM subjects compared with the control group. In conclusion, the present study demonstrates that important dynamic properties of the feedback loop linking insulin secretion and glucose are disrupted not only in established NIDDM but also in conditions where glucose tolerance is only minimally impaired. Further studies are needed to determine how early in the course of beta-cell dysfunction this lack of control by glucose of the ultradian oscillations in insulin secretion occurs and to define more precisely if this phenomenon plays a pathogenetic role in the onset of hyperglycemia in genetically susceptible individuals.

Decreased tyrosine kinase activity in partially purified insulin receptors from muscle of young, non-obese first degree relatives of patients with type 2 (non-insulin-dependent) diabetes mellitus

Recently, we demonstrated insulin resistance due to reduced glucose storage in young relatives of Type 2 diabetic patients. To investigate whether this was associated with a defective insulin receptor kinase, we studied ten of these young (27 +/- 1 years old) non-obese glucose tolerant first degree relatives of patients with Type 2 diabetes and eight matched control subjects with no family history of diabetes. Insulin sensitivity was assessed by a hyperinsulinaemic, euglycaemic clamp. Insulin receptors were partially purified from muscle biopsies obtained in the basal and the insulin-stimulated state during the clamp. Insulin binding capacity was decreased by 28% in the relatives (p < 0.05) in the basal biopsy. Tyrosine kinase activity in the receptor preparation was decreased by 50% in both basal and insulin-stimulated biopsies from the relatives. After stimulation with insulin "in vitro", kinase activity was reduced in the relatives in basal (p < 0.005) and insulin-stimulated (p < 0.01) biopsies and also when expressed per insulin binding capacity (p approximately 0.05). Insulin stimulation of non-oxidative glucose metabolism correlated with "in vitro" insulin-stimulated tyrosine kinase activity (r = 0.61, p < 0.01) and also when expressed per binding capacity (r = 0.53, p < 0.025). We suggest that the marked defect in tyrosine kinase activity in partially purified insulin receptors from skeletal muscle is an early event in the development of insulin resistance and contributes to the pathophysiology of Type 2 diabetes.

Type II diabetes: search for primary defects

Type 2 diabetes is a familial disease, but recent analysis of nuclear families indicates it is unlikely to be due to a single dominant gene with high penetrance and that it could be polygenic. Insulin resistance is a major feature, with obesity being a major determinant. Beta cell deficiency is a sine qua non of Type 2 diabetes. It is possible that obesity, insulin resistance independent from obesity and impaired beta cell function are independently inherited factors. None of these can be said to be 'primary' as diabetes usually results from the interaction of several geometric and environmental factors. This makes linkage analysis of Type 2 diabetes of uncertain benefit, since heterogeneity can occur within a pedigree. The only mutation so far discovered is of glucokinase producing maturity-onset diabetes of the young, that has a clearly defined and unusual phenotype. Identification of genes that cause classical Type 2 diabetes is likely to come from population association studies, molecular scanning techniques and direct sequencing of candidate genes rather than linkage analysis.

Ethnic differences in insulin secretion in women at risk of future diabetes

The plasma glucose and insulin responses to oral glucose were studied in 44 women who had previously had gestational diabetes, but had reverted to normal glucose tolerance. Twenty were White, 14 Black, and 10 Asian. A group of race-, age- and weight-matched controls was also studied. Fasting values of glucose and insulin did not differ significantly between the study group and controls. During the 2 h 75-g OGTT the White and Black previously gestational-diabetic women had similar plasma glucose values to their controls, while the Asian previously gestational-diabetic women had significantly higher glucose values at 30 min (9.2 +/- 0.6 (+/- SE) vs 7.1 +/- 0.3 mmol l-1, p less than 0.02) and at 60 min (8.6 +/- 0.8 vs 6.2 +/- 0.4 mmol l-1, p less than 0.02). Compared with their race-matched controls, the White previously gestational-diabetic women had significantly lower insulin values at 60 min (median 41 range 2-91) vs 56 (15-118) mU l-1, p less than 0.05), and the Black previously gestational-diabetic women had lower values at both 30 min (17 (4-116) vs 53 (22-197) mU l-1) and 60 min (36 (4-148) vs 99 (12-169) mU l-1, p less than 0.05). The insulin values were similar during the OGTT in the Asian previously gestational-diabetic women and their controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Abnormalities of intermediary metabolism following a gestational diabetic pregnancy

OBJECTIVE

The aim of this study was to compare intermediary metabolism in glucose tolerant women with previous gestational diabetes and control women without a history of gestational diabetes.

SUBJECTS

Fifteen women with previous gestational diabetes and 15 controls individually matched for race, age and body mass index were included. Only subjects with normal glucose tolerance were included in this study.

METHODS

Plasma glycerol, 3-OH butyrate, non-esterified fatty acids (NEFA), glucose and insulin were measured fasting and following a 75 g oral glucose load.

RESULTS

The women with previous gestational diabetes and their matched controls were of similar racial origin, age and body mass index. There was no difference between those with previous gestational diabetes and controls in fasting glycerol, 3-OH butyrate, NEFA, glucose or insulin concentrations. Following the oral glucose load, glycerol, 3-OH butyrate and NEFA concentrations fell in both groups. However, compared with controls at 120 minutes, those with previous gestational diabetes had significantly higher concentrations of glycerol (median 57, range 24-216 vs 27, range 8-89 mumols/l, P less than 0.005) and 3-OH butyrate (9, range 1-18 vs 5, range 2-11 mumols/l, P less than 0.01). NEFA concentrations were similar in the two groups. Despite similar glucose concentrations during the oral glucose tolerance test the insulin response during the first 60 minutes following oral glucose was significantly reduced in the subjects with previous gestational diabetes when compared with controls (insulin area, 0-60 minutes; 2172, range 788-4767 vs 2830, range 996-4784 pmol min/l, P less than 0.05).

CONCLUSIONS

Women with a previous history of gestational diabetes, despite having normal glucose tolerance, have defective insulin release with resultant abnormalities of intermediary metabolism.

Glucose tolerance and insulin response in parents of patients with insulin-dependent and juvenile-onset non-insulin-dependent diabetes mellitus

Glucose tolerance and insulin response were examined using a 100 g oral glucose tolerance test (OGTT) in 108 parents of 23 patients with insulin-dependent (IDDM) and 31 patients with non-insulin-dependent diabetes mellitus (NIDDM), whose age of onset of diabetes was less than 35 years. Thirty-two age-matched healthy volunteers without a family history of diabetes were also examined as a control group. Diabetes and impaired glucose tolerance (IGT) were significantly more frequent in parents of NIDDM (diabetes 34%, IGT 27%) than in parents of IDDM (diabetes 7%, IGT 13%) (P less than 0.001). At least one parent had diabetes or IGT in 30% of IDDM and 84% of NIDDM patients (P less than 0.001), and both parents had diabetes or IGT in 9% of IDDM and 39% of NIDDM patients (P less than 0.02). Even in cases with 'normal' glucose tolerance, the mean plasma glucose was higher in parents of NIDDM than in control subjects, suggesting a high prevalence of abnormal glucose tolerance including the marginal degree of abnormality in the families of NIDDM. The early phase insulin response was decreased more among parents of NIDDM with the greater impairment of glucose tolerance. However, among those with 'normal' glucose tolerance, early phase insulin response did not differ between parents of IDDM and NIDDM, and control subjects. The results confirmed a stronger familial background in NIDDM patients of younger onset than in IDDM. The different patterns of glucose tolerance among two parents of young-onset NIDDM patients suggest heterogeneity of the mode of inheritance of NIDDM among families.

Genetics of non-insulin dependent diabetes mellitus in 1990

Family studies suggest a strong genetic component in the aetiology of non-insulin dependent diabetes (NIDDM), with evidence for a major gene of co-dominant or dominant effect. A gene-dosage effect, whereby diabetes develops earlier in people with two susceptibility genes than in those with one susceptibility gene is likely. The search for the diabetes gene has led to the cloning and characterization of many genes involved in controlling glucose homeostasis. These include the insulin, insulin receptor, glucose transporter, amylin and glucokinase genes. Molecular techniques have permitted rapid screening of these genes in NIDDM patients and controls. There is now a rather contradictory genetic literature for NIDDM, with weak disease associations reported and refuted for most candidate genes. However, pedigree analyses and DNA sequencing of available candidate genes and their regulatory regions have failed to implicate any of these in the common form of diabetes, NIDDM. Methodical application of random clones in well-defined NIDDM families may be the strategy of choice in finding the NIDDM genes, given the wide range of genes potentially involved in the glucose and lipoprotein metabolic disturbances seen in NIDDM.

Genetics of non-insulin dependent diabetes mellitus

It is probable that NIDDM has a multifactorial origin in which environmental factors hasten the progression of the disease in genetically predisposed individuals. The importance of the genetic contribution to NIDDM has been established by the study of certain inbred populations, the almost 100% concordance of disease in monozygotic twins and by familial clustering. However, progress in identifying specific genetic factors involved in NIDDM has been slow and no consistent evidence has emerged supporting a major aetiological role for any of the genes so far studied. This may be due in part to methodological problems encountered in the identification of such disease susceptibility genes.

Non-linkage of the islet amyloid polypeptide gene with type 2 (non-insulin-dependent) diabetes mellitus

Type 2 (non-insulin-dependent) diabetes is associated with the deposition of islet amyloid. The major formative peptide, islet amyloid polypeptide, has recently been characterised and an abnormality of the structure or expression of this gene is a possible candidate for the inherited component of Type 2 diabetes. A restriction fragment length polymorphism of the gene has been identified with Pvu II. To study the relationship between the islet amyloid polypeptide gene and Type 2 diabetes, two distinct genetic approaches have been undertaken. Firstly, non-linkage has been demonstrated in four pedigrees, with four normoglycaemic first degree relatives having an allele associated with diabetes in other family members, and one affected relative not having the putatively associated allele. The LOD score taking age-related penetrance into account was -1.68, making linkage unlikely (p = 0.02). Secondly, in a population-based restriction fragment length polymorphism survey, no linkage disequilibrium of the alleles was found between a population of unrelated Caucasian subjects with Type 2 diabetes and a normal population. A mutation in or near the islet amyloid polypeptide gene is thus unlikely to be a common cause of Type 2 diabetes.

Impaired glucose tolerance precedes but does not predict insulin-dependent diabetes mellitus: a study of identical twins

Non-diabetic identical twins of insulin-dependent diabetic patients were studied within five years of the diagnosis of their index twin in order to determine whether changes in intermediary metabolism precede the onset of insulin-dependent diabetes mellitus. Two studies were performed: a cross-sectional study of 12 non-diabetic twins and a prospective study of a separate group of 41 non-diabetic twins. Of the 12 twins tested in the cross-sectional study six developed insulin-dependent diabetes and six did not; the six who developed diabetes were given an oral glucose load a mean of 10 months before diagnosis; they then had normal fasting blood glucose levels but worse glucose tolerance than control subjects (120 min post-load (mean +/- SD) blood glucose 8.5 +/- 3.5 vs 4.9 +/- 0.9 mmol/l respectively, p less than 0.05). However, blood lactate, pyruvate, alanine, glycerol, 3-hydroxybutyrate and serum insulin levels were similar. In contrast, the six twins in this cross-sectional study who did not develop diabetes and are now unlikely to do so, as a group, had no significant changes compared with the control subjects though one had impaired glucose tolerance. To determine the predictive value of impaired glucose tolerance a separate group of 41 non-diabetic twins was studied prospectively for 8 to 22 years having a total of 147 glucose tolerance tests in this period; in this group six developed diabetes. Eight of the 41 had impaired glucose tolerance; impaired glucose tolerance was found in four of the six who developed diabetes as compared with only four of the 35 who did not (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

[Intolerance to carbohydrates: the seven questions]

The borderline between diabetes and intolerance to carbohydrates has been drawn on the basis of prospective studies which determined a glycaemic threshold marking the risk for microangiopathy. On the other hand, the borderline between intolerance to carbohydrates and normal glucose tolerance remains arbitrary: 25% for subjects who are intolerant to carbohydrates return to normal glucose tolerance within 10 years. This is due to the fact that intolerance to carbohydrates is a heterogeneous entity which should be dismembered according to the severity of insulin deficiency and to the degree of insulin resistance. Alteration of insulin secretion is perhaps the most specific marker of susceptibility to non insulin dependent diabetes, but insulin resistance is certainly the principal factor exhausting insulin secretion and leading to non insulin dependent diabetes. Insulin resistance and the hyperinsulinism it creates seem to facilitate atherogenesis, even when glucose tolerance is still normal, so that the oral glucose tolerance test is not only poorly reproducible but loses a great deal of its value in the early detection of vascular risk. Measurements of fasting and post-prandial glucose levels and of A1C haemoglobin, cholesterol, triglyceride, and HDL cholesterol levels usually make it possible to classify subjects into one of the three following categories: (1) no risk of macro- or microangiopathy; (2) diabetes with a risk of macro- or microangiopathy; (3) intolerance to glucose with risk of atherogenesis but no risk of microangiopathy. The oral glucose tolerance test probably remains useful within a small set of values that are either very slightly above normal or dissociated. Measuring blood insulin levels might be a better way of assessing the risk of atherogenesis, but the clinical use of this test requires evaluation.

Islet function and insulin sensitivity in the non-diabetic offspring of conjugal type 2 diabetic patients

To determine whether the genetic predisposition towards Type 2 diabetes was associated with a defect in either islet-cell function or insulin action, 12 non-diabetic offspring each of whose parents both had Type 2 diabetes were studied, together with 12 control subjects matched for age, sex, and weight. Fasting plasma glucose was higher in the offspring (5.5 +/- 0.1 mmol l-1 (mean +/- SE)) than in the matched controls (5.1 +/- 0.1 mmol l-1) (p less than 0.05). Using an IVGTT insulin sensitivity was not significantly lower in the offspring compared with their controls (3.1 +/- 0.5 vs 3.8 +/- 1.0 min-1 mU-1 l 10(-4)). There was no significant difference in any of the measures of insulin secretion (first- and second-phase response to IV glucose, slope of glucose potentiation, and maximal glucose regulated insulin secretory capacity). Glucagon secretion measured before and after a stimulus of IV arginine at varying plasma glucose concentrations was virtually identical in the offspring and their controls. Among a total of 28 non-diabetic subjects of differing body-weights there was a significant inverse relationship between insulin sensitivity and insulin secretion. When adjusted for their generally lower insulin sensitivity, maximal insulin secretory capacity was reduced in the offspring (p = 0.038, one-tailed t-test). The results suggest that the genetic predisposition to Type 2 diabetes is not associated in young adults with any major pre-morbid impairment in insulin secretion or insulin action but the relationship between the two may be abnormal. Islet A-cell function appears to be normal.

Metabolic abnormalities in obese patients with impaired glucose tolerance

It is not clear whether the glucose tolerance test diagnosis of Impaired Glucose Tolerance introduced in the recent revisions of diagnostic criteria is associated with abnormalities of intermediary metabolism other than glucose. Intermediary metabolite concentrations have therefore been studied fasting and in response to oral glucose in 35 patients referred with morbid obesity accompanied by either normal glucose tolerance (18 patients) or Impaired Glucose Tolerance (17 patients). When fasting obese patients with Impaired Glucose Tolerance had significantly higher blood total ketone body concentrations, 0.24 (0.19-0.30) vs 0.14 (0.12-0.16) mmol l-1 (antilog of mean-SE to mean + SE) (p less than 0.05), and lower blood glycerol concentrations, 0.14 +/- 0.01 vs 0.18 +/- 0.01 mmol l-1 (mean +/- SE) (p less than 0.05), than obese patients with normal glucose tolerance. There were no significant differences in fasting insulin, 16 (15-18) vs 14 (12-15) mU l-1, or glucose levels, 5.3 +/- 0.2 vs 5.1 +/- 0.2 mmol l-1. After oral glucose there was an exaggerated rise in glucose, insulin, lactate, and pyruvate in patients with Impaired Glucose Tolerance.

Early metabolic defects in persons at increased risk for non-insulin-dependent diabetes mellitus

To identify early metabolic abnormalities in non-insulin-dependent diabetes mellitus (NIDDM), we measured sensitivity to insulin and insulin secretion in 26 first-degree relatives of patients with NIDDM and compared these subjects both with 14 healthy control subjects with no family history of NIDDM and with 19 patients with NIDDM. The euglycemic insulin-clamp technique, indirect calorimetry, and infusion of [3-3H]glucose were used to assess insulin sensitivity. Total-body glucose metabolism was impaired in the first-degree relatives as compared with the controls (P less than 0.01). The defect in glucose metabolism was almost completely accounted for by a defect in nonoxidative glucose metabolism (primarily the storage of glucose as glycogen). The relatives with normal rates of metabolism (mean +/- SEM, 1.81 +/- 0.27 mg per kilogram of body weight per minute) and impaired rates (1.40 +/- 0.22 mg per kilogram per minute) in oral glucose-tolerance tests had the same degree of impairment in glucose storage as compared with healthy control subjects (3.76 +/- 0.55 mg per kilogram per minute; P less than 0.01 for both comparisons). During hyperglycemic clamping, first-phase insulin secretion was lacking in patients with NIDDM (P less than 0.01) and severely impaired in their relatives with impaired glucose tolerance (P less than 0.05) as compared with control subjects; insulin secretion was normal in the relatives with normal glucose tolerance. We conclude that impaired glucose metabolism is common in the first-degree relatives of patients with NIDDM, despite their normal results on oral glucose-tolerance tests. Both insulin resistance and impaired insulin secretion are necessary for the development of impaired glucose tolerance in these subjects.

On the role of vitamin D binding globulin in glucose homeostasis: results from the San Luis Valley Diabetes Study

Several studies have reported association between noninsulin-dependent diabetes mellitus and GC, the vitamin D binding protein of human plasma, with the GC 1 allele in significant excess among diabetics. Additionally, there is a considerable body of animal data suggesting that vitamin D has a significant impact on insulin secretion. Examination of the insulin levels in Dogrib Indians showed that the lowest levels of fasting insulin were associated with the GC IF-IF genotype. The present study examined levels of glucose, C-peptide, and insulin at fasting and 1 hr and 2 hr following a 75 g oral glucose challenge, in a population of Hispanic-Americans and Anglos in the San Luis Valley of southern Colorado. The sample comprised a total of 468 individuals with normal glucose tolerance. Of these, 289 were Anglos and 179 were Hispanic-Americans. An analysis of covariance was performed to determine the effect of the GC genotypes on mean levels of the primary variables--glucose, C-peptide, and insulin--and a secondary variable--insulinogenic index adjusting for the covariates age, body mass index (BMI), gender, and ethnicity. The analyses revealed that there is a significant difference in mean levels of glucose at fasting (F value = 2.46; P = 0.033) among the GC genotypes in the sample. Additionally, the differences in mean levels of 1 hr postprandial glucose among the GC genotypes although not significant at a 5% level, were significant at the 10% level. No other significant phenotypic effects were observed. These analyses are not in concordance with the results of an earlier study, where lower fasting insulin was associated with the GC 1F-1F genotype.

Risk factors for type 2 (non-insulin-dependent) diabetes mellitus. Thirteen and one-half years of follow-up of the participants in a study of Swedish men born in 1913

This report presents data on antecedents of Type 2 (non-insulin-dependent) diabetes mellitus in a homogeneous sample of randomly selected 54-year-old men from an urban Swedish population with a diabetes incidence of 6.1% during 13.5 years of follow-up. The increased risk leading to diabetes for those in the top quintile compared to the lowest quintile of the distribution of statistically significant risk factors were: body mass index = 21.7, triglycerides = 13.5, waist-to-hip circumference ratio = 9.6, diastolic blood pressure = 6.7, uric acid = 5.8, glutamic pyruvic transaminase = 3.9, bilirubin = 3.2, blood glucose = 2.7, lactate = 2.4 and glutamic oxaloacetic transaminase = 2.0. Those with a positive family history of diabetes had 2.4-fold higher risk for developing diabetes than those without such a history. In a multivariate analysis glutamic pyruvic transaminase, blood glucose, body mass index, bilirubin, systolic blood pressure, uric acid and a family history of diabetes were all significantly associated with the development of diabetes. Our study demonstrates the great importance of adiposity and body fat distribution for the risk of diabetes. A number of established risk factors for coronary heart disease are risk factors for diabetes as well. Disturbed liver function and increased levels of lactate are early risk factors for diabetes - presumably indicators of the presence of impaired glucose tolerance and/or hyperinsulinaemia.

Pathogenesis of NIDDM--a disease of deficient insulin secretion

Type 2 diabetes is a familial disease and studies of both Caucasian and Japanese families have raised the possibility that a major susceptibility gene is involved. The majority of patients have both beta cell dysfunction and impaired insulin sensitivity but studies of relatives of Type 2 diabetic patients suggest that beta cell dysfunction is an early feature of the disease. Impaired insulin sensitivity, from acromegaly, Cushing's disease or steroid therapy, induces diabetes only in a small proportion of the population, and they may be those who have an inherited cell defect. We postulate that a single beta cell defect gene, on its own, may be insufficient to cause overt diabetes and would lead to life-long glucose intolerance unless associated with other defects such as impaired insulin sensitivity. The nature of such a postulated beta cell defect is uncertain. Whilst it has been reported to be specific to glucose, and not to non-glucose stimuli, this feature may be secondary to hyperglycaemia. The occurrence of islet amyloid in 70-90% of Type 2 diabetic patients, and rarely in the normal population, raises the possibility that amyloid deposition causing disruption of the islet is a factor which might affect beta cell function. Amyloid formation may be a primary abnormality or could be secondary to beta cell dysfunction induced by hyperglycaemia. A major susceptibility gene might predispose a proportion, perhaps 10-15%, of a Caucasian population towards diabetes. The subsequent development of diabetes in a particular patient is likely to depend on many factors including other genetic factors, a sedentary life style and obesity. In different populations different genetic influences may operate, including abnormalities of insulin receptor genes and glucose transporter genes, which may allow a beta cell abnormality to become expressed clinically.