Maturity-onset diabetes of the young

Maturity-onset diabetes of the young (MODY) is a subtype of noninsulin dependent diabetes mellitus (NIDDM). It is characterized by an early age of onset and autosomal dominant mode of inheritance. These features and the availability of large multigenerational pedigrees make MODY useful for genetic studies of diabetes. In the large, 5-generational RW pedigree, MODY is tightly linked to genetic markers on chromosome 20q. Affected subjects in this family show abnormalities of carbohydrate metabolism varying from impaired glucose tolerance (IGT) to severe diabetes. Approximately 30% of diabetic subjects become insulin requiring and vascular complications occur. MODY is also linked to the glucokinase gene on chromosome 7p and many different mutations associated with MODY have been identified in this gene. MODY due to mutations in the glucokinase gene is a relatively mild form of diabetes with mild fasting hyperglycemia and IGT in the majority. It is rarely insulin requiring and rarely has vascular complications. Clinical studies indicate that the genetic or primary defect in MODY is characterized by deranged and deficient insulin secretion and not by insulin resistance and that there are quantitative and qualitative differences in insulin secretory defects which differentiate subjects with MODY due to glucokinase mutations from those with mutations in the gene on chromosome 20q. These differences correlate with the severity of diabetes between these two genetic forms of MODY.     

线粒体基因突变与糖尿病的相关性研究综述

糖尿病是以出现慢性高血糖为特征的。遗传因素在出现这种紊乱中可能占有重要角色。有研究表明核基因突变对胰岛素的分泌有影响,此外,在有些家庭中,糖尿病出现母系遗传,很可能是因为线粒体基因突变导致母系遗传。事实上,线粒体基因可能可以导致糖尿病,因为线粒体的氧化磷酸化在β细胞中血糖刺激胰岛素的分泌占有重要作用。已有大量研究表明线粒体基因突变与糖尿病的发病有关,在糖尿病患者的线粒体基因中发现大量的新发突变体,并且证实这些新发突变与糖尿病以及糖尿病并发症的发病有相关性。本文主要综述国内外近五年有关线粒体基因突变与糖尿病相关性的研究论文,从而探索线粒体基因突变与糖尿病的相关性,为糖尿病的发病机制提供新的见解。     

Type II diabetes of early onset: a distinct clinical and genetic syndrome?

The inheritance of non-insulin-dependent (type II) diabetes was studied by a continuous infusion of glucose test in all available first degree relatives of 48 diabetic probands of various ages and with differing severity of disease. In an initial study of 38 type II diabetic subjects and their first degree relatives six islet cell antibody negative patients with early onset disease (aged 25-40 at diagnosis) were found to have a particularly high familial prevalence of diabetes or glucose intolerance. Nine of 10 parents available for study either had type II diabetes or were glucose intolerant. A high prevalence of diabetes or glucose intolerance was also found in their siblings (11/16;69%). In a second study of the families of a further 10 young diabetic probands (presenting age 25-40) whose islet cell antibody state was unknown a similar high prevalence of diabetes or glucose intolerance was found among parents of the five islet cell antibody negative probands (8/9; 89%) but not among parents of the five islet cell antibody positive probands (3/8;38%). Islet cell antibody negative diabetics with early onset type II disease may have inherited a diabetogenic gene or genes from both parents. They commonly need insulin to maintain adequate glycaemic control and may develop severe diabetic complications. Early onset type II diabetes may represent a syndrome in which characteristic pedigrees, clinical severity, and absence of islet autoimmunity make it distinct from either type I diabetes, maturity onset diabetes of the young, or late onset type II diabetes.     

In vivo mutagenesis of the insulin receptor

Mice bearing targeted gene mutations that affect insulin receptor (Insr) function have contributed important new information on the pathogenesis of type 2 diabetes. Whereas complete Insr ablation is lethal, conditional mutagenesis in selected tissues has more limited consequences on metabolism. Studies of mice with tissue-specific ablation of Insr have indicated that both canonical (e.g. muscle and adipose tissue) and noncanonical (e.g. liver, pancreatic beta-cells, and brain) insulin target tissues can contribute to insulin resistance, albeit in a pathogenically distinct fashion. Furthermore, experimental crosses of Insr mutants with mice carrying mutations that affect insulin action at more distal steps of the insulin signaling cascade have begun to unravel the genetics of type 2 diabetes. These studies are consistent with an oligogenic inheritance, in which synergistic interactions among few alleles may account for the genetic susceptibility to diabetes. In addition to mutant alleles conferring an increased risk of diabetes, these studies have uncovered mutations that protect against insulin resistance, thus providing proof-of-principle for the notion that certain alleles may confer resistance to diabetes.     

Loss-of-Function Mutations in APPL1 in Familial Diabetes Mellitus

Diabetes mellitus is a highly heterogeneous disorder encompassing several distinct forms with different clinical manifestations including a wide spectrum of age at onset. Despite many advances, the causal genetic defect remains unknown for many subtypes of the disease, including some of those forms with an apparent Mendelian mode of inheritance. Here we report two loss-of-function mutations (c.1655T>A [p.Leu552^∗] and c.280G>A [p.Asp94Asn]) in the gene for the Adaptor Protein, Phosphotyrosine Interaction, PH domain, and leucine zipper containing 1 (APPL1) that were identified by means of whole-exome sequencing in two large families with a high prevalence of diabetes not due to mutations in known genes involved in maturity onset diabetes of the young (MODY). APPL1 binds to AKT2, a key molecule in the insulin signaling pathway, thereby enhancing insulin-induced AKT2 activation and downstream signaling leading to insulin action and secretion. Both mutations cause APPL1 loss of function. The p.Leu552^∗ alteration totally abolishes APPL1 protein expression in HepG2 transfected cells and the p.Asp94Asn alteration causes significant reduction in the enhancement of the insulin-stimulated AKT2 and GSK3β phosphorylation that is observed after wild-type APPL1 transfection. These findings—linking APPL1 mutations to familial forms of diabetes—reaffirm the critical role of APPL1 in glucose homeostasis.     

Thymus‐specific deletion of insulin induces autoimmune diabetes

Insulin expression in the thymus has been implicated in regulating the negative selection of autoreactive T cells and in mediating the central immune tolerance towards pancreatic β‐cells. To further explore the function of this ectopic insulin expression, we knocked out the mouse Ins2 gene specifically in the Aire‐expressing medullary thymic epithelial cells (mTECs), without affecting its expression in the β‐cells. When further crossed to the Ins1 knockout background, both male and female pups (designated as ID‐TEC mice for insulin‐deleted mTEC) developed diabetes spontaneously around 3 weeks after birth. β‐cell‐specific autoimmune destruction was observed, as well as islet‐specific T cell infiltration. The presence of insulin‐specific effector T cells was shown using ELISPOT assays and adoptive T cell transfer experiments. Results from thymus transplantation experiments proved further that depletion of Ins2 expression in mTECs was sufficient to break central tolerance and induce anti‐insulin autoimmunity. Our observations may explain the rare cases of type 1 diabetes onset in very young children carrying diabetes‐resistant HLA class II alleles. ID‐TEC mice could serve as a new model for studying this pathology.     

Insulin resistance does not influence gene expression in skeletal muscle

Insulin resistance is commonly observed in patients prior to the development of type 2 diabetes and may predict the onset of the disease. We tested the hypothesis that impairment in insulin stimulated glucose-disposal in insulin resistant patients would be reflected in the gene expression profile of skeletal muscle. We performed gene expression profiling on skeletal muscle of insulin resistant and insulin sensitive subjects using microarrays. Microarray analysis of 19,000 genes in skeletal muscle did not display a significant difference between insulin resistant and insulin sensitive muscle. This was confirmed with real-time PCR. Our results suggest that insulin resistance is not reflected by changes in the gene expression profile in skeletal muscle.     

Effect of media conditioned by concanavalin A activated spleen cells on pancreatic islet cells

The effect of media conditioned by concanavalin A-activated spleen cells (C-sup) on insulin release and its islet cell cytotoxicity were studied. In a functional study, C-sup significantly inhibited both basal insulin release and glucose-stimulated insulin release. Morphologically, C-sup had a destructive effect on isolated islets after 72 h incubation. Islet cell cytotoxicity was shown by lactate dehydrogenase (LDH) release assay after 5 days incubation with C-sup in a dose-dependent manner. These results suggest that acceleration of the onset of diabetes in young diabetes prone (DP) Bio-Breeding/Worcester (BB/W) rats following the injection of C-sup may depend on the suppressive and cytotoxic effects of C-sup on pancreatic islet cells.     

Chronic β2 adrenergic agonist, but not exercise, improves glucose handling in older type 2 diabetic mice

Insulin resistant type 2 diabetes mellitus in the obese elderly has become a worldwide epidemic. While exercise can prevent the onset of diabetes in young subjects its role in older diabetic people is less clear. Exercise stimulates the release of the β(2)-agonist epinephrine more in the young. Although epinephrine and β(2)-agonist drugs cause acute insulin resistance, their chronic effect on insulin sensitivity is unclear. We fed C57BL/6 mice a high fat diet to induce diabetes. These overweight animals became very insulin resistant. Exhaustive treadmill exercise 5 days a week for 8 weeks had no effect on their diabetes, nor did the β(2)-blocking drug ICI 118551. In contrast, exercise combined with the β(2)-agonist salbutamol (albuterol) had a beneficial effect on both glucose tolerance and insulin sensitivity after 4 and 8 weeks of exercise. The effect was durable and persisted 5 weeks after exercise and β(2)-agonist had stopped. To test whether β(2)-agonist alone was effective, the animals that had received β(2)-blockade were then given β(2)-agonist. Their response to a glucose challenge improved but their response to insulin was not significantly altered. The β(2)-agonists are commonly used to treat asthma and asthmatics have an increased incidence of obesity and type 2 diabetes. Although β(2)-agonists cause acute hyperglycemia, chronic treatment improves insulin sensitivity, probably by improving muscle glucose uptake.     

HLA-linked genes and islet-cell antibodies in diabetes mellitus.

In a random series of 139 insulin-dependent diabetics aged 30 or under at the onset of disease islet-cell antibody (ICA) was detected in 33 cases (24%). In 27 patients who had had diabetes for less than one year 16 (59%) had ICA. Only one out of 51 patients with maturity onset diabetes who were not dependent on insulin were positive for ICA. Four out of 19 patients with late onset insulin-dependent diabetes had ICA. There was no association between the presence of ICA and any particular HLA phenotype. Within families containing two or more HLA haploidentical siblings with juvenile onset diabetes ICA was a variable finding both in its occurrence and in its relation to the duration of disease. A possible mode of action for the HLA-linked gene may be to permit a rapid immunological destructive process, possibly associated with viral infection.     

Genetic susceptibility in diabetes mellitus: analysis of the HLA association.

Two hundred and eighty-eight patients with insulin-dependent diabetes w,o were aged 30 or under at onset and 150 patients with late-onset diabetes, 50 of them dependent on insulin and 100 not dependent on insulin, were HLA-typed. There was a significant positive association between the young-onset insulin-dependent patients and HLA-B8, BW15, and B18 and a significant negative association with B7. These data were combined with those from two other centres. There was a significant concordance for the distribution of all the HLA antigens among these three series, producing evidence in favour of an HLA-linked diabetogenic gene (or genes) having a major role in all cases of juvenile-onset insulin-dependent diabetes. There was a positive association between late-onset insulin-dependent diabetes and B8, but no association between non-insulin-dependent diabetes and the HLA system. This provides further evidence for the existence of different pathogenetic mechanisms in the two major clinical forms of diabetes mellitus.     

Type I (insulin dependent) diabetes: a disease of slow clinical onset?

Type I (insulin dependent) diabetes is usually believed to present acutely and it is assumed that metabolic decompensation is sudden. In a prospective family study, however, 10 of 13 subjects developing the disease showed progressive or intermittent development of hyperglycaemia over many months and the others had non-specific symptoms over a long period. All were first degree relatives of a child with type I diabetes; 10 were siblings (aged 5-24) and three were parents (aged 45-58). All possessed HLA-DR4 or DR3, or both, and all but two had been positive for islet cell antibodies for six to 86 months before diagnosis. Ten had non-specific symptoms for two to 14 months before the onset of thirst and polyuria; one remained asymptomatic even when insulin became necessary. Six subjects had an oral glucose tolerance test before clinical onset, of whom five were diabetic by World Health Organisation criteria four, four, six, seven, and 21 months before insulin was needed. Nine showed random blood glucose concentrations above the 97.5th centile (6.3 mmol/l) six to 34 months (median 12) before diagnosis. Two others had a glucose tolerance test result compatible with diabetes but had not reached the stage of needing insulin. Hyperglycaemia is often of insidious onset in type I diabetes, even in children and young adults. Diagnosis will inevitably be late if considered only when acute symptoms of thirst and polyuria develop.     

Adenoviral insulin gene therapy prolongs survival of IDDM model BB rats by improving hyperlipidemia.

Diabetes is frequently associated with hyperlipidemia, which results in atherogenic complications. Insulin-dependent diabetes mellitus (IDDM) model BB/Wor//Tky (BB) rats exhibit both hyperglycemia and hyperlipidemia and die within 3 weeks after the onset of diabetes unless insulin therapy is given. We performed insulin gene therapy in BB rats with adenovirus vectors through the tail vein. After infusion, plasma triglyceride levels dropped quickly and maintained low levels for 1 week, whereas blood glucose levels showed a slight decrease. The survival period of diabetic BB rats was prolonged to up to 75 days by infusing insulin gene-expressing adenoviral vectors. We suggest that the control of hyperlipidemia can be a life-saving measure when combined with hyperglycemia control in the treatment of diabetes.