A difference between the inheritance of classical juvenile-onset and maturity-onset type diabetes of young people

Role of molecular genetics in transforming diagnosis of diabetes mellitus

Most common diseases also run in families as rare, monogenic forms. Diabetes is no exception. Mutations in approximately 20 different genes are now known to cause monogenic diabetes, a disease group that can be subclassified into maturity-onset diabetes of the young, neonatal diabetes and mitochondrial diabetes. In some families, additional features, such as urogenital malformations, exocrine pancreatic dysfunction and neurological abnormalities, are present and may aid the diagnostic classification. The finding of a mutation in monogenic diabetes may have implications for the prediction of prognosis and choice of treatment. Mutations in the GCK gene cause a mild form of diabetes, which seldom needs insulin and has a low risk for complications. By contrast, HNF1A mutations lead to a diabetes form that in severity, treatment and complication risk resembles Type 1 diabetes, although these patients may experience a good effect of sulfonylurea treatment. The majority of neonatal diabetes cases are caused by mutations in the K(ATP) channel genes ABCC8 and KCNJ11, and sulfonylurea therapy is then usually superior to insulin. Diseases with a considerable genetic component may now be explored by genome-wide approaches using next-generation DNA sequencing technology. We expect that within a few years important breakthroughs will be made in mapping cases of diabetes with a suspected, but still unsolved monogenic basis.

Identification of novel variants in the hepatocyte nuclear factor-1alpha gene in South Indian patients with maturity onset diabetes of young

CONTEXT

Mutations in the HNF 1A gene are the most common cause of maturity-onset diabetes of the young (MODY) in most populations. India currently has the largest number of people with diabetes in the world, and onset of type 2 diabetes occurs at a younger age with possible overlap with MODY. There are very few data on MODY mutations from India.

OBJECTIVE

The objective was to screen coding and promoter regions of HNF1A gene for mutations in unrelated South Indian subjects in whom a clinical diagnosis of MODY was made.

DESIGN

This was an observational cross-sectional study.

SETTING

The study was conducted at a diabetes specialties centre in Chennai in southern India.

PATIENTS

Ninety-six unrelated south Indian subjects in whom clinical diagnosis of MODY was made were included in the study. The control population comprised of 57 unrelated nondiabetic subjects selected from the Chennai Urban Rural Epidemiology Study, a study conducted on a representative population (aged > or =20 yr) of Chennai.

RESULTS

We identified nine novel variants comprising seven mutations (one novel mutation -538G>C at promoter region and six novel coding region mutations) and two polymorphisms in the HNF1A gene. Functional studies revealed reduced transcriptional activity of the HNF1A promoter for two promoter variants. We also observed cosegregation with diabetes of the Arg263His coding region mutation in eight members of one MODY family, whereas it was absent in nondiabetic subjects of this family.

CONCLUSION

This study suggests that mutations in the HNF1A gene comprise about 9% of clinically diagnosed MODY subjects in southern India and a novel Arg263His mutation cosegregates with MODY in one family.

A family with dominantly inherited mild juvenile diabetes

A family of 53 members is described in which mild diabetes in young, non-obese subjects is transmitted through four generations from parents to children, the ratio diabetic/non-diabetic offspring of diabetic parents being 3:2 and all affected individuals having a diabetic parent. In this family, mild juvenile diabetes thus appears to be inherited as an autosomal Mendelian dominant.

Successful discontinuation of insulin treatment after gestational diabetes is shown to be a case of MODY due to a glucokinase mutation

We describe a woman who first presented with gestational diabetes at 26 weeks gestation and was managed with insulin. Following delivery of a healthy baby she had an abnormal OGTT (oral glucose tolerance test) 6 weeks post partum and was managed with diet. In her second pregnancy she was diagnosed with gestational diabetes at 10 weeks and required insulin. Following delivery she was again managed on diet alone. Four years later, during her third pregnancy, she was managed with insulin from the outset. She remained on insulin post partum and for several years. Later her two younger children, aged 11 years and 7 years, were found to have GCK mutation causing MODY (Maturity Onset Diabetes Of the Young) subtype glucokinase. Following this she underwent molecular genetic testing and was also shown to have the GCK mutation. She was gradually taken off insulin and is now managed on diet alone with excellent glycaemic control. Her two children are under regular follow up care and on no medication for diabetes.

Best practice guidelines for the molecular genetic diagnosis of maturity-onset diabetes of the young

AIMS/HYPOTHESIS

Mutations in the GCK and HNF1A genes are the most common cause of the monogenic forms of diabetes known as 'maturity-onset diabetes of the young'. GCK encodes the glucokinase enzyme, which acts as the pancreatic glucose sensor, and mutations result in stable, mild fasting hyperglycaemia. A progressive insulin secretory defect is seen in patients with mutations in the HNF1A and HNF4A genes encoding the transcription factors hepatocyte nuclear factor-1 alpha and -4 alpha. A molecular genetic diagnosis often changes management, since patients with GCK mutations rarely require pharmacological treatment and HNF1A/4A mutation carriers are sensitive to sulfonylureas. These monogenic forms of diabetes are often misdiagnosed as type 1 or 2 diabetes. Best practice guidelines for genetic testing were developed to guide testing and reporting of results.

METHODS

A workshop was held to discuss clinical criteria for testing and the interpretation of molecular genetic test results. The participants included 22 clinicians and scientists from 13 countries. Draft best practice guidelines were formulated and edited using an online tool (http://www.coventi.com).

RESULTS

An agreed set of clinical criteria were defined for the testing of babies, children and adults for GCK, HNF1A and HNF4A mutations. Reporting scenarios were discussed and consensus statements produced.

CONCLUSIONS/INTERPRETATION

Best practice guidelines have been established for monogenic forms of diabetes caused by mutations in the GCK, HNF1A and HNF4A genes. The guidelines include both diagnostic and predictive genetic tests and interpretation of the results.

Challenges in studies of the genetic basis of Type 2 diabetes

The prevalence of diabetes is increasing worldwide in epidemic proportions. This increase is mainly due to increased incidence and prevalence of Type 2 diabetes, which accounts for 80-90% of all cases of diabetes. The susceptibility to develop Type 2 diabetes is determined by genetic and environmental factors. Major genes responsible for Type 2 diabetes have not yet been identified. The most replicated susceptibility gene for Type 2 diabetes is TCF7L2, recently published by investigators from Iceland. The second most widely replicated association between a genetic variation and the risk of Type 2 diabetes is that of the Pro12Ala polymorphism in the peroxisome proliferator-activated receptor γ2 gene. Furthermore, the common E23K polymorphism in the KCJN11 gene, encoding the ATP-sensitive potassium-channel subunit Kir6.2, and variants in the calpain-10 gene have been associated with increased susceptibility to Type 2 diabetes in meta-analyses. Several studies have investigated the possibility that rare, highly penetrant mutations in the maturity-onset diabetes of the young genes lead to monogenic diabetes, while common polymorphisms increase the susceptibility to Type 2 diabetes. Indeed, there is increasing evidence that single nucleotide polymorphisms in hepatic nuclear factor-4α are significantly associated with the risk of Type 2 diabetes. In this review, different approaches to identify susceptibility genes for Type 2 diabetes are discussed. In particular, the importance of prospective population-based cohort studies and prospective intervention studies are emphasized. Finally, genome-wide association studies using single nucleotide polymorphisms randomly spaced across the entire genome may be useful in the identification of susceptibility genes for Type 2 diabetes.

Asian MODY: are we missing an important diagnosis?

AIMS

Maturity onset diabetes of the young (MODY) is a monogenic form of diabetes where correct diagnosis alters treatment, prognosis and genetic counselling. The first UK survey of childhood MODY identified 20 White, but no Asian children with MODY. We hypothesized that MODY causes diabetes in UK Asians, but is underdiagnosed.

METHODS

Children with dominant family histories of diabetes were recruited. Direct sequencing for mutations in the two most common MODY genes; HNF1A (TCF1) and GCK was performed in autoantibody-negative probands. We also compared MODY testing data for Asian and White cases from the Exeter MODY database, to 2001 UK census data.

RESULTS

We recruited 30 families and identified three Asian families with MODY gene mutations (two HNF1A, one GCK) and three White UK families (two HNF1A, one GCK). Heterozygous MODY phenotypes were similar in Asians and Whites. Only eight (0.5%) of 1369 UK referrals for MODY testing were known to be Asian, but in 2001 Asians represented 4% of the English/Welsh population and have a higher prevalence of diabetes.

CONCLUSIONS

We identified three cases of childhood MODY in UK Asians and demonstrated reduced rates of MODY testing in Asians, which has negative implications for treatment. It is unclear why this is. MODY should be considered in autoantibody-negative Asian diabetes patients lacking evidence of insulin resistance.

Genetic and clinical characteristics of maturity-onset diabetes of the young

Genetic factors play an important role in various forms of diabetes mellitus (DM), but inheritance is complex and interacts with environmental factors. Although in most cases type 2 DM (T2DM) and T1DM are polygenic disorders, several monogenic forms have been identified. Among them, maturity-onset diabetes of the young (MODY) has been the most intensively investigated. MODY is a group of six different forms of monogenic diabetes, characterized by insulin secretion defects in pancreatic beta-cells, supposed to be responsible for 2-5% of all cases of diabetes. The most common are MODY2 and MODY3, caused by mutations in the genes encoding glucokinase and hepatocyte nuclear factor 1-alpha respectively. MODY2 is characterized by glucose sensing defects, leading to an increase in insulin secretion threshold. This causes lifelong sustained and mild hyperglycaemia from birth, most often in non-diabetic levels. Diagnosis is incidental in most cases. These patients are asymptomatic, seldom need treatment and rarely present chronic complications. MODY3 is characterized by a severe insulin secretion defect in response to glucose. Diagnosis is made usually in adolescence and early adulthood, often by osmotic symptoms. Hyperglycaemia is progressive, and patients frequently need treatment with oral drugs or insulin some time in their follow up. This group seems to have a marked sensitivity to sulphonylureas compared to other types of diabetes. The recognition of MODY as a monogenic disorder and a thorough understanding of its pathophysiology are important for correct diagnosis and treatment, with great impact on prognosis. Besides, the study of these forms of diabetes brings important contributions to the understanding of glucose homeostasis as a whole.

Genetics of Type 2 diabetes

Type 2 diabetes (T2D) has become a health-care problem worldwide, with the rise in disease prevalence being all the more worrying as it not only affects the developed world but also developing nations with fewer resources to cope with yet another major disease burden. Furthermore, the problem is no longer restricted to the ageing population, as young adults and children are also being diagnosed with T2D. In recent years, there has been a surge in the number of genetic studies of T2D in attempts to identify some of the underlying risk factors. In this review, I highlight the main genes known to cause uncommon monogenic forms of diabetes (e.g. maturity-onset diabetes of the young--MODY--and insulin resistance syndromes), as well as describe some of the main approaches used to identify genes involved in the more common forms of T2D that result from the interaction between environmental risk factors and predisposing genotypes. Linkage and candidate gene studies have been highly successful in the identification of genes that cause the monogenic variants of diabetes and, although progress in the more common forms of T2D has been slow, a number of genes have now been reproducibly associated with T2D risk in multiple studies. These are discussed, as well as the main implications that the diabetes gene discoveries will have in diabetes treatment and prevention.

Genetics of type 2 diabetes mellitus: status and perspectives

Throughout the last decade, molecular genetic studies of non-autoimmune diabetes mellitus have contributed significantly to our present understanding of this disease's complex aetiopathogenesis. Monogenic forms of diabetes (maturity-onset diabetes of the young, MODY) have been identified and classified into MODY1-6 according to the mutated genes that by being expressed in the pancreatic beta-cells confirm at the molecular level the clinical presentation of MODY as a predominantly insulin secretory deficient form of diabetes mellitus. Genomewide linkage studies of presumed polygenic type 2 diabetic populations indicate that loci on chromosomes 1q, 5q, 8p, 10q, 12q and 20q contain susceptibility genes. Yet, so far, the only susceptibility gene, calpain-10 (CAPN10), which has been identified using genomewide linkage studies, is located on chromosome 2q37. Mutation analyses of selected 'candidate' susceptibility genes in various populations have also identified the widespread Pro12Ala variant of the peroxisome proliferator-activated receptor-gamma and the common Glu23Lys variant of the ATP-sensitive potassium channel, Kir6.2 (KCNJ11). These variants may contribute significantly to the risk type 2 diabetes conferring insulin resistance of liver, muscle and fat (Pro12Ala) and a relative insulin secretory deficiency (Glu23Lys). It is likely that, in the near future, the recent more detailed knowledge of the human genome and insights into its haploblocks together with the developments of high-throughput and cheap genotyping will facilitate the discovery of many more type 2 diabetes gene variants in study materials, which are statistically powered and phenotypically well characterized. The results of these efforts are likely to be the platform for major progress in the development of personalized antidiabetic drugs with higher efficacy and few side effects.

Missense mutations in the human insulin promoter factor-1 gene are not a common cause of type 2 diabetes mellitus in Taiwan

Type 2 diabetes mellitus (T2DM) is a common metabolic disorder characterized by a hyperglycemia resulting from defect in insulin secretion and insulin action. Recent studies showed that dominant negative mutations in the insulin promoter factor-1 (IPF-1), a pancreatic beta-cell specific transcription factor, cause maturity-onset diabetes of the young (MODY), a subtype of T2DM with early onset and monogenic autosomal inheritance. In addition to MODY, IPF-1 mutations are suggested to predispose to common late-onset T2DM with different penetration of the mutations reflected in their in vitro activity. Thus, we investigated IPF-1 C18R, Q59L, D76N and R197H mutations in Taiwanese patients with common late-onset T2DM, because research into IPF-1 variants in Taiwanese diabetic patients--a population with the lowest range of diabetic incidence--has never been documented. Peripheral blood samples were collected and genomic DNA was extracted from 434 patients with T2DM and 194 non-diabetes control study subjects. IPF-1 genetic variations were analyzed by PCR and restriction fragment length polymorphism (RFLP) analysis. We did not find any of these four IPF-1 mutations in our patients. Our results suggested that IPF-1 mutations were not a common cause associated with Taiwanese T2DM.

Acquired non-type 1 diabetes in childhood: subtypes, diagnosis, and management

Over the past 30 years it has become apparent that not all diabetes presenting in childhood is autoimmune type 1. Increasingly type 2 diabetes, maturity onset diabetes of the young, iatrogenic diabetes, and rare syndromic forms of diabetes such as Wolfram's syndrome have been identified in children. This review is aimed at the general paediatrician looking after children with diabetes, and aims to provide an algorithm for assessment, investigation, and suggested management for the newly diagnosed child with suspected non-type 1 diabetes. This article will also be relevant to the child with atypical diabetes-that is, on low insulin doses outside the honeymoon period.

Diabetes Mellitus do Tipo MODY

Estima-se que perto de 5% dos indivíduos classificados como portadores de diabetes mellitus (DM) tipo 2 e 10% daqueles considerados como tipo 1 (anteriormente classificado como juvenil) sejam, na verdade, portadores de mutações MODY. Nesta forma de DM ocorre uma co-segregação evidente de algumas mutações com a hiperglicemia, fato este reproduzido em inúmeras famílias estudadas em várias populações do mundo. Caracteriza-se por ser uma das poucas causas de DM cujo modo de transmissão da predisposição genética ocorre de uma forma autossômica-dominante, compondo o grupo chamado de DM monogênicos, onde os outros representantes têm uma prevalência bastante rara. As mutações nos genes MODY, mesmo no estado heterozigoto, apresentam um forte impacto no fenótipo (alta penetrância), sendo que 95% dos indivíduos nascidos com alguma mutação MODY serão diabéticos ou apresentarão alterações no âmbito do metabolismo glicídico antes dos 55 anos de idade. Este trabalho objetiva a discussão desta forma de DM, enfatizando suas características clínicas e genéticas mais relevantes. A pesquisa sistemática de mutações MODY começa a ser feita de forma rotineira em vários países, havendo uma tendência de se colocar este recurso diagnóstico como um exame na prática da diabetologia.

Type 2 diabetes mellitus in UK children--an emerging problem

AIMS

Type 2 diabetes mellitus has never previously been described in UK children, although an increasing incidence in childhood is recognized in international studies. The prevalence of obesity in UK children is increasing and is a recognized risk factor for the development of diabetes. The aim of this study was to identify and characterize children with Type 2 diabetes in the West Midlands and Leicester.

METHODS

Children were identified by contacting paediatricians responsible for diabetes in five hospitals. Details were collected on demographics, mode of presentation, investigations and treatment on a standard proforma.

RESULTS

Eight girls were identified with Type 2 diabetes, aged 9-16 years and who were of Pakistani, Indian or Arabic origin. They were all overweight (percentage weight for height 141-209%) and had a family history of diabetes in at least two generations. They presented insidiously with hyperglycaemia and glycosuria without ketosis and five were asymptomatic. Islet cell antibodies measured in seven patients were negative. Four had acanthosis nigricans which is a cutaneous marker of insulin resistance and the other four had high plasma levels of insulin and/or C peptide. These patients are distinct from those with maturity-onset diabetes of the young (MODY). All were initially managed with dietary measures, seven have been treated with oral anti-diabetic agents of whom two have subsequently required insulin.

CONCLUSIONS

These are the first UK case reports of Type 2 diabetes in children. Paediatricians need to be aware of the risk of Type 2 diabetes developing in childhood in high-risk ethnic groups, particularly in association with obesity and a positive family history.

Familial clustering of type II diabetes mellitus (DM) diagnosed under the age of 40 years in Yemen: Is it early-onset type II DM or maturity-onset diabetes of the young?

BACKGROUND

Clinical presentation of type II diabetes mellitus (DM) has frequently been observed at an early age in developing countries, probably as a result of genetic, epidemiological and demographic factors. This study aimed to investigate the pattern of familial clustering of type II DM in patients who developed clinical diabetes before the age of 40 years.

PATIENTS AND METHOD

The study involved family pedigrees, clinical assessments and laboratory investigations of 191 patients with type II DM, and 260 age-matched randomly selected non-diabetic controls.

RESULTS

The prevalence of type II DM was found to be statistically higher among parents (P<0.0001), fullsiblings (P<0.0001), half-siblings (P<0.001), uncles (P<0.01) and aunts (P<0.001) of the index patients, as compared to the corresponding relatives of nondiabetic controls. The odds ratio of the family history index (FHI), in association with type II DM in probands who had no family history of diabetes (FHI=0.0), was significantly negative (OR=0.34; 95% CI 0.23, 0.52; P<0.0001). At an FHI level of 0.5-1.0, there was a slight nonsignificant increase in odds ratio for diabetes (OR=1.53; 95% CI 0.95, 2.45; P=0.08). A higher level of FHI (A(3)1.5) was associated with a significant increase in odds ratio for diabetes (OR=3.75; 95% CI 2.13, 6.64; P<0.0001). The age-corrected relative risk of type II DM for the offspring of diabetic parents was found to be progressively increasing from a nonconsanguineous diabetic father (22%) or mother (26.5%), to nonconsanguineous conjugal diabetic parents (27%) and to the offspring of consanguineous single or conjugal diabetic parents (37.5%). On the contrary, the age-corrected relative risk for the offspring of nonconsanguineous and consanguineous nondiabetic parents was characteristically lower (14% for each). Maturityonset diabetes of the young (MODY) was suspected in 10 probands (5%), and early-onset type II DM in the offspring of conjugal diabetic parents in 16 probands (9%). The remaining 165 probands (86%) were unclassified due to lack of specific classification criteria.

CONCLUSION

The considerable familial clustering of type II DM diagnosed under the age of 40 years in this study population reflects the presence of a strong genetic component in its etiology. In addition, the development of early-onset type II DM was more likely associated with a consanguineous and/or conjugal diabetic parents and probably MODY subtype among a substantial number of patients. Epidemiological and demographic factors might have been implicated, especially in those with negative parental diabetic history.

Insulin promoter factor-1 gene mutation linked to early-onset type 2 diabetes mellitus directs expression of a dominant negative isoprotein

The homeodomain transcription factor insulin promoter factor-1 (IPF-1) is required for development of the pancreas and also mediates glucose-responsive stimulation of insulin gene transcription. Earlier we described a human subject with pancreatic agenesis attributable to homozygosity for a cytosine deletion in codon 63 of the IPF-1 gene (Pro63fsdelC). Pro63fsdelC resulted in the premature truncation of an IPF-1 protein which lacked the homeodomain required for DNA binding and nuclear localization. Subsequently, we linked the heterozygous state of this mutation with type 2 diabetes mellitus in the extended family of the pancreatic agenesis proband. In the course of expressing the mutant IPF-1 protein in eukaryotic cells, we detected a second IPF-1 isoform, recognized by COOH- but not NH2-terminal-specific antisera. This isoform localizes to the nucleus and retains DNA-binding functions. We provide evidence that internal translation initiating at an out-of-frame AUG accounts for the appearance of this protein. The reading frame crosses over to the wild-type IPF-1 reading frame at the site of the point deletion just carboxy proximal to the transactivation domain. Thus, the single mutated allele results in the translation of two IPF-1 isoproteins, one of which consists of the NH2-terminal transactivation domain and is sequestered in the cytoplasm and the second of which contains the COOH-terminal DNA-binding domain, but lacks the transactivation domain. Further, the COOH-terminal mutant IPF-1 isoform does not activate transcription and inhibits the transactivation functions of wild-type IPF-1. This circumstance suggests that the mechanism of diabetes in these individuals may be due not only to reduced gene dosage, but also to a dominant negative inhibition of transcription of the insulin gene and other beta cell-specific genes regulated by the mutant IPF-1.

Non-insulin dependent diabetes mellitus (NIDDM) in minority youth: research priorities and needs

The prevalence of non-insulin dependent diabetes mellitus (NIDDM) is increasing in Native American and African-American youth, with females more frequently affected than males. This increase is related to increasing rates of obesity and to the greater demand for insulin at adolescence. This review examines the epidemiologic data about NIDDM in minority youth and addresses questions about the type of diabetes minority youth have, the relative contributions of environment and genetics to their diabetes, and whether prevention or control is possible. The heterogeneity of NIDDM in the minority youth population includes: typical NIDDM; atypical diabetes mellitus (ADM), which has been described in a substantial number of African-American youngsters; and a small proportion with a range of defects in the pathway of insulin action. Clinical and experimental evidence that insulin resistance or insulin deficiency is the primary defect in NIDDM are reviewed, as is evidence that fetal undernutrition may be a contributing factor. The numerous reports of linkages, associations, and mutations or polymorphisms in candidate genes account for a very small proportion of non-type 1 diabetes. Environmental and genetic contributors to obesity are also important. Research issues relating to the questions discussed include the need for data comparing various populations and assessing risk factors associated with the epidemic of NIDDM and obesity, costs to the health system and attendant personal and societal costs, clarification of the types of NIDDM in minority populations that will permit appropriate therapy and counseling, and extensive studies of environmental and genetic factors. Genetic studies include a genome wide search and continued analysis for candidate genes for both NIDDM and obesity. Environmental factors for study include the role of fetal and perinatal nutrition and drug exposure. Finally, collaborative multicenter studies are needed of prevention or control of obesity and NIDDM.

Insulin resistance and the polycystic ovary syndrome: mechanism and implications for pathogenesis

It is now clear that PCOS is often associated with profound insulin resistance as well as with defects in insulin secretion. These abnormalities, together with obesity, explain the substantially increased prevalence of glucose intolerance in PCOS. Moreover, since PCOS is an extremely common disorder, PCOS-related insulin resistance is an important cause of NIDDM in women (Table 3). The insulin resistance in at least 50% of PCOS women appears to be related to excessive serine phosphorylation of the insulin receptor. A factor extrinsic to the insulin receptor, presumably a serine/threonine kinase, causes this abnormality and is an example of an important new mechanism for human insulin resistance related to factors controlling insulin receptor signaling. Serine phosphorylation appears to modulate the activity of the key regulatory enzyme of androgen biosynthesis, P450c17. It is thus possible that a single defect produces both the insulin resistance and the hyperandrogenism in some PCOS women (Fig. 19). Recent studies strongly suggest that insulin is acting through its own receptor (rather than the IGF-I receptor) in PCOS to augment not only ovarian and adrenal steroidogenesis but also pituitary LH release. Indeed, the defect in insulin action appears to be selective, affecting glucose metabolism but not cell growth. Since PCOS usually has a menarchal age of onset, this makes it a particularly appropriate disorder in which to examine the ontogeny of defects in carbohydrate metabolism and for ascertaining large three-generation kindreds for positional cloning studies to identify NIDDM genes. Although the presence of lipid abnormalities, dysfibrinolysis, and insulin resistance would be predicted to place PCOS women at high risk for cardiovascular disease, appropriate prospective studies are necessary to directly assess this.

Characterization of the MODY3 phenotype. Early-onset diabetes caused by an insulin secretion defect

Maturity-onset diabetes of the young (MODY) type 3 is a dominantly inherited form of diabetes, which is often misdiagnosed as non-insulin-dependent diabetes mellitus (NIDDM) or insulin-dependent diabetes mellitus (IDDM). Phenotypic analysis of members from four large Finnish MODY3 kindreds (linked to chromosome 12q with a maximum lod score of 15) revealed a severe impairment in insulin secretion, which was present also in those normoglycemic family members who had inherited the MODY3 gene. In contrast to patients with NIDDM, MODY3 patients did not show any features of the insulin resistance syndrome. They could be discriminated from patients with IDDM by lack of glutamic acid decarboxylase antibodies (GAD-Ab). Taken together with our recent findings of linkage between this region on chromosome 12 and an insulin-deficient form of NIDDM (NIDDM2), the data suggest that mutations at the MODY3/NIDDM2 gene(s) result in a reduced insulin secretory response, that subsequently progresses to diabetes and underlines the importance of subphenotypic classification in studies of diabetes.

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

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

Clinical characteristics of subjects with a missense mutation in glucokinase

The clinical characteristics of subjects with a missense glucokinase mutation, gly299-->arg, were studied in a large pedigree, BX, initially characterized by some members having Maturity Onset Diabetes of the Young (MODY). Glucose tolerance, beta cell function and insulin sensitivity were measured with Homeostasis Model Assessment (HOMA) and with a 'Continuous Infusion of Glucose with Model Assessment' (CIGMA) test. Diabetic complications were clinically assessed. Subjects with glucokinase gly299-->arg were the same age, height, and obesity as the subjects without the mutation. Diabetes was usually asymptomatic at diagnosis and was treated with diet alone in 15 of the 18 subjects. Five of the 11 adult females had been diagnosed when they developed gestational diabetes. The fasting plasma glucose concentrations at the time of study were 4.3-12.6 mmol l-1, with the higher levels being in the more obese (p < 0.05) and in the older subjects (p < 0.05). In subjects with the mutation, beta cell function was impaired, being geometric mean 63% (normal-100%) compared with 126% in the subjects without the mutation (p < 0.001) measured by HOMA and in a subset assessed by CIGMA 59% and 127% (p < 0.01), respectively. There was no difference in fasting insulin concentrations, insulin sensitivity, lipid concentrations or blood pressure between the groups. The haemoglobin A1c was raised (mean 6.5% compared with 5.5% in the subjects without the mutation), but microvascular and macrovascular complications were uncommon. The subjects with the mutation did not have microalbuminuria but had an impaired vibration perception threshold compared with subjects without the mutation.(ABSTRACT TRUNCATED AT 250 WORDS)

Maternally inherited diabetes mellitus: the role of mitochondrial DNA defects

Several studies have shown a consistent maternal effect in the transmission of Type 2 diabetes (NIDDM). The mitochondrial encephalomyopathies are a group of diseases characterized by maternal inheritance and a variety of mitochondrial DNA defects. Diabetes is a feature of some of these disorders and therefore the hypothesis arose that mitochondrial DNA mutations might play a role in patients with diabetes but no other features of neurological disease. Recent studies have confirmed that a specific point mutation in the gene encoding the mitochondrial tRNA for leucine segregates with diabetes and nerve deafness in families from the UK, Holland, France and Japan. Mitochondrial gene deletions have also been reported. Affected subjects present with progressive insulin deficiency and may fall into the broad classifications of either Type 1 (IDDM) or Type 2 diabetes (NIDDM). Future studies are aimed at searching for other mitochondrial gene defects in diabetes and attempting to explain the mechanism of hyperglycaemia by the development of phenotypic expression systems. Although an exciting development in the genetics of diabetes, currently described mitochondrial mutations do not fully explain the maternal effect in the transmission of Type 2 diabetes.

Mitochondrial diabetes mellitus: prevalence and clinical characterization of diabetes due to mitochondrial tRNA(Leu(UUR)) gene mutation in Japanese patients

Mutations in the mitochondrial gene were recently identified in a large pedigree of diabetes mellitus and deafness. As the mitochondrial gene is materially inherited, Japanese diabetic patients whose mothers were also diabetic were screened, using peripheral leucocytes, for an A to G transition at nucleotide pair 3243 of the mitochondrial gene, a tRNA(Leu(UUR)) mutation. This mutation was identified in four pedigrees from among 300 unrelated patients who were screened. Diabetes co-segregated with the mutation, except in one young subject, and was maternally inherited. The apparent onset of disease occurred between 11 and 68 years of age. Some of the affected members developed hearing impairment and congestive heart failure due to cardiomyopathy, though generally long after the onset of diabetes, and these patients had therefore not been diagnosed as having a specific form of diabetes. The duration of sulphonyl-urea treatment was not more than 8 years in these pedigrees and affected members were prone to progression to insulin-requiring diabetes. Thus, these patients were secondary sulphonylurea failures. Long-term follow-up revealed that the underlying disorder in affected members is a progressive impairment of insulin secretion. Some were initially diagnosed as having IDDM based on an apparent acute onset in youth and the clinical severity of their diabetes. Others were regarded as having MODY with an aggressive course. The mitochondrial gene mutation or diabetes is not transmitted to all offspring of the affected mothers.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Nonsense mutation of glucokinase gene in late-onset non-insulin-dependent diabetes mellitus

A nonsense mutation at codon 186 in exon 5 of the gene for glucokinase, an enzyme important for glucose-induced insulin secretion, was identified in a Japanese patient with late-onset non-insulin-dependent diabetes mellitus (NIDDM). All affected members of her family were heterozygous for the mutation and had late-onset NIDDM or impaired glucose tolerance, whereas unaffected members showed normal glucose tolerance. The early insulin response to oral glucose was impaired in affected relatives, but was normal in those unaffected. These findings suggest that the glucokinase mutation raises the set-point of pancreatic beta cells for glucose-induced insulin secretion, leading to abnormal glucose tolerance in some patients with late-onset NIDDM.

Linkage of type 2 diabetes to the glucokinase gene

Maturity-onset diabetes of the young (MODY) is a subtype of type 2 diabetes that presents from the second decade and has an autosomal dominant mode of inheritance. We have investigated the glucokinase gene, a candidate gene for diabetes, in two MODY pedigrees. In a large 5-generation pedigree (BX) with 15 diabetic members, use of a microsatellite polymorphism revealed linkage of diabetes to the glucokinase locus on chromosome 7p. A peak lod score of 4.60 was obtained at a recombination fraction (theta) of zero. This finding suggests that a defective glucokinase gene contributes to the diabetes phenotype in this pedigree. This is not universal in MODY since linkage to the glucokinase locus was excluded in a second pedigree M (lod score = -7.36 at theta = 0). The affected members in pedigree BX were diagnosed either when young (in pregnancy or on screening) or when they presented symptomatically in middle and old age; most of them were treated by diet alone. Defects in the glucokinase gene may play an important part in the pathogenesis of type 2 diabetes.

Close linkage of glucokinase locus on chromosome 7p to early-onset non-insulin-dependent diabetes mellitus

Non-insulin-dependent diabetes mellitus (NIDDM) is a major health problem, affecting 5% of the world population. Genetic factors are important in NIDDM, but the mechanisms leading to glucose intolerance are unknown. Genetic linkage has been investigated in multigeneration families to localize, and ultimately identify, the gene(s) predisposing to NIDDM. Here we report linkage between the glucokinase locus on chromosome 7p and diabetes in 16 French families with maturity-onset diabetes of the young, a form of NIDDM characterized by monogenic autosomal dominant transmission and early age of onset. Statistical evidence of genetic heterogeneity was significant, with an estimated 45-95% of the 16 families showing linkage to glucokinase. Because glucokinase is a key enzyme of blood glucose homeostasis, these results are evidence that a gene involved in glucose metabolism could be implicated in the pathogenesis of NIDDM.

Diabetes mellitus in Saudi Arabia: The clinical pattern and complications in 1,000 patients

A retrospective and prospective study of 1,000 ambulatory and hospitalized diabetic patients was done in Riyadh, Saudi Arabia. Saudis completed 777 (77.7%) and non-Saudis 223 (22.3%). Sex distribution was equal among Saudis, males 389 (50.1%) and females 388 (49.9%), but non-Saudi males were predominant at 153 (68.6%), non-Saudi females 70 (31.4%) reflecting the preponderant male expatriate labor force. A proportion of different types of diabetes was: IDDM 115 (11.7%), non-obese non-insulin dependent diabetes mellitus (NIDDM) 405 (41.0%), obese NIDDM 412 (42.1%), and early onset non-insulin dependent diabetes (diagnosis under 30 years of age), 43 (4.4%). Regarding treatment, 388 (40.6%) received insulin followed by sulfonylurea, alone in 330 (33.5%), diet only 117 (12.0%), combination sulfonylurea and biguanide in 113 (11.6%), biguanide alone in 13 (1.3%) and insulin plus tablets in 7 (0.8%). Of 472 and 426 patients, 29.7% and 30.0% had elevated total cholesterol or triglycerides respectively, while 77.2% of 373 patients had elevated glycosylated hemoglobin (HbA1). At least once in 998 patients, diabetic ketoacidosis occurred in 7.6%.

Islet amyloid polypeptide (IAPP). A short review

The islet amyloid polypeptide (IAPP) was originally identified by chemical analysis of the amyloid component in a human pancreatic islet cell tumor. It consists of 37 amino acids and displays about 50% homology with the neuropeptide calcitonin gene-related peptide (CGRP). In the pancreatic islets the IAPP is confined to the beta-cells, co-stored with insulin in the secretory granules and apparently co-secreted with insulin on glucose stimulation. In beta-cell depletion states such as streptozotocin diabetes in animals and in human type I diabetes mellitus both the IAPP and the insulin levels display reduction or are even absent. Within the mature IAPP molecule the amino acid sequence 23-29 shows considerable amino acid heterogenicity among various mammalian species. The amino acid composition of human IAPP in this specific region promotes the development of pancreatic islet amyloidosis, a phenomenon related to the ability to develop type II diabetes in that particular species. However, as type II diabetes is an inherited disease affecting a subpopulation of humans, not only the gene coding mature IAPP, but also one or several other hereditary factors of unknown origin are needed for the disease to develop. We have established a radioimmunoassay for plasma measurements of IAPP. During screening investigations of a large material of endocrine tumors we found a patient with extremely elevated plasma levels of IAPP, about 20,000 pmol/l. Immunohistochemical investigations confirmed the IAPP content and also revealed amyloid deposits. While performing an oral glucose tolerance test insulin levels remained unchanged whereas there was an increase in the glucose and IAPP levels. It is thus concluded that IAPP can be used as a tumor marker in pancreatic islet cell tumors and that high plasma levels of IAPP can inhibit glucose stimulated insulin secretion.

Definition and classification of diabetes

Diabetes mellitus is a state of absolute or relative insulin deficiency leading to hyperglycemia and profound changes in the body lipids and proteins. The World Health Organisation (WHO) classification of diabetes distinguishes between: insulin dependent diabetes mellitus (IDDM), non-insulin dependent diabetes mellitus (NIDDM) and malnutrition related diabetes mellitus (MRDM). In childhood the overwhelming majority is due to an autoimmune betacell disease leading to IDDM.

Maturity-onset diabetes of the young (MODY)

This review summarized aspects of the widening scope, phenotypic expression, natural history, recognition, pathogeneses, and heterogenous nature of maturity-onset diabetes of the young (MODY), an autosomal dominant inherited subtype of NIDDM, which can be recognized at a young age. There are differences in metabolic, hormonal, and vascular abnormalities in different ethnic groups and even among Caucasian pedigrees. In MODY patients with low insulin responses, there is a delayed and decreased insulin and C-peptide secretory response to glucose from childhood or adolescence, even before glucose intolerance appears; it may represent the basic genetic defect. The nondiabetic siblings have had normal insulin responses for decades. The fasting hyperglycemia of some MODY has been treated successfully with sulfonylureas for more than 30 years. In a few, after years or decades of diabetes, the insulin and C-peptide responses to glucose are so low that they may resemble those of early Type I diabetes. The rate of progression of the insulin secretory defect over time does distinguish between these two types of diabetes. In contrast are patients from families who have very high insulin responses to glucose despite glucose intolerance and fasting hyperglycemia similar to those seen in patients with low insulin responses. In many of these patients, there is in vivo and in vitro evidence of insulin resistance. Whatever its mechanism, the compensatory insulin responses to nutrients must be insufficient to maintain normal carbohydrate tolerance. This suggests that diabetes occurs only in those patients who have an additional islet cell defect, i.e., insufficient beta cell reserve and secretory capacity. In a few MODY pedigrees with high insulin responses to glucose and lack of evidence of insulin resistance, an insulin is secreted which is a structurally abnormal, mutant insulin molecule that is biologically ineffective. No associations have been found between specific HLA antigens and MODY in Caucasian, black, and Asian pedigrees. Linkage studies of the insulin gene, the insulin receptor gene, the erythrocyte/Hep G2 glucose transporter locus, and the apolipoprotein B locus have shown no association with MODY. Vascular disease may be as prevalent as in conventional NIDDM. Because of autosomal dominant transmission and penetrance at a young age, MODY is a good model for further investigations of etiologic and pathogenetic factors in NIDDM, including the use of genetic linkage strategies to identify diabetogenic genes.