Phenotypic characteristics of early-onset autosomal-dominant type 2 diabetes unlinked to known maturity-onset diabetes of the young (MODY) genes

Gain of Function of Malate Dehydrogenase 2 and Familial Hyperglycemia

CONTEXT

Genes causing familial forms of diabetes mellitus are only partially known.

OBJECTIVE

We set out to identify the genetic cause of hyperglycemia in multigenerational families with an apparent autosomal dominant form of adult-onset diabetes not due to mutations in known monogenic diabetes genes.

METHODS

Existing whole-exome sequencing (WES) data were used to identify exonic variants segregating with diabetes in 60 families from the United States and Italy. Functional studies were carried out in vitro (transduced MIN6-K8 cells) and in vivo (Caenorhabditis elegans) to assess the diabetogenic potential of 2 variants in the malate dehydrogenase 2 (MDH2) gene linked with hyperglycemia in 2 of the families.

RESULTS

A very rare mutation (p.Arg52Cys) in MDH2 strongly segregated with hyperglycemia in 1 family from the United States. An infrequent MDH2 missense variant (p.Val160Met) also showed disease cosegregation in a family from Italy, although with reduced penetrance. In silico, both Arg52Cys and Val160Met were shown to affect MDH2 protein structure and function. In transfected HepG2 cells, both variants significantly increased MDH2 enzymatic activity, thereby decreasing the NAD+/NADH ratio-a change known to affect insulin signaling and secretion. Stable expression of human wild-type MDH2 in MIN6-K8 cell lines enhanced glucose- and GLP-1-stimulated insulin secretion. This effect was blunted by the Cys52 or Met160 substitutions. Nematodes carrying equivalent changes at the orthologous positions of the mdh-2 gene showed impaired glucose-stimulated insulin secretion.

CONCLUSION

Our findings suggest a central role of MDH2 in human glucose homeostasis and indicate that gain of function variants in this gene may be involved in the etiology of familial forms of diabetes.

Disentangling the heterogeneity of adulthood-onset non-autoimmune diabetes: a little closer but lot more to do

Diabetes diagnosed in adults is a highly heterogeneous disorder. It mostly consists of what is referred to as type 2 diabetes but also comprises other entities (i.e. different diseases), including latent autoimmune diabetes, late onset forms of monogenic diabetes and familial diabetes of the adulthood, which has recently been the source of new diabetogenes discovery. Notably, type 2 diabetes is itself heterogeneous as it includes subtypes with onset at the extremes of age and/or weight distributions characterized by different degree of hyperglycemia and cardiovascular risk as compared to common forms of type 2 diabetes occurring in middle-aged, overweight/obese individuals. Understanding whether these are different presentations of one, highly heterogeneous disease or separate nosological entities with different clinical trajectories and requiring different treatments is essential to effectively pursue the path of precision medicine.

HNF1A variant, energy-reduced diets and insulin resistance improvement during weight loss: The POUNDS Lost trial and DIRECT

AIM

To determine whether weight-loss diets varying in macronutrients modulate the genetic effect of hepatocyte nuclear factor 1α (HNF1A) rs7957197 on weight loss and improvement of insulin resistance.

MATERIALS AND METHODS

We analysed the interaction between HNF1A rs7957197 and weight-loss diets with regard to weight loss and insulin resistance improvement among 722 overweight/obese adults from a 2-year randomized weight-loss trial, the POUNDS Lost trial. The findings were replicated in another independent 2-year weight-loss trial, the Dietary Intervention Randomized Controlled Trial (DIRECT), in 280 overweight/obese adults.

RESULTS

In the POUNDS Lost trial, we found that a high-fat diet significantly modified the genetic effect of HNF1A on weight loss and reduction in waist circumference (P for interaction = .006 and .005, respectively). Borderline significant interactions for fasting insulin and insulin resistance (P for interaction = .07 and .06, respectively) were observed. We replicated the results in DIRECT. Pooled results showed similar significant interactions with weight loss, waist circumference reduction, and improvement in fasting insulin and insulin resistance (P values for interaction = .001, .005, .02 and .03, respectively). Greater decreases in weight, waist circumference, fasting insulin level and insulin resistance were observed in participants with the T allele compared to those without the T allele in the high-fat diet group (P = .04, .03 and .01, respectively).

CONCLUSIONS

Our replicable findings provide strong evidence that individuals with the HNF1A rs7957197 T allele might obtain more benefits in weight loss and improvement of insulin resistance by choosing a hypocaloric and high-fat diet.

Drivers: A Biologically Contextualized, Cross-Inferential View of the Epidemiology of Neurodegenerative Disorders

Background:

Sutherland et al. (2011) suggested that, instead of risk factors for single neurodegenerative disorders (NDDs), there was a need to identify specific “drivers”, i.e., risk factors with impact on specific deposits, such as amyloid-β, tau, or α-synuclein, acting across entities.

Objectives and Methods:

Redefining drivers as “neither protein/gene- nor entity-specific features identifiable in the clinical and general epidemiology of conformational NDDs (CNDDs) as potential footprints of templating/spread/transfer mechanisms”, we conducted an analysis of the epidemiology of ten CNDDs, searching for patterns.

Results:

We identified seven potential drivers, each of which was shared by at least two CNDDs: 1) an age-at-exposure-related susceptibility to Creutzfeldt-Jakob disease (CJD) and several late-life CNDDs; 2) a relationship between age at onset, survival, and incidence; 3) shared genetic risk factors for CJD and late-life CNNDs; 4) partly shared personal (diagnostic, educational, behavioral, and social risk factors) predating clinical onset of late-life CNDDs; 5) two environmental risk factors, namely, surgery for sporadic CJD and amyotrophic lateral sclerosis, and Bordetella pertussis infection for Parkinson’s disease; 6) reticulo-endothelial system stressors or general drivers (andropause or premenopausal estrogen deficiency, APOEɛ4, and vascular risk factors) for late-life CNDDs such as dementia/Alzheimer’s disease, type-2 diabetes mellitus, and some sporadic cardiac and vascular degenerative diseases; and 7) a high, invariant incidence ratio of sporadic to genetic forms of mid- and late-life CNDDs, and type-2 diabetes mellitus.

Conclusion:

There might be a systematic epidemiologic pattern induced by specific proteins (PrP, TDP-43, SOD1, α-synuclein, amyloid-β, tau, Langerhans islet peptide, and transthyretin) or established combinations of these.

Molecular and phenotypic characteristics of maturity-onset diabetes of the young compared with early onset type 2 diabetes in China

BACKGROUND

The aim of the present study was to investigate the contribution of maturity-onset diabetes of the young (MODY) genes to the etiology of 14 Chinese MODY families and to assess phenotypic differences between patients with MODY but without a known genetic cause of diabetes (MODYX) and those with early onset type 2 diabetes (T2D).

METHODS

The study included 14 MODY probands from unrelated families and 59 patients (age of onset ≤35 years) diagnosed as early onset T2D. A standard meal test and metabolic studies were performed to characterize the clinical features of all patients. All probands with MODY were analyzed for nucleotide variations in promoters, exons, and exon-intron boundaries of 13 known MODY genes by direct DNA sequencing.

RESULTS

Mutations in 13 known MODY genes were not present in the 14 Chinese families and they were classified as MODYX. However, different polymorphisms were identified, with I27L (42.9%; 12/28) and S487N (46.4%; 13/28) of hepatocyte nuclear factor 4α (HNF1α/MODY3) being two most frequent polymorphisms. Two new polymorphisms, namely T412I and D504H, were detected in carboxyl ester lipase (CEL/MODY8). Compared with patients with early onset T2D, patients with MODYX were diagnosed with diabetes at a younger age (28.3 ± 6.5 vs 24.3 ± 6.5 years; P < 0.05) and had a lower body mass index (BMI; 28.3 ± 6.1 vs 24.1 ± 4.3 kg/m(2) ; P < 0.01) and homeostatic model assessment of β-cell function (47.6 [22.2-89.4] vs 18.5 [6.5-33.7]; P < 0.05).

CONCLUSION

Herein we report on 14 Chinese families with MODYX and describe its phenotype. Compared with early onset T2D, MODYX is characterized by lower BMI and decreased insulin-secreting capacity.

Identification and Clinical Characterization of Adult Patients with Multigenerational Diabetes Mellitus

BACKGROUND

Some patients diagnosed as having type 2 diabetes mellitus (T2DM) are, instead, affected by multigenerational diabetes whose clinical characteristics are mostly undefined.

OBJECTIVE

1. To identify among patients who had been previously defined as affected by T2DM those, in fact, affected by multigenerational diabetes; 2. After excluding patients carrying the most common MODY genes and mitochondrial mutations, we compared clinical features of remaining patients with those of patients with T2DM.

METHODS

Among 2,583 consecutive adult patients who had been defined as affected by T2DM, we looked for those with diabetes in ≥3 consecutive generations. All probands were screened for mutations in six MODY genes (HNF4A, GCK, HNF1A, PDX1, HNF1B and NeuroD1) and for the A3243G mitochondrial mutation. After excluding patients with mutations in one of such genes, we compared clinical features of the remaining 67 patients (2.6% of the whole initial sample) affected by multigenerational "familial diabetes of the adulthood" (FDA) and of their diabetic relatives (n = 63) to those with T2DM (n = 1,028) by generalized hierarchical linear models followed by pairwise comparisons.

RESULTS

Age, age at diagnosis, proportion of hypertension (all p<0.001), and waist circumference (p<0.05) were lower in FDA than T2DM. Nonetheless, the two groups had similar age-adjusted incidence rate of all-cause mortality.

CONCLUSIONS

Beside younger age at diagnosis, FDA patients show lower waist circumference and reduced proportion of hypertension as compared to those with T2DM; despite such reduced potential cardiovascular risk factors, FDA patients did not show a reduced mortality risk than patients with T2DM.

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.

Mutations in KCNJ11 are associated with the development of autosomal dominant, early-onset type 2 diabetes

AIMS/HYPOTHESIS

More than 90% of Chinese familial early-onset type 2 diabetes mellitus is genetically unexplained. To investigate the molecular aetiology, we identified and characterised whether mutations in the KCNJ11 gene are responsible for these families.

METHODS

KCNJ11 mutations were screened for 96 familial early-onset type 2 diabetic probands and their families. Functional significance of the identified mutations was confirmed by physiological analysis, molecular modelling and population survey.

RESULTS

Three novel KCNJ11 mutations, R27H, R192H and S116F117del, were identified in three families with early-onset type 2 diabetes mellitus. Mutated KCNJ11 with R27H or R192H markedly reduced ATP sensitivity (E23K>R27H>C42R>R192H>R201H), but no ATP-sensitive potassium channel currents were detected in the loss-of-function S116F117del channel in vitro. Molecular modelling indicated that R192H had a larger effect on the channel ATP-binding pocket than R27H, which may qualitatively explain why the ATP sensitivity of the R192H mutation is seven times less than R27H. The shape of the S116F117del channel may be compressed, which may explain why the mutated channel had no currents. Discontinuation of insulin and implementation of sulfonylureas for R27H or R192H carriers and continuation/switch to insulin therapy for S116F117del carriers resulted in good glycaemic control.

CONCLUSIONS/INTERPRETATION

Our results suggest that genetic diagnosis for the KCNJ11 mutations in familial early-onset type 2 diabetes mellitus may help in understanding the molecular aetiology and in providing more personalised treatment for these specific forms of diabetes in Chinese and other Asian patients.

Challenges in diagnosing type 1 diabetes in different populations

Diabetes affects today an estimated 366 million people world-wide, including 20 million to 40 million of patients with type 1 diabetes (T1D). While T1D accounts for 5% to 20% of those with diabetes, it is associated with higher morbidity, mortality and health care cost than the more prevalent type 2 diabetes. Patients with T1D require exogenous insulin for survival and should be identified as soon as possible after diagnosis to avoid high morbidity due to a delay in insulin treatment. It is also important to present to the patient correct prognosis that differs by the type of diabetes. From the research point of view, correct classification should help to identify the etiologies and to develop specific prevention for T1D. This review summarizes evidence that may be helpful in diagnosing T1D in various ethnic groups. Challenges in interpretation of results commonly used to determine the type of diabetes are highlighted.

HNF1A gene polymorphisms and cardiovascular risk factors in individuals with late-onset autosomal dominant diabetes: a cross-sectional study

Background

Type 2 diabetes mellitus (T2DM) is a genetically heterogeneous disease, hepatocyte nuclear factor-1 homeobox A (HNF1A) single-nucleotide polymorphisms (SNPs) playing a minor role in its pathogenesis. HNF1A is a frequent cause of monogenic diabetes, albeit with early-onset. Some uncommon subgroups like late-onset autosomal dominant diabetes mellitus (LOADDM) may present peculiar inheritance patterns with a stronger familial component. This study aims to investigate the relationship of HNF1A SNPs with cardiovascular risk factors in this group, as well as to characterize them in contrast with classical T2DM (CT2DM).

Methods

eighteen LOADDM (age at onset > 40 y.o.; diabetes in 3 contiguous generations, uniparental lineage) along with 48 CT2DM patients and 42 normoglycemic controls (N group) have been evaluated for cardiovascular risk factors and SNPs of HNF1A.

Results

LOADDM showed significantly higher frequencies of SNPs A98V (22.2% vs 2.1%, p = 0.02) and S487N (72.2% vs 43.8%, p = 0.049) of HNF1A compared to CT2DM. I27L did not show significant difference (66.7% vs 45.8%), but associated with lower risk of hypertriglyceridemia (OR 0.16, 95% CI 0.04–0.65, p = 0.01). "Protective effect" was independent from other well-known predictive risk factors for hypertriglyceridemia, such as waist circumference (OR 1.09 per 1 cm increase, p = 0.01) and HDL (OR 0.01 per 1 mmol/l, p = 0.005), after logistic regression.

Conclusion

Late onset autosomal dominant diabetes mellitus is clinically indistinguishable from classical type 2 diabetes individuals. However, LOADDM group is enriched for common HNF1A polymorphisms A98V and S487N. I27L showed "protective effect" upon hypertriglyceridemia in this sample of individuals, suggesting a role for HNF1A on diabetic individuals' lipid profile. These data contribute to the understanding of the complex interactions between genes, hyperglycemia and cardiovascular risk factors development in type 2 diabetes mellitus.

Mutations of maturity-onset diabetes of the young (MODY) genes in Thais with early-onset type 2 diabetes mellitus

OBJECTIVE

Six known genes responsible for maturity-onset diabetes of the young (MODY) were analysed to evaluate the prevalence of their mutations in Thai patients with MODY and early-onset type 2 diabetes.

PATIENTS AND METHODS

Fifty-one unrelated probands with early-onset type 2 diabetes, 21 of them fitted into classic MODY criteria, were analysed for nucleotide variations in promoters, exons, and exon-intron boundaries of six known MODY genes, including HNF-4alpha, GCK, HNF-1alpha, IPF-1, HNF-1beta, and NeuroD1/beta2, by the polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) method followed by direct DNA sequencing. Missense mutations or mutations located in regulatory region, which were absent in 130 chromosomes of non-diabetic controls, were classified as potentially pathogenic mutations.

RESULTS

We found that mutations of the six known MODY genes account for a small proportion of classic MODY (19%) and early-onset type 2 diabetes (10%) in Thais. Five of these mutations are novel including GCK R327H, HNF-1alpha P475L, HNF-1alphaG554fsX556, NeuroD1-1972 G > A and NeuroD1 A322N. Mutations of IPF-1 and HNF-1beta were not identified in the studied probands.

CONCLUSIONS

Mutations of the six known MODY genes may not be a major cause of MODY and early-onset type 2 diabetes in Thais. Therefore, unidentified genes await discovery in a majority of Thai patients with MODY and early-onset type 2 diabetes.

Phenotypical aspects of maturity-onset diabetes of the young (MODY diabetes) in comparison with Type 2 diabetes mellitus (T2DM) in children and adolescents: experience from a large multicentre database

AIMS

To analyse and compare clinical characteristics in young patients with maturity-onset diabetes of the young (MODY) and Type 2 diabetes mellitus (T2DM).

METHODS

We conducted an observational investigation using the DPV-Wiss database containing clinical data on 40 757 diabetic patients < 20 years of age from Germany and Austria.

RESULTS

Three hundred and thirty-nine cases were clinically categorized as MODY (0.83%); 562 patients were diagnosed as T2DM (1.4%). In 20% of cases, the diagnosis of MODY was based on clinical findings only. Of the 272 subjects where genetic testing was available, 3% did not carry mutations in the three examined MODY genes. Glucokinase-MODY was commoner than HNF1A-MODY and HNF4A-MODY. Age at diagnosis was younger in MODY patients. The body mass index of T2DM was significantly higher compared with all MODY subgroups. Macrovascular risk factors such as dyslipidaemia and hypertension were commoner in T2DM, but 23% of MODY patients had dyslipidaemia and 10% hypertension. Glycaemic control was within the therapeutic target (HbA(1c) < 7.5%) in 86% of MODY and 70% of T2DM patients.

CONCLUSIONS

The prevalence of MODY in children and adolescents in Germany and Austria is lower than that of T2DM in this age group. Dyslipidaemia and hypertension are less frequent in MODY compared with T2DM patients, but do occur.

Childhood obesity complicating the differential diagnosis of maturity-onset diabetes of the young and type 2 diabetes

OBJECTIVE

To describe a proband with features of type 2 diabetes who was found to have concomitant maturity-onset diabetes of the young (MODY) and the consequent multigeneration genetic analysis.

DESIGN

Familial genetic analysis.

SETTING

Tertiary university medical center.

PARTICIPANTS

The proband was a 13.5-yr-old boy with marked non-ketotic hyperglycemia, obesity, systolic hypertension, and insulin resistance. His mother, maternal aunt, grandmother, and great grandmother had diabetes; his father was obese and had early ischemic heart disease.

INTERVENTIONS

Clinical examination, laboratory work-up, and DNA study.

OUTCOME MEASURES

Mutation in hepatocyte nuclear factor-1alpha gene, the most common cause of MODY.

RESULTS

The proband showed elevated C-peptide level and was negative for beta-cell antibodies. On genetic analysis for MODY, the 291fsinsC mutation was identified in all affected family members. A younger sister who was obese but had no signs of impaired glucose tolerance was also tested on the basis of these findings and was found to have the same mutation.

CONCLUSIONS

The patient, who presented with apparent type 2 diabetes, had concomitant MODY 3, inherited from his mother's side, and some features of type 2 diabetes secondary to marked obesity. This combination probably caused an earlier and more severe presentation of the disease and had significant implications for medical management. A search for MODY mutations should be considered in patients with a history of diabetes in three generations of one side of the family, even those in whom the clinical picture resembles type 2 diabetes.

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.

Diagnosis and Management of Maturity-Onset Diabetes of the Young

Maturity-onset diabetes of the young (MODY) is a dominantly inherited form of non-ketotic diabetes mellitus. It results from a primary defect of insulin secretion, and usually develops at childhood, adolescence, or young adulthood. MODY is a heterogeneous disease with regard to genetic, metabolic, and clinical features. All MODY genes have not been identified, but heterozygous mutations in six genes cause the majority of the MODY cases. By far MODY2 (due to mutations of the glucokinase gene) and MODY3 (due to mutations in hepatocyte nuclear factor-1alpha) are the most frequent. As with MODY3, all the other MODY subtypes are associated with mutations in transcription factors. The clinical presentations of the different MODY subtypes differ, particularly in the severity and the course of the insulin secretion defect, the risk of microvascular complications of diabetes, and the defects associated with diabetes. Patients with MODY2 have mild, asymptomatic, and stable hyperglycemia that is present from birth. They rarely develop microvascular disease, and seldom require pharmacologic treatment of hyperglycemia. In patients with MODY3, severe hyperglycemia usually occurs after puberty, and may lead to the diagnosis of type 1 diabetes. Despite the progression of insulin defects, sensitivity to sulfonylureas may be retained in MODY3 patients. Diabetic retinopathy and nephropathy frequently occur in patients with MODY3, making frequent follow-up mandatory. By contrast, other risk factors are not present in patients with MODY and the frequency of cardiovascular disease is not increased. The clinical spectrum of MODY is wider than initially described, and might include multi-organ involvement in addition to diabetes. In patients with MODY5, due to mutations in hepatocyte nuclear factor-1beta, diabetes is associated with pancreatic atrophy, renal morphologic and functional abnormalities, and genital tract and liver test abnormalities. Although MODY is dominantly inherited, penetrance or expression of the disease may vary and a family history of diabetes is not always present. Thus, the diagnosis of MODY should be raised in various clinical circumstances. Molecular diagnosis has important consequences in terms of prognosis, family screening, and therapy.

Genetic and clinical characteristics of maturity-onset diabetes of the young in Chinese patients

In Caucasians, maturity-onset diabetes of the young (MODY) is mostly caused by mutations in the hepatocyte nuclear factor (HNF)-1alpha (MODY3) and glucokinase (MODY2) genes. Most Japanese MODY patients, however, are not linked to known MODY genes. In this study, we examined the genetic and clinical characteristics of Chinese subjects with MODY. The study included 146 unrelated families fulfilling the minimum criteria for MODY: two consecutive generations of type II diabetes with at least one member diagnosed under the age of 25. We screened for mutations in the HNF-4alpha (MODY1), MODY2 and MODY3 genes by direct sequencing. Antibody to glutamic acid decarboxylase (GAD-Ab) was measured in subjects with MODY of unknown cause (MODYX). Insulin resistance index and other clinical data were compared in sex-, age- and duration-matched MODY3 and MODYX patients. In all, 13 families had MODY3 mutations and two had MODY2 mutations. No MODY1 mutation was found. Four of the 12 different MODY3 mutations were newly identified novel mutations (Q243E, A311D, P379R and P488fsdelC). In subjects with MODYX, 3% were GAD-Ab positive and 60% were overweight. Compared to MODY3 patients, MODYX patients had higher body mass index (P<0.02), higher insulin resistance index (P=0.001) and triglyceride level (P<0.02), lower HDL level (P=0.001) and more hypertension (P<0.05), but no significant difference in the prevalence of diabetic complications. In conclusion, MODY3 and MODY2 account for only 9 and 1%, respectively, of Chinese MODY. A majority of Chinese MODY patients are due to defects in unknown genes and appear to be characterized by insulin resistance.

Genetic modifiers of the age at diagnosis of diabetes (MODY3) in carriers of hepatocyte nuclear factor-1alpha mutations map to chromosomes 5p15, 9q22, and 14q24

Mutations in hepatocyte nuclear factor (HNF)-1alpha (MODY3) account for the largest proportion of maturity-onset diabetes of the young (MODY) cases in the U.S. This form of diabetes is characterized by impaired insulin secretion in response to glucose, but wide variability exists in the severity of hyperglycemia and in the age at which it becomes clinically manifest. We have previously shown that the age at onset of diabetes in MODY3 families is influenced by familial factors (including modifying genes) and exposure to diabetes in utero. To identify genes influencing the onset of MODY3, we conducted a genome scan in 13 extended MODY families in which diabetes segregates with an HNF-1alpha mutation. Linkage with age at onset of diabetes was assessed by genetic variance component analysis using SOLAR. The locus with the strongest evidence of linkage was on chromosome 14q24 (D14S588; logarithm of odds [LOD] = 2.58, P = 0.0004). This location overlaps with IDDM11 and includes SEL1L, a negative regulator of the Notch pathway that may control islet development. Linkage evidence also supported loci on 5p15 (D5S817; LOD = 2.44, P = 0.0004) and 9q22 (D9S910; LOD = 2.02, P = 0.0018). The latter matches a region linked to 2-h insulin levels in Pima Indians. Less strong linkage evidence was observed at three other regions: chromosomes 3p24 (LOD = 1.44), 7q21 (1.20), and 16q23 (1.51). Our data are consistent with the existence of multiple loci that contribute to the expression of the MODY3 phenotype. Identification of these genes will offer new insights into the pathophysiology of MODY that may, in turn, increase our understanding of the cellular events underlying more common forms of diabetes.

A genome-wide scan in families with maturity-onset diabetes of the young: evidence for further genetic heterogeneity

Maturity-onset diabetes of the young (MODY) is a heterogeneous single gene disorder characterized by non-insulin-dependent diabetes, an early onset and autosomal dominant inheritance. Mutations in six genes have been shown to cause MODY. Approximately 15-20% of families fitting MODY criteria do not have mutations in any of the known genes. These families provide a rich resource for the identification of new MODY genes. This will potentially enable further dissection of clinical heterogeneity and bring new insights into mechanisms of beta-cell dysfunction. To facilitate the identification of novel MODY loci, we combined the results from three genome-wide scans on a total of 23 families fitting MODY criteria. We used both a strict parametric model of inheritance with heterogeneity and a model-free analysis. We did not identify any single novel locus but provided putative evidence for linkage to chromosomes 6 (nonparametric linkage [NPL]score 2.12 at 71 cM) and 10 (NPL score 1.88 at 169-175 cM), and to chromosomes 3 (heterogeneity LOD [HLOD] score 1.27 at 124 cM) and 5 (HLOD score 1.22 at 175 cM) in 14 more strictly defined families. Our results provide evidence for further heterogeneity in MODY.

Determinants of the development of diabetes (maturity-onset diabetes of the young-3) in carriers of HNF-1alpha mutations: evidence for parent-of-origin effect

OBJECTIVE

To determine the distribution of the age at onset of diabetes (maturity-onset diabetes of the young-3 [MODY3]) and to identify determinants of the onset of diabetes in carriers of HNF-1alpha mutations.

RESEARCH DESIGN AND METHODS

Extended families (n = 104) with type 2 diabetes inherited in a dominant pattern were recruited and screened for diabetes-causing mutations in HNF-1alpha.

RESULTS

HNF-1alpha mutations cosegregated with diabetes in only 13 families, all with a mean age at onset <35 years. Insulin secretion was diminished or absent in mutation carriers (n = 101), and diabetes developed in 65% by age 25 years and in 100% by age 50 years. If the mutation was inherited from the mother, diabetes onset was very young in those exposed to diabetes in utero; 57 +/- 8% were affected by age 15 years as compared with 0.0% in those not exposed (P < 7 x 10(-6)). By age 25 years, the difference was reduced (85 +/- 6 and 55 +/- 12%, respectively; P = 0.02). If the mutation was inherited from the father, diabetes developed in 52 +/- 8% by age 25 years. Age at diagnosis was shown to be highly heritable (h(2) = 0.47, P = 0.003). When parent of origin was included in the analyses, the magnitude of genetic contribution increased markedly (h(2) = 0.91).

CONCLUSIONS

Mutations in HNF-1alpha accounts for diabetes in a small proportion of families with a dominant pattern of inheritance. Age at onset of diabetes in MODY3 families varied widely and was influenced by familial factors (including modifying genes) and parent of origin (whether a mutation carrier was exposed to diabetes in utero).

Prevalence and characteristics of early-onset type 2 diabetes in Mexico

OBJECTIVE

To investigate the prevalence and characteristics of patients with type 2 diabetes diagnosed before the age of 40 years (early-onset disease) in a nationwide, population-based study.

METHODS

Using a multistage sampling procedure, we enrolled a representative sample of Mexican urban adults aged 20 to 69 years. Weight, height, blood pressure, and plasma levels of glucose, insulin, and other metabolic parameters were measured in all subjects.

RESULTS

We identified 993 subjects with type 2 diabetes, including 143 subjects aged 20 to 39 years (14% of those with diabetes). Subjects with early-onset diabetes had a greater prevalence of obesity and higher plasma insulin and lipid levels than did age-matched controls, and a greater prevalence of high-density lipoprotein cholesterol levels <35 mg/dL and severe hypertriglyceridemia than did older subjects with diabetes. Those (n = 32) with a normal body mass index (20 to 25 kg/m(2)) tended to have insulin deficiency as the main abnormality, whereas the "metabolic syndrome" characterized the remaining 111 subjects with early-onset diabetes.

CONCLUSION

Most patients with early-onset type 2 diabetes in Mexico are obese or overweight, suggesting that obesity treatment and prevention programs may be effective in reducing the prevalence of this disease.

Contribution of known and unknown susceptibility genes to early-onset diabetes in scandinavia: evidence for heterogeneity

In an attempt to identify novel susceptibility genes predisposing to early-onset diabetes (EOD), we performed a genome-wide scan using 433 markers in 222 individuals (119 with diabetes) from 29 Scandinavian families with > or =2 members with onset of diabetes < or =45 years. The highest nonparametric linkage (NPL) score, 2.7 (P < 0.01), was observed on chromosome 1p (D1S473/D1S438). Six other regions on chromosomes 3p, 7q, 11q, 18q, 20q, and 21q showed a nominal P value <0.05. Of the EOD subjects in these 29 families, 20% were GAD antibody positive and 68% displayed type 1 diabetes HLA risk alleles (DQB*02 or 0302). Mutations in maturity-onset diabetes of the young (MODY) 1-5 genes and the A3243G mitochondrial DNA mutation were detected by single-strand conformation polymorphism and direct sequencing. To increase homogeneity, we analyzed a subsample of five families with autosomal dominant inheritance of EOD (greater than or equal to two members with age at diagnosis < or =35 years). The highest NPL scores were found on chromosome 1p (D1S438-D1S1665; NPL 3.0; P < 0.01) and 16q (D16S419; NPL 2.9; P < 0.01). After exclusion of three families with MODY1, MODY3, and mitochondrial mutations, the highest NPL scores were observed on chromosomes 1p (D1S438; NPL 2.6; P < 0.01), 3p (D3S1620; NPL 2.2; P < 0.03), 5q (D5S1465; NPL 2.1; P < 0.03), 7q (D7S820; NPL 2.0; P < 0.03), 18q (D18S535; NPL 1.9; P < 0.04), 20q (D20S195; NPL 2.5; P < 0.02), and 21q (D21S1446; NPL 2.2; P < 0.03). We conclude that considerable heterogeneity exists in Scandinavian subjects with EOD; 24% had MODY or maternally inherited diabetes and deafness, and approximately 60% were GAD antibody positive or had type 1 diabetes-associated HLA genotypes. Our data also point at putative chromosomal regions, which could harbor novel genes that contribute to EOD.

Genetic variability in insulin action inhibitor Ikkbeta (IKBKB) does not play a major role in the development of type 2 diabetes

Recent evidence indicates that IkappaB kinase beta (Ikkbeta) may be a mediator of acquired forms of insulin-resistance. In this study, we examined whether genetic variability at the Ikkbeta locus (IKBKB) contributes to the development of genetic forms of early-onset type 2 diabetes transmitted with an autosomal dominant mode of inheritance. Linkage with four markers flanking the IKBKB gene was evaluated in 32 multigenerational families. Included in the study were 233 diabetic (mean age at Dx = 37 +/- 18) and 152 nondiabetic subjects. The overall LOD scores were negative (-54.9 and -46.2 on the centromeric and telomeric sides, respectively) indicating that variability in IKBKB was not a major determinant of diabetes in these families. Positive values, however, were observed for selected pedigrees. All 17 families for which linkage with the IKBKB locus could not be excluded were screened for sequence differences in the 22 exons and 1.6 kb of the 5' flanking region by dideoxyfingerprinting or direct sequencing. Polymorphisms were identified in the 5' flanking region (-1775del/insC and -1547T > A), exon 11 (c.1083A > G, L361L) and in intron 12 (IVS12+14t > a). However, no mutations segregating with diabetes could be found in these families. Furthermore, all four polymorphisms had similar allele frequencies in the 32 family probands, 171 individuals with common, later-onset type 2 diabetes, and 182 nondiabetic controls. We conclude that sequence differences in the IKBKB gene do not play a major role in either early-onset, autosomal dominant type 2 diabetes, or common forms with a later-onset.

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.

The insulin gene in diabetes

Lack of insulin production or abnormalities affecting insulin secretion are key to the development of almost all forms of diabetes, including the common type 1 (insulin-dependent) and type 2 (non-insulin-dependent) diabetes and the more rare forms of maturity-onset diabetes of the young (MODY). Because insulin has such a central role in the pathogenesis of both forms of diabetes, the insulin gene (INS) has always been considered a candidate susceptibility gene. A number of studies have shown that the allelic variation and parent-of-origin effects affect the transmission and expression of the insulin gene in pancreatic beta-cells and extra-pancreatic tissues. These observations have led to the formulation of new hypotheses to explain the biological mechanisms by which functional differences in the expression of the insulin gene may contribute to diabetes susceptibility.

Familial early-onset type 2 diabetes in Chinese patients: obesity and genetics have more significant roles than autoimmunity

OBJECTIVE

We examined the prevalence of different forms of diabetes in Hong Kong Chinese patients with familial early-onset type 2 diabetes and compared their clinical features with patients with familial late-onset type 2 diabetes.

RESEARCH DESIGN AND METHODS

A total of 145 young patients with early-onset diabetes (age and age at diagnosis < or = 40 years) and a family history of diabetes were studied. They were screened for mutations in the genes encoding glucokinase, hepatocyte nuclear factor (HNF)-4alpha, and HNF-1alpha. The mitochondrial DNA A-->G at nucleotide 3243 (mt3243) and amyLin S20G mutations were studied, and antibodies to GAD (anti-GADs) were also examined.

RESULTS

The prevalence of putative diabetogenic gene mutations and autoimmune markers were 4% for glucokinase, 0% for HNF-4alpha, 5% for HNF-1alpha, 3% for mt3243, 2% for amylin 520G, and 4% for anti-GAD. Compared with late-onset patients, the patients with early-onset diabetes had a higher prevalence of a parental history of diabetes and were generally more obese. When classified by obesity indexes (BMI and waist circumference), the obese patients, especially those with early-onset diabetes, had a clustering of cardiovascular risk factors and increased rates of retinopathy and albuminuria. CONCLUSIONS; Genetic factors (up to 14%) and obesity (55%) play more significant roles than autoimmunity (4%) in familial type 2 diabetes in young Chinese patients. The significance of obesity-related genes and other gene-gene and gene-environment interactions in these young patients remains to be determined.

Mutations in the small heterodimer partner gene are associated with mild obesity in Japanese subjects

Mutations in several genes encoding transcription factors of the hepatocyte nuclear factor (HNF) cascade are associated with maturity-onset diabetes of the young (MODY), a monogenic form of early-onset diabetes mellitus. The ability of the orphan nuclear receptor small heterodimer partner (SHP, NR0B2) to modulate the transcriptional activity of MODY1 protein, the nuclear receptor HNF-4alpha, suggested SHP as a candidate MODY gene. We screened 173 unrelated Japanese subjects with early-onset diabetes for mutations in this gene and found five different mutations (H53fsdel10, L98fsdel9insAC, R34X, A195S, and R213C) in 6 subjects as well as one apparent polymorphism (R216H), all present in the heterozygous state. Interestingly, all of the subjects with the mutations were mildly or moderately obese at onset of diabetes, and analysis of the lineages of these individuals indicated that the SHP mutations were associated with obesity rather than with diabetes. Therefore, an additional group of 101 unrelated nondiabetic subjects with early-onset obesity was screened for mutations in the SHP gene. Two of the previously observed mutations (R34X and A195S) and two additional mutations (R57W and G189E) were identified in 6 subjects, whereas no mutations were identified in 116 young nondiabetic lean controls (P = 0.0094). Functional studies of the mutant proteins show that the mutations result in the loss of SHP activity. These results suggest that genetic variation in the SHP gene contributes to increased body weight and reveal a pathway leading to this common metabolic disorder in Japanese.

Mutations in the small heterodimer partner gene are associated with mild obesity in Japanese subjects

Mutations in several genes encoding transcription factors of the hepatocyte nuclear factor (HNF) cascade are associated with maturity-onset diabetes of the young (MODY), a monogenic form of early-onset diabetes mellitus. The ability of the orphan nuclear receptor small heterodimer partner (SHP, NR0B2) to modulate the transcriptional activity of MODY1 protein, the nuclear receptor HNF-4alpha, suggested SHP as a candidate MODY gene. We screened 173 unrelated Japanese subjects with early-onset diabetes for mutations in this gene and found five different mutations (H53fsdel10, L98fsdel9insAC, R34X, A195S, and R213C) in 6 subjects as well as one apparent polymorphism (R216H), all present in the heterozygous state. Interestingly, all of the subjects with the mutations were mildly or moderately obese at onset of diabetes, and analysis of the lineages of these individuals indicated that the SHP mutations were associated with obesity rather than with diabetes. Therefore, an additional group of 101 unrelated nondiabetic subjects with early-onset obesity was screened for mutations in the SHP gene. Two of the previously observed mutations (R34X and A195S) and two additional mutations (R57W and G189E) were identified in 6 subjects, whereas no mutations were identified in 116 young nondiabetic lean controls (P = 0.0094). Functional studies of the mutant proteins show that the mutations result in the loss of SHP activity. These results suggest that genetic variation in the SHP gene contributes to increased body weight and reveal a pathway leading to this common metabolic disorder in Japanese.

Type 2 diabetes locus on 12q15. Further mapping and mutation screening of two candidate genes

We recently reported evidence of a novel type 2 diabetes locus placed on chromosome 12q15 between markers D12S375 and D12S1684 (Diabetes 48:2246-2251, 1999). Four multigenerational families having logarithm of odds (LOD) scores >1.0 in the original analysis were genotyped for 11 additional markers in this interval to refine this mapping; this allowed us to narrow the linked region to the interval between markers D12S1693 and D12S326. In a multipoint parametric analysis using the VITESSE software, the LOD score for linkage at this location reached 3.1 in one of these families. This interval contains the gene for protein tyrosine phosphatase receptor type R (PTPRR)--a protein that may be involved in both insulin secretion and action. After determining PTPRR exon-intron structure, we identified several polymorphisms in this gene but no mutation segregating with diabetes. The search for mutations was also negative for carboxypeptidase M (CPM)--another candidate gene mapped to this region. In summary, our data provide further evidence for the existence of a type 2 diabetes locus on chromosome 12q15. This locus, however, does not appear to correspond to the PTPRR or CPM, although a contribution of mutations in regulatory regions cannot be excluded at this time.

Molecular and genetic bases for maturity onset diabetes of youth

Maturity onset diabetes of youth (MODY) occurs in children, adolescents and young adults as a non-insulin-requiring form of diabetes mellitus that is inherited as an autosomal dominant trait. Maturity onset diabetes of youth in whites presents subtly similar to type 2 diabetes in adults. In contrast, a MODY variant that occurs in young blacks, termed atypical diabetes mellitus, presents as an acute-onset form of diabetes. Months to years after diagnosis, atypical diabetes mellitus reverts to a noninsulin requiring course similar to MODY in whites. Five molecular causes for MODY have been identified: mutations in four transcription factors and mutations in one enzyme (glucokinase). Transcription factors regulate gene expression within cells. Mutations in hepatocyte nuclear factor-4alpha, hepatocyte nuclear factor-1alpha, insulin promoter factor-1 and hepatocyte nuclear factor-1beta, respectively, cause MODY1, MODY3, MODY4, and MODY5. Glucokinase is the glucosensor of the beta cell. MODY2 is caused by glucokinase mutations. Although testing for MODY mutations is only available in research laboratories, a careful history and review of the patient's clinical course can often allow the clinician to diagnose MODY. The diagnosis of MODY has implications for the clinical management of the patient's diabetes.

Role of islet autoimmunity in the aetiology of different clinical subtypes of diabetes mellitus in young north Indians

AIMS

To determine the role of islet autoimmunity in the aetiology of different clinical subtypes of diabetes mellitus in young north Indian patients by measuring islet autoantibodies.

METHODS

In a cross-sectional study, 145 young patients with diabetes (onset < 30 years) were subdivided into the following categories: Type 1 diabetes (n = 83), malnutrition-modulated diabetes mellitus (MMDM, n = 31) and fibro-calculous pancreatic diabetes (FCPD, n = 31). MMDM subjects presented with emaciation and severe insulin-requiring but ketosis-resistant diabetes, while FCPD was associated with idiopathic chronic calcific pancreatitis. Antibodies to glutamic acid decarboxylase (GADA) and IA-2 (IA-2 A) were detected by immunoprecipitation of 35S-labelled recombinant antigens and cytoplasmic islet cell antibody (ICA) by indirect immunofluorescence.

RESULTS

GADA were present in a significant proportion (23%) of patients with MMDM. In contrast, IA-2 A was increased only among patients with Type 1 diabetes (22%), but not MMDM (3%, P < 0.05). Among patients with a duration of diabetes < 2 years, GADA and/or IA-2 A were found in 61% of Type 1 diabetic and 37% of MMDM patients (P < 0.01). MMDM patients who were positive for GADA had a shorter duration of diabetes, but did not differ in their age at onset of diabetes, body mass index, fasting plasma C-peptide, or frequency of thyroid microsomal and parietal cell antibodies. FCPD subjects had the lowest prevalence of autoantibodies: IA-2 and ICA were absent, while GADA were present in 7% (P < 0.05 vs. Type 1 diabetes).

CONCLUSIONS

GADA, though not IA-2 A, were present in a substantial proportion of patients with the MMDM variant of diabetes, suggesting that islet autoimmunity may play a role in its pathogenesis. In contrast, none of the islet antibodies was increased in subjects with FCPD, making it likely that it is a secondary type of diabetes.

Urinary albumin excretion in families with type 2 diabetes is heritable and genetically correlated to blood pressure

Urinary albumin excretion in families with type 2 diabetes is heritable and genetically correlated to blood pressure.

BACKGROUND

Levels of urinary albumin excretion (UAE) are used to define both the diagnosis of diabetic nephropathy and its progression. Predisposition to high blood pressure is also a risk factor for susceptibility to nephropathy, but its relationship with UAE in type 2 diabetes remains unclear. In this study, we have estimated heritabilities of UAE and blood pressure and their correlation attributable to genetic effects using 96 large families ascertained for type 2 diabetes.

METHODS

In these families, 630 individuals with type 2 diabetes and 639 individuals with normoglycemia were examined. All of them had a determination of UAE as the urinary albumin creatinine ratio (ACR), a convenient index of UAE, together with blood pressure and other variables, such as age, sex, and body mass index. A variance components approach was used to estimate heritability and genetic correlations for ACR and systolic and diastolic blood pressures (SBP and DBP) after adjustment for relevant covariates.

RESULTS

In the 96 pedigrees, 6481 usable pairs of relatives were identified. In the total collection of pairs, heritability for ACR (h2 = 0.27, P < 0.001) was similar to that for blood pressure. When only pairs of diabetic relatives were analyzed (N = 1732), the estimates of heritability increased slightly for ACR (h2 = 0.31), SBP (h2 = 0.33), and DBP (h2 = 0.23). A significant genetic correlation was found between ACR and SBP (rg 0.27) and DBP (rg 0.26) in all pairs of relatives (P < 0.001). In pairs of diabetic relatives, these values were higher for SBP and DBP, 0.38 and 0.52, respectively.

CONCLUSION

In families with type 2 diabetes, UAE is a heritable trait, with a heritability similar to that for blood pressure. A significant genetic correlation between UAE and blood pressure, particularly in the presence of diabetes, indicates that these traits share common genetic determinants.

Monogenic diabetes mellitus in youth. The MODY syndromes

Maturity onset diabetes of the young is characterized by early onset diabetes inherited in an autosomal dominant pattern. Classic MODY occurs predominantly in Caucasians and presents before age 25, is nonketotic, and is generally not insulin-requiring. Less than 5% of cases of childhood diabetes in Caucasians are caused by MODY. ADM is a subtype of MODY that occurs in approximately 10% of African-Americans with youth onset diabetes. In contrast to MODY in Caucasians, ADM presents clinically as acute onset diabetes often associated with weight loss, ketosis, and even diabetic ketoacidosis. Approximately 50% of patients with ADM are obese. Therefore, based strictly on clinical grounds, at onset, ADM cannot be distinguished from type 1 diabetes. Months to years following diagnosis, a non-insulin-dependent clinical course develops in patients with ADM that is clearly different from type 1 diabetes. Mutations in five genes can cause MODY. These genes encode hepatocyte nuclear factor-4 alpha (HNF-4 alpha, MODY1), glucokinase (MODY2), hepatocyte nuclear factor-1 alpha (HNF-1 alpha, MODY3), insulin promoter factor-1 (IPF-1, MODY4), and hepatocyte nuclear factor-1 beta (HNF-1 beta, MODY5). These monogenic forms of MODY have been used as model systems to investigate the inheritance and pathophysiology of type 2 diabetes. Clinicians, should be able to diagnose MODY. Type 1 diabetes, the most common form of diabetes in Caucasians, is always insulin-requiring for control and survival, whereas patients with MODY do not usually require long-term insulin for survival. Diagnostic confusion can lead to inappropriate management and patient expectations. Primary care physicians must be alert to avoid therapeutic confusion when patients with ADM enter into the non-insulin-dependent stage. An approach to the diagnosis of childhood diabetes is offered in Table 4. The majority of youth onset diabetes remains type 1; however, the frequency of type 2 diabetes is rising in obese children and adolescents and especially in obese minority youth. The diagnosis of MODY can be made through a careful review of the patient's clinical course, severity of hyperglycemia, and family history. The identification of islet autoantibodies is confirmatory evidence of autoimmune (type 1) diabetes. Because testing for MODY mutations is expensive and is performed at a select number of research laboratories only, routine molecular genetic studies to search for the various MODY mutations should be limited to research investigations. In the future, the availability of gene chip technology may allow rapid screening of mitochondrial and MODY mutations.

Mutations in NEUROD1 are associated with the development of type 2 diabetes mellitus

The helix-loop-helix (HLH) protein NEUROD1 (also known as BETA2) functions as a regulatory switch for endocrine pancreatic development. In mice homozygous for a targeted disruption of Neurod, pancreatic islet morphogenesis is abnormal and overt diabetes develops due in part to inadequate expression of the insulin gene (Ins2). NEUROD1, following its heterodimerization with the ubiquitous HLH protein E47, regulates insulin gene (INS) expression by binding to a critical E-box motif on the INS promoter. Here we describe two mutations in NEUROD1, which are associated with the development of type 2 diabetes in the heterozygous state. The first, a missense mutation at Arg 111 in the DNA-binding domain, abolishes E-box binding activity of NEUROD1. The second mutation gives rise to a truncated polypeptide lacking the carboxy-terminal trans-activation domain, a region that associates with the co-activators CBP and p300 (refs 3,4). The clinical profile of patients with the truncated NEUROD1 polypeptide is more severe than that of patients with the Arg 111 mutation. Our findings suggest that deficient binding of NEUROD1 or binding of a transcriptionally inactive NEUROD1 polypeptide to target promoters in pancreatic islets leads to the development of type 2 diabetes in humans.