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

Identification of monogenic diabetes in an Australian cohort using the Exeter maturity-onset diabetes of the young (MODY) probability calculator and next-generation sequencing gene panel testing

AIMS

This study aims to describe the prevalence of monogenic diabetes in an Australian referral cohort, in relation to Exeter maturity-onset diabetes of the young (MODY) probability calculator (EMPC) scores and next-generation sequencing with updated testing where relevant.

METHODS

State-wide 5-year retrospective cohort study of individuals referred for monogenic diabetes genetic testing.

RESULTS

After excluding individuals who had cascade testing for a familial variant (21) or declined research involvement (1), the final cohort comprised 40 probands. Incorporating updated testing, the final genetic result was positive (likely pathogenic/pathogenic variant) in 11/40 (27.5%), uncertain (variant of uncertain significance) in 8/40 (20%) and negative in 21/40 (52.5%) participants. Causative variants were found in GCK, HNF1A, MT-TL1 and HNF4A. Variants of uncertain significance included a novel multi-exonic GCK duplication. Amongst participants with EMPC scores ≥ 25%, a causative variant was identified in 37%. Cascade testing was positive in 9/10 tested relatives with diabetes and 0/6 tested relatives with no history of diabetes.

CONCLUSIONS

Contemporary genetic testing produces a high yield of positive results in individuals with clinically suspected monogenic diabetes and their relatives with diabetes, highlighting the value of genetic testing for this condition. An EMPC score cutoff of ≥ 25% correctly yielded a positive predictive value of ≥ 25% in this multiethnic demographic. This is the first Australian study to describe EMPC scores in the Australian clinic setting, albeit a biased referral cohort. Larger studies may help characterise EMPC performance between ethnic subsets, noting differences in the expected probability of monogenic diabetes relative to type 2 diabetes.

Vitamin D Receptor Gene ApaI and TaqI Polymorphisms in Type 2 Diabetes among Saudi Population

Background: Variants of vitamin D receptor (VDR) gene have been linked to a variety of diseases, including metabolic syndrome, cancer, bone disease, and tuberculosis. The relationship between VDR gene mutations and the susceptibility of type 2 diabetes mellitus (T2DM) in different ethnic groups is yet unknown. Vitamin D and its receptor complex have a function in regulating β-cell insulin secretion as a transcription factor. Objectives: The goal of this study was to see if there is a link between VDR Apa1 and Taq1 polymorphisms and T2DM susceptibility in the Saudis of Makkah environ. Materials and Methods: DNA was separated from peripheral blood and genotyped in 110 healthy controls and 110 unrelated people with T2DM for the VDR ApaI (G/T) rs7975232 and TaqI (A/G) rs731236 single nucleotide polymorphisms (SNPs) using polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP) technique. Results: The distributions of genotypes and alleles of VDR ApaI and TaqI polymorphisms were statistically indifferent across the groups investigated (P >0.05). Conclusion: These findings showed that polymorphisms in the VDR ApaI and TaqI genes may not be linked to T2DM risk in Saudis.

Hepatic energy metabolism in a family with a glucokinase gene mutation and dysglycemia

Carriers heterozygous for the D124N (c.370, GAC > AAC in exon 4) variant of GCK not only exhibit reduced insulin-secretion, but also impaired adipose insulin sensitivity, which may shift fatty acids towards the liver. This could contribute to increased hepatic lipid-accumulation and alterations of liver energy metabolism resulting in dysglycemia. ClinicalTrial.gov registration no: NCT01055093.

Screening for extremely rare pathogenic variants of monogenic diabetes using targeted panel sequencing

AIMS

Maturity-onset diabetes of the young (MODY) is one of the rare monogenic forms of diabetes. To date, about 12 genes in the scientific literature are closely related to the occurrence of the disease phenotype. However, there is still a high prevalence of undiagnosed cases of so-called MODY-X whose genetic background is still unknown.

METHODS

We performed tNGS for 523 patients with suspected MODY. Next 357 selected patients, in whom no damaging variants were found in 12 major genes causing MODY, were screened for the presence of pathogenic variants in four candidate genes (MNX1, RFX6, NKX2.2, and NKX6.1). All data were generated in one tNGS sequencing reaction and confirmed by Sanger sequencing.

RESULTS

In total, we selected five potentially damaging variants, in eight patients, in RFX6, NKX2.2, and NKX6.1 genes. Four of them have never been described in literature before. The frequency of occurrence of two of them in the RFX6 gene significantly differed in relation to the healthy population. The analysis of segregation in the family did not reveal that they were the only cause of the disease phenotype.

CONCLUSIONS

The very-rare variants indicated in this study show that this type of research on large population groups may help in the future for better understanding and more accurate diagnostics of extremely rare forms of MODY.

Association of Vitamin D Receptor Gene Polymorphisms With the Evolution of MODY Diabetes: Study in Tunisian Patients

Vitamin D (VD) cannot be considered as a true vitamin, but rather as a hormone, which exerts its action via a vitamin D receptor (VDR). Many genes have been shown to be involved in the evolution of diabetes in various populations, such as the vitamin D receptor gene. The aim of our study was to investigate if BsmI, TaqI, ApaI, FokI, and Tru9I, polymorphisms of VDR gene have an impact on MODY diabetes and its clinical aspects in a Tunisian population. A total of 95 patients and 153 controls were genotyped using PCR-RFLP. The comparison of the allelic and genotypic frequencies of the five polymorphisms between MODY subjects and control groups revealed the association of MODY diabetes with TaqI, Tru9I and BsmI polymorphisms and no significant differences were observed in the distributions for the ApaI and FokI polymorphisms. After stratification with biochemical and clinical parameters and TaqI, Tru9I and BsmI polymorphisms, we found an association between the three SNPs and different parameters such as age of diagnosis, therapy, hsCRP and HDL-C levels. Our results revealed that TaqI, Tru9I and BsmI polymorphisms may be more related to the progression of MODY diabetes. The possible role of vitamin D in the pathogenesis of MODY is far from being completely understood. Further knowledge on this issue may identify new candidate targets in the treatment and prevention of the disease. Our findings suggest that the TaqI, Tru9I and BsmI polymorphisms may be more related to the progression of MODY diabetes.

Simplifying Detection of Copy-Number Variations in Maturity-Onset Diabetes of the Young

OBJECTIVES

Copy-number variations (CNVs) are large-scale deletions or duplications of DNA that have required specialized detection methods, such as microarray-based genomic hybridization or multiplex ligation probe amplification. However, recent advances in bioinformatics have made it possible to detect CNVs from next-generation DNA sequencing (NGS) data. Maturity-onset diabetes of the young (MODY) 5 is a subtype of autosomal-dominant diabetes that is often caused by heterozygous deletions involving the HNF1B gene on chromosome 17q12. We evaluated the utility of bioinformatic processing of raw NGS data to detect chromosome 17q12 deletions in MODY5 patients.

METHODS

NGS data from 57 patients clinically suspected to have MODY but who were negative for pathogenic mutations using a targeted panel were re-examined using a CNV calling tool (CNV Caller, VarSeq version 1.4.3). Potential CNVs for MODY5 were then confirmed using whole-exome sequencing, cytogenetic analysis and breakpoint analysis when possible.

RESULTS

Whole-gene deletions in HNF1B, ranging from 1.46 to 1.85 million basepairs in size, were detected in 3 individuals with features of MODY5. These were confirmed by independent methods to be part of a more extensive 17q12 deletion syndrome. Two additional patients carrying a 17q12 deletion were subsequently diagnosed using this method.

CONCLUSIONS

Large-scale deletions are the most common cause of MODY5 and can be detected directly from NGS data, without the need for additional methods.

MODY2 in Asia: analysis of GCK mutations and clinical characteristics

AIMS

Heterozygous inactivating mutations in the GCK gene cause the familial, mild fasting hyperglycaemia named MODY2. Many patients with MODY2 in Asia have delayed timely treatment because they did not receive the correct diagnosis. This study aims to analyze the clinical characteristics and GCK mutations in Asian MODY2.

METHODS

We have collected 110 Asian patients with MODY2 from the PubMed, Embase, Medline, Web of Science, CNKI, and Wanfang with the following search terms: 'maturity-onset diabetes of the young' OR 'MODY' OR 'maturity-onset diabetes of the young type 2' OR 'MODY2' OR 'GCK-DM' OR 'GCK-MODY'. Both mutations of GCK and clinical characteristics of MODY2 were analyzed.

RESULTS

There were 96 different mutations that occurred in coding regions and non-coding regions. Exon 5 and 7 were the most common location in coding regions and missense was the primary mutation type. The proportion of probands younger than 25 was 81.8%, and 81.4% of the probands had family history of hyperglycaemia. Ninety percent and 93% of Asian MODY2 probands exhibited mild elevation in FPG (5.4-8.3 mmol/L) and HbA1c (5.6-7.6%), respectively.

CONCLUSIONS

In most Asian patients, MODY2 occurred due to GCK mutation in coding regions, and exon 5 and 7 were the most common locations. FPG, HbA1c, and familial diabetes were important reference indicators for diagnosing MODY2. Altogether, the study indicates that for the young onset of diabetes with mild elevated blood glucose and HbA1c and family history of hyperglycaemia, molecular genetic testing is suggested in order to differentiate MODY2 from other types of diabetes earlier.

Copy Number Variation in GCK in Patients With Maturity-Onset Diabetes of the Young

PURPOSE

Next generation sequencing (NGS) methods to diagnose maturity-onset diabetes of the young (MODY), a monogenic autosomal dominant cause of diabetes, do not typically detect large-scale copy number variations (CNVs). New techniques may allow assessment for CNVs using output data from targeted NGS, without requiring additional sequencing. Using this technique, two kindreds of patients presenting with features of MODY were found to bear the same heterozygous large-scale deletion in GCK.

METHODS

Patients suspected of having MODY but with negative targeted NGS pathogenic variant calling were reanalyzed using the CNV caller tool (VarSeq v1.4.3). Two patients were identified as having a possible heterozygous whole exon deletion affecting exon 1 of GCK. For confirmation and determination of the exact breakpoints, whole exome sequencing followed by Sanger sequencing were used. Familial samples from both affected and nonaffected first-degree relatives were then analyzed for each proband.

RESULTS

A heterozygous whole-exon deletion spanning 4763 bp affecting the entire exon 1 of GCK was detected in two apparently unrelated patients with clinical features of MODY. This deletion showed segregation concordance across generations in affected and nonaffected family members.

CONCLUSIONS

Our findings confirm the utility of applying the CNV caller tool to screen for CNVs in GCK from NGS data. In so doing, we identified a deletion of exon 1 of GCK as likely causal for MODY. Our data indicate that incorporating CNV analysis routinely when assessing for MODY via targeted NGS may increase diagnostic yield and reduce false negative genetic testing rates.

Searching for mutations in the HNF1B gene in a Brazilian cohort with renal cysts and hyperglycemia

OBJECTIVE

To verify the presence of variants in HNF1B in a sample of the Brazilian population selected according to the presence of renal cysts associated with hyperglycemia.

SUBJECTS AND METHODS

We evaluated 28 unrelated patients with clinical suspicion of HNF1B mutation because of the concomitant presence of diabetes mellitus (DM) or prediabetes and renal cysts. Genotyping was accomplished using Sanger sequencing or multiplex ligation-dependent probe amplification (MLPA). In positive cases, available relatives were recruited.

RESULTS

We found two patients with HNF1B mutations. The first presented the variant p.Pro328Leufs*48(c.983delC) and had DM, renal cysts, and hypomagnesemia. The second presented a heterozygous whole gene deletion in HNF1B, DM, renal cysts, body and tail pancreatic agenesis, and hypomagnesemia; this alteration was also found in his two siblings and his father.

CONCLUSION

The recruitment of suspected cases of HNF1B gene mutations in Brazilians due to hyperglycemia and renal cysts presents two positive cases. Our cases contribute to the annotation of clinical and biochemical phenotypes of this rare form of maturity-onset diabetes of the young (MODY).

More than kin, less than kind: one family and the many faces of diabetes in youth

Identification of the correct etiology of diabetes brings important implications for clinical management. In this report, we describe a case of a 4-year old asymptomatic girl with diabetes since age 2, along with several individuals in her family with different etiologies for hyperglycemia identified in youth. Genetic analyses were made by Sanger sequencing, laboratory measurements included HbA1c, lipid profile, fasting C-peptide, pancreatic auto-antibodies (glutamic acid decarboxylase [GAD], Islet Antigen 2 [IA-2], and anti-insulin). We found a Gly178Ala substitution in exon 5 of GCK gene in three individuals co-segregating with diabetes, and type 1 diabetes was identified in two other individuals based on clinical and laboratory data. One individual with previous gestational diabetes and other with prediabetes were also described. We discuss difficulties in defining etiology of hyperglycemia in youth in clinical practice, especially monogenic forms of diabetes, in spite of the availability of several genetic, laboratory, and clinical tools.

The prevalence of monogenic diabetes in Australia: the Fremantle Diabetes Study Phase II

OBJECTIVE

To determine the prevalence of monogenic diabetes in an Australian community.

DESIGN

Longitudinal observational study of a cohort recruited between 2008 and 2011.

SETTING

Urban population of 157 000 people (Fremantle, Western Australia).

PARTICIPANTS

1668 (of 4639 people with diabetes) who consented to participation (36.0% participation).

MAIN OUTCOME MEASURES

Prevalence of maturity-onset diabetes of the young (MODY) and permanent neonatal diabetes in patients under 35 years of age, from European and non-European ethnic backgrounds, who were at risk of MODY according to United Kingdom risk prediction models, and who were then genotyped for relevant mutations.

RESULTS

Twelve of 148 young participants with European ethnic backgrounds (8%) were identified by the risk prediction model as likely to have MODY; four had a glucokinase gene mutation. Thirteen of 45 with non-European ethnic backgrounds (28%) were identified as likely to have MODY, but none had a relevant mutation (DNA unavailable for one patient). Two patients with European ethnic backgrounds (one likely to have MODY) had neonatal diabetes. The estimated MODY prevalence among participants with diagnosed diabetes was 0.24% (95% confidence interval [CI], 0.08-0.66%), an overall population prevalence of 89 cases per million; the prevalence of permanent neonatal diabetes was 0.12% (95% CI, 0.02-0.48%) and the population prevalence 45 cases per million.

CONCLUSIONS

One in 280 Australians diagnosed with diabetes have a monogenic form; most are of European ethnicity. Diagnosing MODY and neonatal diabetes is important because their management (including family screening) and prognosis can differ significantly from those for types 1 and 2 diabetes.

Sex-gender-related therapeutic approaches for cardiovascular complications associated with diabetes

Diabetes is a chronic disease associated with micro- and macrovascular complications and is a well-established risk factor for cardiovascular disease. Cardiovascular complications associated with diabetes are among the most important causes of death in diabetic patients. Interestingly, several sex-gender differences have been reported to significantly impact in the pathophysiology of diabetes. In particular, sex-gender differences have been reported to affect diabetes epidemiology, risk factors, as well as cardiovascular complications associated with diabetes. This suggests that different therapeutic approaches are needed for managing diabetes-associated cardiovascular complications in men and women. In this review, we will discuss about the sex-gender differences that are known to impact on diabetes, mainly focusing on the cardiovascular complications associated with the disease. We will then discuss the therapeutic approaches for managing diabetes-associated cardiovascular complications and how differences in sex-gender can influence the existing therapeutic approaches.

Maturity-onset diabetes of the young (MODY) in Brazil: Establishment of a national registry and appraisal of available genetic and clinical data

AIMS

Maturity-Onset Diabetes of the Young (MODY) comprises a heterogeneous group of monogenic forms of diabetes caused by mutations in at least 14 genes, but mostly by mutations in Glucokinase (GCK) and hepatocyte nuclear factor-1 homeobox A (HNF1A). This study aims to establish a national registry of MODY cases in Brazilian patients, assessing published and unpublished data.

METHODS

311 patients with clinical characteristics of MODY were analyzed, with unpublished data on 298 individuals described in 12 previous publications and 13 newly described cases in this report.

RESULTS

72 individuals had GCK mutations, 9 described in Brazilian individuals for the first time. One previously unpublished novel GCK mutation, Gly178Ala, was found in one family. 31 individuals had HNF1A mutations, 2 described for the first time in Brazilian individuals. Comparisons of GCK probands vs HNF1A: age 16±11 vs 35±20years; age at diagnosis 11±8 vs 21±7years; BMI 19±6 vs 25±6kg/m²; sulfonylurea users 5 vs 83%; insulin users 5 vs 17%; presence of arterial hypertension 0 vs. 33%, all p<0.05. No differences were observed in lipids and C-peptide.

CONCLUSIONS

Most MODY cases in Brazil are due to GCK mutations. In agreement with other studied populations, novel mutations are common. Only 14% of patients with familial diabetes carry a HNF1A mutation. Diagnosis of other rare forms of MODY is still a challenge in Brazilian population, as well as adequate strategies to screen individuals for molecular diagnosis.

Unexpected finding of a whole HNF1B gene deletion during the screening of rare MODY types in a series of Brazilian patients negative for GCK and HNF1A mutations

Thirty-two patients with diabetes negative for point mutations in GCK and HNF1A underwent further molecular screening of GCK, HNF1A, HNF4A, and HNF1B by MLPA analysis. We described the first Brazilian case of MODY5 due to a heterozygous whole-gene deletion in HNF1B, who developed rapidly progressive renal failure and death.

Pancreatic Cancer Genetics

Although relatively rare, pancreatic tumors are highly lethal [1]. In the United States, an estimated 48,960 individuals will be diagnosed with pancreatic cancer and 40,560 will die from this disease in 2015 [1]. Globally, 337,872 new pancreatic cancer cases and 330,391 deaths were estimated in 2012 [2]. In contrast to most other cancers, mortality rates for pancreatic cancer are not improving; in the US, it is predicted to become the second leading cause of cancer related deaths by 2030 [3, 4]. The vast majority of tumors arise in the exocrine pancreas, with pancreatic ductal adenocarcinoma (PDAC) accounting for approximately 95% of tumors. Tumors arising in the endocrine pancreas (pancreatic neuroendocrine tumors) represent less than 5% of all pancreatic tumors [5]. Smoking, type 2 diabetes mellitus (T2D), obesity and pancreatitis are the most consistent epidemiological risk factors for pancreatic cancer [5]. Family history is also a risk factor for developing pancreatic cancer with odds ratios (OR) ranging from 1.7-2.3 for first-degree relatives in most studies, indicating that shared genetic factors may play a role in the etiology of this disease [6-9]. This review summarizes the current knowledge of germline pancreatic cancer risk variants with a special emphasis on common susceptibility alleles identified through Genome Wide Association Studies (GWAS).

Pathophysiological Mechanism of Bone Loss in Type 2 Diabetes Involves Inverse Regulation of Osteoblast Function by PGC-1α and Skeletal Muscle Atrogenes: AdipoR1 as a Potential Target for Reversing Diabetes-Induced Osteopenia

Type 2 diabetes is associated with increased fracture risk and delayed fracture healing; the underlying mechanism, however, remains poorly understood. We systematically investigated skeletal pathology in leptin receptor-deficient diabetic mice on a C57BLKS background (db). Compared with wild type (wt), db mice displayed reduced peak bone mass and age-related trabecular and cortical bone loss. Poor skeletal outcome in db mice contributed high-glucose- and nonesterified fatty acid-induced osteoblast apoptosis that was associated with peroxisome proliferator-activated receptor γ coactivator 1-α (PGC-1α) downregulation and upregulation of skeletal muscle atrogenes in osteoblasts. Osteoblast depletion of the atrogene muscle ring finger protein-1 (MuRF1) protected against gluco- and lipotoxicity-induced apoptosis. Osteoblast-specific PGC-1α upregulation by 6-C-β-d-glucopyranosyl-(2S,3S)-(+)-5,7,3',4'-tetrahydroxydihydroflavonol (GTDF), an adiponectin receptor 1 (AdipoR1) agonist, as well as metformin in db mice that lacked AdipoR1 expression in muscle but not bone restored osteopenia to wt levels without improving diabetes. Both GTDF and metformin protected against gluco- and lipotoxicity-induced osteoblast apoptosis, and depletion of PGC-1α abolished this protection. Although AdipoR1 but not AdipoR2 depletion abolished protection by GTDF, metformin action was not blocked by AdipoR depletion. We conclude that PGC-1α upregulation in osteoblasts could reverse type 2 diabetes-associated deterioration in skeletal health.

Maturity onset diabetes of the young (MODY)--history, first case reports and recent advances

The world is seemingly facing a global increase in people suffering from diabetes especially in developing countries. The worldwide occurrence of diabetes for all age groups in year 2000 was estimated to be 2.8% and this number is most certainly expected to rise to 4.4% by 2030. Maturity-onset of diabetes of the young, or MODY, is a form of monogenic diabetes that is caused by mutations occurring in a number of different genes. Mutations in different genes tend to cause a slightly different variant of diabetes. MODY is typically diagnosed during late childhood, adolescence, or early adulthood and is usually observed to develop in adults during their late 50's. One of the main drawbacks in its diagnosis is that many people with MODY are misdiagnosed as having type 1 or type 2 diabetes. However, a molecular and genetic diagnosis can result in a better treatment and could also help in identifying other family members with MODY. This article explores the historical prospect and the genetic background of MODY, a brief summary of the first case reported and the significant factors that differentiate it from type 1 and type 2 diabetes.

Transcriptome analysis of pancreatic cancer reveals a tumor suppressor function for HNF1A

Pancreatic ductal adenocarcinoma (PDAC) is driven by the accumulation of somatic mutations, epigenetic modifications and changes in the micro-environment. New approaches to investigating disruptions of gene expression networks promise to uncover key regulators and pathways in carcinogenesis. We performed messenger RNA-sequencing in pancreatic normal (n = 10) and tumor (n = 8) derived tissue samples, as well as in pancreatic cancer cell lines (n = 9), to determine differential gene expression (DE) patterns. Sub-network enrichment analyses identified HNF1A as the regulator of the most significantly and consistently dysregulated expression sub-network in pancreatic tumor tissues and cells (median P = 7.56×10(-7), median rank = 1, range = 1-25). To explore the effects of HNF1A expression in pancreatic tumor-derived cells, we generated stable HNF1A-inducible clones in two pancreatic cancer cell lines (PANC-1 and MIA PaCa-2) and observed growth inhibition (5.3-fold, P = 4.5×10(-5) for MIA PaCa-2 clones; 7.2-fold, P = 2.2×10(-5) for PANC-1 clones), and a G0/G1 cell cycle arrest and apoptosis upon induction. These effects correlated with HNF1A-induced down-regulation of 51 of 84 cell cycle genes (e.g. E2F1, CDK2, CDK4, MCM2/3/4/5, SKP2 and CCND1), decreased expression of anti-apoptotic genes (e.g. BIRC2/5/6 and AKT) and increased expression of pro-apoptotic genes (e.g. CASP4/9/10 and APAF1). In light of the established role of HNF1A in the regulation of pancreatic development and homeostasis, our data suggest that it also functions as an important tumor suppressor in the pancreas.

Premature chondrocyte apoptosis and compensatory upregulation of chondroregulatory protein expression in the growth plate of Goto-Kakizaki diabetic rats

Type 2 diabetes mellitus (T2DM) is much more detrimental to bone than previously thought. Specifically, it is associated with aberrant bone remodeling, defective bone microstructure, poor bone quality, and growth retardation. The T2DM-associated impairment of bone elongation may result from a decrease in growth plate function, but the detailed mechanism has been unknown. The present study, therefore, aimed to test hypothesis that T2DM led to premature apoptosis of growth plate chondrocytes in Goto-Kakizaki (GK) type 2 diabetic rats, and thus triggered the compensatory responses to overcome this premature apoptosis, such as overexpression of Runt-related transcription factor (Runx)-2 and vascular endothelial growth factor (VEGF), the essential mediators for bone elongation. The terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) of epiphyseal sections successfully revealed increases in chondrocyte apoptosis in the hypertrophic zone (HZ) and chondro-osseous junction of GK rats. Quantitative immunohistochemical analysis further confirmed the overexpression of parathyroid hormone-related protein (PTHrP), Runx2 and VEGF, but not Indian hedgehog (Ihh) in the HZ. Analysis of blood chemistry indicated suppression of bone remodeling with a marked decrease in parathyroid hormone level. In conclusion, GK rats manifested a premature increase in chondrocyte apoptosis in the HZ of growth plate, and a compensatory overexpression of chondroregulatory proteins, such as PTHrP, Runx2, and VEGF. Our results, therefore, help explain how T2DM leads to impaired bone elongation and growth retardation.

Clinical and molecular characterization of maturity onset-diabetes of the young caused by hepatocyte nuclear factor-4 alpha mutation: red flags for prediction of the diagnosis

BACKGROUND AND OBJECTIVES

The prevalence of maturity-onset diabetes of the young (MODY) in Saudi population remains unknown, and data on molecular etiology of this condition is limited. Therefore, the present study was undertaken to elucidate clinical and molecular characteristics of a Saudi family with MODY 1.

DESIGN AND SETTINGS

This is a case series study conducted at Saad Specialist Hospital in Alkhobar, Saudi Arabia.

PATIENTS AND METHODS

A 12-year-old female presented to us with symptoms suggestive of diabetes. Investigations revealed hyperglycemia, glycosuria, and ketonuria without acidosis. Pancreatic antibodies were negative. She responded well to subcutaneous insulin. Her family history revealed that 2 of her siblings were diagnosed with type 1 diabetes (T1DM), while her father and mother had type 2 diabetes (T2DM). In view of this strong family history, the possibility of monogenic diabetes was raised, and the 2 genes consistent with this phenotype, hepatocyte nuclear factor-1 alpha (HNF1a) and hepatocyte nuclear factor-4 alpha (HNF4a), were studied. Accordingly, genomic DNA was isolated from peripheral blood lymphocytes of the 8 members of this family, polymerase chain reaction was carried out, and sequencing of the whole HNF4a and HNF1a genes was done.

RESULTS

DNA study of the proband revealed a heterozygous substitution in intron 1 (IVS1b C > T-5)(c.50-5C > T) of the HNF1a gene. This mutation was identified in other 5 members of the family.

CONCLUSION

This study alerts physicians to suspect MODY in patients who have a strongly positive family history of diabetes over a few generations with negative pancreatic antibodies and absence of ketoacidosis and obesity.

Detection and characterization of two novel mutations in the HNF4A gene in maturity-onset diabetes of the young type 1 in two Japanese families

BACKGROUND

Maturity-onset diabetes of the young (MODY) is a subgroup of monogenic diabetes mellitus, of which MODY1, caused by HNF4A mutations, accounts for only 5% or less and has been rarely reported in East Asian countries. Here we report two novel HNF4A mutations in two Japanese families with MODY1.

METHODS

Proband 1 is an 8-year-old girl and proband 2 is a 14-year-old girl. Both were nonobese, demonstrated elevated HbA1c and negative serum anti-glutamic acid decarboxylase antibodies, and had a family history of diabetes. We directly sequenced HNF4A and performed functional analysis of the detected missense mutation.

RESULTS

Proband 1 had a heterozygous missense mutation, c.824A>G (p.Asn275Ser). Luciferase assay demonstrated a significant reduction in transcriptional activity. A heterozygous frame shift mutation, c.692-695delAGGA (p.Lys231ThrfsX5), was detected in proband 2. Affected family members shared the same mutations, showing high penetrance. Both mutations reside in the HNF4α dimerization domain and the corresponding amino acids are well conserved between species.

CONCLUSIONS

These two mutations are most likely the cause of MODY1 in these families. Considering the effectiveness of sulfonylureas, it is important to correctly diagnose MODY1.

The spectrum of HNF1A gene mutations in Greek patients with MODY3: relative frequency and identification of seven novel germline mutations

OBJECTIVE

Maturity-Onset Diabetes of the Young (MODY) is the most common type of monogenic diabetes accounting for 1-2% of the population with diabetes. The relative incidence of HNF1A-MODY (MODY3) is high in European countries; however, data are not available for the Greek population. The aims of this study were to determine the relative frequency of MODY3 in Greece, the type of the mutations observed, and their relation to the phenotype of the patients.

DESIGN AND METHODS

Three hundred ninety-five patients were referred to our center because of suspected MODY during a period of 15 yr. The use of Denaturing Gradient Gel Electrophoresis of polymerase chain reaction amplified DNA revealed 72 patients carrying Glucokinase gene mutations (MODY2) and 8 patients carrying HNF1A gene mutations (MODY3). After using strict criteria, 54 patients were selected to be further evaluated by direct sequencing or by multiplex ligation probe amplification (MLPA) for the presence of HNF1A gene mutations.

RESULTS

In 16 unrelated patients and 13 of their relatives, 15 mutations were identified in the HNF1A gene. Eight of these mutations were previously reported, whereas seven were novel. Clinical features, such as age of diabetes at diagnosis or severity of hyperglycemia, were not related to the mutation type or location.

CONCLUSIONS

In our cohort of patients fulfilling strict clinical criteria for MODY, 12% carried an HNF1A gene mutation, suggesting that defects of this gene are responsible for a significant proportion of monogenic diabetes in the Greek population. No clear phenotype-genotype correlations were identified.

A novel glucokinase deletion (p.Lys32del) and five previously described mutations co-segregate with the phenotype of mild familial hyperglycaemia (MODY2) in Brazilian families

Six Brazilian families with mild familial hyperglycaemia have been screened for glucokinase (GCK) mutations. All had mutations that co-segregated with the phenotype. One of the mutations, the deletion 96_98delAAG (p.Lys32del), had not been previously described, reinforcing the worldwide prevalence of GCK MODY and widespread existence of undetected new mutations.

Increased prevalence of mood disorders and suicidal ideation in type 2 diabetic patients

This study evaluated the association of mood disorders, suicidal ideation and the quality of life in patients with type 2 diabetes. We used a case-control study employing 996 patients suffering with type 2 diabetes (using insulin for over 1 year), and 2.145 individuals without diabetes. The groups were then used to evaluate the presence of different mood disorders and suicidal ideation, beyond quality of life. In addition to this, fasting glucose and glycosylated hemoglobin (Hb1C) were also evaluated. The data were analyzed using the Pearson chi-squared test, logistic regression, ANCOVA and Student's t-tests. We showed an association between type 2 diabetes and depressive episodes (adjusted OR = 1.8, CI 95 % 1.7-2.0, p < 0.001), recurrent depressive episodes (adjusted OR = 2.4, CI 95 % 2.2-2.6, p < 0.001), dysthymia (adjusted OR = 5.2, CI 95 % 4.9-5.5, p < 0.001), mood disorder with psychotic symptoms (adjusted OR = 2.5, CI 95 % 1.5-3.4, p < 0.001) and suicidal ideation (adjusted OR = 3.6, CI 95 % 2.5-4.8, p < 0.001, light; adjusted OR = 4.6, CI 95 % 1.5-7.7, p < 0.01, moderate and severe). The recurrent depression (OR = 1.3, CI 95 % 1.1-1.7, p < 0.05) and psychotic symptoms (OR = 4.1, CI 95 % 1.1-15.1, p < 0.05) were associated with higher levels of Hb1C. Dysthymia was associated with high blood glucose (OR = 1.6, CI 95 % 1.1-2.5, p < 0.05). Patients had lower mean scores in the following domains: physical [36.5 (13.6) × 56.0 (4.9), p < 0.001)], psychological [42.6 (8.6) × 47.9 (8.6), p < 0.001] and environmental [40.0 (8.6) × 49.3 (8.3), p < 0.001], but had higher scores in the area of social relations [50.2 (16.9) × 35.7 (27.9), p < 0.001]. The data demonstrated a worse quality of life, a high comorbidity of type 2 DM with depressive disorders and suicidal ideation. In addition, the poor control of DM is associated with the severity of mood disorders.

A preliminary examination of the effects of genetic variants of redox enzymes on susceptibility to oedematous malnutrition and on percentage cytotoxicity in response to oxidative stress in vitro

BACKGROUND

The causes of oedematous vs non-oedematous childhood malnutrition (OM vs NOM) remain elusive. It is possible that inherited differences in handling oxidant stressors are a contributing factor.

AIMS

To test for associations between polymorphisms in five genes and (i) risk of OM, a case-control study, and (ii) percentage cytotoxicity in peripheral blood mononuclear cells (PBMCs) exposed to hydrogen peroxide (H(2)O(2)), an in vitro cell challenge study.

METHODS

Participants had been admitted previously for treatment of OM (cases, n = 74) or NOM (controls, n = 50), or were an independent set of healthy pregnant women (n = 47) who donated peripheral blood mononuclear cells. We tested for associations between genetic variation and outcome using single markers or a bivariate score constructed by counting numbers of deleterious alleles for each of 15 possible pairs of markers.

RESULTS

In the case-control study there were no significant single-marker associations with OM. We did find that higher bivariate scores were associated with OM for the pair of NAD(P)H:quinone oxidoreductase 1 and catalase (odds ratio 2·00, 95% CI 1·05-3·82). In the cell challenge experiments, there were no significant associations with percentage cytotoxicity.

CONCLUSIONS

Variation in this small set of genes seems unlikely to have a large impact on either risk of OM or cytotoxicity after H(2)O(2) exposure. The use of larger sample sizes to test the effects of a much larger set of genetic variants will be required in order to determine whether genetic variation contributes to the risk of OM. Such studies have potential for improving our understanding of causal pathways in OM.

Brain energy metabolism parameters in an animal model of diabetes

A growing body of evidence has indicated that altered mitochondrial function may be involved in mechanism for the development of diabetic complications. Thus, we investigated whether animal model of diabetes induced by alloxan alters energy metabolism parameters. Wistar rats received one single injection of alloxan (250 mg/kg) and after 15 days we evaluated mitochondrial respiratory chain complexes I, II, II-III and IV, creatine kinase and citrate synthase activities in prefrontal cortex, hippocampus and striatum. We observed that animal model of diabetes induced by alloxan increased complexes I and IV activities in hippocampus, complexes II and II-III activities in prefrontal cortex and striatum and complex IV in prefrontal cortex; however decreased complex IV activity in striatum. Moreover, diabetes rats decreased creatine kinase activity in striatum and increased citrate synthase activity in hippocampus. In conclusion, this study indicates that the alteration in mitochondrial function is probably involved in the pathophysiology of diabetes.

Glucokinase diabetes in 103 families from a country-based study in the Czech Republic: geographically restricted distribution of two prevalent GCK mutations

BACKGROUND

Glucokinase diabetes, also called GCK-MODY or maturity-onset diabetes of the young type 2 (MODY2), is caused by heterozygous mutations in the gene encoding glucokinase (GCK).

OBJECTIVE

The aim of study was to investigate the current prevalence of GCK mutations in a large cohort of Czech patients with typical clinical appearance of GCK-MODY. In addition, we reanalyzed the negative results obtained previously by screening using the denaturing high-performance liquid chromatography (dHPLC).

METHODS

We studied 140 unrelated Czech probands with clinical picture of GCK-MODY who were referred to our center from the whole of the Czech Republic between the years 1999-2009 by direct sequencing of GCK gene.

RESULTS

A mutation in GCK was identified in 103 of 140 probands (74%). We identified 46 different GCK mutations of which 13 were novel. Several mutations were detected in multiple families: p.Glu40Lys (20 families), p.Gly318Arg (12), p.Leu315His (7) and p.Val33Ala (six families). Direct sequencing detected a GCK mutations in 9 of 20 previously dHPLC-negative samples; the sensitivity of the dHPLC screening was calculated as 84%.

CONCLUSIONS

The study shows a relatively high proportion of GCK mutations among individuals with GCK-like phenotype, confirming the effectiveness of carefully applied clinical criteria prior to genetic testing. In the Czech MODY registry, GCK-MODY represents the biggest subgroup of MODY (35%). We report several prevalent GCK mutations with a likely founder effect in the Czech population. Furthermore, our results provide ground for a possible recommendation to reinspect all negative results previously obtained by screening using dHPLC.

Pancreatic beta cells require NeuroD to achieve and maintain functional maturity

NeuroD, a transactivator of the insulin gene, is critical for development of the endocrine pancreas, and NeuroD mutations cause MODY6 in humans. To investigate the role of NeuroD in differentiated beta cells, we generated mice in which neuroD is deleted in insulin-expressing cells. These mice exhibit severe glucose intolerance. Islets lacking NeuroD respond poorly to glucose and display a glucose metabolic profile similar to immature beta cells, featuring increased expression of glycolytic genes and LDHA, elevated basal insulin secretion and O2 consumption, and overexpression of NPY. Moreover, the mutant islets appear to have defective K(ATP) channel-mediated insulin secretion. Unexpectedly, virtually all insulin in the mutant mice is derived from ins2, whereas ins1 expression is almost extinguished. Overall, these results indicate that NeuroD is required for beta cell maturation and demonstrate the importance of NeuroD in the acquisition and maintenance of fully functional glucose-responsive beta cells.

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.

Increased insulin sensitivity in mice lacking collectrin, a downstream target of HNF-1alpha

Collectrin is a downstream target of the transcription factor hepatocyte nuclear factor-1alpha (HNF-1alpha), which is mutated in maturity-onset diabetes of the young subtype 3 (MODY3). Evidence from transgenic mouse models with collectrin overexpression in pancreatic islets suggests divergent roles for collectrin in influencing beta-cell mass and insulin exocytosis. To clarify the function of collectrin in the pancreas, we used a mouse line with targeted deletion of the gene. We examined pancreas morphology, glucose homeostasis by ip glucose tolerance testing (IPGTT) and insulin tolerance testing (IPITT), and pancreas function by in vivo acute-phase insulin response determination and glucose-stimulated insulin secretion from isolated islets. We find no difference in either pancreas morphology or function between wild-type and collectrin-deficient animals (Tmem27(-/y)). However, we note that by 6 months of age, Tmem27(-/y) mice exhibit increased insulin sensitivity by IPITT and decreased adiposity by dual-energy x-ray absorptiometry scanning compared with wild-type. We have previously reported that Tmem27(-/y) mice exhibit profound aminoaciduria due to failed renal recovery. We now demonstrate that Tmem27(-/y) animals also display inappropriate excretion of some short-chain acylcarnitines derived from amino acid and fatty acid oxidation. We provide further evidence for compensatory up-regulation of oxidative metabolism in Tmem27(-/y) mice, along with enhanced protein turnover associated with preserved lean mass even out to 1.5 yr of age. Our studies suggest that collectrin-deficient mice activate a number of adaptive mechanisms to defend energy homeostasis in the setting of ongoing nutrient losses.

[Childhood-onset diabetes treated with sulphonylureas]

MODY 3 type diabetes belongs to the group of monogenic diabetes and is caused by mutations in the gene for hepatocyte nuclear factor 1-alpha (HNF1-alpha). Although MODY 2 type diabetes is the most frequent form of MODY diabetes in childhood, type 3 is the most frequent in the general population. We report the case of a 12 year old child with basal and post-prandrial hyperglycaemia. No cardinal symptoms of type 1 diabetes mellitus were present. There are numerous cases of diabetes in his family. C-Peptide was 1.13 ng/ml and pancreatic autoimmunity markers were negative. HNF-1alpha gene mutation was found in the patient as well as in his father and sister. Treatment with glibenclamide was started at a dose of 2.5 mg/day in order to reduce the risk of microvascular disease, as this as high in MODY 3 type diabetes as in type 1 diabetes mellitus. Blood glucose returned to normal and glycosylated haemoglobin was maintained between 4.9 and 5.6 %. Side-effects were not observed except some mild hypoglycaemias.

ApoM: gene regulation and effects on HDL metabolism

The recently discovered apolipoprotein M (apoM) is a plasma protein of the lipocalin family associated with the lipoproteins (mainly high-density lipoproteins, or HDLs). Expression of the apoM gene in the liver is regulated by transcription factors that control key steps in hepatic lipid and glucose metabolism. Although the concentration of plasma apoM correlates with that of cholesterol, apoM was not identified as a risk factor for cardiovascular disease in two prospective studies. In genetically modified mice, however, changes in plasma apoM concentration caused quantitative and qualitative changes in HDLs, and overexpression of the apoM gene reduced atherosclerosis. In conclusion, it seems that apoM plays a part in lipoprotein metabolism; however, the biological impact of apoM in humans remains to be determined.

MODY-like diabetes associated with an apparently balanced translocation: possible involvement of MPP7 gene and cell polarity in the pathogenesis of diabetes

Background

Characterization of disease-associated balanced translocations has led to the discovery of genes responsible for many disorders, including syndromes that include various forms of diabetes mellitus. We studied a man with unexplained maturity onset diabetes of the young (MODY)-like diabetes and an apparently balanced translocation [46,XY,t(7;10)(q22;p12)] and sought to identify a novel diabetes locus by characterizing the translocation breakpoints.

Results

Mutations in coding exons and splice sites of known MODY genes were first ruled out by PCR amplification and DNA sequencing. Fluorescent in situ hybridization (FISH) studies demonstrated that the translocation did not disrupt two known diabetes-related genes on 10p12. The translocation breakpoints were further mapped to high resolution using FISH and somatic cell hybrids and the junctions PCR-amplified and sequenced. The translocation did not disrupt any annotated transcription unit. However, the chromosome 10 breakpoint was 220 kilobases 5' to the Membrane Protein, Palmitoylated 7 (MPP7) gene, which encodes a protein required for proper cell polarity. This biological function is shared by HNF4A, a known MODY gene. Databases show MPP7 is highly expressed in mouse pancreas and is expressed in human islets. The translocation did not appear to alter lymphoblastoid expression of MPP7 or other genes near the breakpoints.

Conclusion

The balanced translocation and MODY-like diabetes in the proband could be coincidental. Alternatively, the translocation may cause islet cell dysfunction by altering MPP7 expression in a subtle or tissue-specific fashion. The potential roles of MPP7 mutations in diabetes and perturbed islet cell polarity in insulin secretion warrant further study.

HNF1α mutations are present in half of clinically defined MODY patients in South-Brazilian individuals

Maturity-onset diabetes of the young (MODY) is a monogenic form of diabetes mellitus characterized by autosomal dominant inheritance, early age of onset, and pancreatic beta cell dysfunction. Heterozygous mutations in at least seven genes can cause MODY. In the present study we investigated the relative prevalence of GCK (glucokinase) and HNF1α (hepatocyte nuclear factor 1α) mutations, the more frequent causes of MODY, in 13 South-Brazilian families with multiple cases of diabetes consistent with MODY. Heterozygous variants in GCK and HNF1α genes were observed respectively in one (7.7%), and six (46.2%) families. The six HNF1α variants are likely to cause diabetes in the families where they were observed. However, we could not ascertain whether the GCK Gly117Ser variant found in one family is a causal mutation. In conclusion, we have confirmed in a South-Brazilian population that HNF1α mutations are a common cause of monogenic diabetes in adults selected with strict clinical diagnostic criteria.

Low prevalence of MODY2 and MODY3 mutations in Brazilian individuals with clinical MODY phenotype

Prevalence of MODY2 and MODY3 mutations has been assessed in 23 Brazilian families with MODY phenotype. Mutations in HNF-1alpha have been found in 3 families (13%) and 2 families (8.7%) had new glucokinase mutations. These genes do not explain the majority of MODY cases in Brazilian population.

Function of HNF1 in the pathogenesis of diabetes

The importance of hepatocyte nuclear factors (HNFs), as well as other transcription factors in β-cell development and function, was underlined by the characterization of human mutations causing maturity-onset diabetes of the young (MODY). HNF1A and HNF1B mutations lead to MODY forms 3 and 5, respectively. Thus, transcriptional control is an essential mechanism underlying the precise metabolic control exerted by β-cells in regulating insulin release. The diabetes phenotype of MODY3 (HNF1α) and the phenotypes of MODY5 (HNF1β), which can also include renal disease and genitourinary malformations, as well as neonatal diabetes and pancreatic agenesis, have now been described. However, detailed molecular pathology remains elusive. The large array of dominant-negative and deletion mutations, and the lack of structure-phenotype relationships for most mutations, have not helped us to formulate a mechanistic understanding. Further molecular studies of HNF1 actions and gene regulation are anticipated to provide useful insights into β-cell biology and potential therapeutic tools.

Are the available experimental models of type 2 diabetes appropriate for a gender perspective?

Several experimental models have so far been developed to improve our knowledge of the pathogenetic mechanisms of type 2 diabetes mellitus (T2D), to determine the possible pharmacological targets of this disease and to better evaluate diabetes-associated complications, e.g. the cardiovascular disease. In particular, the study of T2D gained the attention of several groups working with different animal species: rodents, cats or pigs, as well as other non-human primate species. Each of these species provided useful and different clues. However, T2D has to be considered as a gender-associated disease: sex differences play in fact a key role in the onset as well as in the progression of the disease and a higher mortality for cardiovascular diseases is detected in diabetic women with respect to men. The results obtained from all the available animal models appear to only partially address this issue so that the search for more precise information in this respect appears to be mandatory. In this review we summarize these concepts and literature in the field and propose a reappraisal of the various animal models for a study of T2D that would take into consideration a gender perspective.

Structural basis of disease-causing mutations in hepatocyte nuclear factor 1beta

HNF1beta is an atypical POU transcription factor that participates in a hierarchical network of transcription factors controlling the development and proper function of vital organs such as liver, pancreas, and kidney. Many inheritable mutations on HNF1beta are the monogenic causes of diabetes and several kidney diseases. To elucidate the molecular mechanism of its function and the structural basis of mutations, we have determined the crystal structure of human HNF1beta DNA binding domain in complex with a high-affinity promoter. Disease-causing mutations have been mapped to our structure, and their predicted effects have been tested by a set of biochemical/ functional studies. These findings together with earlier findings with a homologous protein HNF1alpha, help us to understand the structural basis of promoter recognition by these atypical POU transcription factors and the site-specific functional disruption by disease-causing mutations.

Hepatocyte nuclear factor 1 alpha is a factor responsible for the interindividual variation of OATP1B1 mRNA levels in adult Japanese livers

PURPOSE

The aim of the present study was to clarify the factors responsible for interindividual variability of organic anion transporting polypeptide (OATP, gene symbol SLCO) 1B1 mRNA expression level in the human liver.

MATERIALS AND METHODS

OATP1B1 mRNA expression levels were determined by real-time PCR in 31 human liver samples. The results were analyzed in relation to a single nucleotide polymorphism (-11187G>A) located in the promoter region and levels of hepatocyte nuclear factor (HNF) 1alpha mRNA.

RESULTS

There was a 4.9-fold interindividual variability of OATP1B1 mRNA expression level in the livers analyzed, which was not associated with -11187G>A polymorphism. Accordingly, the -11187G>A polymorphism did not alter the SLCO1B1 gene promoter activity in luciferase assays. On the other hand, OATP1B1 mRNA levels showed a significant correlation with HNF1alpha mRNA levels (r=0.83, P<0.0001). This correlation was consistent with the results of luciferase assays and chromatin immunoprecipitation assays showing functional interaction between HNF1alpha and SLCO1B1 gene promoter.

CONCLUSIONS

Our results suggest that HNF1alpha is an essential regulator of OATP1B1 mRNA expression and thus the level of HNF1alpha expression is one of the major determinants of interindividual variability in OATP1B1 mRNA expression.

Prevalence and clinical phenotype of the p.Val226Met glucokinase gene mutation in French Canadians in Quebec, Canada

Our objectives were to describe the clinical phenotype of maturity-onset diabetes of the young (MODY) type 2 in a group of French Canadians and estimate its prevalence in this population. Index cases were identified by an abnormal fasting blood glucose (FBG) upon metabolic evaluation for dyslipidemia. Mutational analyses confirmed that all probands and affected family members were positive for the same glucokinase mutation, p.Val226Met. The prevalence of this mutation was estimated from a representative sample of French Canadians. Eleven individuals in 5 different families were diagnosed with MODY 2. Four of the five families originated from the same region in Quebec. In affected children (n = 6), the median age at diagnosis was 7.6 years (range = 2.9-9.4). All were asymptomatic. The range of FBG was 4.4-7.0 mmol/L; 5 out of the 6 pediatric patients had normal FBG values during the course of follow-up. One child presented with consistently normal FBG. Four of the adults who screened positive for MODY 2 had been previously misdiagnosed with type 2 DM, and one female had a history of gestational DM. The estimated prevalence of heterozygotes for the p.Val226Met mutation in French Canadians was 0.057% (95%CI 0.01-0.32%). In conclusion, this report presents the first confirmed case of MODY 2 with persistently normal FBG. In children and adolescents, a normal FBG does not allow for the exclusion of a MODY 2 diagnosis. Our results are consistent with a founder effect for the p.Val226Met glucokinase gene mutation in Quebec, Canada.

Islet beta cell failure in type 2 diabetes

The major focus of this Review is on the mechanisms of islet beta cell failure in the pathogenesis of obesity-associated type 2 diabetes (T2D). As this demise occurs within the context of beta cell compensation for insulin resistance, consideration is also given to the mechanisms involved in the compensation process, including mechanisms for expansion of beta cell mass and for enhanced beta cell performance. The importance of genetic, intrauterine, and environmental factors in the determination of "susceptible" islets and overall risk for T2D is reviewed. The likely mechanisms of beta cell failure are discussed within the two broad categories: those with initiation and those with progression roles.

Molecular approaches to study control of glucose homeostasis

Type 2 diabetes is a polygenic disease that can lead to severe complications in multiple tissues. Rodent models have been used widely for investigating the pathophysiology underlying type 2 diabetes and for examining the potential link with obesity, largely due to the limitations of invasive testing and of studying detailed molecular mechanisms in human tissues. Among rodents, the mouse model is especially popular because mice are easy to manipulate genetically, have a short generation time, and are relatively inexpensive. The most commonly used inbred mouse strains are reviewed in addition to several genetically engineered mouse models that have been generated to study type 2 diabetes in the context of obesity, with a focus on insulin, leptin, and peroxisome proliferator-activated receptor (PPAR) signaling pathways.

Crystallization of hepatocyte nuclear factor 1beta in complex with DNA

Hepatocyte nuclear factor 1beta (HNF1beta) is a member of the POU transcription-factor family and binds the target DNA as a dimer with nanomolar affinity. The HNF1beta-DNA complex has been prepared and crystallized by hanging-drop vapor diffusion in 6%(v/v) PEG 300, 5%(w/v) PEG 8000, 8%(v/v) glycerol and 0.1 M Tris pH 8.0. The crystals diffracted to 3.2 A (93.9% completeness) using a synchrotron-radiation source under cryogenic (100 K) conditions and belong to space group R3, with unit-cell parameters a = b = 172.69, c = 72.43 A. A molecular-replacement solution has been obtained and structure refinement is in progress. This structure will shed light on the molecular mechanism of promoter recognition by HNF1beta and the molecular basis of the disease-causing mutations found in it.