Identification of a novel beta-cell glucokinase (GCK) promoter mutation (-71G>C) that modulates GCK gene expression through loss of allele-specific Sp1 binding causing mild fasting hyperglycemia in humans

From glucose sensing to exocytosis: takes from maturity onset diabetes of the young

Monogenic diabetes gave us simplified models of complex molecular processes occurring within β-cells, which allowed to explore the roles of numerous proteins from single protein perspective. Constellation of characteristic phenotypic features and wide application of genetic sequencing techniques to clinical practice, made the major form of monogenic diabetes - the Maturity Onset Diabetes of the Young to be distinguishable from type 1, type 2 as well as neonatal diabetes mellitus and understanding underlying molecular events for each type of MODY contributed to the advancements of antidiabetic therapy and stem cell research tremendously. The functional analysis of MODY-causing proteins in diabetes development, not only provided better care for patients suffering from diabetes, but also enriched our comprehension regarding the universal cellular processes including transcriptional and translational regulation, behavior of ion channels and transporters, cargo trafficking, exocytosis. In this review, we will overview structure and function of MODY-causing proteins, alterations in a particular protein arising from the deleterious mutations to the corresponding gene and their consequences, and translation of this knowledge into new treatment strategies.

A comprehensive map of human glucokinase variant activity

BACKGROUND

Glucokinase (GCK) regulates insulin secretion to maintain appropriate blood glucose levels. Sequence variants can alter GCK activity to cause hyperinsulinemic hypoglycemia or hyperglycemia associated with GCK-maturity-onset diabetes of the young (GCK-MODY), collectively affecting up to 10 million people worldwide. Patients with GCK-MODY are frequently misdiagnosed and treated unnecessarily. Genetic testing can prevent this but is hampered by the challenge of interpreting novel missense variants.

RESULT

Here, we exploit a multiplexed yeast complementation assay to measure both hyper- and hypoactive GCK variation, capturing 97% of all possible missense and nonsense variants. Activity scores correlate with in vitro catalytic efficiency, fasting glucose levels in carriers of GCK variants and with evolutionary conservation. Hypoactive variants are concentrated at buried positions, near the active site, and at a region of known importance for GCK conformational dynamics. Some hyperactive variants shift the conformational equilibrium towards the active state through a relative destabilization of the inactive conformation.

CONCLUSION

Our comprehensive assessment of GCK variant activity promises to facilitate variant interpretation and diagnosis, expand our mechanistic understanding of hyperactive variants, and inform development of therapeutics targeting GCK.

"Pesto" Mutation: Phenotypic and Genotypic Characteristics of Eight GCK/MODY Ligurian Patients

Maturity Onset Diabetes of the Young (MODY) is a monogenic form of diabetes mellitus (DM) that accounts for around 2-5% of all types of diabetes. Autosomal dominant inheritance in pathogenic variations of 14 genes related to β-cell functions can lead to monogenic types of diabetes. In Italy, GCK/MODY is the most frequent form and it is caused by mutations of the glucokinase (GCK). Patients with GCK/MODY usually have stable mild fasting hyperglycaemia with mildly elevated HbA1c levels and rarely need pharmacological treatment. Molecular analysis of the GCK coding exons was carried out by Sanger sequencing in eight Italian patients. All the probands were found to be heterozygous carriers of a pathogenic gross insertion/deletion c.1279_1358delinsTTACA; p.Ser426_Ala454delinsLeuGln. It was previously described for the first time by our group in a large cohort of Italian GCK/MODY patients. The higher levels of HbA1c (6.57% vs. 6.1%), and the higher percentage of patients requiring insulin therapy (25% vs. 2%) compared to the previously studied Italian patients with GCK/MODY, suggest that the mutation discovered could be responsible for a clinically worse form of GCK/MODY. Moreover, as all the patients carrying this variant share an origin from the same geographic area (Liguria), we postulate a possible founder effect and we propose to name it the "pesto" mutation.

Frequency and spectrum of glucokinase mutations in an adult Maltese population

AIM

To investigate the frequency and spectrum of glucokinase (GCK) mutations in a cohort of adults from an island population having a high prevalence of diabetes mellitus (DM).

METHODS

A single-centre cohort study was conducted, including 145 non-obese adults of Maltese-Caucasian ethnicity with impaired fasting glycaemia (IFG) or non-autoimmune diabetes diagnosed before the age of 40 years. Bidirectional sequencing of the GCK coding regions was performed. Genotype-phenotype associations and familial segregation were explored and the effects of missense variants on protein structure were evaluated using computational analysis.

RESULTS

Three probands with pathogenic/likely pathogenic GCK variants in the heterozygous state having clinical features consistent with GCK-diabetes were detected. The missense variants have structurally destabilising effects on protein structure. GCK variant carriers exhibited a significantly lower body mass index and serum triglyceride levels when compared to GCK variant non-carriers.

CONCLUSIONS

The frequency of GCK-diabetes is approximately 2% in non-obese Maltese adults with diabetes or prediabetes. This study broadens the mutational spectrum of GCK and highlights clinical features that could be useful in discriminating GCK-DM from type 2 DM or prediabetes. It reinforces the need for increased molecular testing in young adults with diabetes having a suspected monogenic aetiology.

Identification of Novel Regulatory Regions Induced by Intrauterine Growth Restriction in Rat Islets

Intrauterine growth restriction (IUGR) leads to the development of type 2 diabetes in adulthood, and the permanent alterations in gene expression implicate an epigenetic mechanism. Using a rat model of IUGR, we performed TrueSeq-HELP Tagging to assess the association of DNA methylation changes and gene dysregulation in islets. We identified 511 differentially methylated regions (DMRs) and 4377 significantly altered single CpG sites. Integrating the methylome and our published transcriptome data sets resulted in the identification of pathways critical for islet function. The identified DMRs were enriched with transcription factor binding motifs, such as Elk1, Etv1, Foxa1, Foxa2, Pax7, Stat3, Hnf1, and AR. In silico analysis of 3-dimensional chromosomal interactions using human pancreas and islet Hi-C data sets identified interactions between 14 highly conserved DMRs and 35 genes with significant expression changes at an early age, many of which persisted in adult islets. In adult islets, there were far more interactions between DMRs and genes with significant expression changes identified with Hi-C, and most of them were critical to islet metabolism and insulin secretion. The methylome was integrated with our published genome-wide histone modification data sets from IUGR islets, resulting in further characterization of important regulatory regions of the genome altered by IUGR containing both significant changes in DNA methylation and specific histone marks. We identified novel regulatory regions in islets after exposure to IUGR, suggesting that epigenetic changes at key transcription factor binding motifs and other gene regulatory regions may contribute to gene dysregulation and an abnormal islet phenotype in IUGR rats.

Stem Cell-Derived β Cells: A Versatile Research Platform to Interrogate the Genetic Basis of β Cell Dysfunction

Pancreatic β cell dysfunction is a central component of diabetes progression. During the last decades, the genetic basis of several monogenic forms of diabetes has been recognized. Genome-wide association studies (GWAS) have also facilitated the identification of common genetic variants associated with an increased risk of diabetes. These studies highlight the importance of impaired β cell function in all forms of diabetes. However, how most of these risk variants confer disease risk, remains unanswered. Understanding the specific contribution of genetic variants and the precise role of their molecular effectors is the next step toward developing treatments that target β cell dysfunction in the era of personalized medicine. Protocols that allow derivation of β cells from pluripotent stem cells, represent a powerful research tool that allows modeling of human development and versatile experimental designs that can be used to shed some light on diabetes pathophysiology. This article reviews different models to study the genetic basis of β cell dysfunction, focusing on the recent advances made possible by stem cell applications in the field of diabetes research.

Clinical implications of the glucokinase impaired function - GCK MODY today

Heterozygous inactivating mutations of the glucokinase (GCK) gene are causing GCK-MODY, one of the most common forms of the Maturity Onset Diabetes of the Young (MODY). GCK-MODY is characterized by fasting hyperglycemia without apparent worsening with aging and low risk for chronic vascular complications. Despite the mild clinical course, GCK-MODY could be misdiagnosed as type 1 or type 2 diabetes. In the diagnostic process, the clinical suspicion is often based on the clinical diagnostic criteria for GCK-MODY and should be confirmed by DNA analysis. However, there are several issues in the clinical and also in genetic part that could complicate the diagnostic process. Most of the people with GCK-MODY do not require any pharmacotherapy. The exception are pregnant women with a fetus which did not inherit GCK mutation from the mother. Such a child has accelerated growth, and has increased risk for diabetic foetopathy. In this situation the mother should be treated with substitutional doses of insulin. Therefore, distinguishing GCK-MODY from gestational diabetes in pregnancy is very important. For this purpose, special clinical diagnostic criteria for clinical identification of GCK-MODY in pregnancy are used. This review updates information on GCK-MODY and discusses several currently not solved problems in the clinical diagnostic process, genetics, and treatment of this type of monogenic diabetes.

Analysis of the promoter regions of disease-causing genes in maturity-onset diabetes of the young patients

Maturity-onset diabetes of the young (MODY) is a form of monogenic diabetes caused by the variants in MODY-related genes. In addition to coding variants, variants in the promoter region of MODY-related genes can cause the disease as well. In this study, we screened the promoter regions of the most common MODY-related genes GCK, HNF1A, HNF4A and HNF1B in our cohort of 29 MODY patients. We identified one genetic variant in the HNF1A gene, a 7 bp insertion c.-154-160insTGGGGGT, and three variants in the GCK gene, -282C>T; -194A>G; 402C>G appearing as set. Chloramphenicol acetyltransferase (CAT) assay was performed to test the effect of the 7 bp insertion and the variant set on the activity of the reporter gene in HepG2 and RIN-5F cell, respectively, where a decreasing trend was observed for both variants. In silico analysis and electrophoretic mobility shift assay showed that the 7 bp insertion did not create the binding site for new transcriptional factors, but gave rise to additional binding sites for the existing ones. Results from our study indicated that the 7 bp insertion in the HNF1A gene could be associated with the patient's diabetes. As for the GCK variant set, it is probably not associated with diabetes in patients, but it may modify the fasting glucose level by causing small elevation in variant set carriers. We have presented two promoter variants in MODY-related genes. Variant in the HNF1A gene is presumed to be disease-causing and the GCK promoter variant set could be a phenotype modifier.

Whole‑exome sequencing in Russian children with non‑type 1 diabetes mellitus reveals a wide spectrum of genetic variants in MODY‑related and unrelated genes

The present study reports on the frequency and the spectrum of genetic variants causative of monogenic diabetes in Russian children with non-type 1 diabetes mellitus. The present study included 60 unrelated Russian children with non-type 1 diabetes mellitus diagnosed before the age of 18 years. Genetic variants were screened using whole-exome sequencing (WES) in a panel of 35 genes causative of maturity onset diabetes of the young (MODY) and transient or permanent neonatal diabetes. Verification of the WES results was performed using PCR-direct sequencing. A total of 38 genetic variants were identified in 33 out of 60 patients (55%). The majority of patients (27/33, 81.8%) had variants in MODY-related genes: GCK (n=19), HNF1A (n=2), PAX4 (n=1), ABCC8 (n=1), KCNJ11 (n=1), GCK+HNF1A (n=1), GCK+BLK (n=1) and GCK+BLK+WFS1 (n=1). A total of 6 patients (6/33, 18.2%) had variants in MODY-unrelated genes: GATA6 (n=1), WFS1 (n=3), EIF2AK3 (n=1) and SLC19A2 (n=1). A total of 15 out of 38 variants were novel, including GCK, HNF1A, BLK, WFS1, EIF2AK3 and SLC19A2. To summarize, the present study demonstrates a high frequency and a wide spectrum of genetic variants causative of monogenic diabetes in Russian children with non-type 1 diabetes mellitus. The spectrum includes previously known and novel variants in MODY-related and unrelated genes, with multiple variants in a number of patients. The prevalence of GCK variants indicates that diagnostics of monogenic diabetes in Russian children may begin with testing for MODY2. However, the remaining variants are present at low frequencies in 9 different genes, altogether amounting to ~50% of the cases and highlighting the efficiency of using WES in non-GCK-MODY cases.

Identification and functional analysis of GCK gene mutations in 12 Chinese families with hyperglycemia

AIMS/INTRODUCTION

To investigate the clinical and genetic characteristics of Chinese patients with a phenotype consistent with maturity-onset diabetes of the young type 2 and explore the pathogenic mechanism of their hyperglycemia.

MATERIALS AND METHODS

We studied 12 probands and their extended families referred to our center for screening mutations in the glucokinase gene (GCK). Clinical data were collected and genetic analysis was carried out. The recombinant wild-type and mutant glucokinase were generated in Escherichia coli. The kinetic parameters and thermal stability of the enzymes were determined in vitro.

RESULTS

In the 12 families, 11 GCK mutations (R43C, T168A, K169N, R191W, Y215X, E221K, M235T, R250H, W257X, G261R and A379E) and one variant of uncertain significance (R275H) were identified. R191W was detected in two unrelated families. Of the 11 GCK mutations, three mutations (c.507G>C, K169N; c.645C>A, Y215X; c.771G>A, W257X; NM_000162.3, NP_000153.1) are novel. Basic kinetics analysis explained the pathogenicity of the five mutants (R43C, K169N, R191W, E221K and A379E), which showed reduced enzyme activity with relative activity indexes between ~0.001 and 0.5 compared with the wild-type (1.0). In addition, the thermal stabilities of these five mutants were also decreased to varying degrees. However, for R250H and R275H, there was no significant difference in the enzyme activity and thermal stability between the mutants and the wild type.

CONCLUSIONS

We have identified 11 GCK mutations and one variant of uncertain significance in 12 Chinese families with hyperglycemia. For five GCK mutations (R43C, K169N, R191W, E221K and A379E), the changes in enzyme kinetics and thermostability might be the pathogenic mechanisms by which mutations cause hyperglycemia.

Diagnosis and management of glucokinase monogenic diabetes in pregnancy: current perspectives

Glucokinase-maturity-onset diabetes of the young (GCK-MODY) is an autosomal dominant disorder caused by heterozygous inactivating GCK gene mutations. GCK-MODY is one the most common MODY subtypes, affecting 0.1% of the population and 0.4-1% of women with gestational diabetes mellitus. Glucokinase is predominantly expressed in pancreatic beta cells and catalyzes the phosphorylation of glucose to glucose-6-phosphate. The unique kinetics of glucokinase enable it to change the rate of glucose phosphorylation according to the glucose concentration, thereby regulating insulin secretion. Individuals with GCK-MODY have mildly elevated fasting blood glucose levels (5.5-8.0 mmol/L) and regulate glucose perturbations to a higher set-point, resulting in a relatively flat glucose profile on a 75 g oral glucose tolerance test. The hyperglycemia is usually subclinical and may only be detected on incidental glucose testing. It is important to correctly identify GCK-MODY as the clinical course and management differs substantially from other types of diabetes. Diabetes-related complications are relatively uncommon, so glucose-lowering treatment is not usually required. The exception is pregnancy, where fetal growth and therefore glucose-lowering treatment are predominantly determined by whether or not the fetus inherits the GCK mutation. The fetal genotype is not usually known but can be inferred from serial fetal ultrasound measurements. If there is evidence of accelerating fetal abdominal circumference on serial ultrasounds, the fetus is assumed to not have the GCK mutation and treatment of maternal hyperglycemia is indicated to reduce the risk of macrosomia, Caesarean section and neonatal hypoglycemia. If there is no evidence of accelerating fetal growth, the fetus is assumed to have inherited the GCK mutation and will have a similarly elevated glucose set-point as their mother, so maternal hyperglycemia is not treated. With recent advances in genetic technology, such as next-generation sequencing and noninvasive fetal genotyping, the detection and management of GCK-MODY in pregnancy should continue to improve.

Glucokinase mutations in pediatric patients with impaired fasting glucose

AIMS

Our aim was to detect the frequency of glucokinase (GCK) gene mutations in a cohort of patients with impaired fasting glucose and to describe the clinical manifestations of identified variants. We also aimed at predicting the effect of the novel missense mutations by computational approach.

METHODS

Overall 100 unrelated Italian families with impaired fasting glucose were enrolled and subdivided into two cohorts according to strict and to mild criteria for diagnosis of maturity-onset diabetes of the young (MODY). GCK gene sequencing was performed in all participants.

RESULTS

Fifty-three Italian families with 44 different mutations affecting the GCK and co-segregating with the clinical phenotype of GCK/MODY were identified. All mutations were in heterozygous state. In Sample 1, GCK defects were found in 32/36 (88.9%) subjects selected with strict MODY diagnostic criteria, while in Sample 2 GCK defects were found in 21/64 (32.8%) subjects selected with mild MODY diagnostic criteria.

CONCLUSIONS

Our study enlarged the wide spectrum of GCK defects by adding 9 novel variants. The application of strict recruitment criteria resulted in 88.9% incidence of GCK/MODY, which confirmed it as the commonest form of MODY in the Italian population. In order to avoid misdiagnosis of GCK/MODY, it could be useful to perform molecular screening even if one or more clinical parameters for the diagnosis of MODY are missing. Computational analysis is useful to understand the effect of GCK defect on protein functionality, especially when the novel identified variant is a missense mutation and/or parents' DNA is not available.

Preliminary screening of mutations in the glucokinase gene of Chinese patients with gestational diabetes

Aims/Introduction

Mutations in the glucokinase gene (GCK) are a pathogenetic cause of maturity‐onset diabetes of the young. Studies have found that female patients with GCK maturity‐onset diabetes of the young often present with gestational diabetes during pregnancy. Our aim was to preliminarily assess the prevalence of mutations in the glucokinase gene in Chinese women with gestational diabetes.

Materials and Methods

Chinese gestational diabetes patients who underwent a 100‐g oral glucose tolerance test in Peking Union Medical College Hospital from July 2005 to May 2008 were retrospectively analyzed. Participants were selected for direct sequencing of the GCK gene if they met the following criteria: (i) fasting plasma glucose between 5.5 and 10.0 mmol/L; and (ii) a small increment (<4.6 mmol/L) during a 2‐h oral glucose tolerance test.

Results

Of the 501 participants with gestational diabetes, there were 38 participants who met the criteria for GCK analysis. In the 29 participants whose deoxyribonucleic acid samples were available, two mutations in coding regions were detected, c.626 C>T (p.T209M, NP_000153.1) mutation in exon 6 and c.824 G>A (p.R275H, NP_000153.1; rs767565869) mutation in exon 7. According to our results, the minimum prevalence of GCK mutations in Chinese women with gestational diabetes was estimated to be 0.4%, and the minimum prevalence of GCK maturity‐onset diabetes of the young in the Chinese population might be one in 2,000.

Conclusions

Our screening criteria allowed for the identification of glucokinase‐deficient patients who were diagnosed with gestational diabetes, and these mutations in the GCK gene were not common in Chinese women with gestational diabetes.

Candidate gene studies of diabetic retinopathy in human

Diabetic retinopathy (DR) is a multifactorial disease with complex pathophysiology. It is the main cause of blindness among the people in productive age. The purpose of this literature review is to highlight recent achievements in the genetics of diabetic retinopathy with particular focus on candidate gene studies. We summarized most of the available published data about candidate genes for diabetic retinopathy with the goal to identify main genetic aspects. We conclude that genetic studies reported contradictory findings and no genetic variants meet criteria of a diagnostic marker, or significantly elucidate the root of DR development. Based on these findings it is important to continue with the research in the field of DR genetics, mainly due to the fact that currently new possibilities and approaches associated with utilization of next-generation sequencing are available.

Genetic variation of fasting glucose and changes in glycemia in response to 2-year weight-loss diet intervention: the POUNDS LOST trial

OBJECTIVE

Weight-loss intervention through diet modification has been widely used to improve obesity-related hyperglycemia; however, little is known about whether genetic variation modifies the intervention effect. We examined the interaction between weight-loss diets and genetic variation of fasting glucose on changes in glycemic traits in a dietary intervention trial.

RESEARCH DESIGN AND METHODS

The Preventing Overweight Using Novel Dietary Strategies (POUNDS LOST) trial is a randomized, controlled 2-year weight-loss trial. We assessed overall genetic variation of fasting glucose by calculating a genetic risk score (GRS) based on 14 fasting glucose-associated single nucleotide polymorphisms, and examined the progression in fasting glucose and insulin levels, and insulin resistance and insulin sensitivity in 733 adults from this trial.

RESULTS

The GRS was associated with 6-month changes in fasting glucose (P<0.001), fasting insulin (P=0.042), homeostasis model assessment of insulin resistance (HOMA-IR, P=0.009) and insulin sensitivity (HOMA-S, P=0.043). We observed significant interaction between the GRS and dietary fat on 6-month changes in fasting glucose, HOMA-IR and HOMA-S after multivariable adjustment (P-interaction=0.007, 0.045 and 0.028, respectively). After further adjustment for weight loss, the interaction remained significant on change in fasting glucose (P=0.015). In the high-fat diet group, participants in the highest GRS tertile showed increased fasting glucose, whereas participants in the lowest tertile showed decreased fasting glucose (P-trend <0.001); in contrast, the genetic association was not significant in the low-fat diet group (P-trend=0.087).

CONCLUSIONS

Our data suggest that participants with a higher genetic risk may benefit more by eating a low-fat diet to improve glucose metabolism.

Transcriptional Regulation of the Pancreatic Islet: Implications for Islet Function

Islets of Langerhans contain multiple hormone-producing endocrine cells controlling glucose homeostasis. Transcription establishes and maintains islet cellular fates and identities. Genetic and environmental disruption of islet transcription triggers cellular dysfunction and disease. Early transcriptional regulation studies of specific islet genes, including insulin (INS) and the transcription factor PDX1, identified the first cis-regulatory DNA sequences and trans-acting factors governing islet function. Here, we review how human islet "omics" studies are reshaping our understanding of transcriptional regulation in islet (dys)function and diabetes. First, we highlight the expansion of islet transcript number, form, and function and of DNA transcriptional regulatory elements controlling their production. Next, we cover islet transcriptional effects of genetic and environmental perturbation. Finally, we discuss how these studies' emerging insights should empower our diabetes research community to build mechanistic understanding of diabetes pathophysiology and to equip clinicians with tailored, precision medicine options to prevent and treat islet dysfunction and diabetes.

Recognition and Management of Individuals With Hyperglycemia Because of a Heterozygous Glucokinase Mutation

Glucokinase-maturity-onset diabetes of the young (GCK-MODY), also known as MODY2, is caused by heterozygous inactivating mutations in the GCK gene. GCK gene mutations are present in ∼1 in 1,000 of the population, but most are not diagnosed. They are common causes of MODY (10-60%): persistent incidental childhood hyperglycemia (10-60%) and gestational diabetes mellitus (1-2%). GCK-MODY has a unique pathophysiology and clinical characteristics, so it is best considered as a discrete genetic subgroup. People with GCK-MODY have a defect in glucose sensing; hence, glucose homeostasis is maintained at a higher set point resulting in mild, asymptomatic fasting hyperglycemia (5.4-8.3 mmol/L, HbA1c range 5.8-7.6% [40-60 mmol/mol]), which is present from birth and shows slight deterioration with age. Even after 50 years of mild hyperglycemia, people with GCK-MODY do not develop significant microvascular complications, and the prevalence of macrovascular complications is probably similar to that in the general population. Treatment is not recommended outside pregnancy because glucose-lowering therapy is ineffective in people with GCK-MODY and there is a lack of long-term complications. In pregnancy, fetal growth is primarily determined by whether the fetus inherits the GCK gene mutation from their mother. Insulin treatment of the mother is only appropriate when increased fetal abdominal growth on scanning suggests the fetus is unaffected. The impact on outcome of maternal insulin treatment is limited owing to the difficulty in altering maternal glycemia in these patients. Making the diagnosis of GCK-MODY through genetic testing is essential to avoid unnecessary treatment and investigations, especially when patients are misdiagnosed with type 1 or type 2 diabetes.

Genetic variants in CCNB1 associated with differential gene transcription and risk of coronary in-stent restenosis

BACKGROUND

The development of diagnostic tools to assess restenosis risk after stent deployment may enable the intervention to be tailored to the individual patient, for example, by targeting the use of drug-eluting stent to high-risk patients, with the goal of improving safety and reducing costs. The CCNB1 gene (encoding cyclin B1) positively regulates cell proliferation, a key component of in-stent restenosis. Therefore, we hypothesized that single-nucleotide polymorphisms in CCNB1 may serve as useful tools in risk stratification for in-stent restenosis.

METHODS AND RESULTS

We identified 3 single-nucleotide polymorphisms in CCNB1 associated with increased restenosis risk in a cohort of 284 patients undergoing coronary angioplasty and stent placement (rs350099: TT versus CC+TC; odds ratio [OR], 1.82; 95% confidence interval [CI], 1.09-3.03; P=0.023; rs350104: CC versus CT+TT; OR, 1.82; 95% CI, 1.02-3.26; P=0.040; and rs164390: GG versus GT+TT; OR, 2.27; 95% CI, 1.33-3.85; P=0.002). These findings were replicated in another cohort study of 715 patients (rs350099: TT versus CC+TC; OR, 1.88; 95% CI, 0.92-3.81; P=0.080; rs350104: CC versus CT+TT; OR, 2.23; 95% CI, 1.18-4.25; P=0.016; and rs164390: GG versus GT+TT; OR, 1.87; 95% CI, 1.03-3.47; P=0.040). Moreover, the haplotype containing all 3 risk alleles is associated with higher CCNB1 mRNA expression in circulating lymphocytes and increased in-stent restenosis risk (OR, 1.43; 95% CI, 1.00-1.823; P=0.039). The risk variants of rs350099, rs350104, and rs164390 are associated with increased reporter gene expression through binding of transcription factors nuclear factor-Y, activator protein 1, and specificity protein 1, respectively.

CONCLUSIONS

Allele-dependent transcriptional regulation of CCNB1 associated with rs350099, rs350104, and rs164390 affects the risk of in-stent restenosis. These findings reveal these common genetic variations as attractive diagnostic tools in risk stratification for restenosis.

Molecular genetic analysis of ABO blood group variations reveals 29 novel ABO subgroup alleles

BACKGROUND

Identifying genetic variants of the ABO gene may reveal new biologic mechanisms underlying variant phenotypes of the ABO blood group. We report the molecular genetic analysis of 322 apparently unrelated ABO subgroup individuals in an estimated 2.1 million donors.

STUDY DESIGN AND METHODS

We performed phenotype investigations by serology studies, analyzed the DNA sequence of the ABO gene by direct sequencing or sequencing after cloning, and evaluated promoter activity by reporter assays.

RESULTS

In 62 rare ABO alleles, we identified 29 novel ABO subgroup alleles in 43 apparently unrelated subgroup individuals and their four available pedigrees. Of these alleles, one was a deletion-mutation allele, four were hybrid alleles, and 24 were point-mutation alleles. Most of the point mutations were detected in Exons 6 to 7, while several others were also detected in Exons 1 to 5 or splicing regions. One ABO promoter mutation, -35 to -18 del, was found and verified to reduce promoter activity, as determined by dual luciferase assays. Two mutations, 7G>T and 52C>T, carrying the premature terminal codons E3X and R18X in the 5'-region, were found to be associated with the very weak ABO subgroups "Ael" and "Bel."

CONCLUSION

Twenty-nine ABO subgroup alleles were newly linked to different kinds of ABO variations. We provide the first evidence that promoter abnormality is involved in the formation of weak ABO phenotypes. We also described the first naturally occurring ABO alleles with premature terminal codons in the 5'-region that led to Ael and Bel phenotypes.

APG: an Active Protein-Gene network model to quantify regulatory signals in complex biological systems

Synergistic interactions among transcription factors (TFs) and their cofactors collectively determine gene expression in complex biological systems. In this work, we develop a novel graphical model, called Active Protein-Gene (APG) network model, to quantify regulatory signals of transcription in complex biomolecular networks through integrating both TF upstream-regulation and downstream-regulation high-throughput data. Firstly, we theoretically and computationally demonstrate the effectiveness of APG by comparing with the traditional strategy based only on TF downstream-regulation information. We then apply this model to study spontaneous type 2 diabetic Goto-Kakizaki (GK) and Wistar control rats. Our biological experiments validate the theoretical results. In particular, SP1 is found to be a hidden TF with changed regulatory activity, and the loss of SP1 activity contributes to the increased glucose production during diabetes development. APG model provides theoretical basis to quantitatively elucidate transcriptional regulation by modelling TF combinatorial interactions and exploiting multilevel high-throughput information.

Ancestral mutations may cause a significant proportion of GCK-MODY

BACKGROUND

Although the literature indicates that ancestral mutations in the glucokinase (GCK) gene are rare, we have detected a high frequency of four prevalent mutations that together are responsible for over one third of the GCK mutations in our Czech National Register of monogenic diabetes. Therefore, we studied their potential ancestral origin in our and neighbouring Polish populations.

METHODS

We analysed the lineage of four mutations in the GCK gene - p.Glu40Lys (21 apparently unrelated families), p.Leu315His (15 families), p.Gly318Arg (26 families), and p.Val33Ala (10 families) - using genotypes of 16 single nucleotide polymorphisms that span a 14 Mb region around the gene. Haplotypes were reconstructed using Phase and Haploview programmes, and their age was estimated using dmle+.

RESULTS

We found strong evidence that supports ancestral origin of three of the four mutations: the p.Glu40Lys mutation was associated with an 11-marker long conserved haplotype, the p.Leu315His mutation was associated with a 7-marker haplotype, and the p.Gly318Arg mutation was associated with an 8-marker haplotype. None of these haplotypes were detected in the general population with a frequency >0.5%. The ages of the mutations were roughly estimated to be between 82 and 110 generations old (95% credible sets 65-151). The fourth prevalent mutation, p.Val33Ala, lacked statistically significant evidence for the founder effect, although there were some indications for its common origin.

CONCLUSIONS

The large proportion of families carrying three ancestral mutations in GCK indicates that the previously assumed rarity of the founder effect with regard to GCK-maturity onset diabetes of the young (MODY) should be reconsidered.

Identification and functional characterisation of novel glucokinase mutations causing maturity-onset diabetes of the young in Slovakia

Heterozygous glucokinase (GCK) mutations cause a subtype of maturity-onset diabetes of the young (GCK-MODY). Over 600 GCK mutations have been reported of which ∼65% are missense. In many cases co-segregation has not been established and despite the importance of functional studies in ascribing pathogenicity for missense variants these have only been performed for <10% of mutations. The aim of this study was to determine the minimum prevalence of GCK-MODY amongst diabetic subjects in Slovakia by sequencing GCK in 100 Slovakian probands with a phenotype consistent with GCK-MODY and to explore the pathogenicity of identified variants through family and functional studies. Twenty-two mutations were identified in 36 families (17 missense) of which 7 (I110N, V200A, N204D, G258R, F419S, c.580-2A>C, c.1113-1114delGC) were novel. Parental DNA was available for 22 probands (covering 14/22 mutations) and co-segregation established in all cases. Bioinformatic analysis predicted all missense mutations to be damaging. Nine (I110N, V200A, N204D, G223S, G258R, F419S, V244G, L315H, I436N) mutations were functionally evaluated. Basic kinetic analysis explained pathogenicity for 7 mutants which showed reduced glucokinase activity with relative activity indices (RAI) between 0.6 to <0.001 compared to wild-type GCK (1.0). For the remaining 2 mutants additional molecular mechanisms were investigated. Differences in glucokinase regulatory protein (GKRP) -mediated-inhibition of GCK were observed for both L315H & I436N when compared to wild type (IC(50) 14.6±0.1 mM & 20.3±1.6 mM vs.13.3±0.1 mM respectively [p<0.03]). Protein instability as assessed by thermal lability studies demonstrated that both L315H and I436N show marked thermal instability compared to wild-type GCK (RAI at 55°C 8.8±0.8% & 3.1±0.4% vs. 42.5±3.9% respectively [p<0.001]). The minimum prevalence of GCK-MODY amongst Slovakian patients with diabetes was 0.03%. In conclusion, we have identified 22 GCK mutations in 36 Slovakian probands and demonstrate that combining family, bioinformatic and functional studies can aid the interpretation of variants identified by molecular diagnostic screening.

GCK-MODY (MODY 2) Caused by a Novel p.Phe330Ser Mutation

Maturity onset diabetes of the young (MODY) is a monogenic form of diabetes inherited as an autosomal dominant trait. The second most common cause is GCK-MODY due to heterozygous mutations in the GCK gene which impair the glucokinase function through different mechanisms such as enzymatic activity, protein stability, and increased interaction with its receptor. The enzyme normally acts as a glucose sensor in the pancreatic beta cell and regulates insulin secretion. We report here a three-generation nonobese family diagnosed with diabetes. All affected family members presented with mild hyperglycemia and mostly slightly elevated hemoglobin A1c values. Genetic testing revealed a novel heterozygous T → C exchange in exon 8 of the GCK gene which resulted in a phenylalanine₃₃₀ TTC → serine (TCC)/p.Phe330Ser/F330S substitution.

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.

Transcriptional regulation of glucose sensors in pancreatic β-cells and liver: an update

Pancreatic β-cells and the liver play a key role in glucose homeostasis. After a meal or in a state of hyperglycemia, glucose is transported into the β-cells or hepatocytes where it is metabolized. In the β-cells, glucose is metabolized to increase the ATP:ADP ratio, resulting in the secretion of insulin stored in the vesicle. In the hepatocytes, glucose is metabolized to CO(2), fatty acids or stored as glycogen. In these cells, solute carrier family 2 (SLC2A2) and glucokinase play a key role in sensing and uptaking glucose. Dysfunction of these proteins results in the hyperglycemia which is one of the characteristics of type 2 diabetes mellitus (T2DM). Thus, studies on the molecular mechanisms of their transcriptional regulations are important in understanding pathogenesis and combating T2DM. In this paper, we will review a recent update on the progress of gene regulation of glucose sensors in the liver and β-cells.

Update on mutations in glucokinase (GCK), which cause maturity-onset diabetes of the young, permanent neonatal diabetes, and hyperinsulinemic hypoglycemia

Glucokinase is a key regulatory enzyme in the pancreatic beta-cell. It plays a crucial role in the regulation of insulin secretion and has been termed the glucose sensor in pancreatic beta-cells. Given its central role in the regulation of insulin release it is understandable that mutations in the gene encoding glucokinase (GCK) can cause both hyper- and hypoglycemia. Heterozygous inactivating mutations in GCK cause maturity-onset diabetes of the young (MODY) subtype glucokinase (GCK), characterized by mild fasting hyperglycemia, which is present at birth but often only detected later in life during screening for other purposes. Homozygous inactivating GCK mutations result in a more severe phenotype presenting at birth as permanent neonatal diabetes mellitus (PNDM). A growing number of heterozygous activating GCK mutations that cause hypoglycemia have also been reported. A total of 620 mutations in the GCK gene have been described in a total of 1,441 families. There are no common mutations, and the mutations are distributed throughout the gene. The majority of activating mutations cluster in a discrete region of the protein termed the allosteric activator site. The identification of a GCK mutation in patients with both hyper- and hypoglycemia has implications for the clinical course and clinical management of their disorder.

RD Lawrence Lecture 2009. Old genes, new tricks: learning about blood glucose regulation from naturally occurring genetic variation in humans

The study of rare monogenic forms of diabetes and pancreatic B-cell dysfunction provides an unrivalled opportunity to link a specific change in gene function with precise cellular consequences and clinical phenotype in humans. Over the past 20 years there has been considerable success in determining the genetic aetiology of a number of rare monogenic forms of diabetes, which has had a significant impact on both our understanding of normal physiology and on translational medicine. The impact of these discoveries has been substantial, with insights into both developmental biology and normal physiology. There are clear examples where determining the genetic aetiology for individuals with rare monogenic subtypes of diabetes has led to improved treatment. Although formerly in the shadow of the monogenic diabetes field, over the past 3 years there has been staggering progress in our understanding of the genetic basis of Type 2 diabetes. This has been largely as a result of genome-wide association studies and has seen the list of 'diabetes susceptibility genes' increase from three to close to 20. There is now encouraging evidence to support a potential role for genetics in determining the response of individuals with Type 2 diabetes to different therapeutic options. One of the challenges that lies ahead is determining how the non-coding genetic variants exert their pathogenicity. It is possible that parallels can be drawn from functional work on rare regulatory mutations causing monogenic forms of diabetes. However, it is more likely that comprehensive approaches will be necessary.