Effective treatment with oral sulfonylureas in patients with diabetes due to sulfonylurea receptor 1 (SUR1) mutations

Roles of sulfonylurea receptor 1 and multidrug resistance protein 1 in modulating insulin secretion in human insulinoma

BACKGROUND

Sulfonylurea receptor 1 (SUR1) and multidrug resistance protein 1 (MRP1) are two prominent members of multidrug resistance proteins associated with insulin secretion. The aims of this study were to investigate their expression in insulinomas and their sole and synergistic effects in modulating abnormal insulin secretion.

METHODS

Fasting glucose, insulin and C-peptide were measured in 11 insulinoma patients and 11 healthy controls. Prolonged oral glucose tolerance tests were performed in 6 insulinoma patients. Insulin content, SUR1 and MRP1 were detected in 11 insulinoma patients by immunohistochemistry. SUR1 and MRP1 were also detected in 6 insulinoma patients by immunofluorescence.

RESULTS

Insulinoma patients presented the typical demonstrations of Whipple's triad. Fasting glucose of each insulinoma patient was lower than 2.8 mmol/L, and simultaneous insulin and C-peptide were increased in insulinoma patients. Prolonged oral glucose tolerance tests showed that insulin secretion in insulinoma patients were also stimulated by high glucose. Immunohistochemistry and immunofluorescence staining showed that SUR1 increased, but MRP1 decreased in insulinoma compared with the adjacent islets.

CONCLUSIONS

The hypersecretion of insulin in insulinomas might be, at least partially, due to the enrichment of SUR1. In contrast, MRP1, which is down-regulated in insulinomas, might reflect a negative feedback in insulin secretion.

Transient neonatal diabetes with two novel mutations in the KCNJ11 gene and response to sulfonylurea treatment in a preterm infant

Neonatal diabetes mellitus (NDM) is a rare condition that can be either transient or permanent. K(ATP) channel (Kir6.2 or SUR1) mutation, chromosome 6 abnormalities, insulin, or glucokinase gene mutations can lead to isolated NDM. Cases caused by Kir6.2 mutation usually result in permanent NDM (PNDM) rather than transient NDM (TNDM). The majority of patients with the Kir6.2 or SUR1 mutation can be successfully managed with a sulfonylurea agent, without the need for insulin. We report a preterm male with NDM having two novel missense mutations, E322A and D352H, in the KCNJ11 gene. At 2 months of age, successful transition from insulin to glibenclamide (glyburide) therapy of the patient was managed. At 5 months of age, his diabetes went in to remission.

A new variant of a known mutation in two siblings with permanent neonatal diabetes mellitus

Permanent neonatal diabetes mellitus is a rare disorder usually presenting within the first few weeks or months of life. This disorder is genetically heterogeneous and has been associated with mutations in various genes. The genetic cause remains mostly unknown although several genes have been linked to this disorder. Mutations in KCNJ11, ABCC8, or INS are the cause of permanent neonatal diabetes mellitus in about 50%-60% of the patients. With genetic studies, we hope to increase our knowledge of neonatal diabetes, whereby new treatment models can become possible. Here, we defined a new variant of a known mutation, INS Exon 1-3 homozygous deletion, in two siblings diagnosed with permanent neonatal diabetes mellitus.

Genetic polymorphisms in diabetes: influence on therapy with oral antidiabetics

Due to new genetic insights, etiologic classification of diabetes is under constant scrutiny. Hundreds, or even thousands, of genes are linked with type 2 diabetes. Three common variants (Lys23 of KCNJ11, Pro12 of PPARG, and the T allele at rs7903146 of TCF7L2) have been shown to be predisposed to type 2 diabetes mellitus across many large studies. Individually, each of these polymorphisms is only moderately predisposed to type 2 diabetes. On the other hand, monogenic forms of diabetes such as MODY and neonatal diabetes are characterized by unique clinical features and the possibility of applying a tailored treatment.Genetic polymorphisms in drug-metabolizing enzymes, transporters, receptors, and other drug targets have been linked to interindividual differences in the efficacy and toxicity of a number of medications. Mutations in genes important in drug absorption, distribution, metabolism and excretion (ADME) play a critical role in pharmacogenetics of diabetes.There are currently five major classes of oral pharmacological agents available to treat type 2 diabetes: sulfonylureas, meglitinides, metformin (a biguanide), thiazolidinediones, and α-glucosidase inhibitors. Other classes are also mentioned in literature.In this work, different types of genetic mutations (mutations of the gene for glucokinase, HNF 1α, HNF1β and Kir6.2 and SUR1 subunit of KATP channel, PPAR-γ, OCT1 and OCT2, cytochromes, direct drug-receptor (KCNJ11), as well as the factors that influence the development of the disease (TCF7L2) and variants of genes that lead to hepatosteatosis caused by thiazolidinediones) and their influence on the response to therapy with oral antidiabetics will be reviewed.

Permanent neonatal diabetes due to activating mutations in ABCC8 and KCNJ11

The ATP-sensitive potassium (K(ATP)) channel is composed of two subunits SUR1 and Kir6.2. The channel is key for glucose stimulated insulin release from the pancreatic beta cell. Activating mutations have been identified in the genes encoding these subunits, ABCC8 and KCNJ11, and account for approximately 40% of permanent neonatal diabetes cases. The majority of patients with a K(ATP) mutation present with isolated diabetes however some have presented with the Developmental delay, Epilepsy and Neonatal Diabetes syndrome. This review focuses on mutations in the K(ATP) channel which result in permanent neonatal diabetes, we review the clinical and functional effects as well as the implications for treatment.

The first case report of sulfonylurea use in a woman with permanent neonatal diabetes mellitus due to KCNJ11 mutation during a high-risk pregnancy

Sulfonylureas (SUs) were proven to be more effective than insulin in most Kir6.2 permanent neonatal diabetes mellitus (PNDM) patients. We report SU use during pregnancy in PNDM. A woman with the R201H Kir6.2 mutation became pregnant at the age of 37. The patient had been on glipizide 30 mg for 3 yr; her glycosylated hemoglobin level was 5.8%. She was diagnosed with chronic diabetes complications and a congenital defect of the urogenitary tract-a bicornuate uterus with septum. Because the effect of SU on fetal development is uncertain, she was switched to insulin after the pregnancy diagnosis; however, the subsequent glycemic control was unsatisfactory, with episodes of hyper- and hypoglycemia. Thus, in the second trimester, the patient was transferred to SU (glibenclamide, 40 mg), which resulted in stabilization of glycemic control; glycosylated hemoglobin in the third trimester was 5.8%. Prenatal genetic testing excluded the Kir6.2 R201H mutation in the fetus. A preterm cesarean delivery was carried out in the 35th week. The Apgar score of the newborn boy (weight, 3010 g; 75th percentile) was 8 at 1 min. He presented with hypoglycemia, transient tachypnea of the newborn, and hyperbilirubinemia. The recovery was uneventful. No birth defects were recorded. His development at the ninth month of life was normal. In summary, we show a high-risk pregnancy in long-term PNDM that despite perinatal complications ended with the birth of a healthy child. SUs, which seem to constitute an alternative to insulin during pregnancy in Kir6.2-related PNDM, were used during the conception period and most of the second and third trimesters.

Neonatal diabetes mellitus: a model for personalized medicine

Neonatal diabetes mellitus occurs in approximately 1 out of every 100,000 live births. It can be either permanent or transient, and recent studies indicate that is likely to have an underlying genetic cause, particularly when diagnosed before 6 months of age. Permanent neonatal diabetes is most commonly due to activating mutations in either of the genes encoding the two subunits of the ATP-sensitive potassium channel. In most of these patients, switching from insulin to oral sulfonylurea therapy leads to improved metabolic control, as well as possible amelioration of occasional associated neurodevelopmental disabilities. It remains to be determined what is the most appropriate treatment of other causes. The diagnosis and treatment of neonatal diabetes, therefore, represents a model for personalized medicine.

Electrophysiology of islet cells

Stimulus-Secretion Coupling (SSC) of pancreatic islet cells comprises electrical activity. Changes of the membrane potential (V(m)) are regulated by metabolism-dependent alterations in ion channel activity. This coupling is best explored in beta-cells. The effect of glucose is directly linked to mitochondrial metabolism as the ATP/ADP ratio determines the open probability of ATP-sensitive K(+) channels (K(ATP) channels). Nucleotide sensitivity and concentration in the direct vicinity of the channels are controlled by several factors including phospholipids, fatty acids, and kinases, e.g., creatine and adenylate kinase. Closure of K(ATP) channels leads to depolarization of beta-cells via a yet unknown depolarizing current. Ca(2+) influx during action potentials (APs) results in an increase of the cytosolic Ca(2+) concentration ([Ca(2+)](c)) that triggers exocytosis. APs are elicited by the opening of voltage-dependent Na(+) and/or Ca(2+) channels and repolarized by voltage- and/or Ca(2+)-dependent K(+) channels. At a constant stimulatory glucose concentration APs are clustered in bursts that are interrupted by hyperpolarized interburst phases. Bursting electrical activity induces parallel fluctuations in [Ca(2+)](c) and insulin secretion. Bursts are terminated by I(Kslow) consisting of currents through Ca(2+)-dependent K(+) channels and K(ATP) channels. This review focuses on structure, characteristics, physiological function, and regulation of ion channels in beta-cells. Information about pharmacological drugs acting on K(ATP) channels, K(ATP) channelopathies, and influence of oxidative stress on K(ATP) channel function is provided. One focus is the outstanding significance of L-type Ca(2+) channels for insulin secretion. The role of less well characterized beta-cell channels including voltage-dependent Na(+) channels, volume sensitive anion channels (VSACs), transient receptor potential (TRP)-related channels, and hyperpolarization-activated cyclic nucleotide-gated (HCN) channels is discussed. A model of beta-cell oscillations provides insight in the interplay of the different channels to induce and maintain electrical activity. Regulation of beta-cell electrical activity by hormones and the autonomous nervous system is discussed. alpha- and delta-cells are also equipped with K(ATP) channels, voltage-dependent Na(+), K(+), and Ca(2+) channels. Yet the SSC of these cells is less clear and is not necessarily dependent on K(ATP) channel closure. Different ion channels of alpha- and delta-cells are introduced and SSC in alpha-cells is described in special respect of paracrine effects of insulin and GABA secreted from beta-cells.

Sulfonylurea pharmacogenomics in Type 2 diabetes: the influence of drug target and diabetes risk polymorphisms

The sulfonylureas stimulate insulin release from pancreatic beta cells, and have been a cornerstone of Type 2 diabetes pharmacotherapy for over 50 years. Although sulfonylureas are effective antihyperglycemic agents, interindividual variability exists in drug response (i.e., pharmacodynamics), disposition (i.e., pharmacokinetics) and adverse effects. The field of pharmacogenomics has been applied to sulfonylurea clinical studies in order to elucidate the genetic underpinnings of this response variability. Historically, most studies have sought to determine the influence of polymorphisms in drug-metabolizing enzyme genes on sulfonylurea pharmacokinetics in humans. More recently, polymorphisms in sulfonylurea drug target genes and diabetes risk genes have been implicated as important determinants of sulfonylurea pharmacodynamics in patients with Type 2 diabetes. As such, the purpose of this review is to discuss sulfonylurea pharmacogenomics in the setting of Type 2 diabetes, specifically focusing on polymorphisms in drug target and diabetes risk genes, and their relationship with interindividual variability in sulfonylurea response and adverse effects.

Reevaluation of a case of type 1 diabetes mellitus diagnosed before 6 months of age

BACKGROUND

A 17-year-old female was referred for the reassessment of her type 1 diabetes mellitus, with which she had been diagnosed at the age of 15 weeks owing to symptoms of ketoacidosis. The patient had mild learning difficulties, which resulted in her requiring additional support at school. There was no family history of diabetes.

INVESTIGATIONS

Measurements of plasma C-peptide and glutamate decarboxylase autoantibodies. Molecular genetic testing was performed.

DIAGNOSIS

Intermediate developmental delay, epilepsy and neonatal diabetes mellitus (DEND) syndrome as a result of a 59V>M Kir6.2 mutation.

MANAGEMENT

Treatment with high-dose oral glibenclamide replaced insulin treatment. Good glycemic control was achieved with levels of HbA(1c) consistently below 6.5% and no hypoglycemia.

Identification of First Case of Neonatal Diabetes in Singapore and Successful Conversion from Insulin to Sulphonylurea

Introduction:

To date Neonatal Diabetes Mellitus (NDM) has not been reported in Singapore. Neonatal diabetes is a rare (1 in 100,00–300,000 live births) insulin-requiring form of diabetes with well defined subgroups, permanent neonatal diabetes (PND) and transient neonatal diabetes (TND), each accounting for approximately 50% of patients. Genotyping NDM identifies the exact unique molecular aetiology of very early onset insulin requiring diabetes and has the potential to dramatically alter the management of the patient, who would otherwise be insulin dependent for life.

Method:

We identified a child who presented at 3 and half months of age with diabetic ketoacidosis and determined the phenotypic and genotypic characteristics. Blood samples for molecular genetic analysis were sent to Royal Devon and Exeter Foundation Trust, UK. We determined her Continuous Glucose Monitoring profiles after initiation of sulphonylurea therapy.

Results:

The patient was diagnosed as a heterozygous for a missense mutation R201H, in the KCNJ11 gene. Results confirmed a diagnosis of permanent neonatal diabetes due to a mutation in the Kir6.2 subunit of the KATP channel. We initiated sulphonylurea therapy and subsequently ceased insulin treatment successfully. Currently 2 years old, this patient is no longer insulin dependent.

Conclusion:

This is the first case report of neonatal diabetes in Singapore. It describes the importance of correct identification of the case, and successful conversion of therapy from insulin to sulphonylureas with optimal blood glucose control. We emphasise the need for medical practitioners to consider molecular testing for all patients who present with diabetes below 6 months of age as this will facilitate accurate diagnosis and appropriate therapy.

Successful transfer from insulin to oral sulfonylurea in a 3-year-old girl with a mutation in the KCNJ11 gene

Neonatal diabetes mellitus is considered a rare disease that is diagnosed in the first six months of life, and can be either transient or permanent. Recent advances in molecular genetics have shown that activating mutations in KCNJ11 (the gene that encodes for the Kir6.2 subunit of the K ATP potassium channel of the pancreatic beta-cell) is a common cause of permanent neonatal diabetes mellitus. Patients with mutations in this gene may respond to oral sulfonylureas. We describe a 3-year-old girl with permanent neonatal diabetes mellitus with a mutation in the KCNJ11 gene (R201H), who was successfully transferred from subcutaneous insulin to oral glibenclamide, with a marked improvement in glycemic control. This is the first successful switch from insulin to oral sulfonylurea in a patient with R201H mutation, in the Arabian Gulf.

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.

Interaction between mutations in the slide helix of Kir6.2 associated with neonatal diabetes and neurological symptoms

ATP-sensitive potassium (K(ATP)) channels regulate insulin secretion from pancreatic beta-cells. Gain-of-function mutations in the genes encoding the Kir6.2 and SUR1 subunits of this channel cause neonatal diabetes. We report two novel mutations on the same haplotype (cis), F60Y and V64L, in the slide helix of Kir6.2 in a patient with neonatal diabetes, developmental delay and epilepsy. Functional analysis revealed the F60Y mutation increases the intrinsic channel open probability (Po(0)), thereby indirectly producing a marked decrease in channel inhibition by ATP and an increase in whole-cell K(ATP) currents. When expressed alone, the V64L mutation caused a small reduction in apparent ATP inhibition, by enhancing the ability of MgATP to stimulate channel activity. The V64L mutation also ameliorated the deleterious effects on the F60Y mutation when it was expressed on the same (but not a different) subunit. These data indicate that F60Y is the pathogenic mutation and reveal that interactions between slide helix residues can influence K(ATP) channel gating.

The clinical application of non-genetic biomarkers for differential diagnosis of monogenic diabetes

Diabetes mellitus is not a single disorder but rather a heterogeneous group of diseases that differ in respect to pathogenesis, the clinical picture and the response to dietary and pharmacological treatments. Thus, the differential diagnosis of various types and forms of diabetes is of great practical importance. This is particularly true for monogenic disease forms where some spectacular applications of pharmacogenetics have recently been described. Unfortunately, most patients with monogenic diabetes such as maturity-onset diabetes of the young (MODY) or neonatal diabetes have not undergone diagnostic molecular testing, so they can not benefit from the progress seen in this field. The reasons for this include the complexity and cost of molecular diagnostics. One of ways to change this situation is to find an efficient and cheap test to screen thousands of patients for specific forms of monogenic diabetes. These tests can be based on biomarkers discovered by one of two general strategies: a candidate approach or a systematic search based on metabonomics or proteonomics. This review summarizes recent advances in the search for putative biomarkers and the perspectives of the future progress.

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.

A brief perspective on insulin production

The preeminent role of the beta cell is to manufacture, store and release insulin. The mature insulin molecule is composed of two polypeptide chains designated as A and B that are joined by two pairs of disulfide bonds with an additional intramolecular disulfide bond in the A chain. However, the two chains of the insulin molecule are not synthesized as separate polypeptide chains but rather are generated by specific proteolytic processing of a larger precursor, proinsulin. This discovery in 1967 and the concept of prohormones changed our view of the biosynthesis of hormones and neuropeptides. It allowed studies of the regulation of insulin biosynthesis that highlighted the key role of glucose. In addition, the C-peptide, the polypeptide that joins the A and B chains in proinsulin and is stored with insulin in the secretory granules and secreted in equimolar amounts, allowed studies of pancreatic beta cell function in vivo including in patients with diabetes. Subsequent studies have identified the specific proteases, prohormone convertases 1/3 and 2 and carboxypeptidase E, that are involved in the conversion of proinsulin to proinsulin intermediates and then to insulin. Disorders of (pro)insulin biosynthesis continue to illuminate important aspects of this pathway, revealing important connections to diabetes pathogenesis. Recent studies of patients with insulin gene mutations that cause permanent neonatal diabetes have identified key residues affecting the folding and structural organization of the preproinsulin molecule and its subsequent processing. These findings have renewed interest in the key role of endoplasmic reticulum function in insulin biosynthesis and the maintainance of normal beta cell health.

Mutations in the ABCC8 (SUR1 subunit of the K(ATP) channel) gene are associated with a variable clinical phenotype

OBJECTIVE

Mutations in the ABCC8 gene encoding the SUR1 subunits of the beta-cell K-ATP channel cause neonatal diabetes (ND) mellitus. We aimed to determine the contribution of ABCC8 gene to ND in Poland, to describe the clinical phenotype associated with its mutations and to examine potential modifying factors.

PATIENTS

The Nationwide Registry of ND in Poland includes patients diagnosed before 6 months of age. In total 16 Kir6.2 negative patients with ND, 14 permanent and 2 relapsed transient, were examined.

MEASUREMENTS

ABCC8 gene mutations were detected by direct sequencing. Mutation carriers' characteristics included clinical data and biochemical parameters. In addition, we performed the hyperinsulinaemic euglycaemic clamp and tested for islet-specific antibodies in diabetic subjects.

RESULTS

We identified two probands with permanent ND (one heterozygous F132V mutation carrier and one compound heterozygote with N23H and R826W mutations) and two others with relapsed transient ND (heterozygotes for R826W and V86A substitutions, respectively). One subject, a heterozygous relative with the R826W mutation, had adult onset diabetes. There were striking differences in the clinical picture of the mutation carriers as the carrier of two mutations, N23H and R826W, was controlled on diet alone with HbA(1c) of 7.3%, whereas the F132V mutation carrier was on 0.66 IU/kg/day of insulin with HbA(1c) of 11.7%. The C-peptide level varied from 0.1 ng/ml (F132V) to 0.75 ng/ml (V86A). We also observed a variable insulin resistance, from moderate (M = 5.5 and 5.6 mg/kg/min, respectively, in the two R826W mutation carriers) to severe (M = 2.6 mg/kg/min in the F132V mutation carrier). We were able to transfer two patients off insulin to sulphonylurea (SU) and to reduce insulin dose in one other patient. Interestingly, there was no response to SU in the most insulin resistant F132V mutation carrier despite high dose of glibenclamide. All examined auto-antibodies were present in one of the subjects, the V86A mutation carrier, although this did not seem to influence the clinical picture, as we were able to transfer this girl off insulin.

CONCLUSION

Mutations in SUR1 are the cause of about 15% of Kir6.2 negative permanent ND in Poland. The clinical phenotype of SUR1 diabetic mutation carriers is heterogeneous and it appears to be modified by variable sensitivity to insulin.

Xenopus pancreas development

Understanding how the pancreas develops is vital to finding new treatments for a range of pancreatic diseases, including diabetes and pancreatic cancer. Xenopus is a relatively new model organism for the elucidation of pancreas development, and has already made contributions to the field. Recent studies have shown benefits of using Xenopus for understanding both early patterning and lineage specification aspects of pancreas organogenesis. This review focuses specifically on Xenopus pancreas development, and covers events from the end of gastrulation, when regional specification of the endoderm is occurring, right through metamorphosis, when the mature pancreas is fully formed. We have attempted to cover pancreas development in Xenopus comprehensively enough to assist newcomers to the field and also to enable those studying pancreas development in other model organisms to better place the results from Xenopus research into the context of the field in general and their studies specifically. Developmental Dynamics 238:1271-1286, 2009. (c) 2009 Wiley-Liss, Inc.

Update of mutations in the genes encoding the pancreatic beta-cell K(ATP) channel subunits Kir6.2 (KCNJ11) and sulfonylurea receptor 1 (ABCC8) in diabetes mellitus and hyperinsulinism

The beta-cell ATP-sensitive potassium (K(ATP)) channel is a key component of stimulus-secretion coupling in the pancreatic beta-cell. The channel couples metabolism to membrane electrical events bringing about insulin secretion. Given the critical role of this channel in glucose homeostasis it is therefore not surprising that mutations in the genes encoding for the two essential subunits of the channel can result in both hypo- and hyperglycemia. The channel consists of four subunits of the inwardly rectifying potassium channel Kir6.2 and four subunits of the sulfonylurea receptor 1 (SUR1). It has been known for some time that loss of function mutations in KCNJ11, which encodes for Kir6.2, and ABCC8, which encodes for SUR1, can cause oversecretion of insulin and result in hyperinsulinism of infancy, while activating mutations in KCNJ11 and ABCC8 have recently been described that result in the opposite phenotype of diabetes. This review focuses on reported mutations in both genes, the spectrum of phenotypes, and the implications for treatment on diagnosing patients with mutations in these genes.

Clinical translation of genetic predictors for type 2 diabetes

PURPOSE OF REVIEW

To highlight recent type 2 diabetes (T2D)-associated genetic discoveries and their potential for clinical application.

RECENT FINDINGS

The advent of genome-wide association screening has uncovered many loci newly associated with T2D. This review describes the techniques applied to discover novel T2D genes and compares their relative strengths, biases, and findings to date. The results of large-scale genome-wide association studies carried out since 2007 are summarized, and limitations of interpreting this preliminary data are offered. Recent studies exploring the clinical potential of these discoveries are reviewed, focusing on insights into T2D pathogenesis, risk prediction of future diabetes, and utility in guiding pharmacotherapy. The new T2D-associated loci have been implicated in beta-cell development and function, highlighting insulin secretion in the disease process. Preliminary risk prediction studies show that more loci are needed to improve T2D risk indices. Studies have also revealed that genes may play a role in the pharmacologic response to antidiabetic medications.

SUMMARY

Since 2007, genome-wide association studies have rapidly increased the number of T2D-associated loci. This review summarizes the history of genetic association studies, the results from the new genome-wide association studies, and the clinical application of these findings.

Can geneticists help clinicians to understand and treat non-autoimmune diabetes?

Approximately, a few percent of the European population suffers from diabetes. Scientific evidence showed that specific treatment of this disease could be successfully tailored on the basis of proper differential diagnosis that in many instances also requires genetic testing. This may be helpful in achieving metabolic control of the disease, increasing quality of life and potentially reducing the prevalence of chronic complications. Identification of the molecular background of these specific forms of diabetes gives new insight into the underlying aetiology. This knowledge helps to optimize treatment in specific clinical situations. Monogenic diabetes is an excellent example of a clinical area where new advances in molecular genetics can aid patient care and treatment decisions. The most frequently diagnosed forms of monogenic diabetes are MODY, mitochondrial diabetes, permanent and transient neonatal diabetes (PNDM and TNDM). These rare forms probably constitute at least a few percent of all diabetes cases seen in diabetic clinics. The proper differential diagnosis also helps to predict the progress of diabetes in affected individuals and defines the prognosis in the family. Recently, several genome wide association studies added new facts to the knowledge on complex forms of type 2 diabetes mellitus (T2DM) as the scientists substantially extended the short list of previously identified genes. Most newly identified variants influence beta-cell insulin secretion, while a few modulate peripheral insulin action. It is not clear whether in the future the genetic testing of frequent polymorphisms will influence the treatment of T2DM. In this review, we present the clinical application of genetic testing in non-autoimmune diabetes, mostly monogenic forms of disease.

Interindividual variability in oral antidiabetic drug disposition and response: the role of drug transporter polymorphisms

BACKGROUND

Numerous effective oral pharmacologic therapies are available to treat type 2 diabetes. However, a substantial number of patients do not achieve the expected glucose-lowering response, or may be predisposed to adverse effects, from these agents. The application of pharmacogenetics to the field of type 2 diabetes is one step towards the goal of improved pharmacotherapeutic management of this progressive disease.

METHODS

A PubMed literature search was conducted to identify clinical studies that have examined the extent to which drug-transporter gene polymorphisms influence interindividual variability in oral antidiabetic drug disposition and response in humans.

RESULTS/CONCLUSION

Available data suggest that drug transporters play an important role in the disposition of some oral antidiabetic drugs in the body, particularly the meglitinides and metformin. Moreover, polymorphisms in genes encoding drug transport proteins may alter the pharmacodynamic profile of these agents. Drug transporters, drug-metabolizing enzymes, and drug targets each play a distinct and important role in the disposition and action of many oral antidiabetic agents. Thus, future studies may need to take a pharmacogenomic (i.e., multiple gene) approach in order to comprehensively understand the extent to which genetic variation contributes to interindividual differences in oral antidiabetic drug clinical pharmacology.

Diagnosis and treatment of neonatal diabetes: a United States experience

BACKGROUND/OBJECTIVE

Mutations in KCNJ11, ABCC8, or INS are the cause of permanent neonatal diabetes mellitus in about 50% of patients diagnosed with diabetes before 6 months of age and in a small fraction of those diagnosed between 6 and 12 months. The aim of this study was to identify the genetic cause of diabetes in 77 consecutive patients referred to the University of Chicago with diabetes diagnosed before 1 yr of age.

METHODS

We used Oragene DNA Self-Collection kit to obtain a saliva sample for DNA. We sequenced the protein-coding regions of KCNJ11, ABCC8, and INS using standard methods.

RESULTS

We enrolled 32 patients diagnosed with diabetes before 6 months of age and 45 patients diagnosed between 6 and 12 months. We identified a mutation in KCNJ11 in 14 patients from 12 families and in INS in 7 patients from 4 families. Three of the patients with an INS mutation were diagnosed with diabetes between 6 and 12 months of age. Finally, we found that two patients had an abnormality of chromosome 6q24 associated with transient neonatal diabetes mellitus.

CONCLUSIONS

We were able to establish a genetic cause of diabetes in 63% of patients diagnosed with diabetes before 6 months of age and in 7% of patients diagnosed between 6 and 12 months. Genetic testing, which is critical for guiding appropriate management, should be considered in patients diagnosed with diabetes before 1 yr of age, especially if they are autoantibody negative, although the presence of autoantibodies does not rule out a monogenic cause.

RNA processing and mRNA surveillance in monogenic diabetes

In the eukaryotic cell a number of molecular mechanisms exist to regulate the nature and quantity of transcripts intended for translation. For monogenic diabetes an understanding of these processes is aiding scientists and clinicians in studying and managing this disease. Knowledge of RNA processing and mRNA surveillance pathways is helping to explain disease mechanisms, form genotype-phenotype relationships, and identifying new regions within genes to screen for mutations. Furthermore, recent insights into the regulatory role of micro RNAs (miRNAs) and RNA editing in the pancreas suggests that these mechanisms may also be important in the progression to the diabetic state.

Neonatal diabetes mellitus

An explosion of work over the last decade has produced insight into the multiple hereditary causes of a nonimmunological form of diabetes diagnosed most frequently within the first 6 months of life. These studies are providing increased understanding of genes involved in the entire chain of steps that control glucose homeostasis. Neonatal diabetes is now understood to arise from mutations in genes that play critical roles in the development of the pancreas, of beta-cell apoptosis and insulin processing, as well as the regulation of insulin release. For the basic researcher, this work is providing novel tools to explore fundamental molecular and cellular processes. For the clinician, these studies underscore the need to identify the genetic cause underlying each case. It is increasingly clear that the prognosis, therapeutic approach, and genetic counseling a physician provides must be tailored to a specific gene in order to provide the best medical care.