Sensitivity to sulphonylureas in patients with hepatocyte nuclear factor-1alpha gene mutations: evidence for pharmacogenetics in diabetes

Do genome-wide association scans have potential for translation?

The success of genome-wide association studies (GWAS) in identifying replicating associations has greatly contributed to understanding of the genetic aetiology of complex diseases. This review discusses and provides examples of the potential of GWAS findings to be translated into clinical practice, i.e., diagnosis, prediction, prognosis, novel treatments and response to treatment of common diseases. The biological insights afforded by newly-identified robust associations represent the largest, albeit indirect, translational contribution of GWAS.

Clinical characteristics and diagnostic criteria of maturity-onset diabetes of the young (MODY) due to molecular anomalies of the HNF1A gene

CONTEXT

The diagnosis of maturity-onset diabetes of the young type 3 (MODY3), associated with HNF1A molecular abnormalities, is often missed.

OBJECTIVE

The objective of the study was to describe the phenotypes of a large series of MODY3 patients and to reassess parameters that may improve its diagnosis.

DESIGN, SETTING, AND PATIENTS

This retrospective multicenter study included 487 unrelated patients referred because of suspicion of MODY3. Genetic analysis identified 196 MODY3 and 283 non-MODY3 cases. Criteria associated with MODY3 were assessed by multivariate analysis. The capacity of the model to predict MODY3 diagnosis was assessed by the area under the receiver-operating characteristic curve and was further validated in an independent sample of 851 patients (165 MODY3 and 686 non-MODY3).

RESULTS

In the MODY3 patients, diabetes was revealed by clinical symptoms in 25% of the cases and was diagnosed by screening in the others. Age at diagnosis of diabetes was more than 25 yr in 40% of the MODY3 patients. There was considerable variability and overlap of all assessed parameters in MODY3 and non-MODY3 patients. The best predictive model was based on criteria available at diagnosis of diabetes, including age, body mass index, number of affected generations, presence of diabetes symptoms, and geographical origin. The area under the curve of the receiver-operating characteristic analysis was 0.81. When sensitivity was set to 90%, specificity was 49%.

CONCLUSIONS

Differential diagnosis between MODY3 and early-onset type 2 diabetes remains difficult. Whether the proposed model will improve the pick-up rate of MODY3 diagnosis needs to be confirmed in independent populations.

Effect of genetic polymorphisms on the pharmacokinetics and efficacy of glimepiride in a Korean population

BACKGROUNDS

Glimepiride is a commonly used sulfonylurea hypoglycemic agent. There is considerable interindividual variation in the response to sulfonylurea for patients with type 2 diabetes. The purpose of this study was to investigate whether genetic variations influence the efficacy of glimepiride in healthy Korean subjects.

METHODS

A single 2-mg oral dose of glimepiride was administered to 46 healthy volunteers. Serial blood sampling for 12h after oral dosing was performed for determination of plasma glimepiride, glucose and insulin levels. We tested the association of seven single nucleotide polymorphisms (SNPs) in four candidate genes with the efficacy of glimepiride.

RESULTS

Pharmacodynamic profiles for plasma glucose and insulin showed no statistically significant differences among genotype groups, and parameters were not different from one another. There were no association of the KCNJ11, NOS1AP, TCF7L2 and ABCC8 gene polymorphisms and the efficacy of glimepiride.

CONCLUSIONS

Knowledge of these polymorphisms provides no clinical useful information for the pharmacogenetic therapeutic approach for Korean patients with type 2 diabetes.

Response to oral gliclazide in a pre-pubertal child with hepatic nuclear factor-1 alpha maturity onset diabetes of the young

The term "maturity onset diabetes of the young" (MODY) describes a heterogeneous group of monogenic diabetes of which hepatic nuclear factor-1 alpha (HNF-1α) MODY is the most common. Patients with HNF-1α mutations typically present after puberty, and oral sulfonylureas (SU) have been shown to be effective in adults with this condition. A 7-year-old boy presented with asymptomatic hyperglycemia ranging between 6.2 and 10.1 mmol/L and glycosuria for nearly a year. The child's initial HbA 1c was 6.9% and the pancreatic Islet cell autoantibodies were negative. His response to the oral glucose tolerance test (OGTT) showed a large increment of glucose from basal level of 7.7 to 21.1 mmol/L in 120 min. The mild presentation, family history, and negative autoantibodies were suggestive of HNF-1α MODY, which was confirmed by mutation analysis. Initial management with diet alone was not sufficient, but he responded well to 20 mg oral gliclazide once a day with an improvement of HbA 1C from 7.2% to 6.5% within 3 months of treatment. The case is an illustration of the clinical utility of molecular genetic tests in the management of childhood diabetes.

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.

The molecular mechanisms and pharmacotherapy of ATP-sensitive potassium channel gene mutations underlying neonatal diabetes

Neonatal diabetes mellitus (NDM) is a monogenic disorder caused by mutations in genes involved in regulation of insulin secretion from pancreatic β-cells. Mutations in the KCNJ11 and ABCC8 genes, encoding the adenosine triphosphate (ATP)-sensitive potassium (K(ATP)) channel Kir6.2 and SUR1 subunits, respectively, are found in ∼50% of NDM patients. In the pancreatic β-cell, K(ATP) channel activity couples glucose metabolism to insulin secretion via cellular excitability and mutations in either KCNJ11 or ABCC8 genes alter K(ATP) channel activity, leading to faulty insulin secretion. Inactivation mutations decrease K(ATP) channel activity and stimulate excessive insulin secretion, leading to hyperinsulinism of infancy. In direct contrast, activation mutations increase K(ATP) channel activity, resulting in impaired insulin secretion, NDM, and in severe cases, developmental delay and epilepsy. Many NDM patients with KCNJ11 and ABCC8 mutations can be successfully treated with sulfonylureas (SUs) that inhibit the K(ATP) channel, thus replacing the need for daily insulin injections. There is also strong evidence indicating that SU therapy ameliorates some of the neurological defects observed in patients with more severe forms of NDM. This review focuses on the molecular and cellular mechanisms of mutations in the K(ATP) channel that underlie NDM. SU pharmacogenomics is also discussed with respect to evaluating whether patients with certain K(ATP) channel activation mutations can be successfully switched to SU therapy.

Pharmacogenetics of Anti-Diabetes Drugs

A variety of treatment modalities exist for individuals with type 2 diabetes mellitus (T2D). In addition to dietary and physical activity interventions, T2D is also treated pharmacologically with nine major classes of approved drugs. These medications include insulin and its analogues, sulfonylureas, biguanides, thiazolidinediones (TZDs), meglitinides, α-glucosidase inhibitors, amylin analogues, incretin hormone mimetics, and dipeptidyl peptidase 4 (DPP4) inhibitors. Pharmacological treatment strategies for T2D are typically based on efficacy, yet favorable responses to such therapeutics are oftentimes variable and difficult to predict. Characterization of drug response is expected to substantially enhance our ability to provide patients with the most effective treatment strategy given their individual backgrounds, yet pharmacogenetic study of diabetes medications is still in its infancy. To date, major pharmacogenetic studies have focused on response to sulfonylureas, biguanides, and TZDs. Here, we provide a comprehensive review of pharmacogenetics investigations of these specific anti-diabetes medications. We focus not only on the results of these studies, but also on how experimental design, study sample issues, and definition of 'response' can significantly impact our interpretation of findings. Understanding the pharmacogenetics of anti-diabetes medications will provide critical baseline information for the development and implementation of genetic screening into therapeutic decision making, and lay the foundation for "individualized medicine" for patients with T2D.

Stopping insulin injections following genetic testing in diabetes: impact on identity

BACKGROUND

Identification of genes causing monogenic diabetes has led to treatment change, from insulin to sulphonylureas for many previously considered insulin dependent. Changing treatment has led to improved glycaemic control and quality of life; however, the impact of a genetic diagnosis and consequent treatment change on identity has not been explored.

METHODS

This paper examines the experiences of patients and their families using Bury's theory of biographical disruption in chronic illness to offer insight and comparison with the disruption caused by treatment change following genetic testing. This qualitative study is a longitudinal follow-up using in-depth interviews over time. Thirty-one individuals were interviewed following genetic testing and again 12 months later.

RESULTS

Key themes identified were: (i) embodied practices of diabetes; (ii) perceived identity on insulin; (iii) 'holding on' to insulin treatment; (iv) challenges and benefits of treatment change; (v) identity reconstruction. Participants were categorized into 'Transferers' who successfully transferred to sulphonylureas, 'Attempters' who attempted transfer but recommenced insulin and 'Decliners' who declined treatment change.

CONCLUSIONS

Injecting insulin was integral to participants' lives and fundamental to their identity. Embodied practices of diabetes were deeply embedded in self identity; the possibility of stopping insulin injections was a major challenge contradicting previous beliefs and led to identity reconstruction.

Three novel mutations in MODY and its phenotype in three different Czech families

AIMS/HYPOTHESIS

MODY (Maturity Onset Diabetes of the Young) is an autosomal dominant inherited type of diabetes with significant genetic heterogeneity. New mutations causing MODY are still being found. A genetically confirmed diagnosis of MODY allows application of individualized treatment based on the underlying concrete genetic dysfunction. Detection of novel MODY mutations helps provide a more complete picture of the possible MODY genotypes.

MATERIALS AND METHODS

We tested 43 adult Czech patients with clinical characteristics of MODY, using direct sequencing of HNF1A (hepatocyte nuclear factor 1-alpha), HNF4A (hepatocyte nuclear factor 4-alpha) and GCK (glucokinase) genes.

RESULTS

In three Czech families we identified three novel mutations we believe causing MODY-two missense mutations in HNF1A [F268L (c.802T>C) and P291S (c.871C>T)] and one frame shift mutation in GCK V244fsdelG (c.729delG). Some of the novel HNF1A mutation carriers were successfully transferred from insulin to gliclazide, while some of the novel GCK mutation carriers had a good clinical response when switched from insulin or oral antidiabetic drugs to diet.

CONCLUSION

We describe three novel MODY mutations in three Czech families. The identification of MODY mutations had a meaningful impact on therapy on the mutation carriers.

Distinct regulation of hepatic nuclear factor 1alpha by NKX6.1 in pancreatic beta cells

Hepatic nuclear factor 1alpha (HNF1alpha) is a key regulator of development and function in pancreatic beta cells and is specifically involved in regulation of glycolysis and glucose-stimulated insulin secretion. Abnormal expression of HNF1alpha leads to development of MODY3 (maturity-onset diabetes of the young 3). We report that NK6 homeodomain 1 (NKX6.1) binds to a cis-regulatory element in the HNF1alpha promoter and is a major regulator of this gene in beta cells. We identified an NKX6.1 recognition sequence in the distal region of the HNF1alpha promoter and demonstrated specific binding of NKX6.1 in beta cells by electrophoretic mobility shift and chromatin immunoprecipitation assays. Site-directed mutagenesis of the NKX6.1 core-binding sequence eliminated NKX6.1-mediated activation and substantially decreased activity of the HNF1alpha promoter in beta cells. Overexpression or small interfering RNA-mediated knockdown of the Nkx6.1 gene resulted in increased or diminished HNF1alpha gene expression, respectively, in beta cells. We conclude that NKX6.1 is a novel regulator of HNF1alpha in pancreatic beta cells. This novel regulatory mechanism for HNF1alpha in beta cells may provide new molecular targets for the diagnosis of MODY3.

Dipeptidyl peptidase-IV inhibitors are efficient adjunct therapy in HNF1A maturity-onset diabetes of the young patients--report of two cases

BACKGROUND

In HNF1A maturity-onset diabetes of the young (MODY), sulfonylurea (SU) is the first-line treatment. Over time, such therapy fails, and additional treatment is required. Dipeptidyl peptidase IV (DPP-IV) inhibitors are new agents that lower blood glucose by prolonging the activity of circulating incretins.

METHODS

We applied DPP-IV inhibitors in two HNF1A MODY patients whose earlier therapeutic regimen included SU.

RESULTS

Case 1, a 39-year-old woman, a carrier of the ArgR171X HNF1A mutation, with a 7-year history of diabetes was on 160 mg of gliclazide and 2,000 mg of metformin. Her initial hemoglobin A1c (HbA1c) level was 7.2%, while the mean glucose level on the CGMS((R)) (Medtronic, Northridge, CA) record was 162 mg/dL. Sitagliptine, in a dose of 100 mg/day, was added to the previous treatment. Case 2, a 62-year-old woman, a carrier of the IVS7nt-6G>A mutation, with a 41-year history of diabetes was treated with 240 mg/day gliclazide and 6 IU of insulin/day. Her initial HbA1c was 8.8%, and average glycemia reached 172 mg/dL. In her case, we started the combined therapy with 50 mg of vildagliptine twice daily. Patients were reexamined after 3 months, and HbA1c fell to 6.3% in both subjects. Similarly, significant improvement in glycemic control on CGMS was observed as the average glycemia decreased to 114 mg/dL and 134 mg/dL in Case 1 and Case 2, respectively. No episodes of hypoglycemia or other side effects were recorded. As intravenous glucose tolerance tests (IVGTTs) were performed before and after DPP-IV implementation, we were able to assess their impact on insulin secretion under fasting conditions. We saw a substantial rise in insulin level increment during IVGTT (by 9.8 and13.4 mIU/L in Case 1 and Case 2, respectively).

CONCLUSIONS

DPP-IV inhibitors may be an effective tool of combined therapy in HNF1A MODY, and they seem to improve beta-cell function under fasting conditions.

Increased all-cause and cardiovascular mortality in monogenic diabetes as a result of mutations in the HNF1A gene

AIMS

To investigate all-cause and cardiovascular mortality in subjects with diabetes caused by a mutation in the hepatocyte nuclear factor 1alpha gene (HNF1A).

METHODS

We identified 39 British families with HNF1A mutations. Consenting individuals were asked details of age and cause of death of parents and siblings. Copies of death certificates were requested from the family or were obtained via the Offices for National Statistics.

RESULTS

Data were collated on 241 control subjects and 153 mutation carriers. Of those who died, 66% of mutation carriers died from a cardiovascular-related illness compared with 43% of control subjects (P = 0.02). Family members with HNF1A mutations died at a younger age than familial control subjects [all-cause hazard ratio, adjusting for sex and smoking status: 1.9 (95% confidence interval 1.2, 2.9, P = 0.006; cardiovascular hazard ratio: 2.3, confidence interval 1.3, 4.2, P = 0.006)].

CONCLUSIONS

We have shown that individuals known to have diabetes caused by a mutation in the HNF1A gene have an increased risk of cardiovascular mortality compared with their unaffected family members. As with other forms of diabetes, consideration should be given to early statin therapy despite a seemingly protective lipid profile.

Genetic susceptibility to type 2 diabetes and implications for therapy

Since 2000, we have witnessed an explosion of known genetic determinants of type 2 diabetes risk. These findings have seeded the expectation that our ability to make personalized, predictive, therapeutic clinical decisions is imminent. However, the loci discovered to date explain only a small fraction of overall inheritable risk for this disease. In many cases, the reported associations merely signal regions of the genome that are overrepresented in disease versus health but do not identify the causal variants. Well-powered cohort studies have shown that the set of markers detected thus far does not significantly improve individual risk prediction or stratification over common clinical variables, with the possible exception of younger subjects. On the other hand, risk genotypes may help target subgroups for more intensive surveillance or prevention efforts, although whether such a strategy improves patient outcomes and/or is cost-effective should be examined. Similarly, whether genetic information will help guide therapeutic decisions must be tested in adequately designed and rigorously conducted clinical trials.

[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.

A genetic diagnosis of HNF1A diabetes alters treatment and improves glycaemic control in the majority of insulin-treated patients

BACKGROUND AND AIMS

Hepatocyte nuclear factor-1 alpha (HNF1A) gene mutations are the commonest cause of monogenic diabetes, but patients are often misdiagnosed as having Type 1 diabetes and started on insulin treatment. Patients with HNF1A diabetes are particularly sensitive to the glucose-lowering effect of sulphonylureas, which are the pharmacological treatment of choice. We aimed to assess if patients do change from insulin to sulphonylurea treatment when HNF1A diabetes is confirmed and the impact of this treatment change on long-term glycaemic control.

METHODS

We investigated the clinical course of 43 patients who were insulin treated from diagnosis for a median 4 years (range 1-14) before an HNF1A gene mutation was identified.

RESULTS

Thirty-four patients (79%) stopped insulin following genetic testing and transferred to sulphonylureas. Twenty-four of them (71%) remained off insulin at a median 39 months (range 17-90) post-transfer. The 10 patients who recommenced insulin had a trend towards a longer duration of diabetes (18 vs. 7 years, P = 0.066) compared with those remaining on tablets. The median glycated haemoglobin (HbA(1c)) was good (6.9%; interquartile range 6.3-8.0%) in the patients who remained off insulin and 19/24 patients (79%) achieved HbA(1c) < 7.5% or improved their pre-genetic diagnosis HbA(1c) by > 1.0%. Transfer off insulin was not attempted in eight patients: one of these was planning pregnancy and two chose to remain on insulin.

CONCLUSION

In this observational study we found that a molecular genetic diagnosis of HNF1A diabetes does alter treatment in clinical practice, with 79% attempting transfer to sulphonylureas. Transfer to sulphonylureas was successful in the majority of patients without deterioration in glycaemic control.

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.

Ser1369Ala variant in sulfonylurea receptor gene ABCC8 is associated with antidiabetic efficacy of gliclazide in Chinese type 2 diabetic patients

OBJECTIVE

The purpose of this study was to investigate whether genetic variants could influence the antidiabetic efficacy of gliclazide in type 2 diabetic patients.

RESEARCH DESIGN AND METHODS

A total of 1,268 type 2 diabetic patients whose diabetes was diagnosed within the past 5 years and who had no recent hypoglycemic treatment were enrolled from 23 hospitals in China. All of the patients were treated with gliclazide for 8 weeks. Fasting and oral glucose tolerance test 2-h plasma glucose, fasting insulin, and A1C were measured at baseline and after 8 weeks of treatment. We used two independent cohorts to test the associations of 25 single nuclear polymorphisms in 11 candidate genes with the antidiabetic efficacy of gliclazide. A general linear regression model was used to test the association with adjustment for important covariates.

RESULTS

After 8 weeks of gliclazide therapy, mean fasting plasma glucose (FPG) was reduced from 11.1 mmol/l at baseline to 7.7 mmol/l. In cohort 1, we genotyped all 25 SNPs (n = 661) and found that Ser1369Ala of the ABCC8 gene and rs5210 of the KCNJ11 gene were significantly associated with decreases in FPG (P = 0.002). We further genotyped Ser1369Ala in cohort 2 (n = 607) and confirmed the association identified in cohort 1. In the pooled analysis, compared with subjects with the Ser/Ser genotype, subjects with the Ala/Ala genotype had a 7.7% greater decrease in FPG (P < 0.001), an 11.9% greater decrease in 2-h plasma glucose (P = 0.003), and a 3.5% greater decrease in A1C (P = 0.06) after 8 weeks of treatment with gliclazide.

CONCLUSIONS

In two independent cohorts of Chinese type 2 diabetic patients, we found consistent evidence that the Ser1369Ala variant in the ABCC8 gene can influence the antidiabetic efficacy of gliclazide.

Monogenic diabetes: implications for therapy of rare types of disease

There are two major forms of diabetes: type 1 and type 2. However, monogenic diabetes, associated with severe beta-cell dysfunction or with severe resistance to insulin action, is diagnosed with increasing frequency by genetic testing. The list of such forms of diabetes includes MODY, mitochondrial diabetes, permanent neonatal diabetes (PNDM) and transient neonatal diabetes, familial lipodystrophies and some others. These rare forms constitute probably at least a few per cent of all diabetes cases seen in diabetic clinics. The identification of the molecular background of specific forms of diabetes gives new insight into the underlying aetiology. This knowledge helps to optimize treatment in specific clinical situations. The proper differential diagnosis also helps to predict the progress of diabetes in affected individuals and defines the prognosis in the family. For example, in patients with MODY2 because of glucokinase mutations who have very mild diabetes characterized by modest fasting, hyperglycaemia diet is frequently sufficient. Some other forms of monogenic diabetes associated with impaired function of the beta-cell, such as MODY3 and PNDM linked to mutations in Kir6.2 and SUR1 genes, can be successfully managed by sulphonylurea agents. Although the examples of pharmacogenetics seem to be less spectacular in rare syndromes of insulin resistance, those patients can also benefit from genetic testing. In this paper, the aetiology of some monogenic diabetes forms is reviewed together with the clinical aspects of management of the affected individuals.

A case of new mutation in maturity-onset diabetes of the young type 3 (MODY 3) responsive to a low dose of sulphonylurea

We describe a girl aged 10.5 years with hyperglycemia, whose mother and maternal father had insulin treated diabetes since adolescence. Using genetic analysis in mother and child, we identified identical new mutation of the HNF-1alpha sequence. Treatment with small doses of sulphonylurea was initiated and that therapy gave good results.

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.

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

AIMS/HYPOTHESIS

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

METHODS

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

RESULTS

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

CONCLUSIONS/INTERPRETATION

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

Pharmacogenetics of glucose-lowering drug treatment: a systematic review

Intensive blood glucose lowering can significantly reduce the risk of micro- and macrovascular complications in patients with diabetes mellitus. However, 30% of all treated patients do not achieve optimal blood glucose levels. Genetic factors may influence the response to glucose-lowering medication. A search of MEDLINE-indexed literature published between January 1966 and July 2007 revealed 37 studies reporting data on genetic polymorphisms and response to glucose-lowering drugs. Most studies involving cytochrome P450 (CYP) genes had small sample sizes (21 studies <50 subjects) and were among healthy volunteers. Multiple studies indicated that the CYP2C9 *3 allele (Ile359Leu polymorphism) was associated with decreased clearance of sulfonylurea drugs. Supporting this, one study reported an increased insulin secretion in CYP2C9*3 allele carriers when using the sulfonylurea agent glyburide. The CYP2C9*3 allele was also associated with a decreased clearance of meglitinides, whereas the CYP2C8*3 (Arg139Lys; Lys399Arg) variant increased the clearance of meglitinides. Polymorphisms in genes encoding the inwardly rectifying potassium channel Kir6.2 (KCNJ11) and the insulin receptor substrate-1 (IRS1) were reported to be associated with an increased risk of (secondary) failure to respond to sulfonylurea therapy. A significant decrease in fasting plasma glucose and hemoglobin A(1c) (HbA(1c)) in response to rosiglitazone was seen in subjects carrying the Pro12Ala polymorphism of the peroxisome proliferator-activated receptor-gamma (PPARG) gene. Conversely, carriers of this polymorphism also had a higher conversion to diabetes mellitus when treated with acarbose; this effect was also seen in adiponectin (ADIPOQ) gene polymorphism carriers. Future studies with adequate sample sizes in which several SNPs in multiple candidate genes are genotyped in patients with diabetes should provide reliable information on genetic variants and response to glucose-lowering drugs.

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

OBJECTIVE

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

DESIGN

Familial genetic analysis.

SETTING

Tertiary university medical center.

PARTICIPANTS

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

INTERVENTIONS

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

OUTCOME MEASURES

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

RESULTS

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

CONCLUSIONS

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

What will whole genome searches for susceptibility genes for common complex disease offer to clinical practice?

In the developed world the majority of disease results from common, but complex disorders such as diabetes, obesity and cancer. Genetic variation explains a large proportion of an individual's risk of developing these diseases; however, success in identifying the particular gene variants involved has been limited. Recent advances in high-throughput genotyping technology, and a better understanding of the genetic architecture of complex disease has led to the development of genome-wide association studies (GWA), which are providing novel and important insights into disease processes. The results from these studies could be of substantial clinical importance in the relatively near future. In this review, we present some recent, exciting findings from studies that have used the GWA approach, and discuss the clinical application of identifying disease susceptibility genes and variants.

Recent development in pharmacogenomics: from candidate genes to genome-wide association studies

Genetic diversity, most notably through single nucleotide polymorphisms and copy-number variation, together with specific environmental exposures, contributes to both disease susceptibility and drug response variability. It has proved difficult to isolate disease genes that confer susceptibility to complex disorders, and as a consequence, even fewer genetic variants that influence clinical drug responsiveness have been uncovered. As such, the candidate gene approach has largely failed to deliver and, although the family-based linkage approach has certain theoretical advantages in dealing with common/complex disorders, progress has been slower than was hoped. More recently, genome-wide association studies have gained increasing popularity, as they enable scientists to robustly associate specific variants with the predisposition for complex disease, such as age-related macular degeneration, Type 2 diabetes, inflammatory bowel disease, obesity, autism and leukemia. This relatively new methodology has stirred new hope for the mapping of genes that regulate drug response related to these conditions. Collectively, these studies support the notion that modern high-throughput single nucleotide polymorphism genotyping technologies, when applied to large and comprehensively phenotyped patient cohorts, will readily reveal the most clinically relevant disease-modifying and drug response genes. This review addresses both recent advances in the genotyping field and highlights from genome-wide association studies, which have conclusively uncovered variants that underlie disease susceptibility and/or variability in drug response in common disorders.

Differential diagnosis of type 1 diabetes: which genetic syndromes need to be considered?

Recently it has become apparent that not all diabetes presenting in childhood is type 1. Increasingly type 2 diabetes, secondary diabetes, maturity onset diabetes of the young, and rare syndromic forms of diabetes such as Wolfram syndrome and Alstrom syndrome have been identified in children. Although individually rare, collectively they make up about 5% of children seen in diabetes clinics. The importance of these syndromes for children lies in the recognition of treatable complications, and for their parents, the possibility of genetic counselling. The scientific importance is enormous as they are experiments of nature that reveal basic mechanisms of insulin and glucose metabolism. We are now able to offer mutation analysis to correlate the clinical pattern to the genotype, and seek novel therapeutic approaches based on the developing knowledge of gene and protein functions. This review focuses on monogenic syndromes of diabetes, particularly where significant advances have been made in our understanding recently. Neonatal diabetes is a specialist field in its own right and is not included, except to discuss Kir6.2 diabetes which may develop in infancy. This review is written for the paediatric diabetes specialist and aims to provide information on the clinical features, natural history, genetics and management of children with diabetes as part of a syndrome. Finally there is information on useful investigations to aid diagnosis.

Monogenic disorders of the pancreatic β-cell: personalizing treatment for rare forms of diabetes and hypoglycemia

Over the past 10–20 years, our understanding of the genetic etiology of monogenic disorders of the pancreatic β-cell has greatly improved. This has enabled clinicians to provide patients with more accurate information regarding prognosis and inheritance and has influenced treatment. Maturity-onset diabetes of the young and neonatal diabetes are two such examples. Patients with maturity-onset diabetes of the young due to glucokinase mutations can usually be managed by diet alone, while those affected by HNF-1α and HNF-4α mutations respond well to low doses of sulfonylureas. The identification of mutations in the ATP-dependent potassium channel genes KCNJ11 and ABCC8 as the most common cause of permanent neonatal diabetes has improved treatment regimes for affected children. In addition to enabling patients to stop insulin injections, their glycemic control has also improved. These advances show the importance of unravelling the genetics of a disease to achieve the best individualized treatment for the patients affected.

A new era in finding Type 2 diabetes genes-the unusual suspects

In 1988 the task of identifying Type 2 diabetes genes was described as a nightmare. For the next 17 years this proved to be largely correct. In the meantime the prevalence of Type 2 diabetes rose sharply due to non-genetic factors, compounding the problem of trying to find genes. Despite a huge amount of effort, progress was disappointing and only two genes, PPARG and KCNJ11, were confirmed beyond doubt as Type 2 diabetes risk factors in multiple studies. The reasons for this have been well documented and mainly consist of the use of inappropriate levels of statistical inference given the many hundreds of thousands of potential risk polymorphisms in the genome and their small effect sizes. The good news is that these problems are now surmountable and prospects for finding many more genes are bright. This year saw the identification of a third gene, TCF7L2, that has a greater impact on risk than the first two and provided important lessons for Type 2 diabetes genetic studies. The most important of these lessons was that previously unsuspected genes may be involved. In this review I discuss why this year is the start of a new era in our understanding of Type 2 diabetes genes and how this may lead to improved patient care.

Defining the genetic aetiology of monogenic diabetes can improve treatment

A molecular genetic diagnosis is now possible for > 80% of patients with monogenic diabetes. This not only provides accurate information regarding inheritance and prognosis, but can inform treatment decisions and improve clinical outcome. Mild fasting hyperglycaemia caused by heterozygous GCK mutations rarely requires pharmacological intervention, whereas patients with mutations in the genes encoding the transcription factors HNF-1alpha and HNF-4alpha respond well to low doses of sulphonylureas. The recent discovery that mutations in the KCNJ11 gene (encoding the Kir6.2 subunit of the K(ATP) channel) are the most common cause of permanent neonatal diabetes, has enabled children to stop insulin injections and achieve improved glycaemic control with high doses of sulphonylurea tablets. Molecular genetic testing is an essential prerequisite for the pharmacogenetic treatment of monogenic diabetes.

Asian MODY: are we missing an important diagnosis?

AIMS

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Monogenic diabetes in children and young adults: Challenges for researcher, clinician and patient

Monogenic diabetes results from one or more mutations in a single gene which might hence be rare but has great impact leading to diabetes at a very young age. It has resulted in great challenges for researchers elucidating the aetiology of diabetes and related features in other organ systems, for clinicians specifying a diagnosis that leads to improved genetic counselling, predicting of clinical course and changes in treatment, and for patients to altered treatment that has lead to coming off insulin and injections with no alternative (Glucokinase mutations), insulin injections being replaced by tablets (e.g. low dose in HNFalpha or high dose in potassium channel defects -Kir6.2 and SUR1) or with tablets in addition to insulin (e.g. metformin in insulin resistant syndromes). Genetic testing requires guidance to test for what gene especially given limited resources. Monogenic diabetes should be considered in any diabetic patient who has features inconsistent with their current diagnosis (unspecified neonatal diabetes, type 1 or type 2 diabetes) and clinical features of a specific subtype of monogenic diabetes (neonatal diabetes, familial diabetes, mild hyperglycaemia, syndromes). Guidance is given by clinical and physiological features in patient and family and the likelihood of the proposed mutation altering clinical care. In this article, I aimed to provide insight in the genes and mutations involved in insulin synthesis, secretion, and resistance, and to provide guidance for genetic testing by showing the clinical and physiological features and tests for each specified diagnosis as well as the opportunities for treatment.

Type 2 diabetes in children and adolescents--the next epidemic?

OBJECTIVE

To provide an overview of the incidence of type 2 diabetes in children and adolescents and provide direction for clinicians who care for children and adolescents.

RESEARCH DESIGN AND METHOD

The data presented in this review were obtained from published literature and abstracts presented at scientific meetings. Clinical trials and review articles were identified using the search terms 'metabolic syndrome', 'type 2 diabetes mellitus', 'children', and 'adolescents' in a MEDLINE search from 1995-2005. Additionally, the bibliographies of the identified articles were reviewed.

RESULTS

Type 2 diabetes is rising rapidly in children and adolescents worldwide. Changing a child's living environment to include physical activity, and a well balanced, low fat, high fiber diet, are important for the maintenance of a desirable body weight and improving insulin sensitivity. Maintaining euglycemia with metformin, sulfonylureas, thiazolinediones, and insulin is recommended. Effective treatment of co-morbid problems such as hypertension and dyslipidemia can decrease the risk of cardiovascular complications.

CONCLUSIONS

The prevalence of type 2 diabetes in children will continue to rise until effective measures are taken to prevent obesity in this age group. Ensuring that children have a well-balanced low fat, high fiber, diet, combined with physical activity, will promote weight loss or maintenance, improve insulin sensitivity, and decrease the risk of diabetes and cardiovascular disease. Pharmacologic therapy is recommended for children who are unable to achieve satisfactory glycemic control through physical activity and diet.

Improved prandial glucose control with lower risk of hypoglycemia with nateglinide than with glibenclamide in patients with maturity-onset diabetes of the young type 3

OBJECTIVE

To study the effect of the short-acting insulin secretagogue nateglinide in patients with maturity-onset diabetes of the young type 3 (MODY3), which is characterized by a defective insulin response to glucose and hypersensitivity to sulfonylureas.

RESEARCH DESIGN AND METHODS

We compared the acute effect of nateglinide, glibenclamide, and placebo on prandial plasma glucose and serum insulin, C-peptide, and glucagon excursions in 15 patients with MODY3. After an overnight fast, they received on three randomized occasions placebo, 1.25 mg glibenclamide, or 30 mg nateglinide before a standard 450-kcal test meal and light bicycle exercise for 30 min starting 140 min after the ingestion of the first test drug.

RESULTS

Insulin peaked earlier after nateglinide than after glibenclamide or placebo (median [interquartile range] time 70 [50] vs. 110 [20] vs. 110 [30] min, P = 0.0002 and P = 0.0025, respectively). Consequently, compared with glibenclamide and placebo, the peak plasma glucose (P = 0.031 and P < 0.0001) and incremental glucose areas under curve during the first 140 min of the test (P = 0.041 and P < 0.0001) remained lower after nateglinide. The improved prandial glucose control with nateglinide was achieved with a lower peak insulin concentration than after glibenclamide (47.0 [26.0] vs. 80.4 [71.7] mU/l; P = 0.023). Exercise did not induce hypoglycemia after nateglinide or placebo, but after glibenclamide six patients experienced symptomatic hypoglycemia and three had to interrupt the test.

CONCLUSIONS

A low dose of nateglinide prevents the acute postprandial rise in glucose more efficiently than glibenclamide and with less stimulation of peak insulin concentrations and less hypoglycemic symptoms.

Monogenic and other unusual causes of diabetes mellitus

This article covers some unusual or rare causes of diabetes mellitus chosen not necessarily on the basis of frequency or rarity, but rather on the basis of how well the disease and its implications in diabetes management is understood. A specific diagnosis is of help in these rare syndromes but not absolutely necessary for optimal management. The basic principles of diabetes management are well-defined, regardless of etiology. What is important is to understand the relative contribution of insulin resistance versus insulin deficiency, regardless of etiology, as the most important guide to management.

Genetic basis of type 2 diabetes mellitus: implications for therapy

Type 2 diabetes mellitus represents a multifactorial, heterogeneous group of disorders, which result from defects in insulin secretion, insulin action, or both. The prevalence of type 2 diabetes has increased dramatically worldwide over the past several decades, a trend that has been heavily influenced by the relatively recent changes in diet and physical activity levels. There is also strong evidence supporting a genetic component to type 2 diabetes susceptibility and several genes underlying monogenic forms of diabetes have already been identified. However, common type 2 diabetes is likely to result from the contribution of many genes interacting with different environmental factors to produce wide variation in the clinical course of the disease. Not surprisingly, the etiologic complexity underlying type 2 diabetes has made identification of the contributing genes difficult. Current therapies in the management of type 2 diabetes include lifestyle intervention through diet modification and exercise, and oral or injected hypoglycemic agents; however, not all individuals with type 2 diabetes respond in the same way to these treatments. Because of variability in the clinical course of the disease and in the responsiveness to pharmacologic therapies, identification and characterization of the genetic variants underlying type 2 diabetes susceptibility will be important in the development of individualized treatment. Findings from linkage analyses, candidate gene studies, and animal models will be valuable in the identification of novel pathways involved in the regulation of glucose homeostasis, and will augment our understanding of the gene-gene and gene-environment interactions, which impact on type 2 diabetes etiology and pathogenesis. In addition, identification of genetic variants that determine differences in antidiabetic drug responsiveness will be useful in assessing a first-line pharmacologic therapy for diabetic patients.

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

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

Genes and Type 2 Diabetes Mellitus

Type 2 diabetes (T2DM) comprises a group of entities with different genetic causes. In most patients, T2DM results from alterations of various genes, each having a partial and additive effect. The inheritance pattern is thus complex, and environmental factors play an important role in favoring or delaying the expression of the disease. The identification of susceptibility genes and genetic variants requires different methodological approaches. Here we address some of the most important strategies and findings on the genomic basis of T2DM, as well as evidence of genetic heterogeneity among populations. The identification of the underlying genetic causes of T2DM and other related traits such as obesity and hypertension will lead to the development of new therapeutic targets likely to impact the way we treat these diseases. Survival and quality of life for T2DM patients is expected to eventually increase, significantly lessening the socioeconomic burden of the disease.

Molecular genetics and phenotypic characteristics of MODY caused by hepatocyte nuclear factor 4alpha mutations in a large European collection

AIMS/HYPOTHESIS

Heterozygous mutations in the gene of the transcription factor hepatocyte nuclear factor 4alpha (HNF-4alpha) are considered a rare cause of MODY with only 14 mutations reported to date. The description of the phenotype is limited to single families. We investigated the genetics and phenotype of HNF-4alpha mutations in a large European Caucasian collection.

METHODS

HNF-4alpha was sequenced in 48 MODY probands, selected for a phenotype of HNF-1alpha MODY but negative for HNF-1alpha mutations. Clinical characteristics and biochemistry were compared between 54 HNF-4alpha mutation carriers and 32 familial controls from ten newly detected or previously described families.

RESULTS

Mutations in HNF-4alpha were found in 14/48 (29%) probands negative for HNF-1alpha mutations. The mutations found included seven novel mutations: S34X, D206Y, E276D, L332P, I314F, L332insCTG and IVS5nt+1G>A. I314F is the first reported de novo HNF-4alpha mutation. The average age of diagnosis was 22.9 years with frequent clinical evidence of sensitivity to sulphonylureas. Beta cell function, but not insulin sensitivity, was reduced in diabetic mutation carriers compared to control subjects (homeostasis model assessment of beta cell function 29% p<0.001 vs controls). HNF-4alpha mutations were associated with lower apolipoprotein A2 (p=0.001), A1 (p=0.04) and total HDL-cholesterol (p=0.02) than in control subjects. However, in contrast to some previous reports, levels of triglycerides and apolipoprotein C3 were normal.

CONCLUSIONS/INTERPRETATION

HNF-4alpha mutations are common when no HNF-1alpha mutation is found in strictly defined MODY families. The HNF-4alpha clinical phenotype and beta cell dysfunction are similar to HNF-1alpha MODY and are associated with reduced apolipoprotein A2 levels. We suggest that sequencing of HNF-4alpha should be performed in patients with clinical characteristics of HNF-1alpha MODY in whom mutations in HNF-1alpha are not found.

Preserved insulin response to tolbutamide in hepatocyte nuclear factor-1alpha mutation carriers

AIMS

Diabetic subjects with mutations in the gene encoding hepatocyte nuclear factor (HNF)-1alpha (MODY3) are prone to develop hypoglycaemia at low doses of glibenclamide, interpreted as sulphonylurea hypersensitivity. The present study was undertaken to compare the plasma insulin responses to glucose and tolbutamide in HNF-1alpha mutation carriers with those of healthy control subjects.

METHODS

Seven mutation carriers; three normoglycaemic, two with impaired glucose tolerance, and two with newly detected diabetes, underwent an oral glucose tolerance test and a tolbutamide-modified intravenous glucose tolerance test with measurements of plasma insulin. Twenty-two healthy subjects served as controls.

RESULTS

The plasma insulin response to intravenous glucose was reduced in the HNF-1alpha mutation carriers compared to the control subjects, with an area under the curve (median (interquartile range)) of 812 min pmol/l (421, 1647) and 1933 min pmol/l (1521, 2908), respectively (P = 0.03). In striking contrast, the plasma insulin response to tolbutamide was preserved, with an area under the curve of 2109 min pmol/l (1126, 3172) and 2250 min pmol/l (1614, 3276) in the mutation carriers and control subjects, respectively.

CONCLUSIONS

HNF-1alpha mutation carriers are characterized by preserved tolbutamide-induced insulin secretion. Compared to healthy subjects, our MODY3 individuals did not show any increased serum insulin response to tolbutamide, suggesting that HNF-1alpha mutation carriers are not characterized by sulphonylurea hypersensitivity.

Diagnosis and Management of Maturity-Onset Diabetes of the Young

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