Maciej T. Malecki

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

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

Insulin Mutation Screening in 1,044 Patients With Diabetes: Mutations in the INS Gene Are a Common Cause of Neonatal Diabetes but a Rare Cause of Diabetes Diagnosed in Childhood or Adulthood

OBJECTIVE— Insulin gene (INS) mutations have recently been described as a cause of permanent neonatal diabetes (PND). We aimed to determine the prevalence, genetics, and clinical phenotype of INS mutations in large cohorts of patients with neonatal diabetes and permanent diabetes diagnosed in infancy, childhood, or adulthood. RESEARCH DESIGN AND METHODS— The INS gene was sequenced in 285 patients with diabetes diagnosed before 2 years of age, 296 probands with maturity-onset diabetes of the young (MODY), and 463 patients with young-onset type 2 diabetes (nonobese, diagnosed <45 years). None had a molecular genetic diagnosis of monogenic diabetes. RESULTS— We identified heterozygous INS mutations in 33 of 141 probands diagnosed at <6 months, 2 of 86 between 6 and 12 months, and none of 58 between 12 and 24 months of age. Three known mutations (A24D, F48C, and R89C) account for 46% of cases. There were six novel mutations: H29D, L35P, G84R, C96S, S101C, and Y103C. INS mutation carriers were all insulin treated from diagnosis and were diagnosed later than ATP-sensitive K+ channel mutation carriers (11 vs. 8 weeks, P < 0.01). In 279 patients with PND, the frequency of KCNJ11, ABCC8, and INS gene mutations was 31, 10, and 12%, respectively. A heterozygous R6C mutation cosegregated with diabetes in a MODY family and is probably pathogenic, but the L68M substitution identified in a patient with young-onset type 2 diabetes may be a rare nonfunctional variant. CONCLUSIONS— We conclude that INS mutations are the second most common cause of PND and a rare cause of MODY. Insulin gene mutation screening is recommended for all diabetic patients diagnosed before 1 year of age.

Is the ADA/EASD algorithm for the management of type 2 diabetes (January 2009) based on evidence or opinion? A critical analysis

The ADA and the EASD recently published a consensus statement for the medical management of hyperglycaemia in patients with type 2 diabetes. The authors advocate initial treatment with metformin monotherapy and lifestyle modification, followed by addition of basal insulin or a sulfonylurea if glycaemic goals are not met (tier 1 recommendations). All other glucose-lowering therapies are relegated to a secondary (tier 2) status and only recommended for selected clinical settings. In our view, this algorithm does not offer physicians and patients the appropriate selection of options to individualise and optimise care with a view to sustained control of blood glucose and reduction both of diabetes complications and cardiovascular risk. This paper critically assesses the basis of the ADA/EASD algorithm and the resulting tiers of treatment options.

The pseudokinase tribbles homolog 3 interacts with ATF4 to negatively regulate insulin exocytosis in human and mouse β cells

Insufficient insulin secretion and reduced pancreatic beta cell mass are hallmarks of type 2 diabetes (T2DM). Here, we confirm that a previously identified polymorphism (rs2295490/Q84R) in exon 2 of the pseudokinase-encoding gene tribbles 3 (TRB3) is associated with an increased risk for T2DM in 2 populations of people of mixed European descent. Carriers of the 84R allele had substantially reduced plasma levels of C-peptide, the product of proinsulin processing to insulin, suggesting a role for TRB3 in beta cell function. Overexpression of TRB3 84R in mouse beta cells, human islet cells, and the murine beta cell line MIN6 revealed reduced insulin exocytosis, associated with a marked reduction in docked insulin granules visualized by electron microscopy. Conversely, knockdown of TRB3 in MIN6 cells restored insulin secretion and expression of exocytosis genes. Further analysis in MIN6 cells demonstrated that TRB3 interacted with the transcription factor ATF4 and that this complex acted as a competitive inhibitor of cAMP response element-binding (CREB) transcription factor in the regulation of key exocytosis genes. In addition, the 84R TRB3 variant exhibited greater protein stability than wild-type TRB3 and increased binding affinity to Akt. Mice overexpressing TRB3 84R in beta cells displayed decreased beta cell mass, associated with reduced proliferation and enhanced apoptosis rates. These data link a missense polymorphism in human TRB3 to impaired insulin exocytosis and thus increased risk for T2DM.

New Polymorphism of ENPP1 (PC-1) Is Associated With Increased Risk of Type 2 Diabetes Among Obese Individuals

The K121Q polymorphism in ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1) is associated with type 2 diabetes and obesity. The possibility of other ENPP1 polymorphisms influencing these phenotypes has received little attention. Our aim was to examine the associations of tagging single nucleotide polymorphisms (SNPs) and haplotypes of the linkage disequilibrium (LD) block containing K121Q polymorphism with type 2 diabetes in a Polish population, controlling for any effect of obesity. We genotyped 426 type 2 diabetic case and 370 control subjects for seven SNPs in ENPP1. In the total group, neither type 2 diabetes nor obesity was significantly associated with any SNP. However, in obese subjects, two SNPs were significantly associated with type 2 diabetes: the Q allele of K121Q (odds ratio 1.6 [95% CI 1.003–2.6]) and T allele of rs997509 (4.7 [1.6–13.9]). In the LD block, four SNPs plus the K121Q polymorphism distinguished six haplotypes, three of which carried the Q allele. Interestingly, the T allele of rs997509 sufficed to distinguish a 121Q-carrying haplotype that was significantly more associated with type 2 diabetes than the other two (4.2 [1.3–13.5]). These other two 121Q-carrying haplotypes were not associated with type 2 diabetes. In conclusion, we found a new SNP, rs997509, in intron 1 that is strongly associated with risk of type 2 diabetes in obese individuals. The molecular mechanisms underlying this association are unknown.

Sulfonylurea improves CNS function in a case of intermediate DEND syndrome caused by a mutation in KCNJ11

Background A 12-week-old female presented with neonatal diabetes. Insulin therapy alleviated the diabetes, but the patient showed marked motor and mental developmental delay. The patient underwent genetic evaluation at the age of 6 years, prompted by reports that mutations in the KCNJ11 gene caused neonatal diabetes.Investigations Genomic sequencing of the ATP-sensitive potassium (KATP) channel gene KCNJ11 and in vitro functional analysis of the channel defect, and single-photon emission CT imaging before and after glibenclamide therapy.Diagnosis Genetic evaluation revealed a missense mutation (His46Leu) in KCNJ11, which encodes the Kir6.2 subunit of the KATP channel, conferring reduced ATP sensitivity. Functional studies demonstrated that the mutant channels were strongly inhibited by the sulfonylurea tolbutamide.Management Sulfonylurea (glibenclamide) treatment led to both improved glucose homeostasis and an increase in mental and motor function.

The identification of a R201H mutation in KCNJ11, which encodes Kir6.2, and successful transfer to sustained-release sulphonylurea therapy in a subject with neonatal diabetes: evidence for heterogeneity of beta cell function among carriers of the R201H mutation

To the Editor Diabetes caused by severe mutations in beta cell genes is usually diagnosed as neonatal diabetes [1] or MODY [2]. Activating mutations in KCJN11, the gene encoding the ATP-sensitive potassium channel subunit Kir6.2, have been described in very-early-onset diabetes ( A) was found in a single patient. This child was born at 40 weeks’ gestation and weighed 2,450 g. He was diagnosed with diabetes during the third week of life based on a plasma glucose of 35–50 mmol/l, without ketoacidosis, which was measured when he presented with pneumonia and bilateral acute otitis media. The patient was treatedwith insulin, with a dose of 0.7–1.0 U/kg used initially and subsequently decreased. At 9 years, 11 months he weighed 27.5 kg and his daily insulin requirement was 7 U (0.25 U/kg) as a single morning injection of intermediate-acting insulin. Despite little modification to his diet he rarely experienced hyperglycaemia above 11 mmol/l, and had an HbA1c level of 6.6%. These observations suggested endogenous beta cell function, which was confirmed by a fasting plasma C-peptide of 443 pmol/l (glucose 6.7 mmol/l) and an increase in plasma insulin concentration of 70 pmol/l during an IVGTT (Fig. 1). As patients with Kir6.2 diabetes may respond to sulphonylureas, we assessed whether this patient could successfully transfer to sulphonylurea tablets [3, 4]. Glipizide gastrointestinal therapeutic system (GITS), a controlledrelease sulphonylurea, was introduced [5]. A dose of 5 mg was administered for 2 days, then 10 mg; insulin was simultaneously slowly withdrawn over a period of 5 days. As the patient experienced a few mild hypoglycaemic episodes during the first 2 days after the discontinuation of insulin the glipizide GITS dose was decreased to 5 mg. While on this dose, a day profile of his capillary glucose concentrations revealed that they were between 4 and 6 mmol/l; a result confirmed by a 72-h record obtained using a continuous glucose monitoring system (Medtronic, Northridge, CA, USA). The IVGTT was repeated 3 weeks after a stable glipizide dose was achieved. At this time the patient’s fasting glucose level was 5.4mmol/l, and his C-peptide level was 347 pmol/l. T. Klupa and E. L. Edghill contributed equally to this work

Clinical Usefulness of a Bolus Calculator in Maintaining Normoglycaemia in Active Professional Patients with Type 1 Diabetes Treated with Continuous Subcutaneous Insulin Infusion

This observational study assessed metabolic control in young, active professionals with type 1 diabetes treated with continuous subcutaneous insulin infusion (CSII) with or without the use of a bolus calculator. Eighteen patients aged 19 − 51 years with diabetes duration of 6 − 22 years were included; eight patients used a bolus calculator and 10 did not. Metabolic control was assessed by glycosylated haemoglobin (HbA1c) measurements and blood glucose profiles. A continuous glucose monitoring system (CGMS) was also used by three patients from each group. Mean HbA1c and fasting blood glucose levels were not significantly different between the two groups, but mean post-prandial blood glucose was significantly lower in bolus calculator users than non-users. The CGMS showed more blood glucose levels within the target range in bolus calculator users than non-users, but statistical significance was not achieved. In conclusion, a bolus calculator may help to improve post-prandial blood glucose levels in active professional type 1 diabetes patients treated with CSII, but does not have a major impact on HbA1c levels.

Retinopathy in type 2 diabetes mellitus is associated with increased intima-media thickness and endothelial dysfunction

Background  Microangioathy and macroangiopathy in type 2 diabetes mellitus (T2DM) frequently coexist. Both types of vascular complications share traditional risk factors. It is not clear whether the presence of microangiopathy, such as diabetic retinopathy (DR), constitutes a predictor of atherosclerosis in T2DM. Here we described the search for the association between DR and intima‐media thickness (IMT) in T2DM. We also compared endothelial function in subjects with and without DR.

The Pro12Ala polymorphism of PPARγ2 gene and susceptibility to type 2 diabetes mellitus in a Polish population

INTRODUCTION It has recently been shown that polymorphisms of some genes might influence the genetic susceptibility to complex, multifactorial forms of type 2 diabetes mellitus (T2DM). One of those genes is peroxisome proliferator activated receptor gamma (PPARgamma). The PPARgamma gene product is a nuclear hormone receptor that regulates adipogenesis and is a target for thiazolidinediones, medications enhancing sensitivity to insulin. The Pro12Ala amino acid variant of the PPARgamma2 isoform is associated with T2DM in several populations. AIMS (1) To determine the allele and genotype frequency of the Pro12Ala PPARgamma2 amino acid variant in a Polish population; (2) To search for the association of the Pro12Ala polymorphism with T2DM in the examined population. METHODS We included 644 individuals in this study: 366 T2DM patients with age of diagnosis greater than 35 years and 278 non-diabetic control subjects. The fragment of the PPARgamma2 gene which contains the examined amino acid variant was amplified by polymerase chain reaction (PCR). Alleles and genotypes were determined based on electrophoresis of the DNA digestion products by the specific restriction enzyme BshI. Differences in distribution between the groups were examined by chi2 test. RESULTS The frequency of Pro/Ala alleles was similar in T2DM patients and in the control subjects (83.5%/16.5% vs. 84.5%/15.5%, respectively, P=0.607). Similarly, there was no difference between the groups when we analysed the genotype distribution. Stratification analyses based on age of diagnosis, body mass index (BMI), and family history of T2DM were performed. The Pro/Ala and Ala/Ala genotypes tended to be more frequent in T2DM cases with age of diagnosis >50 years than in controls (36.2% vs. 27.3%, P=0.046). This difference was not significant after Sheffe correction for multiple comparisons. The other stratification analyses did not show any difference between the groups. CONCLUSION The frequency of the Pro12Ala PPARgamma2 polymorphism in the Polish population studied is similar to that in other Caucasian populations. In the case-control study, we were not able to confirm earlier reports that the Pro allele conferred an increased risk for development of T2DM. Moreover, the results of the stratified analysis suggest an opposite trend in late onset T2DM.