Familial hyperinsulinism caused by an activating glucokinase mutation

Neurological aspects of hyperinsulinism-hyperammonaemia syndrome

Hyperinsulinism-hyperammonaemia syndrome (HHS) is a rare cause of congenital hyperinsulinism, due to missense mutations in the GLUD1 gene, resulting in glutamate dehydrogenase (GDH) overactivity. The aim of this study was to document the spectrum of neurological disturbances associated with HHS and to identify possible phenotype-genotype correlations. We retrospectively analyzed the neurological outcomes of 22 consecutive patients (12 males, 10 females) aged from 18 months to 40 years and diagnosed with HHS. We analyzed demographic and clinical features and neuroradiological, biochemical, and genetic findings. Fourteen patients had childhood-onset epilepsy. Learning disability was found in 17 patients. Two patients had pyramidal involvement and one had generalized dystonia. Seizures were observed in 11 of 19 patients with documented GLUD1 mutations, and nine of these 11 patients had a mutation in the guanosine triphosphate (GTP) binding site. Our data demonstrate that neurological disorders in HHS are more frequent than previously thought and might suggest that mutations in the GTP binding site of GDH could be associated with more frequent epilepsy.

Why expression of some genes is disallowed in beta-cells

A differentiated beta-cell results not only from cell-specific gene expression, but also from cell-selective repression of certain housekeeping genes. Indeed, to prevent insulin toxicity, beta-cells should handle insulin stores carefully, preventing exocytosis under conditions when circulating insulin is unwanted. Some ubiquitously expressed proteins would significantly jeopardize this safeguard, when allowed to function in beta-cells. This is illustrated by two studied examples. First, low-K(m) hexokinases are disallowed as their high affinity for glucose would, when expressed, significantly lower the threshold for glucose-induced beta-cell function and cause hypoglycaemia, as happens in patients with beta-cell tumours. Thus the beta-cell phenotype means not only expression of glucokinase but also absence of low-K(m) hexokinases. Secondly, the absence of MCTs (monocarboxylic acid transporters) in beta-cells explains the pyruvate paradox (pyruvate being an excellent substrate for mitochondrial ATP production, yet not stimulating insulin release when added to beta-cells). The relevance of this disallowance is underlined in patients with exercise-induced inappropriate insulin release: these have gain-of-function MCT1 promoter mutations and loss of the pyruvate paradox. By genome-wide ex vivo mRNA expression studies using mouse islets and an extensive panel of other tissues, we have started to identify in a systematic manner other specifically disallowed genes. For each of those, the future challenge is to explore the physiological/pathological relevance and study conditions under which the phenotypically disallowed state in the beta-cell is breached.

Common missense variant in the glucokinase regulatory protein gene is associated with increased plasma triglyceride and C-reactive protein but lower fasting glucose concentrations

OBJECTIVE

Using the genome-wide association approach, we recently identified the glucokinase regulatory protein gene (GCKR, rs780094) region as a novel quantitative trait locus for plasma triglyceride concentration in Europeans. Here, we sought to study the association of GCKR variants with metabolic phenotypes, including measures of glucose homeostasis, to evaluate the GCKR locus in samples of non-European ancestry and to fine- map across the associated genomic interval.

RESEARCH DESIGN AND METHODS

We performed association studies in 12 independent cohorts comprising >45,000 individuals representing several ancestral groups (whites from Northern and Southern Europe, whites from the U.S., African Americans from the U.S., Hispanics of Caribbean origin, and Chinese, Malays, and Asian Indians from Singapore). We conducted genetic fine-mapping across the approximately 417-kb region of linkage disequilibrium spanning GCKR and 16 other genes on chromosome 2p23 by imputing untyped HapMap single nucleotide polymorphisms (SNPs) and genotyping 104 SNPs across the associated genomic interval.

RESULTS

We provide comprehensive evidence that GCKR rs780094 is associated with opposite effects on fasting plasma triglyceride (P(meta) = 3 x 10(-56)) and glucose (P(meta) = 1 x 10(-13)) concentrations. In addition, we confirmed recent reports that the same SNP is associated with C-reactive protein (CRP) level (P = 5 x 10(-5)). Both fine-mapping approaches revealed a common missense GCKR variant (rs1260326, Pro446Leu, 34% frequency, r(2) = 0.93 with rs780094) as the strongest association signal in the region.

CONCLUSIONS

These findings point to a molecular mechanism in humans by which higher triglycerides and CRP can be coupled with lower plasma glucose concentrations and position GCKR in central pathways regulating both hepatic triglyceride and glucose metabolism.

Diagnostic screening of MODY2/GCK mutations in the Norwegian MODY Registry

BACKGROUND

Maturity-onset diabetes of the young, type 2 (MODY2) is caused by mutations in the glucokinase gene (GCK). The aim of our study was to determine the prevalence of GCK mutations in the Norwegian MODY Registry and to delineate the clinical phenotype of identified GCK mutation carriers.

METHODS

We screened 122 probands referred to the MODY Registry for mutations in GCK and studied extended families with MODY2.

RESULTS

We found 2 novel (S76Y and N231S) and 13 previously reported (V62A, G72R, L146R, R191W, A208T, M210K, Y215X, M235T, R275C, E339G, R377C, S453L, and IVS5+1G>C) GCK mutations in 23 probands and in their 33 family members. The prevalence of MODY2 was 12% in the Norwegian MODY Registry. The subjects with GCK mutations had features of mild diabetes. Yet, 15 of 56 MODY2 subjects were treated with oral drugs or insulin. Three subjects had retinopathy and one had macrovascular disease. Also, a limited number of cases had elevated fasting serum triglyceride values. Moreover, two GCK mutation carriers were diagnosed with type 1 diabetes.

CONCLUSIONS

According to our diagnostic screening of GCK in the MODY Registry, MODY2 is less prevalent than MODY3 in Norway but is likely to be underreported. Recognizing MODY2 in diabetic patients is important in order to prevent overtreatment. Finally, our study demonstrates the co-occurrence of MODY2 in families with type 1 or type 2 diabetes.

Dominant versus recessive: molecular mechanisms in metabolic disease

Inborn errors of metabolism used to be regarded as simple monogenic traits, but a closer look at how different alleles of a gene determine different phenotypes shows that the molecular mechanisms in the individual case are often complicated. Most metabolic disorders represent a spectrum of phenotypes from normal via attenuated to severe (and sometimes prenatally fatal), and disease manifestation is often influenced by other specific genetic or exogenous factors. The terms 'dominant' or 'recessive' relate to the functional consequences of differing alleles in the (compound) heterozygous individual; the terms are irrelevant for homozygous individuals and inappropriate for X-linked disorders. Mutations affecting the same amino acid residue may be associated with different inheritance patterns. True dominant inheritance in metabolism is rare; it may be found e.g. in tightly regulated biosynthetic pathways or when minor changes in metabolite concentrations have a functional effect. Some disorders such as erythropoietic protoporphyria show pseudodominant inheritance due to prevalent loss-of-function polymorphisms in the general population and are better acknowledged as recessive traits. The term 'variable expressivity' is not helpful with regard to autosomal recessive disorders when variable phenotypes are explained by different mutations in the respective gene. Clonal unmasking of a heterozygous mutation through somatic loss of the second allele, the main pathomechanism in inherited tumour predisposition syndromes, is rare in metabolic disorders, but focal congenital hyperinsulinism is a notable exception. Somatic mosaicism for an OTC gene mutation is given as an example of an apparently heterozygous mutation pattern in a boy with an X-linked disease.

[Hyperinsulinemic hypoglycemia in adults. Case reports and a short review]

Persistent hyperinsulinemic hypoglycemia (nesidioblastosis) not caused by an insulinoma is rare in adults. Morphologically no insulin secreting tumor is present. Keystones of diagnosis are not only low glucose levels but to maintain normoglycemia by use of intravenous glucose and the presence of high insulin and C-peptide levels. Noninvasive and invasive diagnostic techniques are required to rule out a hormone secreting tumor. Both conservative and/or surgical therapy are suggested to prevent damaging effects of repeated hypoglycemia.

CASE REPORT

Two patients with frequent and serious episodes of hypoglycemia are reported. In the 34-year-old female symptoms appeared with sweating, dizziness, trembling, nervousness and serious neuroglycopenic signs. In the 22-year-old male the main complaint was tympany, a rare and unusual sign of hypoglycemia, and intense feeling of esurience. The 24-hour fasting test was positive in both cases, i.e. it had to be stopped because of symptomatic hypoglycemia. No insulinoma could be localized, despite extensive search, therefore in both cases the diagnosis of adult-onset nesidioblastosis was set up, despite lack of histological confirmation. Diazoxide therapy resulted in symptom-free life for both patients.

CONCLUSION

Several diagnostic methods and treatment options are suggested for the rare disease nesidioblastosis to balance defective insulin secretion. However, once the decision is made in favour of surgical therapy, there is a thin line between successful treatment, persistence of the disease, and pancreatic insufficiency. Therefore it is worth considering to try conservative therapy especially when surgery is of high risk. Our cases suggest that diazoxide therapy is an effective and safe alternative in the treatment of adult-onset nesidioblastosis.

Comprehensive in silico mutagenesis highlights functionally important residues in proteins

MOTIVATION

Mutating residues into alanine (alanine scanning) is one of the fastest experimental means of probing hypotheses about protein function. Alanine scans can reveal functional hot spots, i.e. residues that alter function upon mutation. In vitro mutagenesis is cumbersome and costly: probing all residues in a protein is typically as impossible as substituting by all non-native amino acids. In contrast, such exhaustive mutagenesis is feasible in silico.

RESULTS

Previously, we developed SNAP to predict functional changes due to non-synonymous single nucleotide polymorphisms. Here, we applied SNAP to all experimental mutations in the ASEdb database of alanine scans; we identi.ed 70% of the hot spots (>or=1 kCal/mol change in binding energy); more severe changes were predicted more accurately. Encouraged, we carried out a complete all-against-all in silico mutagenesis for human glucokinase. Many of the residues predicted as functionally important have indeed been con.rmed in the literature, others await experimental veri.cation, and our method is ready to aid in the design of in vitro mutagenesis.

AVAILABILITY

ASEdb and glucokinase scores are available at http://www.rostlab.org/services/SNAP. For submissions of large/whole proteins for processing please contact the author.

Activating glucokinase (GCK) mutations as a cause of medically responsive congenital hyperinsulinism: prevalence in children and characterisation of a novel GCK mutation

OBJECTIVE

Activating glucokinase (GCK) mutations are a rarely reported cause of congenital hyperinsulinism (CHI), but the prevalence of GCK mutations is not known.

METHODS

From a pooled cohort of 201 non-syndromic children with CHI from three European referral centres (Denmark, n=141; Norway, n=26; UK, n=34), 108 children had no K(ATP)-channel (ABCC8/KCNJ11) gene abnormalities and were screened for GCK mutations. Novel GCK mutations were kinetically characterised.

RESULTS

In five patients, four heterozygous GCK mutations (S64Y, T65I, W99R and A456V) were identified, out of which S64Y was novel. Two of the mutations arose de novo, three were dominantly inherited. All the five patients were medically responsive. In the combined Danish and Norwegian cohort, the prevalence of GCK-CHI was estimated to be 1.2% (2/167, 95% confidence interval (CI) 0-2.8%) of all the CHI patients. In the three centre combined cohort of 72 medically responsive children without K(ATP)-channel mutations, the prevalence estimate was 6.9% (5/72, 95% CI 1.1-12.8%). All activating GCK mutations mapped to the allosteric activator site. The novel S64Y mutation resulted in an increased affinity for the substrate glucose (S(0.5) 1.49+/-0.08 and 7.39+/-0.05 mmol/l in mutant and wild-type proteins respectively), extrapolating to a relative activity index of approximately 22 compared with the wild type.

CONCLUSION

In the largest study performed to date on GCK in children with CHI, GCK mutations were found only in medically responsive children who were negative for ABCC8 and KCNJ11 mutations. The estimated prevalence (approximately 7%) suggests that screening for activating GCK mutations is warranted in those patients.

Glucokinase (GCK) and other susceptibility genes for β-cell dysfunction: the candidate approach

There are well-documented examples in the literature of where determining the genetic aetiology of a disorder has provided insights into important regulatory pathways and protein interactions, and, more recently, has led to improved treatment options for patients. The studies of monogenic forms of β-cell dysfunction are no exception. Naturally occurring mutations in the gene for the β-cell enzyme glucokinase (GCK) result in both hyper- and hypo-glycaemia. Over 200 mutations have been described, and careful study of the mutational mechanisms for a number of these has provided important insights into glucokinase regulation. Increased understanding of post-translational regulatory mechanisms holds the promise of novel pharmacotherapeutic options for the treatment of T2DM (Type 2 diabetes mellitus). It is well established that common genetic variation in genes involved in monogenic forms of β-cell dysfunction contributes to susceptibility to T2DM. Recent genome-wide scans for association have identified a number of novel T2DM susceptibility genes which probably influence β-cell mass and/or function. Their identification allows the investigation of the role of rare mutations in monogenic β-cell dysfunction. Current results indicate the importance of these genes in pancreatic development and suggest that mutations which result in a severe functional defect could be lethal.

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.

Non-insulinoma persistent hyperinsulinaemic hypoglycaemia caused by an activating glucokinase mutation: hypoglycaemia unawareness and attacks

OBJECTIVE

Adult-onset non-insulinoma persistent hyperinsulinaemic hypoglycaemia (NI-PHH) and the variant NI-pancreatogenous hypoglycaemia syndrome (NIPHS) are genetically unexplained diseases, without reports of hypoglycaemia unawareness or familial inheritance.

DESIGN AND PATIENTS

In a prospective 8-year follow-up, a boy (i) with NI-PHH since age 14 years, his mother (ii), the mother's brother (iii) and his daughter (iv) were studied.

RESULTS

Patient (i) was characterized by especially postprandial hypoglycaemia down to 1.6 mmol/l and pronounced variability in diazoxide need with obesity; (ii) had asymptomatic blood glucose down to 2.9 mmol/l, but a severe hypoglycaemic postprandial attack after a slimming diet; (iii) had moderate hypoglycaemic symptoms since childhood and need of frequent eating; and (iv) was asymptomatic until a hypoglycaemic accident in the age of 24. After a slimming diet, symptomatic fasting, but especially postprandial hypoglycaemia occurred (blood glucose 1.9 mmol/l after 19 h fasting; 1.6 mmol/l 3.5 h after OGTT). By CT-scan/endoscopic ultrasound in three of the individuals, insulinoma could not be detected. In all four individuals, an activating glucokinase (GCK) mutation A456V was found. No mutations were found in the ABCC8 or KCNJ11 genes. The patients responded to treatment with diazoxide or octreotide long acting release.

CONCLUSION

This is the first report to highlight a genetic cause to adult-onset NI-PHH/NIPHS. The activating GCK mutation was dominantly inherited, but only after year-long follow-up and investigations, other family members were diagnosed symptomatic. Hypoglycaemia unawareness seems to be a prominent feature, but hypoglycaemic attacks occur after slimming, especially postprandially. PHH-GCK was medical responsive.

Too much of a good thing: why it is bad to stimulate the beta cell to secrete insulin

In many countries, first- or second-line pharmacological treatment of patients with type 2 diabetes consists of sulfonylureas (such as glibenclamide [known as glyburide in the USA and Canada]), which stimulate the beta cell to secrete insulin. However, emerging evidence suggests that forcing the beta cell to secrete insulin at a time when it is struggling to cope with the demands of obesity and insulin resistance may accelerate its demise. Studies on families with persistent hyperinsulinaemic hypoglycaemia of infancy (PHHI), the primary defect of which is hypersecretion of insulin, have shown that overt diabetes can develop later in life despite normal insulin sensitivity. In addition, in vitro experiments have suggested that reducing insulin secretion from islets isolated from patients with diabetes can restore insulin pulsatility and improve function. This article will explore the hypothesis that forcing the beta cell to hypersecrete insulin may be counterproductive and lead to dysfunction and death via mechanisms that may involve the endoplasmic reticulum and oxidative stress. We suggest that, in diabetes, therapeutic approaches should be targeted towards relieving the demand on the beta cell to secrete insulin.

What's new in metabolic and genetic hypoglycaemias: diagnosis and management

Hypoglycaemia in children can be a life-threatening situation that needs to be assessed rigorously in order to treat efficiently and avoid relapse that can be responsible for cerebral damage. The diagnosis of impairment in glucose homeostasis requires the knowledge of the mechanisms regulating blood glucose concentration. The clinical history and presentation, when available, especially the timing of hypoglycaemia with respect to the last meal and some simple clinical and biological tests may allow diagnosing the vast majority of patients presenting with hypoglycaemia. Recently, new metabolic and endocrinologic genetic causes of hypoglycaemia have been identified that may give new insight to the complex mechanisms of glucose regulation and thus contribute to the discovery of new genes regulating glucose homeostasis. New diagnostic tests such as the 18-fluoro-Dopa PET-scan have also been recently developed.

Glucokinase activators in diabetes management

Type 2 diabetes is a chronic metabolic disease that adversely affects both the quality and longevity of life. The disease is characterised by elevated blood glucose (hyperglycaemia) that is associated with microvascular complications and increased macrovascular risk. Existing oral agents, either alone or in combination, do not exhibit adequate or sustained glucose lowering efficacy in Type 2 diabetics. Consequently, there is an unmet medical need for improved antidiabetic agents which are both more effective at lowering glucose and which display sustained efficacy over a number of years. Such agents would allow present glycaemic treatment targets to be achieved with greater success. Glucokinase activators (GKAs) represent a novel class of glucose-lowering agents. Preclinical data supports the notion that these agents act to lower blood glucose through effects in both the liver and pancreas. It is predicted that this dual compartment mechanism of action of GKAs will translate to robust glucose lowering in diabetic patients. The potential benefits and risks associated with the pharmacological activation of glucokinase are evaluated. The status of GKAs in preclinical and clinical development is assessed are the future prospects of these agents.

Hyperinsulinism in Infancy and Childhood: When an Insulin Level Is Not Always Enough

Background: Hypoglycemia in infants and children can lead to seizures, developmental delay, and permanent brain damage. Hyperinsulinism (HI) is the most common cause of both transient and permanent disorders of hypoglycemia. HI is characterized by dysregulated insulin secretion, which results in persistent mild to severe hypoglycemia. The various forms of HI represent a group of clinically, genetically, and morphologically heterogeneous disorders.

Content: Congenital hyperinsulinism is associated with mutations of SUR-1 and Kir6.2, glucokinase, glutamate dehydrogenase, short-chain 3-hydroxyacyl-CoA dehydrogenase, and ectopic expression on β-cell plasma membrane of SLC16A1. Hyperinsulinism can be associated with perinatal stress such as birth asphyxia, maternal toxemia, prematurity, or intrauterine growth retardation, resulting in prolonged neonatal hypoglycemia. Mimickers of hyperinsulinism include neonatal panhypopituitarism, drug-induced hypoglycemia, insulinoma, antiinsulin and insulin-receptor stimulating antibodies, Beckwith-Wiedemann Syndrome, and congenital disorders of glycosylation. Laboratory testing for hyperinsulinism may include quantification of blood glucose, plasma insulin, plasma β-hydroxybutyrate, plasma fatty acids, plasma ammonia, plasma acylcarnitine profile, and urine organic acids. Genetic testing is available through commercial laboratories for genes known to be associated with hyperinsulinism. Acute insulin response (AIR) tests are useful in phenotypic characterization. Imaging and histologic tools are also available for diagnosing and classifying hyperinsulinism. The goal of treatment in infants with hyperinsulinism is to prevent brain damage from hypoglycemia by maintaining plasma glucose levels above 700 mg/L (70 mg/dL) through pharmacologic or surgical therapy.

Summary: The management of hyperinsulinism requires a multidisciplinary approach that includes pediatric endocrinologists, radiologists, surgeons, and pathologists who are trained in diagnosing, identifying, and treating hyperinsulinism.

Heterogeneity in disease severity in a family with a novel G68V GCK activating mutation causing persistent hyperinsulinaemic hypoglycaemia of infancy

BACKGROUND/AIM

Glucokinase (GCK)-activating mutations cause persistent hyperinsulinaemic hypoglycaemia of infancy (PHHI). GCK-PHHI patients have regulated insulin secretion and can usually be treated with diazoxide. The six reported cases suggest that the severity of the mutation predicts the clinical phenotype. The aim of this study was to relate genotype to phenotype [clinical phenotype, glucose-stimulated insulin release (GSIR) and GCK functional analysis] in a large pedigree with eight affected individuals.

METHODS

The genes encoding B-cell GCK and the K(ATP) channel subunits (ABCC8 and KCNJ11) were sequenced to identify mutations for functional analysis. Genetic variants influencing B-cell function were genotyped in affected individuals. Islet secretory capacity was determined by oral glucose tolerance test

RESULTS

A novel GCK mutation (G68V) co-segregating with hypoglycaemia was identified in eight family members. Kinetic analysis revealed that G68V-GCK activity is ~16 times more than wild-type-GCK with an increased affinity for glucose [concentration at half maximal activation (S(0.5)) 1.94 +/- 0.16 vs. 7.43 +/- 0.12, mutant vs. wild type, mean +/- sem]. Mathematical modelling predicted a threshold for GSIR of 1.9 mmol/l in the mutant. Oral glucose tolerance tests showed regulated insulin secretion. The severity of hypoglycaemia and related symptoms in affected subjects were heterogeneous. Clinical presentations were asymptomatic (n = 1), extreme hunger (n = 3), seizures (n = 2) and loss of consciousness (n = 2); 7/8 were managed with diet but the proband was treated with diazoxide and octreotide. Phenotypic modification by a second mutation in the K(ATP) channel genes (ABCC8, KCNJ11) or by common genetic variants in KCNJ11, GCK and TCF7L2 was excluded.

CONCLUSION

The novel activating GCK mutation G68V is associated with variable phenotypic severity, supporting modification of GSIR by genetic and/or environmental factors.

Increased nicotinamide nucleotide transhydrogenase levels predispose to insulin hypersecretion in a mouse strain susceptible to diabetes

AIMS/HYPOTHESIS

Insulin hypersecretion may be an independent predictor of progression to type 2 diabetes. Identifying genes affecting insulin hypersecretion are important in understanding disease progression. We have previously shown that diabetes-susceptible DBA/2 mice congenitally display high insulin secretion. We studied this model to map and identify the gene(s) responsible for this trait.

METHODS

Intravenous glucose tolerance tests followed by a genome-wide scan were performed on 171 (C57BL/6 x DBA/2) x C57BL/6 backcross mice.

RESULTS

A quantitative trait locus, designated hyperinsulin production-1 (Hip1), was mapped with a logarithm of odds score of 7.7 to a region on chromosome 13. Production of congenic mice confirmed that Hip1 influenced the insulin hypersecretion trait. By studying appropriate recombinant inbred mouse strains, the Hip1 locus was further localised to a 2 Mb interval, which contained only nine genes. Expression analysis showed that the only gene differentially expressed in islets isolated from the parental strains was Nnt, which encodes the mitochondrial proton pump, nicotinamide nucleotide transhydrogenase (NNT). We also found in five mouse strains a positive correlation (r2 = 0.90, p < 0.01) between NNT activity and first-phase insulin secretion, emphasising the importance of this enzyme in beta cell function. Furthermore, of these five strains, only those with high NNT activity are known to exhibit severe diabetes after becoming obese.

CONCLUSIONS/INTERPRETATION

Insulin hypersecretion is associated with increased Nnt expression. We suggest that NNT must play an important role in beta cell function and that its effect on the high insulin secretory capacity of the DBA/2 mouse may predispose beta cells of these mice to failure.

beta-cell hyperexcitability: from hyperinsulinism to diabetes

Nutrient oxidation in beta cells generates a rise in [ATP]:[ADP] ratio. This reduces K(ATP) channel activity, leading to depolarization, activation of voltage-dependent Ca(2+) channels, Ca(2+) entry and insulin secretion. Consistent with this paradigm, loss-of-function mutations in the genes (KCNJ11 and ABCC8) that encode the two subunits (Kir6.2 and SUR1, respectively) of the ATP-sensitive K(+) (K(ATP)) channel underlie hyperinsulinism in humans, a genetic disorder characterized by dysregulated insulin secretion. In mice with genetic suppression of K(ATP) channel subunit expression, partial loss of K(ATP) channel conductance also causes hypersecretion, but unexpectedly, complete loss results in an undersecreting, mildly glucose-intolerant phenotype. When challenged by a high-fat diet, normal mice and mice with reduced K(ATP) channel density respond with hypersecretion, but mice with more significant or complete loss of K(ATP) channels cross over, or progress further, to an undersecreting, diabetic phenotype. It is our contention that in mice, and perhaps in humans, there is an inverse U-shaped response to hyperexcitabilty, leading first to hypersecretion but with further exacerbation to undersecretion and diabetes. The causes of the overcompensation and diabetic susceptibility are poorly understood but may have broader implications for the progression of hyperinsulinism and type 2 diabetes in humans.

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.

Pancreatic glucokinase is activated by insulin-like growth factor-I

Glucokinase (GK) plays a key role in the regulation of glucose use and glucose-stimulated insulin secretion in pancreatic islet cells. Gene targeting of the IGF-I receptor down-regulated pancreatic islet GK activity. That finding prompted us to examine the potential mechanism that may control GK gene activity using an islet cell line, INS-1, known to express IGF-I receptor. Exposure of these cells to IGF-I induced GK protein expression and activity of the enzyme in a dose-dependent manner. In addition, IGF-I induced activity of a reporter construct containing the GK promoter in parallel with the effect on endogenous GK mRNA levels. The stimulatory effect of IGF-I on GK promoter activity was abrogated by wortmannin and LY294002, specific inhibitors of phosphatidylinositol 3-kinase. Exposure of cells to IGF-I elicited a rapid phosphorylation of Akt and FoxO1, a known target of Akt signaling. Constitutively active Akt stimulates the activity of the GK promoter, and a dominant-negative mutant of Akt or mutagenesis of a FoxO1 response element in the GK promoter abolished the ability of IGF-I to stimulate the promoter activity. Furthermore, cell knockdown of FoxO1 with small interfering RNA disrupted the effect of IGF-I on GK expression. These results demonstrate that the phosphatidylinositol 3-kinase/Akt/FoxO1 pathway contributes to the regulation of GK gene expression in response to IGF-I stimulation.

Glucose-dependent modulation of insulin secretion and intracellular calcium ions by GKA50, a glucokinase activator

Because glucokinase is a metabolic sensor involved in the regulated release of insulin, we have investigated the acute actions of novel glucokinase activator compound 50 (GKA50) on islet function. Insulin secretion was determined by enzyme-linked immunosorbent assay, and microfluorimetry with fura-2 was used to examine intracellular Ca(2+) homeostasis ([Ca(2+)](i)) in isolated mouse, rat, and human islets of Langerhans and in the MIN6 insulin-secreting mouse cell line. In rodent islets and MIN6 cells, 1 micromol/l GKA50 was found to stimulate insulin secretion and raise [Ca(2+)](i) in the presence of glucose (2-10 mmol/l). Similar effects on insulin release were also seen in isolated human islets. GKA50 (1 micromol/l) caused a leftward shift in the glucose-concentration response profiles, and the half-maximal effective concentration (EC(50)) values for glucose were shifted by 3 mmol/l in rat islets and approximately 10 mmol/l in MIN6 cells. There was no significant effect of GKA50 on the maximal rates of glucose-stimulated insulin secretion. In the absence of glucose, GKA50 failed to elevate [Ca(2+)](i) (1 micromol/l GKA50) or to stimulate insulin release (30 nmol/l-10 micromol/l GKA50). At 5 mmol/l glucose, the EC(50) for GKA50 in MIN6 cells was approximately 0.3 micromol/l. Inhibition of glucokinase with mannoheptulose or 5-thioglucose selectively inhibited the action of GKA50 on insulin release but not the effects of tolbutamide. Similarly, 3-methoxyglucose prevented GKA50-induced rises in [Ca(2+)](i) but not the actions of tolbutamide. Finally, the ATP-sensitive K(+) channel agonist diazoxide (200 micromol/l) inhibited GKA50-induced insulin release and its elevation of [Ca(2+)](i.) We show that GKA50 is a glucose-like activator of beta-cell metabolism in rodent and human islets and a Ca(2+)-dependent modulator of insulin secretion.

Glucokinase Thermolability and Hepatic Regulatory Protein Binding Are Essential Factors for Predicting the Blood Glucose Phenotype of Missense Mutations

To better understand how glucokinase (GK) missense mutations associated with human glycemic diseases perturb glucose homeostasis, we generated and characterized mice with either an activating (A456V) or inactivating (K414E) mutation in the gk gene. Animals with these mutations exhibited alterations in their blood glucose concentration that were inversely related to the relative activity index of GK. Moreover, the threshold for glucose-stimulated insulin secretion from islets with either the activating or inactivating mutation were left- or right-shifted, respectively. However, we were surprised to find that mice with the activating mutation had markedly reduced amounts of hepatic GK activity. Further studies of bacterially expressed mutant enzymes revealed that GK(A456V) is as stable as the wild type enzyme, whereas GK(K414E) is thermolabile. However, the ability of GK regulatory protein to inhibit GK(A456V) was found to be less than that of the wild type enzyme, a finding consistent with impaired hepatic nuclear localization. Taken together, this study indicates that it is necessary to have knowledge of both thermolability and the interactions of mutant GK enzymes with GK regulatory protein when attempting to predict in vivo glycemic phenotypes based on the measurement of enzyme kinetics.

Diabetes and hypoglycaemia in young children and mutations in the Kir6.2 subunit of the potassium channel: therapeutic consequences

ATP-sensitive potassium channels (K(ATP)) couple cell metabolism to electrical activity by regulating potassium movement across the membrane. These channels are octameric complex with two kind of subunits: four regulatory sulfonylurea receptor (SUR) embracing four poreforming inwardly rectifying potassium channel (Kir). Several isoforms exist for each type of subunits: SUR1 is found in the pancreatic beta-cell and neurons, whereas SUR2A is in heart cells and SUR2B in smooth muscle; Kir6.2 is in the majority of tissues as pancreatic beta-cells, brain, heart and skeletal muscle, and Kir6.1 can be found in smooth vascular muscle and astrocytes. The K(ATP) channels play multiple physiological roles in the glucose metabolism regulation, especially in beta-cells where it regulates insulin secretion, in response to an increase in ATP concentration. They also seem to be critical metabolic sensors in protection against metabolic stress as hypo or hyperglycemia, hypoxia, ischemia. Persistent hyperinsulinemic hypoglycaemia (HI) of infancy is a heterogeneous disorder which may be divided into two histopathological forms (diffuse and focal lesions). Different inactivating mutations have been implicated in both forms: the permanent inactivation of the K(ATP) channels provokes inappropriate insulin secretion, despite low ATP. Diazoxide, used efficiently in certain cases of HI, opens the K(ATP) channels and therefore overpass the mutation effect on the insulin secretion. Conversely, several studies reported sequencing of KCNJ11, coding for Kir6.2, in patients with permanent neonatal diabetes mellitus and found different mutations in 30 to 50% of the cases. More than 28 heterozygous activating mutations have now been identified, the most frequent mutation being in the aminoacid R201. These mutations result in reduced ATP-sensitivity of the K(ATP) channels compared with the wild-types and the level of channel block is responsible for different clinical features: the "mild" form confers isolated permanent neonatal diabetes whereas the severe form combines diabetes and neurological symptoms such as epilepsy, deve-lopmental delay, muscle weakness and mild dimorphic features. Sulfonylureas close K(ATP) channels by binding with high affinity to SUR suggesting they could replace insulin in these patients. Subsequently, more than 50 patients have been reported as successfully and safely switched from subcutaneous insulin injections to oral sulfonylurea therapy, with an improvement in their glycated hemoglobin. We therefore designed a protocol to transfer and evaluate children who have insulin treated neonatal diabetes due to KCNJ11 mutation, from insulin to sulfonylurea. The transfer from insulin injections to oral glibenclamide therapy seems highly effective for most patients and safe. This shows how the molecular understan-ding of some monogenic form of diabetes may lead to an unexpected change of the treatment in children. This is a spectacular example by which a pharmacogenomic approach improves the quality of life of our young diabetic patients in a tremendous way.

Macrosomia and hyperinsulinaemic hypoglycaemia in patients with heterozygous mutations in the HNF4A gene

BACKGROUND

Macrosomia is associated with considerable neonatal and maternal morbidity. Factors that predict macrosomia are poorly understood. The increased rate of macrosomia in the offspring of pregnant women with diabetes and in congenital hyperinsulinaemia is mediated by increased foetal insulin secretion. We assessed the in utero and neonatal role of two key regulators of pancreatic insulin secretion by studying birthweight and the incidence of neonatal hypoglycaemia in patients with heterozygous mutations in the maturity-onset diabetes of the young (MODY) genes HNF4A (encoding HNF-4alpha) and HNF1A/TCF1 (encoding HNF-1alpha), and the effect of pancreatic deletion of Hnf4a on foetal and neonatal insulin secretion in mice.

METHODS AND FINDINGS

We examined birthweight and hypoglycaemia in 108 patients from families with diabetes due to HNF4A mutations, and 134 patients from families with HNF1A mutations. Birthweight was increased by a median of 790 g in HNF4A-mutation carriers compared to non-mutation family members (p < 0.001); 56% (30/54) of HNF4A-mutation carriers were macrosomic compared with 13% (7/54) of non-mutation family members (p < 0.001). Transient hypoglycaemia was reported in 8/54 infants with heterozygous HNF4A mutations, but was reported in none of 54 non-mutation carriers (p = 0.003). There was documented hyperinsulinaemia in three cases. Birthweight and prevalence of neonatal hypoglycaemia were not increased in HNF1A-mutation carriers. Mice with pancreatic beta-cell deletion of Hnf4a had hyperinsulinaemia in utero and hyperinsulinaemic hypoglycaemia at birth.

CONCLUSIONS

HNF4A mutations are associated with a considerable increase in birthweight and macrosomia, and are a novel cause of neonatal hypoglycaemia. This study establishes a key role for HNF4A in determining foetal birthweight, and uncovers an unanticipated feature of the natural history of HNF4A-deficient diabetes, with hyperinsulinaemia at birth evolving to decreased insulin secretion and diabetes later in life.

Neonatal hyperinsulinism: clinicopathologic correlation

Neonatal hyperinsulinism is a life-threatening disease that, when treated by total pancreatectomy, leads to diabetes and pancreatic insufficiency. A more conservative approach is now possible since the separation of the disease into a nonrecurring focal form, which is cured by partial surgery, and a diffuse form, which necessitates total pancreas removal only in cases of medical treatment failure. The pathogenesis of the disease is now divided into K-channel disease (hyperinsulinemic hypoglycemia, familial [HHF] 1 and 2), which can mandate surgery, and other metabolic causes, HHF 3 to 6, which are treated medically in most patients. The diffuse form is inherited as a recessive gene on chromosome 11, whereas most cases of the focal form are caused by a sulfonylurea receptor 1 defect inherited from the father, which is associated with a loss of heterozygosity on the corresponding part of the mother's chromosome 11. The rare bifocal forms result from a maternal loss of heterozygosity specific to each focus. Paternal disomy of chromosome 11 is a rare cause of a condition similar to Beckwith-Wiedemann syndrome. A preoperative PET scan with fluorodihydroxyphenylalanine and perioperative frozen-section confirmation are the types of studies done before surgery when needed. Adult variants of the disease are less well defined at the present time.

Mechanisms of Disease: advances in diagnosis and treatment of hyperinsulinism in neonates

Hyperinsulinism is the single most common mechanism of hypoglycemia in neonates. Dysregulated insulin secretion is responsible for the transient and prolonged forms of neonatal hypoglycemia, and congenital genetic disorders of insulin regulation represent the most common of the permanent disorders of hypoglycemia. Mutations in at least five genes have been associated with congenital hyperinsulinism: they encode glucokinase, glutamate dehydrogenase, the mitochondrial enzyme short-chain 3-hydroxyacyl-CoA dehydrogenase, and the two components (sulfonylurea receptor 1 and potassium inward rectifying channel, subfamily J, member 11) of the ATP-sensitive potassium channels (K(ATP) channels). K(ATP) hyperinsulinism is the most common and severe form of congenital hyperinsulinism. Infants suffering from K(ATP) hyperinsulinism present shortly after birth with severe and persistent hypoglycemia, and the majority are unresponsive to medical therapy, thus requiring pancreatectomy. In up to 40-60% of the children with K(ATP) hyperinsulinism, the defect is limited to a focal lesion in the pancreas. In these children, local resection results in cure with avoidance of the complications inherent to a near-total pancreatectomy. Hyperinsulinism can also be part of other disorders such as Beckwith-Wiedemann syndrome and congenital disorders of glycosylation. The diagnosis and management of children with congenital hyperinsulinism requires a multidisciplinary approach to achieve the goal of therapy: prevention of permanent brain damage due to recurrent hypoglycemia.

Hypoglycemia

Under physiologic conditions, glucose plays a critical role in providing energy to the central nervous system. A precipitous drop in the availability of this substrate results in dramatic symptoms that signal a medical emergency and warrant immediate therapy aimed at restoring plasma glucose to normal levels. A systemic approach to the differential diagnosis is useful in identifying the cause of hypoglycemia. Once established, a specific and/or definitive intervention that addresses that underlying problem can be implemented. In most cases, this systemic approach to diagnosis and therapy is rewarded with a good outcome for the patient.

Biochemical Basis of Glucokinase Activation and the Regulation by Glucokinase Regulatory Protein in Naturally Occurring Mutations

Glucokinase (GK) has several known polymorphic activating mutations that increase the enzyme activity by enhancing glucose binding affinity and/or by alleviating the inhibition of glucokinase regulatory protein (GKRP), a key regulator of GK activity in the liver. Kinetic studies were undertaken to better understand the effect of these mutations on the enzyme mechanism of GK activation and GKRP regulation and to relate the enzyme properties to the associated clinical phenotype of hypoglycemia. Similar to wild type GK, the transient kinetics of glucose binding for activating mutations follows a general two-step mechanism, the formation of an enzyme-glucose complex followed by an enzyme conformational change. However, the kinetics for each step differed from wild type GK and could be grouped into specific types of kinetic changes. Mutations T65I, Y214C, and A456V accelerate glucose binding to the apoenzyme form, whereas W99R, Y214C, and V455M facilitate enzyme isomerization to the active form. Mutations that significantly enhance the glucose binding to the apoenzyme also disrupt the protein-protein interaction with GKRP to a large extent, suggesting these mutations may adopt a more compact conformation in the apoenzyme favorable for glucose binding. Y214C is the most active mutation (11-fold increase in k(cat)/K(0.5)(h)) and exhibits the most severe clinical effects of hypoglycemia. In contrast, moderate activating mutation A456V nearly abolishes the GKRP inhibition (76-fold increase in K(i)) but causes only mild hypoglycemia. This suggests that the alteration in GK enzyme activity may have a more profound biological impact than the alleviation of GKRP inhibition.

Hyperinsulinemic hypoglycemia due to adult nesidioblastosis in insulin-dependent diabetes

In neonates, persistent hyperinsulinemic hypoglycemia (PHH) is associated with nesidioblastosis. In adults, PHH is usually caused by solitary benign insulinomas. We report on an adult patient who suffered from insulin-dependent diabetes mellitus, and subsequently developed PHH caused by diffuse nesidioblastosis. Mutations of the MEN1 and Mody 2/3 genes were ruled out. Preoperative diagnostic procedures, the histopathological criteria and the surgical treatment options of adult nesidioblastosis are discussed. So far only one similar case of adult nesidioblastosis subsequent to diabetes mellitus II has been reported in the literature. In case of conversion of diabetes into hyperinsulinemic hypoglycemia syndrome, nesidioblastosis in addition to insulinoma should be considered.

Recent advances in hyperinsulinemic hypoglycemia of infancy

Hyperinsulinemia-induced hypoglycemia is the most common cause of persistent hypoglycemia in adults, children, and infants. Our understanding of the disorders responsible for this type of hypoglycemia has been increasing due to the recent discoveries in the molecular and biochemical regulation of insulin secretion. In this article, we review the current knowledge of the pathophysiology, clinical presentation, and diagnosis of disorders that cause hyperinsulinemic hypoglycemia of infancy. We highlight the distinction between the diffuse and focal forms of the disease, especially the promising results with (18)F-L-dopa positive emission tomography (PET) scanning for preoperative localization and distinction to guide the extent of surgical removal of pancreatic tissue that may result in cure rather than persistence of disturbed carbohydrate metabolism.

CONCLUSION

Despite all these discoveries, much remains to be learned, as currently about one third of infants with hyperinsulinemic hypoglycemia have no identifiable cause.

Molecular mechanisms of neonatal hyperinsulinism

Congenital hyperinsulinism (CHI), characterized by profound hypoglycaemia related to inappropriate insulin secretion, may be associated histologically with either diffuse insulin hypersecretion or focal adenomatous hyperplasia, which share a similar clinical presentation, but result from different molecular mechanisms. Whereas diffuse CHI is of autosomal recessive, or less frequently of autosomal dominant, inheritance, focal CHI is sporadic. The most common mechanism underlying CHI is dysfunction of the pancreatic ATP-sensitive potassium channel (K(+)(ATP)). The two subunits of the K(+)(ATP) channel are encoded by the sulfonylurea receptor gene (SUR1 or ABCC8) and the inward-rectifying potassium channel gene (KIR6.2 or KCNJ11), both located in the 11p15.1 region. Germ-line, paternally inherited, mutations of the SUR1 or KIR6.2 genes, together with somatic maternal haplo-insufficiency for 11p15.5, were shown to result in focal CHI. Diffuse CHI results from germ-line mutations in the SUR1 or KIR6.2 genes, but also from mutations in several other genes, namely glutamate dehydrogenase (with associated hyperammonaemia), glucokinase, short-chain L-3-hydroxyacyl-CoA dehydrogenase, and insulin receptor gene. Hyperinsulinaemic hypoglycaemia may be observed in several overlapping syndromes, such as Beckwith-Wiedemann syndrome (BWS), Perlman syndrome, and, more rarely, Sotos syndrome. Mosaic genome-wide paternal isodisomy has recently been reported in patients with clinical signs of BWS and CHI. The primary causes of CHI are genetically heterogeneous and have not yet been completely unveiled. However, secondary causes of hyperinsulinism have to be considered such as fatty acid oxidation deficiency, congenital disorders of glycosylation and factitious hypoglycaemia secondary to Munchausen by proxy syndrome.

Conformational transition pathway in the allosteric process of human glucokinase

Glucokinase (GK) is an important enzyme for regulating blood glucose levels and a potentially attractive target for diabetes of the young type 2 and persistent hyperinsulinemic hypoglycemia of infancy. To characterize the conformational transition of GK from the closed state to the superopen state, a series of conventional molecular dynamics (MD) and target MD (TMD) simulations were performed on both the wild-type enzyme and its mutants. Two 10-ns conventional MD simulations showed that, although the allosteric site of GK is approximately 20 A away from the active site, the activator is able to enhance the activity of the enzyme through conformational restriction. Fourteen TMD simulations on GK and five of its mutants revealed a reliably conformational transition pathway. The overall conformational transition includes three stages, and three likely stable intermediate states were identified by free energy scanning for the snapshots throughout the pathway. The conformational transition feature revealed by our TMD simulations rationalized several important mutagenesis and kinetic data. Remarkably, the TMD simulations predicted that Y61S, I159A, A201R, V203E, and V452S mutations, which have not been investigated so far, may facilitate the opening process of GK. These predictions also have been verified by mutagenesis and kinetic analyses in this study. These observations are beneficial to understanding the mechanism of GK regulation and designing the compounds for treating metabolic diseases.

Persistent Hyperinsulinaemic Hypoglycaemia of Infancy in 43 Children: Long-term Clinical and Surgical Follow-up

OBJECTIVE

To describe the clinical, surgical, biochemical, radiological and electrophysiological features of 43 Saudi children with persistent hyperinsulinaemic hypoglycaemia of infancy (PHHI) who have been followed since 1983.

METHODS

Data from 43 patients were retrospectively analysed. PHHI was diagnosed on the basis of high intravenous glucose requirement, high insulin to glucose ratio, negative urinary ketones and normal tandem mass spectrometry. The patients were assessed radiologically by brain magnetic resonance imaging and/or computed tomography and electrophysiologically by brain stem auditory evoked potential, visual evoked response and electroencephalogram. Patients who failed medical therapy received near total pancreatectomy.

RESULTS

The patients were severely hypoglycaemic and intolerant to fast. Hypoglycaemic convulsion was the most commonly presenting complaint. Eighteen patients were developmentally delayed and 14 of them had brain atrophy. All patients, except nine, did not respond to medical treatment and underwent surgery. Four pancreatectomized patients developed diabetes and two had malabsorption. One baby had 180 cm resection of gangrenous bowel most likely secondary to octreotide. No common bile duct injury was encountered. One patient was treated medically during childhood and developed diabetes and gained weight during adolescence.

CONCLUSION

PHHI is a relatively common and serious disease among Saudi children. Early intervention is necessary to avoid neurological damage in patients who are severely hypoglycaemic and unresponsive to medical therapy. Surgically and probably medically treated patients are at a high risk of developing diabetes, which could be the natural outcome of this disease. Care and spending time during surgery to visualize the common bile duct help in avoiding its injury.

From clinicogenetic studies of maturity-onset diabetes of the young to unraveling complex mechanisms of glucokinase regulation

Glucokinase functions as a glucose sensor in pancreatic beta-cells and regulates hepatic glucose metabolism. A total of 83 probands were referred for a diagnostic screening of mutations in the glucokinase (GCK) gene. We found 11 different mutations (V62A, G72R, L146R, A208T, M210K, Y215X, S263P, E339G, R377C, S453L, and IVS5 + 1G>C) in 14 probands. Functional characterization of recombinant glutathionyl S-transferase-G72R glucokinase showed slightly increased activity, whereas S263P and G264S had near-normal activity. The other point mutations were inactivating. S263P showed marked thermal instability, whereas the stability of G72R and G264S differed only slightly from that of wild type. G72R and M210K did not respond to an allosteric glucokinase activator (GKA) or the hepatic glucokinase regulatory protein (GKRP). Mutation analysis of the role of glycine at position 72 by substituting E, F, K, M, S, or Q showed that G is unique since all these mutants had very low or no activity and were refractory to GKRP and GKA. Structural analysis provided plausible explanations for the drug resistance of G72R and M210K. Our study provides further evidence that protein instability in combination with loss of control by a putative endogenous activator and GKRP could be involved in the development of hyperglycemia in maturity-onset diabetes of the young, type 2. Furthermore, based on data obtained on G264S, we propose that other and still unknown mechanisms participate in the regulation of glucokinase.

Islet Hyperplasia in Adults: Challenge to Preoperatively Diagnose Non-Insulinoma Pancreatogenic Hypoglycemia Syndrome

BACKGROUND

Pancreatic hyperfunctional islet hyperplasia in adults has been more and more frequently described in the literature. Postprandial neuroglycopenia, a negative normal fasting test, negative pancreatic imaging results, and positive intra-arterial calcium stimulation of serum insulin are characteristic. In affected patients the term non-insulinoma pancreatogenic hypoglycemia syndrome (NIPHS) was proposed. MATERIALS AND METHODS/PATIENTS: We also encountered fasting hypoglycemia in such patients and therefore evaluated clinical and biochemical data in patients with NIPHS (n = 11), patients with insulinoma (n = 70), and patients in whom hypoglycemia was ruled out (n = 70).

RESULTS

Patients with NIPHS were younger (median age: 41 years; range: 18-66) and mostly non-obese (median body mass index/BMI: 22.2 kg/m2; range: 19-39) compared with patients with an insulinoma (median age: 50 years; median: BMI 26.1 kg/m2). During an oral glucose tolerance test (OGTT) followed by a standard fasting test, neuroglycopenia was observed postprandially with a mean minimal blood glucose level of 36 +/- 9 mg/dl in 7 out of 11 patients. Spontaneous hypoglycemia during the fast was 38 +/- 5 mg/dl in 8 out of 11 patients. The corresponding insulin levels were 9.2 +/- 9.8 mU/l (OGTT) and 6.8 +/- 5.4 mU/l (fasting), significantly lower than in patients with insulinoma (P < 0.001), but not different from patients without hypoglycemia (P = 0.05). After pancreatic resection 8 patients (73%) were cured with enduring euglycemia. Pathohistological islet abnormalities with hyperplasia, hypertrophy, and microadenomatosis were confirmed in all patients.

CONCLUSION

In patients with postprandial and/or fasting neuroglycopenia NIPHS may be suspected when insulin levels are low but inadequately suppressed and localization studies failed to show a distinct pancreatic tumor.

Effects of novel maturity-onset diabetes of the young (MODY)-associated mutations on glucokinase activity and protein stability

Glucokinase acts as the pancreatic glucose sensor and plays a critical role in the regulation of insulin secretion by the beta-cell. Heterozygous mutations in the glucokinase-encoding GCK gene, which result in a reduction of the enzymatic activity, cause the monogenic form of diabetes, MODY2 (maturity-onset diabetes of the young 2). We have identified and functionally characterized missense mutations in the GCK gene in diabetic families that result in protein mutations Leu165-->Phe, Glu265-->Lys and Thr206-->Met. The first two are novel GCK mutations that co-segregate with the diabetes phenotype in their respective families and are not found in more than 50 healthy control individuals. In order to measure the biochemical effects of these missense mutations on glucokinase activity, we bacterially expressed and affinity-purified islet human glucokinase proteins carrying the respective mutations and fused to GST (glutathione S-transferase). Enzymatic assays on the recombinant proteins revealed that mutations Thr206-->Met and Leu165-->Phe strongly affect the kinetic parameters of glucokinase, in agreement with the localization of both residues close to the active site of the enzyme. In contrast, mutation Glu265-->Lys, which has a weaker effect on the kinetics of glucokinase, strongly affects the protein stability, suggesting a possible structural defect of this mutant protein. Finally, none of the mutations tested appears to affect the interaction of gluco-kinase with the glucokinase regulatory protein in the yeast two-hybrid system.

Intragenic suppression of Gal3C interaction with Gal80 in the Saccharomyces cerevisiae GAL gene switch

Gal4-mediated activation of GAL gene transcription in Saccharomyces cerevisiae requires the interaction of Gal3 with Gal80, the Gal4 inhibitor protein. While it is known that galactose and ATP activates Gal3 interaction with Gal80, neither the mechanism of activation nor the surface that binds to Gal80 is known. We addressed this through intragenic suppression of GAL3C alleles that cause galactose-independent Gal3-Gal80 interaction. We created a new allele, GAL3SOC, and showed that it suppressed a new GAL3C allele. We tested the effect of GAL3SOC on several newly isolated and existing GAL3C alleles that map throughout the gene. All except one GAL3C allele, D368V, were suppressible by GAL3SOC. GAL3SOC and all GAL3C alleles were localized on a Gal3 homology model that is based on the structure of the highly related Gal1 protein. These results provide evidence for allosterism in the galactose- and ATP-activation of Gal3 binding to Gal80. In addition, because D368V and residues corresponding to Gal80-nonbinder mutations colocalized to a domain that is absent in homologous proteins that do not bind to Gal80, we suggest that D368 is a part of the Gal80-binding surface.

Molecular and immunohistochemical analyses of the focal form of congenital hyperinsulinism

Congenital hyperinsulinism is a rare pancreatic endocrine cell disorder that has been categorized histologically into diffuse and focal forms. In focal hyperinsulinism, the pancreas contains a focus of endocrine cell adenomatous hyperplasia, and the patients have been reported to possess paternally inherited mutations of the ABCC8 and KCNJ11 genes, which encode subunits of an ATP-sensitive potassium channel (K(ATP)). In addition, the hyperplastic endocrine cells show loss of maternal 11p15, where imprinted genes such as p57(kip2) reside. In order to evaluate whether all cases of focal hyperinsulinism are caused by this mechanism, 56 pancreatectomy specimens with focal hyperinsulinism were tested for the loss of maternal allele by two methods: immunohistochemistry for p57(kip2) (n=56) and microsatellite marker analysis (n=27). Additionally, 49 patients were analyzed for K(ATP) mutations. Out of 56 focal lesions, 48 demonstrated clear loss of p57(kip2) expression by immunohistochemistry. The other eight lesions similarly showed no nuclear labeling, but the available tissue was not ideal for definitive interpretation. Five of these eight patients had paternal K(ATP) mutations, of which four demonstrated loss of maternal 11p15 within the lesion by microsatellite marker analysis. All of the other three without a paternal K(ATP) mutation showed loss of maternal 11p15. K(ATP) mutation analysis identified 32/49 cases with paternal mutations. There were seven patients with nonmaternal mutations whose paternal DNA material was not available, and one patient with a mutation that was not present in either parent's DNA. These eight patients showed either loss of p57(kip2) expression or loss of maternal 11p15 region by microsatellite marker analysis, as did the remaining nine patients with no identifiable K(ATP) coding region mutations. The combined results from the immunohistochemical and molecular methods indicate that maternal 11p15 loss together with paternal K(ATP) mutation is the predominant causative mechanism of focal hyperinsulinism.

Individual mice can be distinguished by the period of their islet calcium oscillations: is there an intrinsic islet period that is imprinted in vivo?

Pulsatile insulin secretion in vivo is believed to be derived, in part, from the intrinsic glucose-dependent intracellular calcium concentration ([Ca2+]i) pulsatility of individual islets. In isolation, islets display fast, slow, or mixtures of fast and slow [Ca2+]i oscillations. We show that the period of islet [Ca2+]i oscillations is unique to each mouse, with the islets from an individual mouse demonstrating similar rhythms to one another. Based on their rhythmic period, mice were broadly classified as being either fast (0.65 +/- 0.1 min; n = 6 mice) or slow (4.7 +/- 0.2 min; n = 15 mice). To ensure this phenomenon was not an artifact of islet-to-islet communication, we confirmed that islets cultured in isolation (period: 2.9 +/- 0.1 min) were not statistically different from islets cultured together from the same mouse (3.1 +/- 0.1 min, P > 0.52, n = 5 mice). We also compared pulsatile insulin patterns measured in vivo with islet [Ca2+]i patterns measured in vitro from six mice. Mice with faster insulin pulse periods corresponded to faster islet [Ca2+]i patterns, whereas slower insulin patterns corresponded to slower [Ca2+]i patterns, suggesting that the insulin rhythm of each mouse is preserved to some degree by its islets in vitro. We propose that individual mice have characteristic oscillatory [Ca2+]i patterns, which are imprinted in vivo through an unknown mechanism.

Pancreatic regeneration after near-total pancreatectomy in children with nesidioblastosis

BACKGROUND

Nesidioblastosis is often resistant to medical therapy and requires near-total pancreatectomy. There is little information on the postoperative imaging findings of these patients.

OBJECTIVE

To demonstrate by US the late imaging findings in these patients.

MATERIALS AND METHODS

Children diagnosed with nesidioblastosis and who had undergone 90-95% pancreatectomy received preoperative, immediate-postoperative (within 10 days of surgery) and long-term annual US examinations. In the preoperative study, three anterior-posterior (AP) measurements were obtained of the head, body and tail of the pancreas. In the postoperative and long-term follow-up US, AP and transverse measurements of the pancreatic remnant were obtained. Pancreatic echogenicity was also assessed. The results were compared with normal pancreatic dimensions as a function of age. Glucose metabolism and pancreatic enzymes were also analysed.

RESULTS

The study group comprised 22 patients (aged 9 days to 2 years). The pancreas was normal in all preoperative US examinations. The first postoperative examination showed, in all patients, a remnant of the pancreatic head measuring 8-13 mm. The last follow-up US was similar to the first postoperative study in 6 patients, and 12 showed complete pancreatic regeneration (normal size, echogenicity and function), and 4 had incomplete regeneration with head and body normal in size, but lack of a pancreatic tail. All patients were asymptomatic and showed normal laboratory tests.

CONCLUSIONS

US measurements indicated normal age-dependent growth after near-total resection in 54% of patients. The function and echogenicity of the regenerated pancreas indicate that the increase in organ size was due to normal pancreatic tissue.

ATP-sensitive potassium channelopathies: focus on insulin secretion

ATP-sensitive potassium (K(ATP)) channels, so named because they are inhibited by intracellular (ATP), play key physiological roles in many tissues. In pancreatic beta cells, these channels regulate glucose-dependent insulin secretion and serve as the target for sulfonylurea drugs used to treat type 2 diabetes. This review focuses on insulin secretory disorders, such as congenital hyperinsulinemia and neonatal diabetes, that result from mutations in K(ATP) channel genes. It also considers the extent to which defective regulation of K(ATP) channel activity contributes to the etiology of type 2 diabetes.

[Congenital hyperinsulinism in newborn and infant]

Congenital hyperinsulinism (HI) is the most important cause of hypoglycaemia in early infancy. The inappropriate oversecretion of insulin is responsible for profound hypoglycaemias requiring aggressive treatment to prevent severe and irreversible brain damage. Several classifications of HI can be attempted, based on: 1) the onset of hypoglycemia in the neonatal period or later in infancy; 2) the histological lesion: focal or diffuse; 3) the genetic transmission: sporadic, recessive, or less frequently dominant. The most common underlying mechanism of HI is dysfunction of the pancreatic ATP-sensitive potassium channel (K(+)(ATP)). The 2 subunits of the K(+)(ATP) channel are encoded by either the sulfonylurea receptor gene (SUR1 or ABCC8) or the inward-rectifying potassium channel gene (KIR6.2. or KCNJ11), both located in the 11p15.1 region. Focal CHI has been shown to result from a paternally inherited mutation on the SUR1 or KIR6.2 gene and loss of the maternal 11p15 allele restricted to the pancreatic lesion. Diffuse HI, frequently due to mutations of the SUR1 or KIR6.2 genes of autosomal recessive inheritance is genetically heterogeneous. The distinction between the focal and the diffuse HI is very important, because the treatments are different. To distinguish between focal and diffuse HI, transhepatic catheterisation with pancreatic venous sampling was the reference technique, but will likely be replaced by [(18)F] Fluoro-L-Dopa PET scan, which is easier to perform. In absence of response to the medical treatment (diazoxide) a limited pancreatectomy permits to cure focal HI, while a diffuse HI requires a subtotal pancreatectomy with high risk of subsequent diabetes mellitus.

Serum glucagon counterregulatory hormonal response to hypoglycemia is blunted in congenital hyperinsulinism

The mechanisms involved in the release of glucagon in response to hypoglycemia are unclear. Proposed mechanisms include the activation of the autonomic nervous system via glucose-sensing neurons in the central nervous system, via the regulation of glucagon secretion by intra-islet insulin and zinc concentrations, or via direct ionic control, all mechanisms that involve high-affinity sulfonylurea receptor/inwardly rectifying potassium channel-type ATP-sensitive K(+) channels. Patients with congenital hyperinsulinism provide a unique physiological model to understand glucagon regulation. In this study, we compare serum glucagon responses to hyperinsulinemic hypoglycemia versus nonhyperinsulinemic hypoglycemia. In the patient group (n = 20), the mean serum glucagon value during hyperinsulinemic hypoglycemia was 17.6 +/- 5.7 ng/l compared with 59.4 +/- 7.8 ng/l in the control group (n = 15) with nonhyperinsulinemic hypoglycemia (P < 0.01). There was no difference between the serum glucagon responses in children with diffuse, focal, and diazoxide-responsive forms of hyperinsulinism. The mean serum epinephrine and norepinephrine concentrations in the hyperinsulinemic group were 2,779 +/- 431 pmol/l and 2.9 +/- 0.7 nmol/l and appropriately rose despite the blunted glucagon response. In conclusion, the loss of ATP-sensitive K(+) channels and or elevated intraislet insulin cannot explain the blunted glucagon release in all patients with congenital hyperinsulinism. Other possible mechanisms such as the suppressive effect of prolonged hyperinsulinemia on alpha-cell secretion should be considered.