Activating Glucokinase Mutation Research Articles

Phenotypic Characterization of Congenital Hyperinsulinism Due to Novel Activating Glucokinase Mutations.

Our evaluation of six novel and two previously published activating GCK mutations revealed that the detrimental effects of these mutations on glucose homeostasis can be attributed not only to a lowering of the glucose threshold of insulin secretion but also to a decreased counterregulatory glucagon secretory response. These studies provide insights into the pathophysiology of GCK-hyperinsulinism and the dual role of glucokinase in β-cells and α-cells to regulate glucose homeostasis.

Congenital Hyperinsulinism Due to a Novel Activating Glucokinase Mutation: A Case Report and Literature Review

Background: Congenital Hyperinsulinism (CHI) constitutes a major cause of persistent and recurrent hypoglycemia, especially in the neonatal period, showing notable phenotypical heterogeneity among affected subjects. Activating mutations of the Glucokinase gene (GCK) are responsible for mild forms of hypoglycemia, due to CHI, usually easily medically managed. Case report: We present a patient at the age of 3.5 years old investigated for persistent hypoglycemia. Laboratory evaluation showed hyperinsulinism during the hypoglycemic episode with a required glucose infusion rate greater than 8-10 mg/kg/min to maintain normoglycemia. Targeted gene panel sequencing revealed an activating missense novel mutation p.Val71Ala in exon 3 of GCK gene, dominantly inherited by his mother. In silico, analysis of this novel missense variant assessed its pathogenicity as being of uncertain significance Conclusions: GCK gene mutations result in varying phenotypic characteristics and responsiveness to diazoxide depending on the type of activating mutation.

Congenital hyperinsulinism due to a novel activating glucokinase mutation: a case report and literature review

Congenital hyperinsulinism due to a novel activating glucokinase mutation: a case report and literature review

Adult-onset hyperinsulinaemic hypoglycaemia in clinical practice: diagnosis, aetiology and management

ObjectiveIn adults with hyperinsulinaemic hypoglycaemia (HH), in particular those with insulinoma, the optimal diagnostic and management strategies remain uncertain. Here, we sought to characterise the biochemical and radiological assessment, and clinical management of adults with HH at a tertiary centre over a thirteen-year period.DesignClinical, biochemical, radiological and histological data were reviewed from all confirmed cases of adult-onset hyperinsulinaemic hypoglycaemia at our centre between 2003 and 2016. In a subset of patients with stage I insulinoma, whole-exome sequencing of tumour DNA was performed.ResultsTwenty-nine patients were identified (27 insulinoma, including 6 subjects with metastatic disease; 1 pro-insulin/GLP-1 co-secreting tumour; 1 activating glucokinase mutation). In all cases, hypoglycaemia (glucose ≤2.2 mmol/L) was achieved within 48 h of a supervised fast. At fast termination, subjects with stage IV insulinoma had significantly higher insulin, C-peptide and pro-insulin compared to those with insulinoma staged I–IIIB. Preoperative localisation of insulinoma was most successfully achieved with EUS. In two patients with inoperable, metastatic insulinoma, peptide receptor radionuclide therapy (PRRT) with 177Lu-DOTATATE rapidly restored euglycaemia and lowered fasting insulin. Finally, in a subset of stage I insulinoma, whole-exome sequencing of tumour DNA identified the pathogenic Ying Yang-1 (YY1) somatic mutation (c.C1115G/p.T372R) in one tumour, with all tumours exhibiting a low somatic mutation burden.ConclusionOur study highlights, in particular, the utility of the 48-h fast in the diagnosis of insulinoma, EUS for tumour localisation and the value of PRRT therapy in the treatment of metastatic disease.

Heterogeneity in phenotype of hyperinsulinism caused by activating glucokinase mutations: a novel mutation and its functional characterization.

Mutations in the GCK gene lead to different forms of glucokinase (GCK)-disease, activating mutations cause hyperinsulinaemic hypoglycaemia while inactivating mutations cause monogenic diabetes. Hyperinsulinism (HI) is a heterogeneous condition with a significant genetic component. The major causes are channelopathies, the other forms are rare and being caused by mutations in genes such as GCK. To describe the clinical and genetic presentation of four families with activating GCK mutations, and to explore the pathogenicity of the novel mutation identified through functional studies. Four cases of HI with mutations in GCK were identified. These include one novel mutation (p.Trp99Cys). Functional analysis of the purified mutant fusion protein glutathione-S-transferase (GST)-GCK-p.Trp99Cys demonstrated that p.Trp99Cys is an activating mutation as it induces a higher affinity for glucose and increases the relative activity index more than 11 times. Moreover, the thermal stability of the mutant protein was similar to that of its wild type. All patients were responsive to diazoxide treatment. One of the mutations arose de novo, and two were dominantly inherited, although only one of them from an HI affected parent. The age of presentation in our cases varied widely from the neonatal period to adulthood. The clinical phenotype of the GCK activating mutation carriers was heterogeneous, the severity of symptoms and age at presentation varied markedly between affected individuals, even within the same family. The novel activating GCK mutation (p.Trp99Cys) has a strong activating effect in vitro although it has been identified in one case of a milder and late-onset form of HI.

Hyperglycaemia induces metabolic dysfunction and glycogen accumulation in pancreatic β-cells.

Insulin secretion from pancreatic β-cells is impaired in all forms of diabetes. The resultant hyperglycaemia has deleterious effects on many tissues, including β-cells. Here we show that chronic hyperglycaemia impairs glucose metabolism and alters expression of metabolic genes in pancreatic islets. In a mouse model of human neonatal diabetes, hyperglycaemia results in marked glycogen accumulation, and increased apoptosis in β-cells. Sulphonylurea therapy rapidly normalizes blood glucose levels, dissipates glycogen stores, increases autophagy and restores β-cell metabolism. Insulin therapy has the same effect but with slower kinetics. Similar changes are observed in mice expressing an activating glucokinase mutation, in in vitro models of hyperglycaemia, and in islets from type-2 diabetic patients. Altered β-cell metabolism may underlie both the progressive impairment of insulin secretion and reduced β-cell mass in diabetes.

Familial adult onset hyperinsulinism due to an activating glucokinase mutation: implications for pharmacological glucokinase activation.

Glucokinase (GCK) phosphorylates and thereby "traps" glucose in cells, thus serving as a gatekeeper for cellular glucose metabolism, particularly in hepatocytes and pancreatic beta cells. In humans, activating GCK mutations cause familial hyperinsulinaemic hypoglycaemia (GCK-HH), leading to keen interest in the potential of small-molecule glucokinase activators (GKAs) as treatments for diabetes mellitus. Many such agents have been developed; however, observation of side effects including hypertriglyceridaemia and hepatic steatosis has delayed their clinical development. To describe the clinical presentation and metabolic profiles of affected family members in a kindred with familial hyperinsulinism of adult presentation due to a known activating mutation in GCK. Clinical, biochemical and metabolic assessment, and GCK sequencing in affected family members. In the 60-year-old female proband, hyperinsulinaemic hypoglycaemia (blood glucose 2·1mmol/mol, insulin 18pm) was confirmed following 34h of fasting; however, abdominal computed tomography (CT), pancreatic MRI, endoscopic ultrasound, octreotide scintigraphy and selective arterial calcium stimulation failed to localize an insulinoma. A prolonged OGTT revealed fasting hypoglycaemia that was exacerbated after glucose challenge, consistent with dysregulated glucose-stimulated insulin release. A heterozygous activating mutation, p.Val389Leu, in the glucokinase gene (GCK) was found in the proband and four other family members. Of these, two had been investigated elsewhere for recurrent hypoglycaemia in adulthood, while the other two adult relatives were asymptomatic despite profound hypoglycaemia. All three of the available family members with the p.Val389Leu mutation had normal serum lipid profiles, normal rates of fasting hepatic de novo lipogenesis and had hepatic triglyceride levels commensurate with their degree of adiposity. Activating GCK mutations may present in late adulthood with hyperinsulinaemic hypoglycaemia and should be considered even in older patients being investigated for insulinoma. Normal circulating lipids, rates of hepatic de novo lipogenesis and appropriate hepatic triglyceride content for degree of adiposity in the patients we describe suggest that even lifelong GCK activation in isolation is insufficient to produce fatty liver and metabolic dyslipidaemia.

Mutations in pancreatic ß-cell Glucokinase as a cause of hyperinsulinaemic hypoglycaemia and neonatal diabetes mellitus

Glucokinase is a key enzyme involved in regulating insulin secretion from the pancreatic ß-cell. The unique role of glucokinase in human glucose physiology is illustrated by the fact that genetic mutations in glucokinase can either cause hyperglycaemia or hypoglycaemia. Heterozygous inactivating mutations in glucokinase cause maturity-onset diabetes of the young (MODY), homozygous inactivating in glucokinase mutations result in permanent neonatal diabetes whereas heterozygous activating glucokinase mutations cause hyperinsulinaemic hypoglycaemia.

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

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

Glucokinase Activators for the Potential Treatment of Type 2 Diabetes

The search for innovative and clinically-differentiated medicines for the treatment of type 2 diabetes is an active area of research for pharmaceutical companies. The discovery of allosteric Glucokinase (GK) activators in 2003 represents the first time a pharmaceutical agent was used to directly augment the actions of an enzyme by increasing its maximal velocity and substrate affinity. This discovery, coupled with translational medicine which has shown that inactivating and activating GK mutations cause glycemic diseases, has triggered an intensive medicinal chemistry effort in the field of glucokinase activators (GKAs). The antidiabetic effects of GK activators observed in animal models support the notion that these agents act to both augment insulin release from pancreatic beta-cells and suppress hepatic glucose production in the liver. This review describes the unprecedented task of optimizing small molecules in order to affect the appropriate changes in the kinetic parameters of an enzyme. In addition, a pharmacophore model for the various classes of glucokinase activators that have been described in the literature will be presented. Overall, the available data suggests that potent glucokinase activators with the desired effects on the kinetic properties of the enzyme can be designed to achieve strong and persistent antidiabetic effects. GK activators thus represent a promising new treatment for type 2 diabetes.

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

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

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

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

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

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. 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. 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. 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.

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

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

Persistent hyperinsulinemic hypoglycemia in a 7 yr old girl due to a novel activating glucokinase mutation

Background and objective: Persistent hyperinsulinemic hypoglycemia of infancy (PHHI) is a rare disorder due to inappropriately high insulin secretion. It is a rare heterogenous disorder and both spontaneous and familial cases have been described. Heterozygous activating mutations in the glucokinase (GCK) gene have been described in a total of five families to date. Patients with GCK activating mutations have regulated insulin secretion and can usually be treated with diazoxide. We identified a 7 year old female patient with a history of hypoglycemia from infancy. The proband's mother, maternal grandmother, 2 siblings, maternal aunt and 2 maternal cousins are also affected.

Insights into the Structure and Regulation of Glucokinase from a Novel Mutation (V62M), Which Causes Maturity-onset Diabetes of the Young

Glucokinase (GCK) serves as the pancreatic glucose sensor. Heterozygous inactivating GCK mutations cause hyperglycemia, whereas activating mutations cause hypoglycemia. We studied the GCK V62M mutation identified in two families and co-segregating with hyperglycemia to understand how this mutation resulted in reduced function. Structural modeling locates the mutation close to five naturally occurring activating mutations in the allosteric activator site of the enzyme. Recombinant glutathionyl S-transferase-V62M GCK is paradoxically activated rather than inactivated due to a decreased S0.5 for glucose compared with wild type (4.88 versus 7.55 mM). The recently described pharmacological activator (RO0281675) interacts with GCK at this site. V62M GCK does not respond to RO0281675, nor does it respond to the hepatic glucokinase regulatory protein (GKRP). The enzyme is also thermally unstable, but this lability is apparently less pronounced than in the proven instability mutant E300K. Functional and structural analysis of seven amino acid substitutions at residue Val62 has identified a non-linear relationship between activation by the pharmacological activator and the van der Waals interactions energies. Smaller energies allow a hydrophobic interaction between the activator and glucokinase, whereas larger energies prohibit the ligand from fitting into the binding pocket. We conclude that V62M may cause hyperglycemia by a complex defect of GCK regulation involving instability in combination with loss of control by a putative endogenous activator and/or GKRP. This study illustrates that mutations that cause hyperglycemia are not necessarily kinetically inactivating but may exert their effects by other complex mechanisms. Elucidating such mechanisms leads to a deeper understanding of the GCK glucose sensor and the biochemistry of beta-cells and hepatocytes.

Glucokinase (GCK) mutations in hyper- and hypoglycemia: maturity-onset diabetes of the young, permanent neonatal diabetes, and hyperinsulinemia of infancy.

Glucokinase is a key regulatory enzyme in the pancreatic beta-cell. It plays a crucial role in the regulation of insulin secretion and has been termed the pancreatic beta-cell sensor. Given its central role in the regulation of insulin release, it is understandable that mutations in the gene encoding glucokinase (GCK) can cause both hyperglycemia and hypoglycemia. Heterozygous inactivating mutations in GCK cause maturity-onset diabetes of the young (MODY), characterized by mild hyperglycemia, which is present at birth, but is often only detected later in life during screening for other purposes. Homozygous inactivating GCK mutations result in a more severe phenotype, presenting at birth as permanent neonatal diabetes mellitus (PNDM). Several heterozygous activating GCK mutations that cause hypoglycemia have also been reported. A total of 195 mutations in the GCK gene have been described, in a total of 285 families. There are no common mutations and the mutations are distributed throughout the gene. Mutations that cause hypoglycemia are located in various exons in a discrete region of the protein termed the heterotropic allosteric activator site. The identification of a GCK mutation in hyper- and hypoglycemia has implications for the clinical course and clinical management of the disorder.