Characterization of the zebrafish as a model of ATP-sensitive potassium channel hyperinsulinism.

INTRODUCTION: Congenital hyperinsulinism (HI) is the leading cause of persistent hypoglycemia in infants. Current models to study the most common and severe form of HI resulting from inactivating mutations in the ATP-sensitive potassium channel (KATP) are limited to primary islets from patients and the Sur1 -/- mouse model. Zebrafish exhibit potential as a novel KATPHI model since they express canonical insulin secretion pathway genes and those with identified causative HI mutations. Moreover, zebrafish larvae transparency provides a unique opportunity for in vivo visualization of pancreatic islets. RESEARCH DESIGN AND METHODS: We evaluated zebrafish as a model for KATPHI using a genetically encoded Ca2+ sensor (ins:gCaMP6s) expressed under control of the insulin promoter in beta cells of an abcc8 -/- zebrafish line. RESULTS: We observed significantly higher islet cytosolic Ca2+ in vivo in abcc8 -/- compared with abcc8 +/+ zebrafish larvae. Additionally, abcc8 -/- larval zebrafish had significantly lower whole body glucose and higher whole body insulin levels compared with abcc8 +/+ controls. However, adult abcc8 -/- zebrafish do not show differences in plasma glucose, plasma insulin, or glucose tolerance when compared with abcc8 +/+ zebrafish. CONCLUSIONS: Our results identify that zebrafish larvae, but not adult fish, are a demonstrable novel model for advancement of HI research.

Approach to the Neonate with Hypoglycemia.

After birth, healthy neonates undergo a period of altered glucose metabolism, known as "transitional hypoglycemia". During the first 0-4 hours of life, the mean plasma glucose concentration decreases to 57 mg/dL, then by 72-96 hours of life increases to 82 mg/dL, well within the normal adult range. Recent data suggests that transitional hypoglycemia is due to persistence of the fetal beta cell's lower threshold for insulin release, resulting in a transient hyperinsulinemic state. While hypoglycemia is an expected part of the transition to postnatal life, it makes the identification of infants with persistent hypoglycemia disorders challenging. Given the risk of neurologic injury from hypoglycemia, identifying these infants is critical. Hyperinsulinism is the most common cause of persistent hypoglycemia in neonates and infants and carries a high risk of neurocognitive dysfunction given the severity of the hypoglycemia and the inability to generate ketones, a critical alternative cerebral fuel. Screening neonates at risk for persistent hypoglycemia disorders and completing evaluations prior to hospital discharge is essential to prevent delayed diagnoses and neurologic damage.

Role of beta-hydroxybutyrate measurement in the evaluation of plasma glucose concentrations in newborn infants.

OBJECTIVE: The Glucose in Well Babies (GLOW) Study showed that there are two phases of low glucose concentrations in healthy newborn infants: an initial phase in which plasma concentrations of ketones are low; and a second phase in which low glucose concentrations are accompanied by elevated concentrations of ketones. The implications of these two phases for the brain differ depending on whether ketones are available as alternative substrate for brain metabolism. The purpose of this study was to estimate the duration of these two phases of neonatal low glucose concentrations in 66 healthy breastfed newborns from the GLOW Study during the first 5 days of life. METHODS: The sum of glucose and beta-hydroxybutyrate (BOHB) was used as a proxy for the total concentrations of insulin-dependent fuels for the brain; a threshold value below 4 mmol/L was taken to indicate the presence of relative hyperinsulinism and a BOHB concentration above 0.5 mmol/L to indicate ketonaemia. RESULTS: The first phase of low glucose concentrations lasted a median of 40 hours and in 15% of infants, this persisted beyond 60 hours. Fifty (76%) of the 66 infants subsequently had ketonaemia, which resolved at a median age of 76 hours (range 41->120 hours). CONCLUSIONS: These data suggest that monitoring BOHB concentrations may be useful for interpreting glucose concentrations in newborns and screening for persistent hyperinsulinism.

Novel Use of Dasiglucagon, a Soluble Glucagon Analog, for the Treatment of Hyperinsulinemic Hypoglycemia Secondary to Suspected Insulinoma: A Case Report.

INTRODUCTION: Hyperinsulinemic hypoglycemia is the most common cause of persistent hypoglycemia in children and adults. In adolescents and adults, hyperinsulinemic hypoglycemia is most frequently caused by an insulin-producing tumor. CASE PRESENTATION: A 17-year-old, previously healthy male presented with recurrent and severe episodes of hypoglycemia. Diagnostic evaluation was consistent with hyperinsulinemic hypoglycemia, and an insulinoma was suspected. Multiple imaging studies and surgical exploration failed to identify a lesion. Over the course of months, the patient was found to be refractory to conventional medical interventions. CONCLUSION: Upon approval from the US Food and Drug Administration and the Institutional Review Board, the patient was treated with dasiglucagon, a novel soluble glucagon analog, under a single-patient Investigational New Drug. The patient has tolerated the medication and has been able to achieve appropriate glycemic control.

Dasiglucagon for the Treatment of Congenital Hyperinsulinism: A Randomized Phase 3 Trial in Infants and Children.

CONTEXT: Congenital hyperinsulinism (CHI) is characterized by dysregulated insulin secretion causing hypoglycemia and consequent brain damage. Dasiglucagon is a glucagon analogue under investigation to treat CHI. OBJECTIVE: To evaluate the efficacy and safety of dasiglucagon delivered via continuous subcutaneous infusion to children with CHI and persistent hypoglycemia as add-on to standard of care (SoC). METHODS: In this open-label trial, patients were randomized 1:1 to SoC or SoC + dasiglucagon (10-70 µg/h) for 4 weeks. In the following 4 weeks, all patients received dasiglucagon + SoC. Hypoglycemia was assessed by self-monitored plasma glucose (SMPG) and blinded continuous glucose monitoring (CGM). Primary endpoint was average number of SMPG-detected hypoglycemia episodes/week (SMPG <3.9 mmol/L) during Weeks 2 to 4. RESULTS: Thirty-two patients (0.6-10.9 years) were randomly assigned to dasiglucagon + SoC (n = 16) or SoC (n = 16). The rate of SMPG-detected hypoglycemia decreased from baseline in both groups, but with no statistically significant difference during Weeks 2 to 4 (event rate ratio: 0.85 [0.54; 1.36], P = .5028). However, dasiglucagon administration resulted in a 43% reduction in CGM-detected hypoglycemia (<3.9 mmol/L) vs SoC alone during Weeks 2 to 4 (post hoc analysis; event rate ratio: 0.57 [0.39; 0.83], P = .0029). Dasiglucagon enabled reductions (of 37% to 61%) in all other measures of hypoglycemia assessed by CGM vs SoC alone including extent and percent time in hypoglycemia (post hoc analyses). Dasiglucagon appeared safe and well tolerated. Skin and gastrointestinal events were more frequent with dasiglucagon + SoC than SoC only. CONCLUSION: Clinically meaningful reductions in all CGM-recorded measures of hypoglycemia support using dasiglucagon as a potential treatment for CHI.

Case report: Two unexpected cases of DGUOK-related mitochondrial DNA depletion syndrome presenting with hyperinsulinemic hypoglycemia.

Timely diagnosis of persistent neonatal hypoglycemia is critical to prevent neurological sequelae, but diagnosis is complicated by the heterogenicity of the causes. We discuss two cases at separate institutions in which clinical management was fundamentally altered by the results of molecular genetic testing. In both patients, critical samples demonstrated hypoketotic hypoglycemia and a partial glycemic response to glucagon stimulation, thereby suggesting hyperinsulinism (HI). However, due to rapid genetic testing, both patients were found to have deoxyguanosine kinase (DGUOK)-related mitochondrial DNA depletion syndrome, an unexpected diagnosis. Patients with this disease typically present with either hepatocerebral disease in the neonatal period or isolated hepatic failure in infancy. The characteristic features involved in the hepatocerebral form of the disease include lactic acidosis, hypoglycemia, cholestasis, progressive liver failure, and increasing neurologic dysfunction. Those with isolated liver involvement experience hepatomegaly, cholestasis, and liver failure. Although liver transplantation is considered, research has demonstrated that for patients with DGUOK-related mitochondrial DNA depletion syndrome and neurologic symptoms, early demise occurs. Our report advocates for the prompt initiation of genetic testing in patients presenting with persistent neonatal hypoglycemia and for the incorporation of mitochondrial DNA depletion syndromes in the differential diagnosis of HI.

Insulin Immunoassay Interference Due to Human Antimouse Antibodies in a Patient With Ketotic Hypoglycemia.

Misinterpretation of common endocrine hormonal immunoassays can distort the clinical picture and lead to unnecessary medical workups. Potential assay inference is important to recognize when the clinical presentation and laboratory evaluation are inconsistent. This is demonstrated by the case of an 18-month-old girl who initially presented with ketotic hypoglycemia and was found on diagnostic fasting evaluation to have the triad of hypoglycemia, inappropriately high insulin levels, and low C-peptide levels-point-of-care glucose 43 mg/dL (2.39 mmol/L) (confirmatory 52 mg/dL [2.89 mmol/L]), insulin 48.1 µIU/mL (334 pmol/L), and C-peptide 0.2 ng/mL (0.07 nmol/L) concerning for factitious insulin (insulin:C-peptide ratio 4.77). On repeat diagnostic fast, insulin assays measured by liquid chromatography-mass spectrometry were incongruent with prior testing by immunoassay, demonstrating a falsely elevated insulin level when measured by immunoassay, likely due to human antimouse antibody interference (HAMA 181 ng/mL). This case represents a diagnostic challenge in which is it imperative to recognize possible immunoassay interference. It is critical to establish the difference between insulin assay interference and factitious insulin through use of alternative laboratory methods as misdiagnosis could lead to the serious implication of Munchausen by proxy resulting in the removal of a child from their home and potentially parents being charged with a crime.

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

The importance of glucokinase (GK) in the regulation of insulin secretion has been highlighted by the phenotypes of individuals with activating and inactivating mutations in the glucokinase gene (GCK). Here we report 10 individuals with congenital hyperinsulinism (HI) caused by eight unique activating mutations of GCK. Six are novel and located near previously identified activating mutations sites. The first recognized episode of hypoglycemia in these patients occurred between birth and 24 years, and the severity of the phenotype was also variable. Mutant enzymes were expressed and purified for enzyme kinetics in vitro. Mutant enzymes had low glucose half-saturation concentration values and an increased enzyme activity index compared with wild-type GK. We performed functional evaluation of islets from the pancreata of three children with GCK-HI who required pancreatectomy. Basal insulin secretion in perifused GCK-HI islets was normal, and the response to glyburide was preserved. However, the threshold for glucose-stimulated insulin secretion in perifused glucokinase hyperinsulinism (GCK-HI) islets was decreased, and glucagon secretion was greatly suppressed. Our evaluation of novel GCK disease-associated 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. ARTICLE HIGHLIGHTS: 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 ß-cells and α-cells to regulate glucose homeostasis.

International Guidelines for the Diagnosis and Management of Hyperinsulinism.

Hyperinsulinism (HI) due to dysregulation of pancreatic beta-cell insulin secretion is the most common and most severe cause of persistent hypoglycemia in infants and children. In the 65 years since HI in children was first described, there has been a dramatic advancement in the diagnostic tools available, including new genetic techniques and novel radiologic imaging for focal HI, however; there have been almost no new therapeutic modalities since the development of diazoxide. Recent advances in neonatal research and genetics have improved our understanding of the pathophysiology of both transient and persistent forms of neonatal hyperinsulinism. Rapid turnaround of genetic test results combined with advanced radiologic imaging can permit identification and localization of surgically-curable focal lesions in a large proportion of children with congenital forms of HI, but are only available in certain centers in 'developed' countries. Diazoxide, the only drug currently approved for treating HI, was recently designated as an "essential medicine" by the World Health Organization but has been approved in only 16% of Latin American countries and remains unavailable in many under-developed areas of the world. Novel treatments for HI are emerging, but they await completion of safety and efficacy trials before being considered for clinical use. This international consensus statement on diagnosis and management of HI was developed in order to assist specialists, general pediatricians, and neonatologists in early recognition and treatment of HI with the ultimate aim of reducing the prevalence of brain injury caused by hypoglycemia. A previous statement on diagnosis and management of HI in Japan was published in 2017. The current document provides an updated guideline for management of infants and children with HI and includes potential accommodations for less-developed regions of the world where resources may be limited.

Optimization of a Glucagon-Like Peptide 1 Receptor Antagonist Antibody for Treatment of Hyperinsulinism.

Congenital hyperinsulinism (HI) is a genetic disorder in which pancreatic ß-cell insulin secretion is excessive and results in hypoglycemia that, without treatment, can cause brain damage or death. Most patients with loss-of-function mutations in ABCC8 and KCNJ11, the genes encoding the ß-cell ATP-sensitive potassium channel (KATP), are unresponsive to diazoxide, the only U.S. Food and Drug Administration-approved medical therapy and require pancreatectomy. The glucagon-like peptide 1 receptor (GLP-1R) antagonist exendin-(9-39) is an effective therapeutic agent that inhibits insulin secretion in both HI and acquired hyperinsulinism. Previously, we identified a highly potent antagonist antibody, TB-001-003, which was derived from our synthetic antibody libraries that were designed to target G protein-coupled receptors. Here, we designed a combinatorial variant antibody library to optimize the activity of TB-001-003 against GLP-1R and performed phage display on cells overexpressing GLP-1R. One antagonist, TB-222-023, is more potent than exendin-(9-39), also known as avexitide. TB-222-023 effectively decreased insulin secretion in primary isolated pancreatic islets from a mouse model of hyperinsulinism, Sur1-/- mice, and in islets from an infant with HI, and increased plasma glucose levels and decreased the insulin to glucose ratio in Sur1-/- mice. These findings demonstrate that targeting GLP-1R with an antibody antagonist is an effective and innovative strategy for treatment of hyperinsulinism. ARTICLE HIGHLIGHTS: Patients with the most common and severe form of diazoxide-unresponsive congenital hyperinsulinism (HI) require a pancreatectomy. Other second-line therapies are limited in their use because of severe side effects and short half-lives. Therefore, there is a critical need for better therapies. Studies with the glucagon-like peptide 1 receptor (GLP-1R) antagonist, avexitide (exendin-(9-39)), have demonstrated that GLP-1R antagonism is effective at lowering insulin secretion and increasing plasma glucose levels. We have optimized a GLP-1R antagonist antibody with more potent blocking of GLP-1R than avexitide. This antibody therapy is a potential novel and effective treatment for HI.

A selective nonpeptide somatostatin receptor 5 agonist effectively decreases insulin secretion in hyperinsulinism.

Congenital hyperinsulinism (HI), a beta cell disorder most commonly caused by inactivating mutations of beta cell KATP channels, results in dysregulated insulin secretion and persistent hypoglycemia. Children with KATP-HI are unresponsive to diazoxide, the only FDA-approved drug for HI, and utility of octreotide, the second-line therapy, is limited because of poor efficacy, desensitization, and somatostatin receptor type 2 (SST2)-mediated side effects. Selective targeting of SST5, an SST receptor associated with potent insulin secretion suppression, presents a new avenue for HI therapy. Here, we determined that CRN02481, a highly selective nonpeptide SST5 agonist, significantly decreased basal and amino acid-stimulated insulin secretion in both Sur1-/- (a model for KATP-HI) and wild-type mouse islets. Oral administration of CRN02481 significantly increased fasting glucose and prevented fasting hypoglycemia compared to vehicle in Sur1-/- mice. During a glucose tolerance test, CRN02481 significantly increased glucose excursion in both WT and Sur1-/- mice compared to the control. CRN02481 also reduced glucose- and tolbutamide-stimulated insulin secretion from healthy, control human islets similar to the effects observed with SS14 and peptide somatostatin analogs. Moreover, CRN02481 significantly decreased glucose- and amino acid-stimulated insulin secretion in islets from two infants with KATP-HI and one with Beckwith-Weideman Syndrome-HI. Taken together, these data demonstrate that a potent and selective SST5 agonist effectively prevents fasting hypoglycemia and suppresses insulin secretion not only in a KATP-HI mouse model but also in healthy human islets and islets from HI patients.

New approaches to screening and management of neonatal hypoglycemia based on improved understanding of the molecular mechanism of hypoglycemia.

For the past 70 years, controversy about hypoglycemia in newborn infants has focused on a numerical "definition of neonatal hypoglycemia", without regard to its mechanism. This ignores the purpose of screening newborns for hypoglycemia, which is to identify those with pathological forms of hypoglycemia and to prevent hypoglycemic brain injury. Recent clinical and basic research indicates that the three major forms of neonatal hypoglycemia are caused by hyperinsulinism (recognizing also that other rare hormonal or metabolic conditions may also present during this time frame). These include transitional hypoglycemia, which affects all normal newborns in the first few days after birth; perinatal stress-induced hypoglycemia in high-risk newborns, which afflicts ∼1 in 1,200 newborns; and genetic forms of congenital hyperinsulinism which afflict ∼1 in 10,000-40,000 newborns. (1) Transitional hyperinsulinism in normal newborns reflects persistence of the low glucose threshold for insulin secretion during fetal life into the first few postnatal days. Recent data indicate that the underlying mechanism is decreased trafficking of ATP-sensitive potassium channels to the beta-cell plasma membrane, likely a result of the hypoxemic state of fetal life. (2) Perinatal stress-induced hyperinsulinism in high-risk infants appears to reflect an exaggeration of this normal low fetal glucose threshold for insulin release due to more severe and prolonged exposure to perinatal hypoxemia. (3) Genetic hyperinsulinism, in contrast, reflects permanent genetic defects in various steps controlling beta-cell insulin release, such as inactivating mutations of the K ATP-channel genes. The purpose of this report is to review our current knowledge of these three major forms of neonatal hyperinsulinism as a foundation for the diagnosis and management of hypoglycemia in newborn infants. This includes selection of appropriate interventions based on underlying disease mechanism; combined monitoring of both plasma glucose and ketone levels to improve screening for infants with persistent forms of hypoglycemia; and ultimately to ensure that infants at risk of persistent hyperinsulinemic hypoglycemia are recognized prior to discharge from the nursery.

Bridging the gaps: recent advances in diagnosis, care, and outcomes in congenital hyperinsulinism.

PURPOSE OF REVIEW: To highlight advances in congenital hyperinsulinism (HI), including newly described molecular mechanisms of disease, novel therapeutic interventions, and improved understanding of long-term outcomes. RECENT FINDINGS: Important advances have been made elucidating the molecular mechanisms responsible for HI. Non-coding variants in HK1 have been found to cause aberrant hexokinase expression. Inactivating mutations in SLC25A36 have been identified in children with features of the hyperinsulinism hyperammonemia syndrome. Low-level mosaic mutations in known HI genes have been detected in cases of 'genetic testing negative' HI. Identification and localization of focal HI lesions remains a priority, since focal HI can be cured with surgery. Use of 68 Ga-NODAGA-exendin-4 PET has been proposed to localize focal lesions. Additional studies are needed before this technique replaces 18 F-DOPA PET as standard of care. Treatment options for children with diffuse HI remain limited. The long-acting somatostatin analog, lanreotide, was shown to significantly improve glycemic control in a large series of children with HI. New therapies are under development, with promising preliminary results. Long-term quality of life and neurodevelopmental outcomes remain suboptimal. SUMMARY: Advanced genetic and epigenomic analytic techniques have uncovered novel molecular mechanisms of HI. Development of new drugs holds promise to improve long-term outcomes for individuals with HI.

Undiagnosed hypoglycaemia disorders in children detected when hypoglycaemia occurs in the setting of illness: a retrospective study.

OBJECTIVE: Whether hypoglycaemia incidentally detected during intercurrent illness in children requires an endocrine workup remains controversial. This study aimed to determine the yield of conducting a diagnostic evaluation in this setting and to compare clinical and biochemical features between patients ultimately diagnosed with a hypoglycaemic disorder and those who were not. DESIGN: Single-center, retrospective review of children referred to endocrinology between January 2013 and December 2018 for evaluation of hypoglycaemia (defined as plasma glucose<3.9 mmol/L (<70 mg/dL)) in the setting of acute illness. RESULTS: 145 patients met eligibility criteria. A hypoglycaemia disorder was identified in 12 patients (8% of the cohort, 17% of those who underwent a diagnostic fast). There were no cases in which diagnosis was established in the absence of a diagnostic fast. Characteristics associated with identifying an underlying disorder included younger age (1.03 years (IQR: 0.05-1.54) vs 2.18 years [IQR: 1.29-3.99], p<0.001), higher bicarbonate level (22±5.5 mmol/L vs 16±3.6 mmol/L, p<0.001), lower frequency of elevated plasma or urine ketones (25% vs 92%, p=0.004) and lower frequency of other documented medical problems (17% vs 50%, p=0.03). CONCLUSIONS: The yield of diagnostic evaluation among children with incidental detection of hypoglycaemia in the setting of illness is not insignificant. We thus recommend that all children with hypoglycaemia in the setting of illness undergo guided diagnostic evaluation. Younger age and absence of ketosis and acidosis at presentation may serve as useful predictors for establishing a diagnosis. Future studies are needed to confirm these findings.

Congenital Hyperinsulinism: An Historical Perspective.

Congenital hyperinsulinism is the most common cause of persistent hypoglycemia in neonates, infants, and children. Since the first case descriptions in the 1950s, the field has advanced significantly. It was the development of the insulin radioimmunoassay by Yalow and Berson a decade later that made it possible to demonstrate that this form of persistent hypoglycemia was caused by insulin, and a few years later, Drash described the successful treatment of children with hyperinsulinism with the antihypertensive diazoxide, which until today remains the only approved treatment for hyperinsulinism. In the mid 1970s, Baker and Stanley described that hyperinsulinism can be recognized by inappropriate responses of metabolic fuels and hormones during the course of a provocative fasting challenge. Later, advances in molecular genetics led to the discovery of the different genetic subtypes of hyperinsulinism. One of the most impactful discoveries in the field was the recognition of the focal form of hyperinsulinism and the development of 18F-DOPA PET for the localization of focal lesions before surgery which has resulted in the possibility of cure for children with focal disease. However, treatment options for children with nonfocal diazoxide-unresponsive hyperinsulinism have continued to be limited. New drug development programs for hyperinsulinism promise to change this in the next few years. Unfortunately, despite all these advances, children with hyperinsulinism around the world continue to experience neurological sequelae at high rates, highlighting the importance of early diagnosis and effective treatment.

Natural history and neurodevelopmental outcomes in perinatal stress induced hyperinsulinism.

Objective: To describe perinatal stress induced hyperinsulinism (PSIHI), determine the prevalence of neurodevelopmental differences, and identify risk factors for poor developmental prognosis. Methods: Subjects with a history of hyperinsulinism (HI) and perinatal stress and in whom resolution of the HI was demonstrated were included. Medical record review, caregiver interview, and three validated developmental assessments were completed. Results: Of the 107 subjects (75% male), 36% were born between 32 and 37 weeks. Median age of hypoglycemia presentation was 0 days. Median age at HI diagnosis was 12 days (IQR 13.5). Median length of time for initiation of definitive treatment was 14 days (IQR 14).Caregiver interviews were completed for 53 of 79 eligible subjects. Developmental concerns were reported by 51%. Neurodevelopmental assessments were completed by caregivers of 37 of the 53 enrolled subjects. The proportion of subjects scoring >1 SD and >2 SD away from the mean in the direction of concern on the major composite scores was significantly greater than in the general population (40.5% vs. 15.8%, P ≤ 0.0001 and 18.9% vs. 2.2%, P ≤ 0.0001, respectively).Male sex, small for gestational age status (SGA), and treatment with continuous feeds were associated with assessment scores >1 SD from the mean (P < 0.05). SGA and preeclampsia were associated with assessment scores >2 SD from the mean (P < 0.05). Conclusion: While the majority of infants presented with hypoglycemia in the first day of life, diagnosis and treatment occurred 12-14 days later. Children with PSIHI are at high risk of neurodevelopmental deficits and are more likely to perform below average on developmental assessment.

Mosaic GLUD1 Mutations Associated with Hyperinsulinism Hyperammonemia Syndrome.

INTRODUCTION: The hyperinsulinemia-hyperammonemia syndrome (HIHA) is the second most common cause of congenital hyperinsulinism and is caused by activating heterozygous missense mutations in GLUD1. In the majority of HIHA cases, the GLUD1 mutation is found to be de novo. We have identified 3 patients in whom clinical evaluation was suggestive of HIHA but with negative mutation analysis in peripheral blood DNA for GLUD1 as well as other known HI genes. METHODS: We performed next-generation sequencing (NGS) on peripheral blood DNA from two children with clinical features of HIHA in order to look for mosaic mutations in GLUD1. Pancreas tissue was also available in one of these cases for NGS. In addition, NGS was performed on peripheral blood DNA from a woman with a history of HI in infancy whose child had HIHA due to a presumed de novo GLUD1 mutation. RESULTS: Mosaic GLUD1 mutations were identified in these 3 cases at percent mosaicism ranging from 2.7% to 10.4% in peripheral blood. In one case with pancreas tissue available, the mosaic GLUD1 mutation was present at 17.9% and 28.9% in different sections of the pancreas. Two unique GLUD1 mutations were identified in these cases, both of which have been previously reported (c.1493c>t/p.Ser445Leu and c.820c>t/p.Arg221Cys). CONCLUSION: The results suggest that low-level mosaic mutations in known HI genes may be the underlying molecular mechanism in some children with HI who have negative genetic testing in peripheral blood DNA.

Effects of GLP-1 and GIP on Islet Function in Glucose-Intolerant, Pancreatic-Insufficient Cystic Fibrosis.

Impaired insulin and incretin secretion underlie abnormal glucose tolerance (AGT) in pancreatic insufficient cystic fibrosis (PI-CF). Whether the incretin hormones glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) can enhance pancreatic islet function in cystic fibrosis (CF) is not known. We studied 32 adults with PI-CF and AGT randomized to receive either GLP-1 (n = 16) or GIP (n = 16) during glucose-potentiated arginine (GPA) testing of islet function on two occasions, with either incretin or placebo infused, in a randomized, double-blind, cross-over fashion. Another four adults with PI-CF and normal glucose tolerance (NGT) and four matched control participants without CF underwent similar assessment with GIP. In PI-CF with AGT, GLP-1 substantially augmented second-phase insulin secretion but without effect on the acute insulin response to GPA or the proinsulin secretory ratio (PISR), while GIP infusion did not enhance second-phase or GPA-induced insulin secretion but increased the PISR. GIP also did not enhance second-phase insulin in PI-CF with NGT but did so markedly in control participants without CF controls. These data indicate that GLP-1, but not GIP, augments glucose-dependent insulin secretion in PI-CF, supporting the likelihood that GLP-1 agonists could have therapeutic benefit in this population. Understanding loss of GIP's insulinotropic action in PI-CF may lead to novel insights into diabetes pathogenesis.

Localized islet nuclear enlargement hyperinsulinism (LINE-HI) due to ABCC8 and GCK mosaic mutations.

Objective: Congenital hyperinsulinism (HI) is the most common cause of persistent hypoglycemia in children. In addition to typical focal or diffuse HI, some cases with diazoxide-unresponsive congenital HI have atypical pancreatic histology termed Localized Islet Nuclear Enlargement (LINE) or mosaic HI, characterized by histologic features similar to diffuse HI, but confined to only a region of pancreas. Our objective was to characterize the phenotype and genotype of children with LINE-HI. Design: The phenotype and genotype features of 12 children with pancreatic histology consistent with LINE-HI were examined. Methods: We compiled clinical features of 12 children with LINE-HI and performed next-generation sequencing on specimens of pancreas from eight of these children to look for mosaic mutations in genes known to be associated with diazoxide-unresponsive HI (ABCC8, KCNJ11, and GCK). Results: Children with LINE-HI had lower birth weights and later ages of presentation compared to children with typical focal or diffuse HI. Partial pancreatectomy in LINE-HI cases resulted in euglycemia in 75% of cases; no cases have developed diabetes. Low-level mosaic mutations were identified in the pancreas of six cases with LINE-HI (three in ABCC8, three in GCK). Expression studies confirmed that all novel mutations were pathogenic. Conclusion: These results indicate that post-zygotic low-level mosaic mutations of known HI genes are responsible for some cases of LINE-HI that lack an identifiable germ-line mutation and that partial pancreatectomy may be curative for these cases.