Etiology of the Neonatal Hypoglycemias.

To provide a more appropriate foundation for dealing with the problem of hypoglycemia in newborn infants, this article focuses on the mechanisms which underlie the various forms of neonatal hypoglycemia and discusses their implications for newborn care. Evidence indicates that all of the major forms of neonatal hypoglycemia are the result of hyperinsulinism due to dysregulation of pancreatic islet insulin secretion. Based on these observations, the authors propose that routine measurement of B-hydroxybutyrate should be considered an essential part of glucose monitoring in newborn infants.

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.

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.

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.

Case presentation of 8-year follow up of recurrent malignant duodenal Insulinoma and lymph node metastases and literature review of malignant Insulinoma management.

BACKGROUND: Insulinoma is an uncommon insulin-secreting neuroendocrine tumor that presents with severe recurrent hypoglycemia. Although cases of extrapancreatic insulinomas have been reported, the majority of insulinomas occur in the pancreas. The number of reported cases of ectopic insulinomas with follow-up assessments is limited and they do not report disease recurrence. The current report presents the first documented case of recurrent extrapancreatic insulinoma with 8 years of follow-up, provides relevant literature review, and proposes surveillance and treatment strategies. CASE PRESENTATION: We describe an insulinoma localized in the duodenal wall of a 36-year-old female who presented in 2013 with weight gain and Whipple's triad and was successfully managed with duodenotomy and enucleation. She presented again in 2017 with recurrent Whipple's triad and was found to have metastatic disease localized exclusively to peripancreatic lymph nodes. Primary pancreatic insulinoma was not evident and her hypoglycemia resolved following lymph node dissection. Eight years after initial presentation continuous glucose monitoring (CGM) showed a trend for euglycemia, and PET-CT Gallium 68 DOTATATE scan evaluation indicated absence of recurrent disease. CONCLUSION: Insulinomas are rare clinical entities and extrapancreatic insulinomas are particularly uncommon. Follow-up evaluation and treatment strategies for ectopic insulinoma recurrence presents a significant clinical challenge as the condition has hitherto remained undescribed in the literature. Available evidence in the literature indicates that lymph node metastases of intrapancreatic insulinomas likely do not change prognosis. Given the absence of long-term data informing the management and monitoring of patients with extrapancreatic insulinoma, we suggest patient education for hypoglycemic symptoms, monitoring for hypoglycemia with CGM, annual imaging, and a discussion with patients regarding treatment with octreotide or alternative somatostatin receptor analog therapies.

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.

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.

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.

Advances in Understanding the Mechanism of Transitional Neonatal Hypoglycemia and Implications for Management.

Our lack of basic knowledge about the basic mechanisms of transitional hypoglycemia and other forms of hypoglycemia in newborns underlies the ongoing controversies over standards for managing these conditions. To address this deficiency, the authors evaluated regulation of insulin secretion in fetal, newborn, and adult rats. The results demonstrate that transitional hypoglycemia in normal neonates and persistent hypoglycemia in high-risk infants both reflect altered beta-cell insulin regulation. These findings provide a new foundation for improving detection and management and preventing hypoglycemic brain injury in normal neonates and, especially, in infants with persistent hypoglycemia and genetic forms of congenital hyperinsulinism.

Decreased KATP Channel Activity Contributes to the Low Glucose Threshold for Insulin Secretion of Rat Neonatal Islets.

Transitional hypoglycemia in normal newborns occurs in the first 3 days of life and has clinical features consistent with hyperinsulinism. We found a lower threshold for glucose-stimulated insulin secretion from freshly isolated embryonic day (E) 22 rat islets, which persisted into the first postnatal days. The threshold reached the adult level by postnatal day (P) 14. Culturing P14 islets also decreased the glucose threshold. Freshly isolated P1 rat islets had a lower threshold for insulin secretion in response to 2-aminobicyclo-(2, 2, 1)-heptane-2-carboxylic acid, a nonmetabolizable leucine analog, and diminished insulin release in response to tolbutamide, an inhibitor of ß-cell KATP channels. These findings suggested that decreased KATP channel function could be responsible for the lower glucose threshold for insulin secretion. Single-cell transcriptomic analysis did not reveal a lower expression of KATP subunit genes in E22 compared with P14 ß cells. The investigation of electrophysiological characteristics of dispersed ß cells showed that early neonatal and cultured cells had fewer functional KATP channels per unit membrane area. Our findings suggest that decreased surface density of KATP channels may contribute to the observed differences in glucose threshold for insulin release.

Novel dominant KATP channel mutations in infants with congenital hyperinsulinism: Validation by in vitro expression studies and in vivo carrier phenotyping.

Inactivating mutations in the genes encoding the two subunits of the pancreatic beta-cell KATP channel, ABCC8 and KCNJ11, are the most common finding in children with congenital hyperinsulinism (HI). Interpreting novel missense variants in these genes is problematic, because they can be either dominant or recessive mutations, benign polymorphisms, or diabetes mutations. This report describes six novel missense variants in ABCC8 and KCNJ11 that were identified in 11 probands with congenital HI. One of the three ABCC8 mutations (p.Ala1458Thr) and all three KCNJ11 mutations were associated with responsiveness to diazoxide. Sixteen family members carried the ABCC8 or KCNJ11 mutations; only two had hypoglycemia detected at birth and four others reported symptoms of hypoglycemia. Phenotype testing of seven adult mutation carriers revealed abnormal protein-induced hypoglycemia in all; fasting hypoketotic hypoglycemia was demonstrated in four of the seven. All of six mutations were confirmed to cause dominant pathogenic defects based on in vitro expression studies in COSm6 cells demonstrating normal trafficking, but reduced responses to MgADP and diazoxide. These results indicate a combination of in vitro and in vivo phenotype tests can be used to differentiate dominant from recessive KATP channel HI mutations and personalize management of children with congenital HI.

Mechanisms of octanoic acid potentiation of insulin secretion in isolated islets.

A potentiating effect of medium-chain triglycerides on glucose-stimulated insulin secretion (GSIS) has been observed since the 1960s. Subsequent observations identified octanoic acid (OA), the main component of medium-chain triglyceride, as the potentiator of GSIS, but the mechanism was unclear. We used wild-type (WT), short-chain 3-hydroxyacyl-CoA dehydrogenase knockout (Hadh-/-), and sulfonylurea receptor 1 knockout (Sur1-/-) mouse islets to define the mechanism of OA potentiation of insulin secretion. Application of OA alone induced a 2- to 3- fold increase of insulin secretion with an apparent threshold of 3 mM in WT mouse islets, suggesting that OA itself is a weak insulin secretagogue. However, OA at 1 mM strongly potentiated fuel-stimulated insulin secretion, especially GSIS. The potentiating effect on fuel-stimulated insulin secretion by OA did not require fatty acid ß-oxidation because OA also potentiated amino acid-stimulated insulin secretion in islets isolated from Hadh-/- mice, which cannot fully oxidize OA. Measurements using Sur1-/- islets indicated that the potentiating effect of OA on fuel-stimulated insulin secretion is Ca2+ dependent and is often accompanied by ß-cell membrane potential depolarization, and may also involve the Ca2+/calmodulin complex. Experiments using DCPIB, an ethacrynic acid derivative, to inhibit volume-sensitive anion channels (VSACs) in Sur1-/- islets demonstrated that the potentiation effects of OA on insulin secretion are in part medicated by activation of VSAC. In addition, inhibition of IP3 receptor also abolishes the OA-induced intracellular Ca2+ increase in Sur1-/- islets.

Hyperinsulinemic hypoglycemia in seven patients with de novo NSD1 mutations.

Sotos syndrome is an overgrowth syndrome characterized by distinctive facial features and intellectual disability caused by haploinsufficiency of the NSD1 gene. Genotype-phenotype correlations have been observed, with major anomalies seen more frequently in patients with 5q35 deletions than those with point mutations in NSD1. Though endocrine features have rarely been described, transient hyperinsulinemic hypoglycemia (HI) of the neonatal period has been reported as an uncommon presentation of Sotos syndrome. Eight cases of 5q35 deletions and one patient with an intragenic NSD1 mutation with transient HI have been reported. Here, we describe seven individuals with HI caused by NSD1 gene mutations with three having persistent hyperinsulinemic hypoglycemia. These patients with persistent HI and Sotos syndrome caused by NSD1 mutations, further dispel the hypothesis that HI is due to the deletion of other genes in the deleted 5q35 region. These patients emphasize that NSD1 haploinsufficiency is sufficient to cause HI, and suggest that Sotos syndrome should be considered in patients presenting with neonatal HI. Lastly, these patients help extend the phenotypic spectrum of Sotos syndrome to include HI as a significant feature.

Glutamate Dehydrogenase, a Complex Enzyme at a Crucial Metabolic Branch Point.

In-vitro, glutamate dehydrogenase (GDH) catalyzes the reversible oxidative deamination of glutamate to α-ketoglutarate (α-KG). GDH is found in all organisms, but in animals is allosterically regulated by a wide array of metabolites. For many years, it was not at all clear why animals required such complex control. Further, in both standard textbooks and some research publications, there has been some controversy as to the directionality of the reaction. Here we review recent work demonstrating that GDH operates mainly in the catabolic direction in-vivo and that the finely tuned network of allosteric regulators allows GDH to meet the varied needs in a wide range of tissues in animals. Finally, we review the progress in using pharmacological agents to activate or inhibit GDH that could impact a wide range of pathologies from insulin disorders to tumor growth.

Glutamate dehydrogenase: Structure of a hyperinsulinism mutant, corrections to the atomic model, and insights into a regulatory site.

Mammalian glutamate dehydrogenase (GDH) has complex allosteric regulation and the loss of GTP inhibition causes the hyperinsulinism/hyperammonemia syndrome (HHS) where insulin is hypersecreted upon consumption of protein. The archetypical HHS lesion is H454Y and lies in the GTP binding pocket. To better understand the mechanism of HHS, we determined the crystal structure of H454Y. When the bovine GDH crystal structures were minimized to prepare for further computational analysis, unusually large deviations were found at the allosteric NADH binding site due to chemical sequence errors. Notably, 387 lies in an allosteric where several activators and inhibitors bind and should be lysine rather than asparagine. All structures were re-refined and the consequence of this sequence error on NADH binding was calculated using free energy perturbation. The binding free energy penalty going from the correct to incorrect sequence found is +5 kcal/mol per site and therefore has a significant impact on drug development. BROADER AUDIENCE ABSTRACT: Glutamate dehydrogenase is a key enzyme involved in amino acid catabolism. As such, it is heavily regulated in animals by a wide array of metabolites. The importance of this regulation is most apparent in a genetic disorder called hyperinsulinism/hyperammonemia (HHS) where patients hypersecrete insulin upon the consumption of protein. We determined the atomic structure of one of these HHS mutants to better understand the disease and also analyzed an allosteric regulatory site.

Surgical treatment of congenital hyperinsulinism: Results from 500 pancreatectomies in neonates and children.

BACKGROUND: Congenital Hyperinsulinism (HI) causes severe hypoglycemia in neonates and children. We reviewed our experience with pancreatectomy for the various types of HI. METHODS: From 1998 to 2018, 500 patients with HI underwent pancreatectomy: 246 for focal HI, 202 for diffuse HI, 37 for atypical HI (16 for Localized Islet Nuclear Enlargement [LINE], 21 for Beckwith-Wiedemann Syndrome), and 15 for insulinoma. Focal HI neonates were treated with partial pancreatectomy. Patients with diffuse HI who failed medical management underwent near-total (98%) pancreatectomy. Atypical HI patients had pancreatectomies tailored to the PET scan and biopsy findings. RESULTS: The vast majority of pancreatectomies for focal HI were < 50%, and many were 2%-10%. 97% of focal HI patients are cured. For diffuse disease patients, 31% were euglycemic, 20% were hyperglycemic, and 49% required treatment for hypoglycemia; the incidence of diabetes increased with long-term follow-up. All 15 insulinoma patients were cured. CONCLUSIONS: Our approach to patients with focal HI can distinguish focal from diffuse HI, localize focal lesions, and permit partial pancreatectomy with cure in almost all focal patients. Surgery does not cure diffuse disease but can help prevent severe hypoglycemia and brain damage. Surgery can be curative for insulinoma and for some cases of atypical HI. LEVEL OF EVIDENCE: Level IV.

Congenital Hyperinsulinism in Infants with Turner Syndrome: Possible Association with Monosomy X and KDM6A Haploinsufficiency.

BACKGROUND: Previous case reports have suggested a possible association of congenital hyperinsulinism with Turner syndrome. OBJECTIVE: We examined the clinical and molecular features in girls with both congenital hyperinsulinism and Turner syndrome seen at The Children's Hospital of Philadelphia (CHOP) between 1974 and 2017. METHODS: Records of girls with hyperinsulinism and Turner syndrome were reviewed. Insulin secretion was studied in pancreatic islets and in mouse islets treated with an inhibitor of KDM6A, an X chromosome gene associated with hyperinsulinism in Kabuki syndrome. RESULTS: Hyperinsulinism was diagnosed in 12 girls with Turner syndrome. Six were diazoxide-unresponsive; 3 had pancreatectomies. The incidence of Turner syndrome among CHOP patients with hyperinsulinism (10 of 1,050 from 1997 to 2017) was 48 times more frequent than expected. The only consistent chromosomal anomaly in these girls was the presence of a 45,X cell line. Studies of isolated islets from 1 case showed abnormal elevated cytosolic calcium and heightened sensitivity to amino acid-stimulated insulin release; similar alterations were demonstrated in mouse islets treated with a KDM6A inhibitor. CONCLUSION: These results demonstrate a higher than expected frequency of Turner syndrome among children with hyperinsulinism. Our data suggest that haploinsufficiency for KDM6A due to mosaic X chromosome monosomy may be responsible for hyperinsulinism in Turner syndrome.

Clinical heterogeneity of hyperinsulinism due to HNF1A and HNF4A mutations.

BACKGROUND: Dominant inactivating mutations in HNF1A and HNF4A have been described to cause hyperinsulinism (HI) before evolving to diabetes. However, information available in the literature regarding the clinical phenotype is limited. OBJECTIVE: To report the prevalence of HNF1A and HNF4A mutations in a large cohort of children with HI, and to describe their genotypes and phenotypes. DESIGN: Retrospective descriptive study. METHODS: Medical records were reviewed to extract clinical information. Mutation analysis was carried out for 8 genes associated with HI (ABCC8, KCNJ11, GLUD1, GCK, HADH, HNF4A, HNF1A, and UCP2). RESULTS: HNF1A and HNF4A mutations were identified in 5.9% (12 out of 204; HNF1A = 7, HNF4A = 5) of diazoxide-responsive HI probands. The clinical phenotypes were extremely variable. Two children showed evidence of ketone production during hypoglycemia, a biochemical profile atypical for hyperinsulinism. At the time of analysis, diazoxide was discontinued in 5 children at a median age of 6.8 years. None had developed diabetes mellitus at a median age of 7.0 years. CONCLUSIONS: Given the heterogeneous clinical phenotypes of HNF1A- and HNF4A-HI, all children with transient, diazoxide-responsive HI without clear history of perinatal stress, should be screened for HNF1A and HNF4A mutations as it predicts the clinical course and affects the subsequent management plan.