Cause Of Congenital Hyperinsulinism Research Articles

Genotype-histotype-phenotype correlations in hyperinsulinemic hypoglycemia.

Hyperinsulinemic hypoglycemia (HH) of pancreatic origin includes congenital hyperinsulinism (CHI), insulinoma, insulinomatosis, and adult-onset non-insulinoma persistent hyperinsulinemic hypoglycemia syndrome (NI-PHHS). In this review, we describe the genotype-histotype-phenotype correlations in HH and their therapeutic implications. CHI can occur from birth or later on in life. Histologically, diffuse CHI shows diffuse beta cell hypertrophy with a few giant nuclei per islet of Langerhans, most frequently caused by loss-of-function mutations in ABCC8 or KCNJ11. Focal CHI is histologically characterized by focal adenomatous hyperplasia consisting of confluent hyperplastic islets, caused by a paternal ABCC8/KCNJ11 mutation combined with paternal uniparental disomy of 11p15. CHI in Beckwith-Wiedemann syndrome is caused by mosaic changes in the imprinting region 11p15.4-11p15.5, leading to segmental or diffuse overgrowth of endocrine tissue in the pancreas. Morphological mosaicism of pancreatic islets is characterized by occurence of hyperplastic (type 1) islets in one or a few lobules and small (type 2) islets in the entire pancreas. Other rare genetic causes of CHI show less characteristic or unspecific histology. HH with a predominant adult onset includes insulinomas, which are pancreatic insulin-producing endocrine neoplasms, in some cases with metastatic potential. Insulinomas occur sporadically or as part of multiple endocrine neoplasia type 1 due to MEN1 mutations. MAFA mutations may histologically lead to insulinomatosis with insulin-producing neuroendocrine microadenomas or neuroendocrine neoplasms. NI-PHHS is mainly seen in adults and shows slight histological changes in some patients, which have been defined as major and minor criteria. The genetic cause is unknown in most cases. The diagnosis of HH, as defined by genetic, histological, and phenotypic features, has important implications for patient management and outcome.

Дифференциальная диагностика гипогликемий, развившихся на фоне врожденного гиперинсулинизма

Congenital hyperinsulinism (CHI) is a genetic disorder characterized by inappropriate insulin secretion by pancreatic b-cells. CHI may induce the development of severe hypoglycemic conditions already in the neonatal period. The causes of neonatal hypoglycemia are diverse; therefore, an accurate algorithm is needed for diagnosis and differential diagnosis of pathological conditions accompanied by hypoglycemia. One of the causes of low blood glucose levels is hyperinsulinism, both exogenous (administration of insulin or its stimulants) and endogenous (autonomous insulin secretion, disorders of the propulsive or endocrine function of the gastrointestinal tract). An increase in insulin levels in the blood due to hypoketonemia is one of the common signs of this condition. In etiopathogenesis, transient and persistent hyperinsulinism are distinguished. The latter is represented by monogenic (genetic defects in insulin secretion) and syndromic (associated with other hereditary diseases) forms. This article presents data on the characteristics of insulin metabolism, possible causes of CHI, and discusses the algorithm for differential diagnosis of neonatal hypoglycemia for timely detection of CHI. Key words: congenital hyperinsulinism, neonatal hypoglycemia, hyperinsulinism-hyperammonemia syndrome, Sotos syndrome, Beckwith–Wiedemann syndrome, Kabuki syndrome, Costello syndrome, congenital disorders of glycosylation

Non-coding variants disrupting a tissue-specific regulatory element in HK1 cause congenital hyperinsulinism.

Gene expression is tightly regulated, with many genes exhibiting cell-specific silencing when their protein product would disrupt normal cellular function1. This silencing is largely controlled by non-coding elements, and their disruption might cause human disease2. We performed gene-agnostic screening of the non-coding regions to discover new molecular causes of congenital hyperinsulinism. This identified 14 non-coding de novo variants affecting a 42-bp conserved region encompassed by a regulatory element in intron 2 of the hexokinase 1 gene (HK1). HK1 is widely expressed across all tissues except in the liver and pancreatic beta cells and is thus termed a 'disallowed gene' in these specific tissues. We demonstrated that the variants result in a loss of repression of HK1 in pancreatic beta cells, thereby causing insulin secretion and congenital hyperinsulinism. Using epigenomic data accessed from public repositories, we demonstrated that these variants reside within a regulatory region that we determine to be critical for cell-specific silencing. Importantly, this has revealed a disease mechanism for non-coding variants that cause inappropriate expression of a disallowed gene.

CRISPR/Cas9 ADCY7 knockout stimulates the insulin secretion pathway leading to excessive insulin secretion

Brief Summary: This is a single case report describing a possible new candidate gene (ADCY7) for congenital hyperinsulinism. Mutations in the ADCY7 gene may be a new cause of congenital hyperinsulinism but more cases are needed and the molecular mechanisms studied in more detail.

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.

Birth weight and diazoxide unresponsiveness strongly predict the likelihood of congenital hyperinsulinism due to a mutation in ABCC8 or KCNJ11.

ObjectiveMutations in the KATP channel genes, ABCC8 and KCNJ11, are the most common cause of congenital hyperinsulinism. The diagnosis of KATP-hyperinsulinism is important for the clinical management of the condition. We aimed to determine the clinical features that help to identify KATP-hyperinsulinism at diagnosis.DesignWe studied 761 individuals with KATP-hyperinsulinism and 862 probands with hyperinsulinism of unknown aetiology diagnosed before 6 months of age. All were referred as part of routine clinical care.MethodsWe compared the clinical features of KATP-hyperinsulinism and unknown hyperinsulinism cases. We performed logistic regression and ROCanalysis to identify the features that predict KATP-hyperinsulinism.ResultsHigher birth weight, diazoxide unresponsiveness and diagnosis in the first week of life were independently associated with KATP-hyperinsulinism (adjusted Odds Ratio 4.5 (95% CI, 3.4-5.9), 0.09 (0.06-0.13) and 3.3 (2.0- 5.0) respectively). Birth weight and diazoxide unresponsiveness were additive and highly discriminatory for identifying KATP-hyperinsulinism (ROC area under the curve for birth weight 0.80, diazoxide responsiveness 0.77, and together 0.88, 95% CI 0.85-0.90). 86% born large for gestation and 78% born appropriate for gestation who did not respond to diazoxide treatment had KATP-hyperinsulinism. In contrast, of those individuals born small for gestation, none who were diazoxide responsive and only 4% of those who were diazoxide unresponsive had KATP-hyperinsulinism.ConclusionsIndividuals with hyperinsulinism born appropriate or large for gestation and unresponsive to diazoxide treatment are most likely to have an ABCC8 or KCNJ11 mutation. These patients should be prioritised for genetic testing for KATP channel genes.

Clinical Management and Gene Mutation Analysis of Children with Congenital Hyperinsulinism in South China

Objective:To explore the clinical presentation and molecular genetic characteristics of a cohort of congenital hyperinsulinism (CHI) patients from southern China and also to explore the most appropriate therapeutic approaches.Methods:We retrospectively reviewed a cohort of 65 children with CHI. Mutational analysis was performed for KCNJ11 and ABCC8 genes. The GLUD1 gene was sequenced in patients with hyperammonaemia. GCK gene sequencing was performed in those patients with no mutation identified in the ABCC8, KCNJ11 or GLUD1 genes.Results:ABCC8 mutations were identified in 16 (25%) of the cohort, GLUD1 mutations were identified in five children, and no KCNJ11 or GCK mutations were identified. Moreover, some unique features of ABCC8 gene mutations in southern Chinese CHI patients were found in this study. The most common mutation was a deletion/insertion mutation p.Thr1042GlnfsX75 was found in five unrelated patients, which possibly represents a relatively common mutation in southern China. Five novel ABCC8 mutations were detected. The mutations were p.Phe5SerfsX72, p.Gln273ArgfsX85, p.Leu724del, p.Asp1447Gly and IVS 25-1G>T. Five compound heterozygous mutations of ABCC8 gene were identified in this study, and three of these patients were diazoxide-responsive. Forty patients were diazoxide-responsive, 13 patients were diazoxide-unresponsive and 12 patients received dietary treatment only. A pancreatectomy was performed in 10 patients who were unresponsive to medical treatment.Conclusion:To the best of our knowledge, this is the first study of CHI in south China. Mutations in ABCC8 are the most common causes of CHI in this cohort. Diazoxide and dietary treatment were effective in most patients. Multicentre studies are necessary to obtain the long-term follow-up characteristics of such patients at a national level.

Clinical characteristics and phenotype-genotype review of 25 Omani children with congenital hyperinsulinism in infancy. A one-decade single-center experience.

Objectives:To report the genotype-phenotype characteristics, demographic features and clinical outcome of Omani patients with congenital hyperinsulinism (CHI).Methods:We retrospectively analyzed the clinical, biochemical, genotypical, phenotypical characteristics and outcomes of children with CHI who were presented to the pediatric endocrine team in the Royal Hospital, Muscat, Oman between January 2007 and December 2016.Results:Analysis of 25 patients with CHI genetically revealed homozygous mutation in ABCC8 in 23 (92%) patients and 2 patients (8%) with compound heterozygous mutation in ABCC8. Fifteen (60%) patients underwent subtotal pancreatectomy as medical therapy failed and 2 (8%) patients showed response to medical therapy. Three patients expired during the neonatal period, 2 had cardiomyopathy and sepsis, and one had sepsis and severe metabolic acidosis. Out of the 15 patients who underwent pancreatectomy, 6 developed diabetes mellitus, 6 continued to have hypoglycemia and required medical therapy and one had pancreatic exocrine dysfunction post-pancreatectomy, following up with gastroenterology clinic and was placed on pancreatic enzyme supplements, while 2 patients continued to have hypoglycemia and both had abdominal MRI and 18-F-fluoro-L-DOPA positron emission tomography scan (PET-scan), that showed persistent of the disease and started on medical therapy.Conclusion:Mutation in ABCC8 is the most common cause of CHI and reflects the early age of presentation. There is a need for early diagnosis and appropriate therapeutic strategy.

OR05-2 Targeted Inhibition of Glutamate Dehydrogenase by Alpha-Tocopherol: A Potential Novel Treatment for Hyperinsulinism Hyperammonemia Syndrome

Congenital hyperinsulinism is a rare genetic disorder that causes severe hypoglycemia and can lead to permanent brain damage if inadequately controlled. Gain of function mutations in glutamate dehydrogenase (GDH) result in hyperinsulinism hyperammonemia (HI/HA) syndrome, the second most common cause of congenital hyperinsulinism. Current therapies inhibit insulin secretion but do not target GDH overactivity directly and thus fail to treat the spectrum of clinical manifestations observed, which in addition to hyperinsulinism and hyperammonemia, include seizures and developmental delays. The neurological symptoms are profound and occur independent of the hypoglycemia. We investigated the efficacy of alpha-tocopherol as a targeted GDH inhibitor in vitro and in vivo models of HI/HA syndrome. Human embryonic kidney (HEK293T) cells were transduced with lentivirus to overexpress either wild-type GDH or H454Y GDH, a well-characterized disease-causing mutant. GDH enzyme kinetics were determined spectrophotometrically in cell homogenates perfused with escalating concentrations of alpha-tocopherol on a background of 10mM glutamine. To evaluate the inhibitory effect of alpha-tocopherol on GDH in vivo, wild-type (WT, n=10) and H454Y GDH transgenic (Tg, n=13) adult mice were treated with oral alpha-tocopherol (75 μg/g body weight/dose) or vehicle twice daily for 3 doses and then fasted for 6 hours. Nadir fasting plasma glucoses were measured as a clinical correlate of GDH activity and compared between alpha-tocopherol and vehicle-treated wild-type and transgenic mice, respectively. Alpha-tocopherol effectively inhibited activity of wild-type and H454Y mutant GDH in HEK293T cells with 50% inhibitory concentration (IC50) of 4.1 and 3.1 μM, respectively. In vivo, nadir fasting plasma glucose was significantly higher in alpha-tocopherol-treated versus vehicle-treated WT and Tg mice (WT: mean nadir plasma glucose 94.3 ± 9.6 mg/dl v. 80.1 ± 9.6 mg/dl, p=0.003; Tg: mean nadir plasma glucose 71.9± 11.3 mg/dl v. 57.2 ± 12.6 mg/dl, p=0.002). Alpha-tocopherol effectively inhibits GDH in vitro and ameliorates fasting hypoglycemia in vivo in a mouse model of HI/HA syndrome. Based upon these findings, alpha-tocopherol is a promising potential treatment for HI/HA syndrome. Our next step will be to study the safety and efficacy of oral alpha-tocopherol supplementation in human subjects with HI/HA syndrome.

The Genetic and Molecular Mechanisms of Congenital Hyperinsulinism.

Congenital hyperinsulinism (CHI) is a heterogenous and complex disorder in which the unregulated insulin secretion from pancreatic beta-cells leads to hyperinsulinaemic hypoglycaemia. The severity of hypoglycaemia varies depending on the underlying molecular mechanism and genetic defects. The genetic and molecular causes of CHI include defects in pivotal pathways regulating the secretion of insulin from the beta-cell. Broadly these genetic defects leading to unregulated insulin secretion can be grouped into four main categories. The first group consists of defects in the pancreatic KATP channel genes (ABCC8 and KCNJ11). The second and third categories of conditions are enzymatic defects (such as GDH, GCK, HADH) and defects in transcription factors (for example HNF1α, HNF4α) leading to changes in nutrient flux into metabolic pathways which converge on insulin secretion. Lastly, a large number of genetic syndromes are now linked to hyperinsulinaemic hypoglycaemia. As the molecular and genetic basis of CHI has expanded over the last few years, this review aims to provide an up-to-date knowledge on the genetic causes of CHI.

Genetic characteristics of patients with congenital hyperinsulinism.

Congenital hyperinsulinism is the most common cause of persistent hypoglycemia in infants and children. Early and appropriate recognition and treatment of hypoglycemia is vital to minimize neurocognitive impairment. There are at least 11 known monogenic forms of hyperinsulinism and several associated syndromes. Molecular diagnosis allows for prediction of the effectiveness of diazoxide and the likelihood of focal hyperinsulinism. Inactivating mutations in the genes encoding the ATP-sensitive potassium channel (KATP hyperinsulinism) account for 60% of all identifiable mutations, including 85% of diazoxide-unresponsive cases. Syndromes or disorders associated with hyperinsulinism include Beckwith-Wiedemann syndrome, Kabuki syndrome, Turner syndrome, and congenital disorders of glycosylation. Although focal hyperinsulinism can be cured by resection of the lesion, therapeutic options for nonfocal hyperinsulinism remain limited and include diazoxide, octreotide, long-acting somatostatin analogs, and near-total pancreatectomy. Although sirolimus has been reported to improve glycemic control in infants with diazoxide-unresponsive hyperinsulinism, the extent of improvement has been limited, and significant adverse events have been reported. Identification of the cause of congenital hyperinsulinism helps guide management decisions. Use of therapies with limited benefit and significant potential risks should be avoided.

Calcium/calmodulin dependent protein kinase 2 (CaMKK2) mutation - a novel genetic cause of congenital hyperinsulinism

Calcium/calmodulin dependent protein kinase 2 (CaMKK2) mutation - a novel genetic cause of congenital hyperinsulinism

Familial case of congenital hyperinsulinism associated with mutation in the GLUD1 gene

Congenital hyperinsulinism (CHI) is a rare hereditary disease characterized by hypoglycemia in children during the first year of life. Late diagnosis and inadequate therapy may result in severe neurological complications. Mutations in the GLUD1 gene that encodes glutamate dehydrogenase are one of the causes of CHI. This form of CHI is characterized by protein-induced hyperinsulinemic hypoglycemia and hyperammonemia in patients. Diagnosing can be challenging because hyperinsulinemic hypoglycemia cannot be detected using the conventional fasting glucose test. Extensive examination including the protein load test is needed to refine diagnosis. We report a familial case where the mother and two daughters were diagnosed with CHI and had a mutation in the catalytic domain of the GLUD1 gene. The clinical presentation, the laboratory data, the outcome of therapy, and the dynamic follow up data for the patients are presented.

Modeling Congenital Hyperinsulinism with ABCC8-Deficient Human Embryonic Stem Cells Generated by CRISPR/Cas9

Congenital hyperinsulinism (CHI) is a rare genetic disorder characterized by excess insulin secretion, which results in hypoglycemia. Mutation of sulfonylurea receptor 1 (SUR1), encoded by the ABCC8 gene, is the main cause of CHI. Here, we captured the phenotype of excess insulin secretion through pancreatic differentiation of ABCC8-deficient stem cells generated by the CRISPR/Cas9 system. ABCC8-deficient insulin-producing cells secreted higher insulin than their wild-type counterparts, and the excess insulin secretion was rescued by nifedipine, octreotide and nicorandil. Further, we tested the role of SUR1 in response to different potassium levels and found that dysfunction of SUR1 decreased the insulin secretion rate in low and high potassium environments. Hence, pancreatic differentiation of ABCC8-deficient cells recapitulated the CHI disease phenotype in vitro, which represents an attractive model to further elucidate the function of SUR1 and to develop and screen for novel therapeutic drugs.

Clinical and Genetic Characteristics, Management and Long-Term Follow-Up of Turkish Patients with Congenital Hyperinsulinism.

Objective:Mutations in the KATP channel genes is the most common cause of congenital hyperinsulinism (CHI) of infancy. Our aim was to report the clinical and genetic characteristics, treatment modalities, and long-term prognosis of patients with CHI.Methods:Clinical and biochemical findings, operation procedures, and results of genetic analysis were retrospectively evaluated in 22 CHI patients from two pediatric endocrine centers in Turkey.Results:Seven of the patients were born large for gestational age. Hypoglycemia was diagnosed within the first 24 hours of life in 9 patients and treatment with diazoxide (n=21) and/or somatostatin (n=8) had been attempted. Seven patients (31.8%) were unresponsive to medical treatment and underwent pancreatectomy. Histological examination of the pancreas confirmed diffuse disease in 6 patients. Diabetes developed in 3 patients following pancreatectomy (10 years, 2.5 years, and immediately after operation). The remaining four patients had neither recurrence of CHI nor of diabetes during the 3.67±0.7 years of follow-up. Sequence analysis identified mutations in 12 out of 19 patients (63%). Mutations in the ABCC8 gene were the most common finding and were found in 6 out of 7 patients who underwent pancreatectomy. Other mutations included a paternally inherited KCNJ11 mutation, a homozygous HADH mutation, and a heterozygous GLUD1 mutation.Conclusion:Mutations in the ABCC8 gene were the most common cause of CHI in our cohort. These mutations were identified in 85% of patients who underwent pancreatectomy. The development of diabetes mellitus after pancreatectomy may occur at any age and these patients should be screened regularly.

Clinical and genetic characterization of congenital hyperinsulinism in Spain.

Congenital hyperinsulinism (CHI) is a clinically and genetically heterogeneous disease characterized by severe hypoglycemia caused by inappropriate insulin secretion by pancreatic β-cells. To characterize clinically and genetically CHI patients in Spain. We included 50 patients with CHI from Spain. Clinical information was provided by the referring clinicians. Mutational analysis was carried out for KCNJ11, ABCC8, and GCK genes. The GLUD1, HNF4A, HNF1A, UCP2, and HADH genes were sequenced depending on the clinical phenotype. We identified the genetic etiology in 28 of the 50 CHI patients tested: 21 had a mutation in KATP channel genes (42%), three in GLUD1 (6%), and four in GCK (8%). Most mutations were found in ABCC8 (20/50). Half of these patients (10/20) were homozygous or compound heterozygous, with nine being unresponsive to diazoxide treatment. The other half had heterozygous mutations in ABCC8, six of them being unresponsive to diazoxide treatment and four being responsive to diazoxide treatment. We identified 22 different mutations in the KATP channel genes, of which ten were novel. Notably, patients with ABCC8 mutations were diagnosed earlier, with lower blood glucose levels and required higher doses of diazoxide than those without a genetic diagnosis. Genetic analysis revealed mutations in 56% of the CHI patients. ABCC8 mutations are the most frequent cause of CHI in Spain. We found ten novel mutations in the KATP channel genes. The genetic diagnosis is more likely to be achieved in patients with onset within the first week of life and in those who fail to respond to diazoxide treatment.

Managing congenital hyperinsulinism: improving outcomes with a multidisciplinary approach

Congenital hyperinsulinism (CHI) is the most common cause of persistent hypo- glycemia in pediatric patients and is associated with significant risk of hypoglycemic seizures and developmental delays. CHI results from mutations in at least nine genes that play a role in regulating beta-cell insulin secretion. Thus, patients with CHI have dysregulated insulin secretion that is unresponsive to blood glucose level. Each different genetic etiology of CHI is associated with particular clinical characteristics that affect management decisions. Given the broad phe- notypic spectrum and relatively rare prevalence of CHI, it is important that patients with CHI be evaluated by clinicians experienced with CHI and the multiple subspecialty services that are necessary for the management of the disorder. In this review, we summarize the pathophysiology and genetic causes of CHI and then focus primarily on the most common genetic cause (muta- tions in the ATP-gated potassium (K ATP ) channel) for further discussion of diagnosis, medical and surgical management, and potential acute and chronic complications. We provide insight from relevant published studies and reports, in addition to anecdotal information from our center's clinical experience in caring for over 400 patients with CHI. Careful assessment of each patient's individual pathophysiology is necessary to determine the appropriate treatment regimen, and continued close follow-up and monitoring of disease- and treatment-related complications are essential. Although significant improvements have been made in the past several years with regard to diagnosis and management, given the continued high morbidity rate in patients with CHI, improved diagnostic techniques and new therapeutic options would be welcomed.

Congenital hyperinsulinism: clinical and molecular characterisation of compound heterozygous ABCC8 mutation responsive to Diazoxide therapy.

BackgroundMutations in ABCC8 and KCNJ11 are the most common cause of congenital hyperinsulinism (CHI). Recessive as well as dominant acting ABCC8/KCNJ11 mutations have been described. Diazoxide, which is the first line medication for CHI, is usually ineffective in recessive ABCC8 mutations. We describe the clinical and molecular characterisation of a recessive ABCC8 mutation in a CHI patient that is diazoxide response.Clinical caseA term macrosomic female infant presented with symptomatic persistent hypoglycaemia confirmed to be secondary to CHI. She exhibited an excellent response to moderate doses of diazoxide (10 mg/kg/day). Molecular genetic analysis of the proband confirmed a biallelic ABCC8 mutation – missense R526C inherited from an unaffected mother and a frameshift c.1879delC mutation (H627Mfs*20) inherited from an unaffected father. Follow-up highlighted persistent requirement for diazoxide to control CHI. Functional analysis of mutants confirmed them to result in diazoxide-responsive CHI, consistent with the clinical phenotype.ConclusionBiallelic ABCC8 mutations may result in diazoxide-responsive CHI. Irrespective of the molecular genetic analysis results, accurate assessment of the response to diazoxide should be undertaken before classifying a patient as diazoxide-responsive or unresponsive CHI.

Mutational analysis of ABCC8, KCNJ11, GLUD1, HNF4A and GCK genes in 30 Chinese patients with congenital hyperinsulinism.

We conducted a cohort study to elucidate the molecular spectrum of congenital hyperinsulinism (CHI) in Chinese pediatric patients. Thirty Chinese children with CHI were chosen as research subjects, 16 of whom were responsive to diazoxide and 13 of whom were not (1 patient was not given the drug for medical reasons). All exons of the adenosine triphosphate (ATP)-sensitive potassium channel (KATP channel) genes KCNJ11 and ABCC8, the hepatocyte nuclear factor 4 α (HNF4A) gene, and the Glucokinase (GCK) gene as well as exons 6 and 7 and 10-12 of the glutamate dehydrogenase 1 (GLUD1) gene were amplified from genomic DNA and directly sequenced. Mutations were identified in 14 of 30 patients (47%): 3 in GLUD1 (10%) and 11 in the KATP channel genes (37%). Six patients had paternally derived monoallelic KATP channel mutations predictive of the focal CHI form. We found a novel de novo ABCC8 mutation, p. C1000*, a novel paternally inherited ABCC8 mutation, D1505H, and a dominantly inherited ABCC8 mutation, R1217K. The GLUD1 activating mutation R269H was found in 2 patients: 1 de novo and the other paternally inherited. A de novo S445L mutation was found in 1 patient. No significant HNF4A or GCK mutations were found. CHI has complex genetic onset mechanisms. Paternally inherited monoallelic mutations of ABCC8 and KCNJ11 are likely the main causes of KATP-CHI in Chinese patients. Glutamate dehydrogenase-CHI is the second most common cause of CHI, while HNF4A and GCK are rare types of CHI in Chinese patients.

Mechanism of Carbamazepine Mediated Rescue of Trafficking Defective Mutant KATP Channels

The β-cell ATP-sensitive potassium (KATP) channel regulates insulin secretion by coupling glucose metabolism to membrane excitability. Mutations in the constituent protein subunits Kir6.2 and sulfonylurea receptor 1 (SUR1) that prevent channels from trafficking to the cell surface are frequent causes of congenital hyperinsulinism. We recently reported that carbamazepine, an anticonvulsant, corrects the trafficking defects caused by mutations in the N-terminal transmembrane domain of SUR1. In addition, carbamazepine inhibits the function of rescued channels that can be reversed by subsequent drug removal. Here, we investigated the mechanism underlying carbamazepine's effects on KATP channel trafficking and gating by partial proteolysis and electrophysiology, respectively. We show that carbamazepine inhibits channel activity by specifically abolishing channel response to the physiological stimulator MgADP. Our partial proteolysis results show that carbamazepine interacts with the channel complex and protects the N-terminus of Kir6.2 against trypsin digestion. Further, results show that deletion of Kir6.2 N-terminal 30 amino acids severely compromised carbamazepine mediated rescue of the SUR1 trafficking mutant, F27S. Our findings suggest a structural model for carbamazepine mediated rescue of SUR1-TMD0 trafficking mutants and inhibition of KATP channels.