The genetics of neonatal hyperinsulinism

Hyperinsulinemic hypoglycemia in growth restricted convalescent preterm neonates: clinical characteristics and impediments to early diagnosis

OBJECTIVES

Describe clinical characteristics, course, and risk factors for hyper-insulinemic hypoglycemia (HIH) in preterm infants and identify impediments to early diagnosis.

METHODS

Electronic records of infant-mother dyads were used to describe clinical characteristics, lab parameters, and course of HIH.

RESULTS

All eight patients (gestational ages 26w0d-29w3d) had intrauterine growth restriction (IUGR) due to placental insufficiency, (4/8) were small for gestational age. All maintained normal glucose levels with glucose infusion during the first 48 h six of eight patients had cholestasis despite being on parenteral nutrition for short time (average 17 days). Four of eight patients were treated with diazoxide (average 22 days). Four of eight patients who recovered spontaneously (average 49 days after diagnosis) responded to continuous feeds and hydrocortisone for other clinical indications.

CONCLUSIONS

In IUGR preterms, HIH is asymptomatic, may be prolonged, requiring diazoxide treatment. Transient cholestasis is seen in majority of patients. Euglycemia should be demonstrated on bolus gavage feeds, off glucocorticoids before discontinuing blood glucose monitoring.

Approach to hypoglycemia in infants and children

Hypoglycemia is a heterogeneous disorder with many different possible etiologies, including hyperinsulinism, glycogen storage disorders, fatty acid disorders, hormonal deficiencies, and metabolic defects, among others. This condition affects newborns to adolescents, with various approaches to diagnosis and management. This paper will review current literature on the history of hypoglycemia, current discussion on the definition of hypoglycemia, as well as etiologies, diagnosis, and management.

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 molecular data from 61 Brazilian cases of Congenital Hyperinsulinemic Hypoglycemia

OBJECTIVE

To study the clinical and molecular characteristics of a sample of Brazilian patients with Congenital Hyperinsulinemic Hypoglycemia (CHH).

METHODS

Electronic message was sent to members from Endocrinology Department- Brazilian Society of Pediatrics requesting clinical data for all cases of CHH. A whole blood sample from living patients was requested for DNA extraction followed by a search for mutations of the genes ABCC8, KCNJ11, GCK, GLUD1, HADH, SLC16A1 and HNF4A.

RESULTS

Of the 61 patients evaluated, 36 (59%) were boys, and only 16 (26%) were born by normal delivery. Gestational age ranged from 32 to 41 weeks (mean = 37 weeks and 6 days). Birth weight ranged from 1590 to 5250 g (mean = 3430 g). Macrossomia occurred in 14 cases (28%). Age at diagnosis ranged from 1 to 1080 days (mean = 75 days). DNA for molecular analysis was obtained from 53 of the 61 patients. Molecular changes in the ABCC8 gene were detected in 15 (28%) of these 53 cases, and mutations in the KCNJ11 gene were detected in 6 (11%). Mutations in the GLUD1 gene were detected in 9 cases (17%) of the total series. Mutations of the GCK gene in heterozygosis were detected in 3 cases. No mutations were detected in the sequencing of genes HADH, SLC16A1 and HNF4A.

CONCLUSION

The present study conducted in Brazil permitted the collaborative compilation of an important number of CHH cases and showed that the present clinical and molecular data are similar to those of published global series.

Long-term follow-up and mutation analysis of 27 chinese cases of congenital hyperinsulinism

OBJECTIVES

Long-term clinical follow-up and mutation analysis were performed in 27 Chinese congenital hyperinsulinism patients.

METHOD

27 hypoglycemia patients were diagnosed with CHI within 2 years of age. The long-term clinical outcome was analyzed and mutation analysis of 5 hyperinsulinism candidate genes was performed.

RESULTS

The median onset age of hypoglycemia in the patients was 60 days; 11 patients showed hypoglycemic symptoms in the neonatal stage, and hypoglycemia in most of the patients was first expressed as a seizure. Blood was collected during the hypoglycemic episode and insulin levels were significantly elevated. ABCC8, KCNJ11, GCK, HNF4a and GLUD1 genes were screened for mutation analysis. 14 mutations in ABCC8 or KCNJ11 genes in 12 cases were identified (44%). 57% (8/14) of the mutations have not been reported before. 83% (10/12) of the patients have a monoallelic mutation. 58% of these 12 patients were predicted to be focal. 73% of the patients without KATP channel mutations were sensitive to diazoxide. 26 patients were followed over a period of 1-13 years. 50% of all 27 patients showed brain impairment.

CONCLUSIONS

Chinese CHI patients are similar to other ethnic groups in terms of prevalence of KATP-HI, onset age, severity of hypoglycemia and treatment. Mutations in ABCC8 and KCNJ11 are common causes of CHI in Chinese patients. Mutation analysis showed more novel and monoallele mutations in KATP genes.

Novel mutation c.597_598dup in exon 5 of ABCC8 gene causing congenital hyperinsulinism

Congenital hyperinsulinism (CHI), a clinically and genetically heterogeneous disease, characterized by the unregulated secretion of insulin from pancreatic β-cells, is the most common cause of persistent hypoglycemia in infancy. Early diagnosis and maintenance of normoglycaemia are essential to prevent adverse neurodevelopmental outcomes. The most common and severe forms of CHI are caused by inactivating mutations in ABCC8 and KCNJ11 genes, encoding the two subunits of the pancreatic β-cell ATP sensitive potassium channel (KATP). We report a case of neonatal CHI due to a novel homozygous recessive mutation in the ABCC8 gene.

Genetic and epigenetic control of metabolic health

Obesity is characterized as an excess accumulation of body fat resulting from a positive energy balance. It is the major risk factor for type 2 diabetes (T2D). The evidence for familial aggregation of obesity and its associated metabolic diseases is substantial. To date, about 150 genetic loci identified in genome-wide association studies (GWAS) are linked with obesity and T2D, each accounting for only a small proportion of the predicted heritability. However, the percentage of overall trait variance explained by these associated loci is modest (~5-10% for T2D, ~2% for BMI). The lack of powerful genetic associations suggests that heritability is not entirely attributable to gene variations. Some of the familial aggregation as well as many of the effects of environmental exposures, may reflect epigenetic processes. This review summarizes our current knowledge on the genetic basis to individual risk of obesity and T2D, and explores the potential role of epigenetic contribution.

Clinical characteristics of recessive and dominant congenital hyperinsulinism due to mutation(s) in the ABCC8/KCNJ11 genes encoding the ATP-sensitive potasium channel in the pancreatic beta cell

BACKGROUND

Recessive mutations in ABCC8/KCNJ11 of beta-cell K(ATP) channel generally cause severe medically unresponsive hyperinsulinemic hypoglycemia (HH). Rarer dominant mutations in these genes have been described that mostly cause milder, medically responsive congenital hyperinsulinism. Rarer dominant mutations in these genes have been described that mostly cause milder, medically responsive congenital hyperinsulinism. To date the phenotype of patients with dominant mutations seems to be different from those with recessive mutations as the majority of patients are responsive to diazoxide therapy. Controversy exists on whether these dominant ABCC8 or KCNJ11 genes mutations predispose to diabetes mellitus in adulthood or not.

SUBJECTS

We report the clinical and genetic characteristics of five patients with neonatal HH, three had recessively inherited K(ATP) channel mutations and two with a dominantly acting mutation. As a result of failure to medical therapy, patients with recessive K(ATP) channel mutations underwent a near total pancreatectomy. Two siblings with a novel dominant mutation showed good response to medical treatment. Although the HH remitted in early infancy, they became diabetic at the prepubertal age. Their mother, maternal aunt and maternal grandfather had the same mutation without any medical history of neonatal HH.

CONCLUSION

The clinical presentation of our two patients with a dominant ABCC8 mutation was milder than that of patients with the resessive form of the disease as they responded well to medical management.

From congenital hyperinsulinism to diabetes mellitus: the role of pancreatic beta-cell KATP channels

Pancreatic beta-cell adenosine triphosphate (ATP)-sensitive potassium (K(ATP)) channels play a pivotal role in linking glucose metabolism to regulated insulin secretion. K(ATP) channels are hetero-octameric complexes comprising two subunits Kir6.2 and sulfonylurea receptor 1 (SUR1). Changes in the intracellular concentration of nucleotides (ATP) cause alterations in the resting and opening state of the K(ATP) channels. Loss-of-function mutations in the genes encoding the two subunits of K(ATP) channels lead to the most common form of congenital hyperinsulinism (CHI). This causes persistent and severe hypoglycemia in the neonatal and infancy period. CHI can cause mental retardation and epilepsy if not treated properly. On the other hand, now there is evidence of an association between polymorphisms in the Kir6.2 gene and type 2 diabetes mellitus, mutations in the Kir6.2 gene and neonatal diabetes mellitus, and mutations in the SUR1 gene and diabetes mellitus. Interestingly, for reasons that are unclear at present, mice knockout models of K(ATP) channels are different from the human phenotype of CHI. This article is a review focusing on how abnormalities in the pancreatic beta-cell K(ATP) channels can lead to severe hypoglycemia on the one hand and diabetes mellitus on the other.

Contemporary strategies in the diagnosis and management of neonatal hyperinsulinaemic hypoglycaemia

Congenital hyperinsulinism (CHI) is a genetically and phenotypically diverse syndrome. Key management issues involve early diagnosis by ensuring that appropriate samples are taken at the point of hypoglycaemia, prevention of recurrent hypoglycaemia, and detailed characterisation of the clinical, biochemical, and genetic features of each case. Infants with persistent diazoxide resistant CHI require evaluation at specialist referral centres equipped to differentiate those with focal (fo-HI) and diffuse (di-HI) pancreatic disease. Fo-HI is treated with selective pancreatic resection but di-HI is treated by surgery only if intensive medical management regimes are not efficacious.

Assembly, Maturation, and Turnover of KATP Channel Subunits

ATP-sensitive K(+), or K(ATP), channels are comprised of K(IR)6.x and sulfonylurea receptor (SUR) subunits that assemble as octamers, (K(IR)/SUR)(4). The assembly pathway is unknown. Pulse-labeling studies show that when K(IR)6.2 is expressed individually, its turnover is biphasic; approximately 60% is lost with t((1/2)) approximately 36 min. The remainder converts to a long-lived species (t((1/2)) approximately 26 h) with an estimated half-time of 1.2 h. Expressed alone, SUR1 has a long half-life, approximately 25.5 h. When K(IR)6.2 and SUR1 are co-expressed, they associate rapidly and the fast degradation of K(IR)6.2 is eliminated. Based on changes in the glycosylation state of SUR1, the half-time for the maturation of K(ATP) channels, including completion of assembly, transit to the Golgi, and glycosylation, is approximately 2.2 h. Estimation of the turnover rates of mature, fully glycosylated SUR1 associated with K(IR)6.2 and of K(IR)6.2 associated with Myc-tagged SUR1 gave similar values for the half-life of K(ATP) channels, a mean value of approximately 7.3 h. K(ATP) channel subunits in INS-1 beta-cells displayed qualitatively similar kinetics. The results imply the octameric channels are stable. Two mutations, K(IR)6.2 W91R and SUR1 DeltaF1388, identified in patients with the severe form of familial hyperinsulinism, profoundly alter the rate of K(IR)6.2 and SUR1 turnover, respectively. Both mutant subunits associate with their respective partners but dissociate freely and degrade rapidly. The data support models of channel formation in which K(IR)6.2-SUR1 heteromers assemble functional channels and are inconsistent with models where SUR1 can only assemble with K(IR)6.2 tetramers.

Hyperinsulinism in Infancy: From Basic Science to Clinical Disease

Dunne, Mark J., Karen E. Cosgrove, Ruth M. Shepherd, Albert Aynsley-Green, and Keith J. Lindley. Hyperinsulinism in Infancy: From Basic Science to Clinical Disease. Physiol Rev 84: 239–275, 2004; 10.1152/physrev.00022.2003.—Ion channelopathies have now been described in many well-characterized cell types including neurons, myocytes, epithelial cells, and endocrine cells. However, in only a few cases has the relationship between altered ion channel function, cell biology, and clinical disease been defined. Hyperinsulinism in infancy (HI) is a rare, potentially lethal condition of the newborn and early childhood. The causes of HI are varied and numerous, but in almost all cases they share a common target protein, the ATP-sensitive K+channel. From gene defects in ion channel subunits to defects in β-cell metabolism and anaplerosis, this review describes the relationship between pathogenesis and clinical medicine. Until recently, HI was generally considered an orphan disease, but as parallel defects in ion channels, enzymes, and metabolic pathways also give rise to diabetes and impaired insulin release, the HI paradigm has wider implications for more common disorders of the endocrine pancreas and the molecular physiology of ion transport.