Homozygous ABCC8 Research Articles

Marked clinical heterogeneity in congenital hyperinsulinism due to a novel homozygous ABCC8 mutation.

The most severe forms of congenital hyperinsulinism (CHI) are caused by inactivating mutations of two KATP channel genes, KCNJ11 and ABCC8. Unresponsiveness to diazoxide and need for subtotal pancreatectomy can usually be predicted by genetic form, particularly biallelic mutations in KATP channel genes. A few reports indicated marked clinical heterogeneity in siblings with identical biallelic mutations in ABCC8. The clinical heterogeneity in biallelic KATP CHI was speculated to be caused by epigenetic and environmental factors or related to differences in splicing factor machinery. To elucidate the clinical pathophysiology, especially heterogeneity, among three cases with CHI caused by a homogenous novel mutation. We report a case series that includes two siblings and one unrelated individual with CHI caused by a homogenous 1-bp deletion around the splice acceptor site at the exon 35 mutation of ABCC8, which exhibited markedly distinct phenotypes. To assess the effect of the mutation on splicing, we performed digital droplet polymerase chain reaction (ddPCR) on normal pancreas tissue and a patient's lymphocytes. ddPCR of ABCC8 cDNA revealed that expression of exon 35 and its upstream and downstream regions did not differ. These data suggested that clinical heterogeneity may not be caused by differences in splicing factor machinery. The phenotypic variation in homozygotes could not be explained by splicing abnormalities. Though early genetic diagnosis of KATP CHI could contribute to selecting appropriate therapeutic options, more deliberate selection of therapeutic options in diffuse CHI due to biallelic ABCC8 mutations may be required.

Clinical characteristics, outcome, and predictors of neurological sequelae of persistent congenital hyperinsulinism: A single tertiary center experience.

Congenital hyperinsulinism (CHI) is a heterogeneous disease with variable genetic etiology, histopathology, and clinical phenotype. This study aims to describe the clinical characteristics of persistent CHI and evaluate long-term neurological outcome and its risk factors in a cohort of Egyptian children. Clinical, genetic, and biochemical data of 42 patients with CHI were collected. Patients were invited for neurological assessment, electroencephalogram, and magnetic resonance imaging of the brain. ABCC8 mutation was found in (61%) of cases who underwent genetic testing (17/28). Five cases with homozygous biparental ABCC8 mutation responded to combined diazoxide and octreotide without needing surgery. Seven out of twenty-one patients who had pancreatectomy (33%) developed diabetes after a median period of 4.8 (range:1-10) years following surgery. Fifty-five percent of our patients had neurodevelopmental impairment at follow-up. Logistic regression analysis has shown that delayed referral to tertiary centre for more than 8 days, delayed diagnosis of CHI for more than 14 days and hospital admission for more than 30 days, are significant predictors of unfavorable neurological sequelae in CHI; (OR = 12.7 [2.56], p = 0.001), (OR = 12.7 [2.9-56], p = 0.001), and (OR = 3.8 [0.14.5], p = 0.043), respectively. ABCC8 mutation was the commonest genetic mutation underlying CHI in this study group. CHI cases with biparental homozygous ABCC8 mutation may show response to combined octreotide and diazoxide therapy. More than half of our patients had neurodevelopmental impairment at follow-up. Delayed referral to expert centre, delayed diagnosis and longer hospital stay are significant predictors of neurological disability in CHI cases.

Partial diazoxide responsiveness in a neonate with hyperinsulinism due to homozygous ABCC8 mutation.

SummaryWe report a case of partial diazoxide responsiveness in a child with severe congenital hyperinsulinaemic hypoglycaemia (CHI) due to a homozygous ABCC8 mutation. A term baby, with birth weight 3.8 kg, born to consanguineous parents presented on day 1 of life with hypoglycaemia. Hypoglycaemia screen confirmed CHI. Diazoxide was commenced on day 7 due to ongoing elevated glucose requirements (15 mg/kg/min), but despite escalation to a maximum dose (15 mg/kg/day), intravenous (i.v.) glucose requirement remained high (13 mg/kg/min). Genetic testing demonstrated a homozygous ABCC8 splicing mutation (c.2041-1G>C), consistent with a diffuse form of CHI. Diazoxide treatment was therefore stopped and subcutaneous (s.c.) octreotide infusion commenced. Despite this, s.c. glucagon and i.v. glucose were required to prevent hypoglycaemia. A trial of sirolimus and near-total pancreatectomy were considered, however due to the significant morbidity potentially associated with these, a further trial of diazoxide was commenced at 1.5 months of age. At a dose of 10 mg/kg/day of diazoxide and 40 µg/kg/day of octreotide, both i.v. glucose and s.c. glucagon were stopped as normoglycaemia was achieved. CHI due to homozygous ABCC8 mutation poses management difficulties if the somatostatin analogue octreotide is insufficient to prevent hypoglycaemia. Diazoxide unresponsiveness is often thought to be a hallmark of recessively inherited ABCC8 mutations. This patient was initially thought to be non-responsive, but this case highlights that a further trial of diazoxide is warranted, where other available treatments are associated with significant risk of morbidity.Learning points:Homozygous ABCC8 mutations are commonly thought to cause diazoxide non-responsive hyperinsulinaemic hypoglycaemia.This case highlights that partial diazoxide responsiveness in homozygous ABCC8 mutations may be present.Trial of diazoxide treatment in combination with octreotide is warranted prior to considering alternative treatments, such as sirolimus or near-total pancreatectomy, which are associated with more significant side effects.

Genotype and phenotype correlations in Iranian patients with hyperinsulinaemic hypoglycaemia.

BackgroundHyperinsulinaemic hypoglycaemia (HH) is a group of clinically and genetically heterogeneous disorders characterized by unregulated insulin secretion. Abnormalities in nine different genes (ABCC8, KCNJ11, GLUD1, GCK, HADH, SLC16A1, HNF4A, UCP2 and HNF1A) have been reported in HH, the most common being ABCC8 and KCNJ11. We describe the genetic aetiology and phenotype of Iranian patients with HH.MethodsRetrospective clinical, biochemical and genetic information was collected on 23 patients with biochemically confirmed HH. Mutation analysis was carried out for the ATP-sensitive potassium (KATP) channel genes (ABCC8 and KCNJ11), GLUD1, GCK, HADH and HNF4A.Results78 % of the patients were identified to have a genetic cause for HH. 48 % of patients had mutation in HADH, whilst ABCC8/KCNJ11 mutations were identified in 30 % of patients. Among the diazoxide-responsive patients (18/23), mutations were identified in 72 %. These include two novel homozygous ABCC8 mutations. Of the five patients with diazoxide-unresponsive HH, three had homozygous ABCC8 mutation, one had heterozygous ABCC8 mutation inherited from an unaffected father and one had homozygous KCNJ11 mutation. 52 % of children in our cohort were born to consanguineous parents. Patients with ABCC8/KCNJ11 mutations were noted to be significantly heavier than those with HADH mutation (p = 0.002). Our results revealed neurodevelopmental deficits in 30 % and epilepsy in 52 % of all patients.ConclusionsTo the best of our knowledge, this is the first study of its kind in Iran. We found disease-causing mutations in 78 % of HH patients. The predominance of HADH mutation might be due to a high incidence of consanguineous marriage in this population. Further research involving a larger cohort of HH patients is required in Iranian population.

Sirolimus therapy following subtotal pancreatectomy in neonatal hyperinsulinemic hypoglycaemia: a case report

Hyperinsulinemic hypoglycaemia (HH) occurs due to an unregulated insulin production from the pancreatic β-cells in the presence of low blood glucose. Mutations in ABCC8 and KCNJ11 are associated with severe HH that is unresponsive to conventional medical treatment. The only treatment for patients with medically unresponsive diffuse HH is a subtotal pancreatectomy. However, following surgery, hypoglycaemia may persist and some patients develop diabetes and malabsorption. Overexpression of the mTOR pathway is contributory to HH. Sirolimus, an mTOR inhibitor, is currently used in the treatment of congenital hemangiomas and in post renal transplant. Senniappan et al [1] recently reported efficacy of sirolimus in four surgically naive patients with diffuse HH unresponsive to diazoxide and octreotide. We present a patient who was treated with sirolimus due to persistent hypoglycaemia following subtotal pancreatectomy. A term neonate with a birth weight of 4.67kg had persistent hypoglycaemia since birth secondary to hyperinsulinism and was unresponsive to treatment with maximal doses of diazoxide and octreotide with a glucose infusion requirement (GIR) of 38mg/kg/min. Genetic testing revealed a homozygous ABCC8 nonsense mutation, p.Gln1020Ter. A subtotal pancreatectomy was performed on day 40. Post-surgery, he had a GIR of 20mg/kg/min and was recommenced on daily subcutaneous (SC) octreotide, with monthly long acting (LA) octreotide. At 3 months, he was commenced on oral sirolimus. The dose was adjusted to maintain serum trough levels between 5 and 15ng/ml. Parenteral fluids and SC octreotide were weaned over a month. He was discharged home at 4.5 months on sirolimus (2.5mg/m2/day) and LA octreotide. He was monitored with capillary blood glucose testing twice a day with the aim to maintain levels above 3.5mmol/L. Further surgery has been deferred. His growth and development are appropriate at 6 months of age with no side effects from sirolimus. The clinical response in our patient supports sirolimus as a new therapeutic strategy in patients with HH which may facilitate deferment of surgery. Written informed Consent for this patient has been taken including results of the genetic analyses and histopathological images according to the Institutional Ethics Committee procedures of our health service

Three Novel Pathogenic Mutations in KATP Channel Genes and Somatic Imprinting Alterations of the 11p15 Region in Pancreatic Tissue in Patients with Congenital Hyperinsulinism

Background/Aims: This study was performed to investigate the molecular pathology underlying focal and diffuse congenital hyperinsulinism (CHI). Methods: The ABCC8 and KCNJ11 genes were analyzed in 3 patients with focal CHI and in 1 patient with diffuse CHI. Immunohistochemistry, real-time PCR, methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA) and microsatellite marker analyses of the 11p15 region were performed on both normal tissues and adenomatous hyperplasia lesions. Results: The 3 patients with focal CHI harbored paternally inherited ABCC8 or KCNJ11 mutations. Compound heterozygous ABCC8 mutations were identified in the patient with diffuse CHI. In the 3 patients with focal CHI, homozygous ABCC8 or KCNJ11 mutations were identified within the lesions. MLPA and real-time PCR revealed the presence of two copies of 11p15. MS-MLPA and microsatellite analyses demonstrated abnormal imprinting patterns and focal loss of maternal 11p13-15 within the lesions. In contrast, parental heterozygosity was preserved in the normal tissue. In the patient with diffuse CHI, the two ABCC8 mutations were conserved, and imprinting patterns at 11p15 were normal. Conclusions: The epigenetic alteration at the 11p15 region plays a central role in developing focal CHI by paternally derived mutations of the K_ATP channel and maternal allelic loss at this region. MS-MLPA and microsatellite analyses are useful to investigate the molecular etiology of CHI.

A combination of nifedipine and octreotide treatment in an hyperinsulinemic hypoglycemic infant.

Hyperinsulinemic hypoglycemia (HH) is the commonest cause of persistent hypoglycemia in the neonatal and infancy periods. Mutations in the ABCC8 and KCNJ11 genes, which encode subunits of the ATP-sensitive potassium channel in the pancreatic beta cell, are identified in approximately 50% of these patients. The first-line drug in the treatment of HH is diazoxide. Octreotide and glucagon can be used in patients who show no response to diazoxide. Nifedipine, a calcium-channel blocker, has been shown to be an effective treatment in a small number of patients with diazoxide-unresponsive HH. We report a HH patient with a homozygous ABCC8 mutation (p.W1339X) who underwent a near-total pancreatectomy at 2 months of age due to a lack of response to diazoxide and octreotide treatment. Severe hypoglycemic attacks continued following surgery, while the patient was being treated with octreotide. These attacks resolved when nifedipine was introduced. Whilst our patient responded well to nifedipine, the dosage could not be increased to 0.75 mg/kg/day due to development of hypotension, a reported side effect of this drug. Currently, our patient, now aged 4 years, is receiving a combination of nifedipine and octreotide treatment. He is under good control and shows no side effects. In conclusion, nifedipine treatment can be started in patients with HH who show a poor response to diazoxide and octreotide treatment.

Permanent neonatal diabetes mellitus in Jordan

Permanent neonatal diabetes mellitus (PNDM) is a rare heterogeneous form of diabetes that develops within the first 6 months of life. The objective of this study is to define the genetic etiology and incidence of permanent neonatal diabetes mellitus in Jordan. This study was conducted in Jordan at the National Center of Diabetes, Endocrinology and Genetics, Amman, between 2006 and 2012. The study included 22 cases diagnosed with diabetes within the first year of life. The incidence of PNDM in Jordan was calculated as one case for every 203,221 live births. Mutations were found in six out of ten cases diagnosed before 6 months and included one homozygous ABCC8 p.R826W mutation, three cases with a heterozygous KCNJ11 p.R201C mutation, and two cases with a homozygous EIF2AK3 splicing mutation. The genetic etiology of PNDM in Jordan is different from that seen in European countries and more similar to other Arab countries.

Personalized Medicine Switching from Insulin to Sulfonylurea in Permanent Neonatal Diabetes Mellitus Dictated by a Novel Activating ABCC8 Mutation

Neonatal diabetes mellitus (NDM) is a rare but important condition affecting approximately 1 in 100,000 newborns. Permanent form requires life-long treatment with difficulties in long-term compliance and metabolic complications. Exact genetic diagnosis can enable improved outcome and patient satisfaction by switching insulin injection to oral sulfonylureas. Successful cases have been reported with most experience on the KCNJ11-mutated permanent form. Here we report a successful experience in an ABCC8-mutated infant with permanent NDM. A 4-month-old Chinese girl was incidentally found to have hyperglycemia with baseline C-peptide of 0.05 nmol/L requiring insulin injection of 0.2 IU/kg/d. Genetic analysis of KCNJ11 and ABCC8 was performed by polymerase chain reaction and direct DNA sequencing at the age of 3 years. Sulfonylurea transition was conducted after the ABCC8 mutation detection. A novel homozygous ABCC8 NM_000352.3: c.3068 A>G; NP_000343.2: p.H1023R mutation was detected. C-peptide level increased to 0.14 nmol/L and HbA1c was normalized to 5.8% from 8.0% after 8 months of oral glibenclamide treatment with a maintenance dosage of 0.65 mg/kg/d. In this patient with ABCC8-mutated permanent NDM, oral sulfonylurea is also effective in achieving satisfactory diabetic control. Our study adds information to the personalized medicine practice of ABCC8-mutated permanent NDM.