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So Eun Park, Sarah E Flanagan, Khalid Hussain, Sian Ellard, Choong Ho Shin and Sei Won Yang

Objective

Congenital hyperinsulinism (CHI) is characterized by persistent hypoglycemia due to the inappropriate insulin secretion. Inactivating mutations in the ABCC8 and KCNJ11 genes, which encode the sulfonylurea receptor 1 and Kir6.2 subunits of the ATP-sensitive K+ (KATP) channel in pancreatic β-cell, are the most common cause of CHI. We studied the genetic etiology and phenotypes of CHI in Korean patients.

Methods

ABCC8 and KCNJ11 mutational analysis was performed in 17 patients with CHI. Medical records were retrospectively reviewed to identify phenotypes.

Results

Mutations (12 ABCC8 and three KCNJ11) were identified in 82% (14/17) of patients. Of these, nine ABCC8 mutations (E100X, W430X, c.1630+1G>C, D813N, Q923X, E1087_A1094delinsDKSDT, Q1134H, H1135W, and E1209Rfs) and one KCNJ11 mutation (W91X) were novel. Of the 14 patients, four had confirming recessively inherited CHI. The remaining ten patients had single heterozygous mutations. The majority (12/17) of patients were medically responsive. Of the five diazoxide-responsive patients, four had an ABCC8 mutation. The five patients unresponsive to medical management and one diazoxide-responsive patient underwent pancreatectomy and had diffuse histology. Of the operated six patients, two had recessively inherited mutations; three patients had a single heterozygous mutation (one maternally and two paternally inherited); and one patient had no identifiable KATP channel mutation.

Conclusions

This is the first study to report genotype and phenotype correlations among Korean patients with CHI. Mutations in ABCC8 and KCNJ11 are the most common causes of CHI in Korean patients. Similar to other studies, there is marked genetic heterogeneity and no clear genotype–phenotype correlation.

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So Eun Park, Sarah E Flanagan, Khalid Hussain, Sian Ellard, Choong Ho Shin and Sei Won Yang

Open access

Ritika R Kapoor, Sarah E Flanagan, Ved Bhushan Arya, Julian P Shield, Sian Ellard and Khalid Hussain

Background

Congenital hyperinsulinism (CHI) is a clinically heterogeneous condition. Mutations in eight genes (ABCC8, KCNJ11, GLUD1, GCK, HADH, SLC16A1, HNF4A and HNF1A) are known to cause CHI.

Aim

To characterise the clinical and molecular aspects of a large cohort of patients with CHI.

Methodology

Three hundred patients were recruited and clinical information was collected before genotyping. ABCC8 and KCNJ11 genes were analysed in all patients. Mutations in GLUD1, HADH, GCK and HNF4A genes were sought in patients with diazoxide-responsive CHI with hyperammonaemia (GLUD1), raised 3-hydroxybutyrylcarnitine and/or consanguinity (HADH), positive family history (GCK) or when CHI was diagnosed within the first week of life (HNF4A).

Results

Mutations were identified in 136/300 patients (45.3%). Mutations in ABCC8/KCNJ11 were the commonest genetic cause identified (n=109, 36.3%). Among diazoxide-unresponsive patients (n=105), mutations in ABCC8/KCNJ11 were identified in 92 (87.6%) patients, of whom 63 patients had recessively inherited mutations while four patients had dominantly inherited mutations. A paternal mutation in the ABCC8/KCNJ11 genes was identified in 23 diazoxide-unresponsive patients, of whom six had diffuse disease. Among the diazoxide-responsive patients (n=183), mutations were identified in 41 patients (22.4%). These include mutations in ABCC8/KCNJ11 (n=15), HNF4A (n=7), GLUD1 (n=16) and HADH (n=3).

Conclusions

A genetic diagnosis was made for 45.3% of patients in this large series. Mutations in the ABCC8 gene were the commonest identifiable cause. The vast majority of patients with diazoxide-responsive CHI (77.6%) had no identifiable mutations, suggesting other genetic and/or environmental mechanisms.

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Clementine S Fraser, Oscar Rubio-Cabezas, Jennifer A Littlechild, Sian Ellard, Andrew T Hattersley and Sarah E Flanagan

Background

Mutations in the KCNJ11 gene, which encodes the Kir6.2 subunit of the β-cell KATP channel, are a common cause of neonatal diabetes. The diabetes may be permanent neonatal diabetes mellitus (PNDM) or transient neonatal diabetes mellitus (TNDM), and in ∼20% of patients, neurological features are observed. A correlation between the position of the mutation in the protein and the clinical phenotype has previously been described; however, recently, this association has become less distinct with different mutations at the same residues now reported in patients with different diabetic and/or neurological phenotypes.

Methods

We identified from the literature, and our unpublished series, KCNJ11 mutations that affected residues harbouring various amino acid substitutions (AAS) causing differences in diabetic or neurological status. Using the Grantham amino acid scoring system, we investigated whether the difference in properties between the wild-type and the different AAS at the same residue could predict phenotypic severity.

Results

Pair-wise analysis demonstrated higher Grantham scores for mutations causing PNDM or diabetes with neurological features when compared with mutations affecting the same residue that causes TNDM (P=0.013) or diabetes without neurological features (P=0.016) respectively. In just five of the 25 pair-wise analyses, a lower Grantham score was observed for the more severe phenotype. In each case, the wild-type residue was glycine, the simplest amino acid.

Conclusion

This study demonstrates the importance of the specific AAS in determining phenotype and highlights the potential utility of the Grantham score for predicting phenotypic severity for novel KCNJ11 mutations affecting previously mutated residues.

Open access

Ritika R Kapoor, Sarah E Flanagan, Piers Fulton, Anupam Chakrapani, Bernadette Chadefaux, Tawfeg Ben-Omran, Indraneel Banerjee, Julian P Shield, Sian Ellard and Khalid Hussain

Background

Activating mutations in the GLUD1 gene (which encodes for the intra-mitochondrial enzyme glutamate dehydrogenase, GDH) cause the hyperinsulinism–hyperammonaemia (HI/HA) syndrome. Patients present with HA and leucine-sensitive hypoglycaemia. GDH is regulated by another intra-mitochondrial enzyme sirtuin 4 (SIRT4). Sirt4 knockout mice demonstrate activation of GDH with increased amino acid-stimulated insulin secretion.

Objectives

To study the genotype–phenotype correlations in patients with GLUD1 mutations. To report the phenotype and functional analysis of a novel mutation (P436L) in the GLUD1 gene associated with the absence of HA.

Patients and methods

Twenty patients with HI from 16 families had mutational analysis of the GLUD1 gene in view of HA (n=19) or leucine sensitivity (n=1). Patients negative for a GLUD1 mutation had sequence analysis of the SIRT4 gene. Functional analysis of the novel P436L GLUD1 mutation was performed.

Results

Heterozygous missense mutations were detected in 15 patients with HI/HA, 2 of which are novel (N410D and D451V). In addition, a patient with a normal serum ammonia concentration (21 μmol/l) was heterozygous for a novel missense mutation P436L. Functional analysis of this mutation confirms that it is associated with a loss of GTP inhibition. Seizure disorder was common (43%) in our cohort of patients with a GLUD1 mutation. No mutations in the SIRT4 gene were identified.

Conclusion

Patients with HI due to mutations in the GLUD1 gene may have normal serum ammonia concentrations. Hence, GLUD1 mutational analysis may be indicated in patients with leucine sensitivity; even in the absence of HA. A high frequency of epilepsy (43%) was observed in our patients with GLUD1 mutations.

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Ved Bhushan Arya, Maria Guemes, Azizun Nessa, Syeda Alam, Pratik Shah, Clare Gilbert, Senthil Senniappan, Sarah E Flanagan, Sian Ellard and Khalid Hussain

Context

Congenital hyperinsulinism (CHI) has two main histological types: diffuse and focal. Heterozygous paternally inherited ABCC8/KCNJ11 mutations (depending upon whether recessive or dominant acting and occurrence of somatic maternal allele loss) can give rise to either phenotype. However, the relative proportion of these two phenotypes in a large cohort of CHI patients due to paternally inherited heterozygous ABCC8/KCNJ11 mutations has not been reported.

Objective

The purpose of this study is to highlight the variable clinical phenotype and to characterise the distribution of diffuse and focal disease in a large cohort of CHI patients due to paternally inherited heterozygous ABCC8/KCNJ11 mutations.

Design

A retrospective chart review of the CHI patients due to heterozygous paternally inherited ABCC8/KCNJ11 mutations from 2000 to 2013 was conducted.

Results

Paternally inherited heterozygous ABCC8/KCNJ11 mutations were identified in 53 CHI patients. Of these, 18 (34%) either responded to diazoxide or resolved spontaneously. Fluorine-18 l-3, 4-dihydroxyphenylalanine positron emission tomography computerised tomography (18F DOPA–PET CT) scanning in 3/18 children showed diffuse disease. The remaining 35 (66%) diazoxide-unresponsive children either had pancreatic venous sampling (n=8) or 18F DOPA–PET CT (n=27). Diffuse, indeterminate and focal disease was identified in 13, 1 and 21 patients respectively. Two patients with suspected diffuse disease were identified to have focal disease on histology.

Conclusions

Paternally inherited heterozygous ABCC8/KCNJ11 mutations can manifest as a wide spectrum of CHI with variable 18F DOPA–PET CT/histological findings and clinical outcomes. Focal disease was histologically confirmed in 24/53 (45%) of CHI patients with paternally inherited heterozygous ABCC8/KCNJ11 mutations.

Open access

Huseyin Demirbilek, Ved Bhushan Arya, Mehmet Nuri Ozbek, Jayne A L Houghton, Riza Taner Baran, Melek Akar, Selahattin Tekes, Heybet Tuzun, Deborah J Mackay, Sarah E Flanagan, Andrew T Hattersley, Sian Ellard and Khalid Hussain

Background

Neonatal diabetes mellitus (NDM) is a rare form of monogenic diabetes and usually presents in the first 6 months of life. We aimed to describe the clinical characteristics and molecular genetics of a large Turkish cohort of NDM patients from a single centre and estimate an annual incidence rate of NDM in South-Eastern Anatolian region of Turkey.

Design and methods

NDM patients presenting to Diyarbakir Children State Hospital between 2010 and 2013, and patients under follow-up with presumed type 1 diabetes mellitus, with onset before 6 months of age were recruited. Molecular genetic analysis was performed.

Results

Twenty-two patients (59% males) were diagnosed with NDM (TNDM-5; PNDM-17). Molecular genetic analysis identified a mutation in 20 (95%) patients who had undergone a mutation analysis. In transient neonatal diabetes (TNDM) patients, the genetic cause included chromosome 6q24 abnormalities (n=3), ABCC8 (n=1) and homozygous INS (n=1). In permanent neonatal diabetes (PNDM) patients, homozygous GCK (n=6), EIF2AK3 (n=3), PTF1A (n=3), and INS (n=1) and heterozygous KCNJ11 (n=2) mutations were identified. Pancreatic exocrine dysfunction was observed in patients with mutations in the distal PTF1A enhancer. Both patients with a KCNJ11 mutation responded to oral sulphonylurea. A variable phenotype was associated with the homozygous c.-331C>A INS mutation, which was identified in both a PNDM and TNDM patient. The annual incidence of PNDM in South-East Anatolian region of Turkey was one in 48 000 live births.

Conclusions

Homozygous mutations in GCK, EIF2AK3 and the distal enhancer region of PTF1A were the commonest causes of NDM in our cohort. The high rate of detection of a mutation likely reflects the contribution of new genetic techniques (targeted next-generation sequencing) and increased consanguinity within our cohort.

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Indraneel Banerjee, Bindu Avatapalle, Anjali Petkar, Mars Skae, Raja Padidela, Sarah Ehtisham, Leena Patel, Lindsey Rigby, Sarah Flanagan, Sian Ellard, Caroline Jones, Giovanna Ciotti, Nilima Malaiya and Peter E Clayton

Objective

Ventricular hypertrophy (VH) has been observed in children with congenital hyperinsulinism (CHI), a condition of hypoglycaemia characterised by dysregulated insulin secretion, but the prevalence is not known.

Patients and methods

Cardiac assessment was performed in children (n=49) with CHI at diagnosis and follow-up. Two dimensional and Doppler echocardiography studies were used to assess cardiac structures, while M-mode study was used to measure left ventricular (LV) dimensions, subsequently converted to Z scores. Where possible, LV hypertrophy was confirmed by LV mass index (g/m2.7) >95th centile.

Results

Cardiac structural lesions were found in 14 (28%) children. At initial echocardiography, VH was present in 31 (65%) children with median (range) LV posterior wall dimension in diastole Z scores of +1.6 (−2.4 to +5.8) and interventricular septal wall dimension in end diastole Z scores of +1.9 (−1.7 to +17.2). At follow-up echocardiography, performed after an interval of 178 (45–390) days, VH persisted in 16 (33%) children. In regression analysis, the presence of VH (odds ratio (95% confidence intervals) 1.1 (1.0–1.2), P=0.04) at initial echocardiography was correlated with maximum glucose requirement at diagnosis, indicating that severity of CHI at presentation may play a role in the pathogenesis of VH.

Conclusions

A significant proportion of children with CHI have cardiac structural lesions. A majority also have VH, which may be associated with the severity of CHI at diagnosis. VH may persist in some children, which requires careful long-term cardiac review.

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Huseyin Demirbilek, Ved Bhushan Arya, Mehmet Nuri Ozbek, Aysehan Akinci, Murat Dogan, Fatma Demirel, Jayne Houghton, Sultan Kaba, Fatma Guzel, Riza Taner Baran, Sevim Unal, Selahattin Tekkes, Sarah E Flanagan, Sian Ellard and Khalid Hussain

Objective

Congenital hyperinsulinism (CHI) is the commonest cause of hyperinsulinaemic hypoglycaemia in the neonatal, infancy and childhood periods. Its clinical presentation, histology and underlying molecular biology are extremely heterogeneous. The aim of this study was to describe the clinical characteristics, analyse the genotype–phenotype correlations and describe the treatment outcome of Turkish CHI patients.

Design and methods

A total of 35 patients with CHI were retrospectively recruited from four large paediatric endocrine centres in Turkey. Detailed clinical, biochemical and genotype information was collected.

Results

Diazoxide unresponsiveness was observed in nearly half of the patients (n=17; 48.5%). Among diazoxide-unresponsive patients, mutations in ABCC8/KCNJ11 were identified in 16 (94%) patients. Among diazoxide-responsive patients (n=18), mutations were identified in two patients (11%). Genotype–phenotype correlation revealed that mutations in ABCC8/KCNJ11 were associated with an increased birth weight and early age of presentation. Five patients had p.L1171fs (c.3512del) ABCC8 mutations, suggestive of a founder effect. The rate of detection of a pathogenic mutation was higher in consanguineous families compared with non-consanguineous families (87.5 vs 21%; P<0.0001).

Among the diazoxide-unresponsive group, ten patients were medically managed with octreotide therapy and carbohydrate-rich feeds and six patients underwent subtotal pancreatectomy. There was a high incidence of developmental delay and cerebral palsy among diazoxide-unresponsive patients.

Conclusions

This is the largest study to report genotype–phenotype correlations among Turkish patients with CHI. Mutations in ABCC8 and KCNJ11 are the commonest causes of CHI in Turkish patients (48.6%). There is a higher likelihood of genetic diagnosis in patients with early age of presentation, higher birth weight and from consanguineous pedigrees.

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Henrik B T Christesen, Nicholas D Tribble, Anders Molven, Juveria Siddiqui, Tone Sandal, Klaus Brusgaard, Sian Ellard, Pål R Njølstad, Jan Alm, Bendt Brock Jacobsen, Khalid Hussain and Anna L Gloyn

Objective

Activating glucokinase (GCK) mutations are a rarely reported cause of congenital hyperinsulinism (CHI), but the prevalence of GCK mutations is not known.

Methods

From a pooled cohort of 201 non-syndromic children with CHI from three European referral centres (Denmark, n=141; Norway, n=26; UK, n=34), 108 children had no KATP-channel (ABCC8/KCNJ11) gene abnormalities and were screened for GCK mutations. Novel GCK mutations were kinetically characterised.

Results

In five patients, four heterozygous GCK mutations (S64Y, T65I, W99R and A456V) were identified, out of which S64Y was novel. Two of the mutations arose de novo, three were dominantly inherited. All the five patients were medically responsive. In the combined Danish and Norwegian cohort, the prevalence of GCK-CHI was estimated to be 1.2% (2/167, 95% confidence interval (CI) 0–2.8%) of all the CHI patients. In the three centre combined cohort of 72 medically responsive children without KATP-channel mutations, the prevalence estimate was 6.9% (5/72, 95% CI 1.1–12.8%). All activating GCK mutations mapped to the allosteric activator site. The novel S64Y mutation resulted in an increased affinity for the substrate glucose (S0.5 1.49±0.08 and 7.39±0.05 mmol/l in mutant and wild-type proteins respectively), extrapolating to a relative activity index of ∼22 compared with the wild type.

Conclusion

In the largest study performed to date on GCK in children with CHI, GCK mutations were found only in medically responsive children who were negative for ABCC8 and KCNJ11 mutations. The estimated prevalence (∼7%) suggests that screening for activating GCK mutations is warranted in those patients.